Animal Kingdome

Question 1

Phylum Arthropoda in superphylum ecdysozoa

Answer 1

“jointed legs”

make up 85% of animal kingdome

functional segmentation of the body and presence of jointed appendages

exoskeleton made principally of chitin,

insects form the single largest class within this phylum.

are eucoelomate, protostomic organisms.

terrestrial, aquatic, and aerial habitats.

five subphyla:
Trilobitomorpha (trilobites, all extinct),
Hexapoda (insects and relatives),
Myriapoda (millipedes, centipedes, and relatives),
Crustaceans (crabs, lobsters, crayfish, isopods, barnacles, and some zooplankton),
and Chelicerata (horseshoe crabs, arachnids, scorpions, and daddy longlegs).

Question 2

Arthropod morphology

Answer 2

presence of a segmented body and fusion of sets of segments that give rise to functional body regions called tagma.

Tagma may be in the form of a head, thorax, and abdomen, or a cephalothorax and abdomen, or a head and trunk.

have a central cavity: hemocoel (or blood cavity),

open circulatory system regulated by a tubular or single-chambered heart.

cuticle= covering of arthropods: 2 layers epicuticle thin waxy layer water resistent, layer beneath is the chintin layer: procuticle

to grow they shed the exoskelleton and are extra vulnerable to predators

Question 3

Subphylum Hexapoda from arthropoda

Answer 3

(ants, cockroaches, butterflies, and flies

six legs,a head, thorax, and abdomen, constituting three tagma.

thorax bears the wings as well as six legs in three pairs

insects largest class in terms of species diversity and biomass in terrestrial habitats

head bears one pair of sensory antennae mandibles as mouthparts, a pair of compound eyes, and some ocelli (simple eyes) along with numerous sensory hairs

thorax bears three pairs of legs (one pair per segment) and two pairs of wings, with one pair each on the second and third thoracic segments.

abdomen usually has eleven segments and bears reproductive apertures.

Question 4

Subphylum Myriapoda

Answer 4

noumerous legs 10-750

13.000 species millipedes and centapedes famous

all terrestrial and like humidity (moist soils, decaying biological material, and leaf litter)

divided into four classes: Chilopoda, Symphyla, Diplopoda, and Pauropoda

bear two pairs of legs per diplosegment( a feature that results from embryonic fusion of adjacent pairs of body segments, are usually rounder in cross-section, and are herbivores or detritivores)

Scutigera coleoptrata is a chilopod, one pair of legs per segment mandibles as mouthparts and somewhat dorsoventrally flattened

legs in first segment are modified to form forcipules (poison claws): deliver poison to prey like spiders and cockroaches, as these animals are all predatory

Question 5

Subphylum Crustacea (from arthropods)

Answer 5

most dominant aquatic arthropods

67,000 aquatic species

Krill, shrimp, lobsters, crabs, and crayfish

Terrestrial species like the wood lice (Armadillidium spp.) (also called pill bugs, rolly pollies, potato bugs, or isopods) are also crustaceans

possess two pairs of antennae, mandibles as mouthparts, and biramous (“two branched”) appendages, which means that their legs are formed in two parts, as distinct from the uniramous (“one branched”) myriapods and hexapods

the head and thorax of most crustaceans is fused to form a cephalothorax, covered by a plate called the carapace, thus producing a body structure of two tagma

chitinous exoskeleton that is shed by molting, also infused with calcium carbonate, which makes them even stronger than in other arthropods

open circulatory system where blood is pumped into the hemocoel by the dorsally located heart

Hemocyanin and hemoglobin are the respiratory pigments present in these animals

possess a tripartite brain and two compound eyes

are carnivorous but also herbivorus and detrivorous are known not usually but sometimes cannibalistic

dioecious: the sexes are separate

Some species like barnacles may be hermaphrodites (Serial hermaphroditism, where the gonad can switch from producing sperm to ova, seen in some species)

Fertilized eggs within the female or released in the water

Terrestrial crustaceans seek out damp spaces to lay eggs

Question 6

Subphylum Chelicerata (arthropods)

Answer 6

spiders, scorpions, horseshoe crabs, and sea spiders

predominantly terrestrial, although some marine species also exist,found in almost all habitats

77,000 species

Body divided two parts: prosoma and opisthosoma, basically cephalothorax (usually smaller) and abdomen (usually larger)

usually cant tell head tagmum

first pair of appendages: the chelicerae: specialized, claw-like or fang-like mouthparts for feeding or venomous fangs in spiders

dont have antennae

second pair of appendages:pedipalps

for some like sea spiders ovigers, is present between the chelicerae and pedipalps

open circulatory system with a heart that pumps blood into the hemocoel

Aquatic species = gills
terrestrial species = trachea or book lungs for gaseous exchange

Most ingest food using a preoral cavity formed by chelicerae and pedipalps

some secrete digestive enzymes to pre-digest food before ingesting it

Parasitic chelicerates like ticks and mites have evolved blood-sucking apparatuses

nervous system consists of brain and two ventral nerve cords

external fertilization as well as internal fertilization

some dont care for children some care a little

Question 7

Superphylum Deutrerostomia

Answer 7

“mouth second,” anus is first to develop

humans are part of this

internal pockets of the endodermal lining called the archenteron fuse to form the coelom

endodermal lining of the archenteron (or the primitive gut) forms membrane protrusions that bud off and become the mesodermal layer

When these buds (coelomic pouches) seperate from mesodermal layer they fuse to form the coelomic cavity

The resultant coelom is termed an enterocoelom

archenteron develops into alimentary canal,

a mouth opening is formed by invagination of ectoderm at the pole opposite the blastopore of the gastrula

The blastopore forms anus of alimentary system in the juvenile and adult forms

The fates of embryonic cells in deuterostomes can be altered if they are experimentally moved to a different location in the embryo due to indeterminant cleavage in early embryogenesis.

Question 8

Phylum Echinodermata from Superphylum Deuterostomia

Answer 8

7,000 species

exclusively marine organisms

Sea stars, sea cucumbers, sea urchins, sand dollars, and brittle stars

Question 9

Phylum Echinodermata Morphology and Anatomy

Answer 9

Adults exhibit pentaradial symmetry, have a calcareous endoskeleton made of ossicles

early larval stages of all echinoderms have bilateral symmetry

endoskeleton developed by epidermal cells and may possess pigment cells–>vivid colors
as well as cells laden with toxins

Gonads are present in each arm

sea stars every arm bears two rows of tube feet on oral side–> help attaching to substratum

true coelom—> modified into a unique circulatory system: water vascular system

can regenerate, even when over 75 percent of their body mass is lost

Question 10

Phylum Echinodermata Water Vascular System

Answer 10

consisting of a central ring canal and radial canals that extend along each arm

Water circulates through these structures –>facilitates gaseous exchange, nutrition, predation, and locomotion

projects from holes in the skeleton in form of tube feet: can expand or contract based on volume of water in the system of that arm

using hydrostatic pressure, the animal can either protrude or retract the tube feet

Water enters the madreporite on the aboral side of the echinoderm. From there, it passes into the stone canal, which moves water into the ring canal. The ring canal connects the radial canals (there are five in a pentaradial animal), and the radial canals move water into the ampullae, which have tube feet through which the water moves

By moving water through the unique water vascular system, the echinoderm can move and force open mollusk shells during feeding.

Question 11

Phylum Echinodermata: nervous-, excretory system and reproduction

Answer 11

nervous system is a relatively simple structure with a nerve ring at the center and five radial nerves extending outward along the arms. no brain/ ganglia

Podocytes, cells specialized for ultrafiltration of bodily fluids, are present near the center of echinoderms. These podocytes are connected by an internal system of canals to an opening called the madreporite.

Echinoderms are sexually dimorphic and release their eggs and sperm cells into water; fertilization is external. In some species, the larvae divide asexually and multiply before they reach sexual maturity. Echinoderms may also reproduce asexually, as well as regenerate body parts lost in trauma.

Question 12

Classes of Echinoderms

Answer 12

5 classes:
-Asteroidea (sea stars)
-Ophiuroidea (brittle stars)
-Echinoidea (sea urchins and sand dollars)
-Crinoidea (sea lilies or feather stars)
-Holothuroidea (sea cucumbers)

Question 13

class Asteroidea of enchioderms

Answer 13

variety of shapes colors and sizes

1.800 species

key characteristic= thick arms (ambulacra) extend from a central disk where organs penetrate into the arms

use tube feet for gripping surfaces also for grasping prey

Sea stars have two stomachs, one of which can protrude through their mouths and secrete digestive juices into or onto prey, even before ingestion. This process can essentially liquefy the prey and make digestion easier.

Question 14

class Ophiuroidea of Echinoderms

Answer 14

brittle stars

have long, thin arms that are sharply demarcated from the central disk

move by lashing out their arms or wrapping them around objects and pulling themselves forward

Question 15

class Echinoidea of Echinoderms

Answer 15

Sea urchins and sand dollars

do not have arms, but are hemispherical or flattened with five rows of tube feet that help them in slow movement; tube feet are extruded through pores of a continuous internal shell called a test

Question 16

class Crinoidea of Echinoderms

Answer 16

Sea lilies and feather stars

suspension feeders

Question 17

class Holothuroidea of Echinoderms

Answer 17

sea cucumbers

extended in the oral-aboral axis and have five rows of tube feet

only echinoderms that demonstrate “functional” bilateral symmetry as adults, because the uniquely extended oral-aboral axis compels the animal to lie horizontally rather than stand vertically

Question 18

Phylum Chordata

Answer 18

four key features that appear at some stage of their development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail

sometimes only during embryotic phase

contaims vertabrates and 2 invertabrate classes:
Urochordata (tunicates) and Cephalochordata (lancelets)
Most tunicates live on the ocean floor and are suspension feeders. Lancelets are suspension feeders that feed on phytoplankton and other microorganisms

Question 19

characteristics of Chordata

Answer 19

4 key features:
- notochord
- dorsal hollow nerve cord
- pharyngeal slits
- post anal tail
sometimes only present during embryotic development

Question 20

notochord (chordates)

Answer 20

a flexible, rod-shaped structure, found in the embryonic stage of all chordates & adult stage of some chordate species

located between digestive tube and nerve cord

provides skeletal support through length of body

In some it acts as primary axial support of body throughout the animal’s lifetime

In vertebrates notochord is present during embryonic development, induces development of neural tube and serves as support for the developing embryonic body

not found in postnatal stage of vertebrates it gets replaced by the vertebral column (that is, the spine)

Question 21

dorsal hollow nerve cord (chordates)

Answer 21

derives from ectoderm that rolls into a hollow tube during development

In chordates, it is located dorsal to the notochord

other animal phyla are characterized by solid nerve cords, located either ventrally or laterally

nerve cord develops into the brain and spinal cord–>compose central nervous system

Question 22

Pharyngeal slits (chordates)

Answer 22

openings in the pharynx (the region just posterior to the mouth), extend to the outside environment

aquatic environments organisms, pharyngeal slits allow for the exit of water that enters the mouth during feeding

Some use slits to filter food out of water that enters the mouth

In vertebrate fishes, the pharyngeal slits are modified into gill supports

in jawed fishes, into jaw supports

In tetrapods, slits are modified into components of the ear and tonsils

Question 23

post-anal tail (chordates)

Answer 23

posterior elongation of the body, beyond the anus

tail contains skeletal elements and muscles, provide a source of locomotion in aquatic species

some terrestrial vertebrates, tail helps with balance, courting, and signaling when danger is near

In humans, the post-anal tail is vestigial, that is, reduced in size and nonfunctional

Question 24

Urchordata (Chordates and the Evolution of Vertebrates)

Answer 24

also known as tunicates

have cellulose-like carbohydrate material (the tunic) –>covers the outer body of tunicates

adult tunicates are classified as chordates but do not have a notochord, a dorsal hollow nerve cord, or a post-anal tail

they do have pharyngeal slits

–> larval form has all four strictures

most are hermaphrodites

larvae hatch from eggs inside adults body, swims a few days to find surface to attach to, usually dark location

attaches via head and undergoes metamorphosis to adult form

usually seesil on ocean floor

suspension feeders ( plankton and detritus)

water enters body through incurrent siphon, suspended material is filtered out by a mucous net (pharyngeal slits)–> passed to intestine via action od cilia–> anus empties to excurrent siphon which expells waste and water

Question 25

Cephalochordata (Chordates and the Evolution of Vertebrates)

Answer 25

lanceletes

possess a notochord, dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail in the adult stage

notochord extends into the head hence the subphylums name

extinct members include pikaia fossils were found in canada, lived during middle of cambrian age–> more than 500 mil years old

lancelets few cm long buried in sand tropical seas, suspension feeders

Question 26

Craniata and Vertebrata (Chordates and the Evolution of Vertebrates)

Answer 26

A cranium is a bony, cartilaginous, or fibrous structure surrounding the brain, jaw, and facial bones

Most bilaterally symmetrical animals have a head; of these, those that have a cranium compose the clade Craniata

includes hagfishes, have cranium but no backbone and all organisims that are called vertebrates

Vertebrates are members of the clade Vertebrata

share the 4 traids of chordates but have additional derived characteristics that distinguish them from invertabrates.

vertebral collumn: vertebra, series of seperate bones jointed as a backbone (in adults it replaces the embryotic notochord)

Vertebrates are the largest group of chordates, with more than 62,000 living species

grouped based on physiological traits

Agnatha, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves, and Mammalia

Question 27

Chordates and the Evolution of Vertebrates

Answer 27

vertebrates appear to be more closely related to lancelets (cephalochordates) than to tunicates (urochordates)

suggests that the cephalochordates diverged from Urochordata and the vertebrates subsequently diverged from the cephalochordates

fossil in China from the genus Haikouella–> intermediate form between cephalochordates and vertebrates , about 530 million years old and appear similar to modern lancelets –> had a brain and eyes, as do vertebrates, but lack the skull found in craniates
–>This evidence suggests that vertebrates arose during the Cambrian explosion

Question 28

Jawless Fishes

Answer 28

are craniates, lineage arose over one and a half billion years ago

In the past, the hagfishes and lampreys were classified together as agnathans. Today, hagfishes and lampreys are recognized as separate clades

lack of paired lateral appendages (fins)

earliest jawless fish=ostracoderms , encased in boney armor(present day jawless fishes lack bone in scales)

Question 29

Myxini: Hagfishes

Answer 29

clade Myxini includes at least 20 species of hagfishes

Hagfishes are eel-like scavengers that live on the ocean floor and feed on dead invertebrates, other fishes, and marine mammals

entirely marine

slime glands beneath the skin that release mucus through surface pores–> escape predators, can also twist into knot

skeleton made oit of cartilage, includes a cartilaginous notochord that runs the length of the body–> provides support, do not replace notochord

Question 30

Petromyzontidae: Lampreys

Answer 30

The clade Petromyzontidae includes approximately 35–40 or more species of lampreys

Lampreys are similar to hagfishes in size and shape;but possess some vertebral elements

lack paired appendages and bone, as do the hagfishes

toothed, funnel-like sucking mouth as adults

paracitic stage ectoparasites of fishes

primarily in coastal and fresh water

some marine but all spawn in fresh water

eggs are fertallized externally larvae distinctly differ from adult form 3-15 years as suspension feeders as soon as fertile they reproduce and die

Lampreys possess a notochord as adults; however, this notochord is surrounded by a cartilaginous structure called an arcualia, which may resemble an evolutionarily early form of the vertebral column

Question 31

Gnathostomes: Jawed Fishes

Answer 31

jaw, which is a hinged structure attached to the cranium that allows an animal to grasp and tear its food

Early gnathostomes also possessed two sets of paired fins, allowing the fishes to maneuver accurately

Pectoral fins are typically located on the anterior body, and pelvic fins on the posterior

evolution of jaws and paired fins allowed them to go from sedimentary suspension feeding jawless fish to become mobile predators

exploited new nutrient sources, probably replaced most jawless fish in devonian period

early groups of gnathostomes were the acanthodians and placoderms now extinct

modern fishes are gnathostomes that belong to the clades Chondrichthyes and Osteichthyes

Question 32

Chondrichthyes: Cartilaginous Fishes (clade from gnathostomes)

Answer 32

consisting of sharks, rays, and skates, together with sawfishes and a few dozen species of fishes called chimaeras, or “ghost” sharks”

jawed fishes that possess paired fins and a skeleton made of cartilage

370 million years ago in the early or middle Devonian

descended from the placoderms, which had skeletons made of bone; thus, the cartilaginous skeleton of Chondrichthyes is a later development

Parts of shark skeleton are strengthened by granules of calcium carbonate, but this is not the same as bone

Most sharks are carnivores that feed on live prey

Shark teeth likely evolved from the jagged scales that cover their skin, called placoid scales

Some species of sharks and rays are suspension feeders that feed on plankton

sharks: well developed sense organs, help locating prey, keen sense of smell and electroreception (most sensitive of any animal)

Organs called ampullae of Lorenzini allow sharks to detect the electromagnetic fields that are produced by all living things, including their prey

Sharks, together with most fishes and aquatic and larval amphibians, also have a sense organ called the lateral line, which is used to detect movement and vibration in the surrounding water, and is often considered homologous to “hearing” in terrestrial vertebrates. The lateral line is visible as a darker stripe that runs along the length of a fish’s body.

reproduce sexually, and eggs are fertilized internally

Most species are ovoviviparous: The fertilized egg is retained in the oviduct of the mother’s body and the embryo is nourished by the egg yolk. The eggs hatch in the uterus, and young are born alive and fully functional

Some species of sharks are oviparous: They lay eggs that hatch outside of the mother’s body. Embryos are protected by a shark egg case or “mermaid’s purse” that has the consistency of leather. The shark egg case has tentacles that snag in seaweed and give the newborn shark cover

A few species of sharks are viviparous: The young develop within the mother’s body and she gives live birth

Rays and skates comprise more than 500 species and are closely related to sharks

distinguished from sharks by flattened bodies, pectoral fins that are enlarged and fused to the head, gills slits on ventral surface

rays and skates have a cartilaginous skeleton

Question 33

Osteichthyes: Bony Fishes

Answer 33

characterized by a bony skeleton

vast majority of present-day fishes belong to this group, which consists of approximately 30,000 species, making it the largest class of vertebrates in existence today

Nearly all bony fishes have an ossified skeleton with specialized bone cells (osteocytes) that produce and maintain a calcium phosphate matrix–> has only reversed in a few groups of Osteichthyes, such as sturgeons and paddlefish, which have primarily cartilaginous skeletons

skin mostly covered in overlapping scales, glands in skin secrete mucus–> p+reduces drag when swimming, aids osmoregulation

bony fishes have a lateral line system that detects vibrations in water like sharks

use gills to breathe

Water is drawn over gills that are located in chambers covered and ventilated by a protective, muscular flap called the operculum

most have swim bladder, a gas-filled organ that helps to control the buoyancy of the fish

further divided into two extant clades: Actinopterygii (ray-finned fishes) and Sarcopterygii (lobe-finned fishes)

Actinopterygii, the ray-finned fishes, include many familiar fishes—tuna, bass, trout, and salmon

Ray-finned fishes–> fins that are webs of skin supported by bony spines called rays

In contrast, the fins of Sarcopterygii are fleshy and lobed, supported by bone Living members of this clade include the less-familiar lungfishes and coelacanths

Question 34

Amphibians

Answer 34

vertebrate tetrapods

frogs, salamanders and caecilians

metamorphosis

Amphibians evolved during the Devonian period and were the earliest terrestrial tetrapods

Question 35

Characteristics of Amphibians

Answer 35

four well-developed limbs

Some species of salamanders and all caecilians are functionally limbless; their limbs are vestigial

characteristic of extant amphibians is a moist, permeable skin that is achieved via mucus glands that keep the skin moist; thus, exchange of oxygen and carbon dioxide with the environment can take place through it (cutaneous respiration)

pedicellate teeth—teeth in which the root and crown are calcified, separated by a zone of noncalcified tissue

papilla amphibiorum and papilla basilaris, structures of the inner ear that are sensitive to frequencies below and above 10,00 hertz, respectively

auricular operculum, which is an extra bone in the ear that transmits sounds to the inner ear

all extant adult amphibians are carnivorous and some have a sticky tounge to capture prey

Question 36

Evolution of Amphibians

Answer 36

nearly 400 million years ago

Evolution of tetrapods from fishes represented a significant change in body plan from one suited to organisms that respired and swam in water, to organisms that breathed air and moved onto land

changes occurred over a span of 50 million years during the devonian period

One of the earliest known tetrapods is from the genus Acanthostega
- aquatic
- gills are similar to fishes
- 4 limbs
- same skeletal structure of limbs found in present day tetrapods
- assumed theey lived in shallow waters, intermediate form between lobe finned fishes and early full terrestrial tetrapods

In 2006, researchers published news of their discovery of a fossil of a “tetrapod-like fish,” Tiktaalik roseae, which seems to be an intermediate form between fishes having fins and tetrapods having limbs. Tiktaalik likely lived in a shallow water environment about 375 million years ago

Question 37

Modern Amphibians

Answer 37

6,770 extant species

inhabit tropical and temperate regions

Amphibians can be divided into three clades:
Urodela (“tailed-ones”) the salamanders;
Anura (“tail-less ones”), the frogs;
Apoda (“legless ones”), the caecilians.

Question 38

Urodela: Salamanders (amphibians)

Answer 38

living approximately 620 species

aquatic, terrestrial some only live on land as adults

generalized tetrapod body plan with four limbs and a tail

move by bending their bodies from side to side, called lateral undulation, in a fish-like manner while “walking” their arms and legs fore and aft

their gait is similar to that used by early tetrapods

Respiration differs among different species

majority lungless, and respiration occurs through the skin or through external gills

Some terrestrial salamanders have primitive lungs; a few species have both gills and lungs

internal fertilization of the eggs

The only male amphibians that possess copulatory structures are the caecilians, so fertilization among salamanders typically involves an elaborate and often prolonged courtship

successful transfer of sperm from male to female via a spermatophore

Development in many of the most highly evolved salamanders, which are fully terrestrial, occurs during a prolonged egg stage, with the eggs guarded by the mother

gilled larval stage is found only within the egg capsule, with the gills being resorbed, and metamorphosis being completed, before hatching–> Hatchlings thus resemble tiny adults

Question 39

Anura: Frogs (amphibians)

Answer 39

most diverse groups of vertebrates

5,965 species

on all of the continents except Antarctica

body plan that is more specialized for movement

skin that acts as camouflage

release defensive chemicals from glands in the skin that are poisonous to predators

Frog eggs are fertilized externally, usually in moist environments

eggs lack a shell and thus dehydrate quickly in dry environments

diversity of parental behavior
- laying eggs and little care
- carry eggs and tadpoles on hind legas and backs

life cycle consists of two stages
-larval stage
- metamorphosis into adult stage

larval stage is tadpole, filter feeding herbivore, have gills, lateral line system, long finned tails and lack limbs

during metamorphosis
- the gills, tail, and lateral line system disappear
- four limbs develop
- jaws become larger and are suited for carnivorous feeding
- digestive system transforms into the typical short gut of a predator
- eardrum and air-breathing lungs also develop

Question 40

Apoda: Caecilians (amphibians)

Answer 40

185 species

complete lack of limbs leads to their resemblance to earthworms in appearance

adapted for a soil-burrowing or aquatic lifestyle, nearly blind

found in the tropics of South America, Africa, and Southern Asia

vestigial limbs, evidence that they evolved from a legged ancestor

Question 41

amniotes

Answer 41

reptiles, birds and mammals

distinguished from amphibians by their terrestrially adapted egg, which is protected by amniotic membranes

evolution of amniotic membranes meant that the embryos of amniotes were provided with their own aquatic environment, which led to less dependence on water for development and thus allowed the amniotes to branch out into drier environments

shells of various amniotic species vary significantly, they all allow retention of water

shells of bird eggs are composed of calcium carbonate and are hard, but fragile

reptile eggs are leathery and require a moist environment

Most mammals do not lay eggs (except for monotremes)–> embryo grows within the mother’s body; however, even with this internal gestation, amniotic membranes are still present

Question 42

Characteristics of Amniotes

Answer 42

amniotic egg is the key characteristic of amniotes

shell of the egg provides protection for the developing embryo while being permeable enough to allow for the exchange of carbon dioxide and oxygen

albumin, or egg white, provides the embryo with water and protein

fattier egg yolk is the energy supply for the embryo

eggs of amniotes contain three additional extra-embryonic membranes: the chorion, amnion, and allantois

Extra-embryonic membranes are not a part of the body of the developing embryo

inner amniotic membrane surrounds the embryo itself, protects the embryo from mechanical shock and supports hydration

the chorion surrounds the embryo and yolk sac, facilitates exchange of oxygen and carbon dioxide between the embryo and the egg’s external environment

allantois stores nitrogenous wastes produced by the embryo and also facilitates respiration

in mammals, membranes that are homologous to the extra-embryonic membranes in eggs are present in the placenta.

Question 43

Evolution of Amniotes

Answer 43

first amniotes evolved from amphibian ancestors approximately 340 million years ago during the Carboniferous period

diverged into two main lines soon after the first amniotes arose
-synapsids–> include all mammals+extinct mammalian species, therapsids were mammal-like reptiles from which mammals evolved

-sauropsids–> include reptiles and birds, and can be further divided into anapsids and diapsids. The key differences between the synapsids, anapsids, and diapsids are the structures of the skull and the number of temporal fenestrae behind each eye

Temporal fenestrae are post-orbital openings in the skull that allow muscles to expand and lengthen

Anapsids have no temporal fenestrae, include extinct organisms and may, based on anatomy, include turtles, diverged into two groups,
- the Archosauromorpha (“ancient lizard form”) archosaurs include modern crocodiles and alligators, and the extinct pterosaurs (“winged lizard”) and dinosaurs (“terrible lizard”) Clade Dinosauria includes birds, which evolved from a branch of dinosaurs
- Lepidosauromorpha (“scaly lizard form”) lepidosaurs include modern lizards, snakes, and tuataras during the Mesozoic period

synapsids have one

diapsids have two, include birds and all other living and extinct reptiles

In the past, the most common division of amniotes has been into the classes Mammalia, Reptilia, and Aves

Birds are descended, however, from dinosaurs, so this classical scheme results in groups that are not true clades

Question 44

Characteristics of Reptiles

Answer 44

Limbless reptiles—snakes and other squamates—have vestigial limbs and, like caecilians, are classified as tetrapods because they are descended from four-limbed ancestors

Reptiles lay eggs enclosed in shells on land

aquatic reptiles return to the land to lay eggs

usually reproduce sexually with internal fertilization

Some species display ovoviviparity, with the eggs remaining in the mother’s body until they are ready to hatch. Other species are viviparous, with the offspring born alive

scaly skin, containing the protein keratin and waxy lipids, which reduced water loss from the skin. This occlusive skin means that reptiles cannot use their skin for respiration, like amphibians, and thus all breathe with lungs

ectotherms, animals whose main source of body heat comes from the environment

categorized as poikilotherms, or animals whose body temperatures vary rather than remain stable

behavioral adaptations to help regulate body temperature, such as basking in sunny places to warm up and finding shady spots or going underground to cool down

advantage of ectothermy is that metabolic energy from food is not required to heat the body; therefore, reptiles can survive on about 10 percent of the calories required by a similarly sized endotherm

some brumate in cold weather

Brumation is similar to hibernation in that the animal becomes less active and can go for long periods without eating, but differs from hibernation in that brumating reptiles are not asleep or living off fat reserves. Rather, their metabolism is slowed in response to cold temperatures, and the animal is very sluggish

Question 45

Evolution of Reptiles

Answer 45

300 million years ago during the Carboniferous period

oldest known amniotes is Casineria
- has both amohibian and reptilian characteristics

earliest undisputed reptiles was Hylonomus

diverged into three groups—synapsids, anapsids, and diapsids—during the Permian period

Permian period also saw a second major divergence of diapsid reptiles into archosaurs (predecessors of crocodilians and dinosaurs) and lepidosaurs (predecessors of snakes and lizards)

groups remained inconspicuous until the Triassic period, when the archosaurs became the dominant terrestrial group due to the extinction of large-bodied anapsids and synapsids during the Permian-Triassic extinction

About 250 million years ago, archosaurs radiated into the dinosaurs and the pterosaurs

Pterosaurs had a number of adaptations that allowed for flight, including hollow bones (birds also exhibit hollow bones, a case of convergent evolution). Their wings were formed by membranes of skin that attached to the long, fourth finger of each arm and extended along the body to the legs

dinosaurs were a diverse group of terrestrial reptiles with more than 1,000 species identified to date

Some dinosaurs were quadrupeds others were bipeds

Some were carnivorous, whereas others were herbivorous

Dinosaurs laid eggs, number of nests containing fossilized eggs have been found

It is not known whether dinosaurs were endotherms or ectotherms However, given that modern birds are endothermic, the dinosaurs that served as ancestors to birds likely were endothermic as well

Some fossil evidence exists for dinosaurian parental care, and comparative biology supports this hypothesis since the archosaur birds and crocodilians display parental care

Dinosaurs dominated the Mesozoic Era, known as the “age of reptiles”

dominance of dinosaurs lasted until end of the Cretaceous ( last period of the Mesozoic Era)

The Cretaceous-Tertiary extinction resulted in the loss of most of the large-bodied animals of the Mesozoic Era

Birds are the only living descendants of one of the major clades of dinosaurs

Question 46

Modern Reptiles

Answer 46

classified into four living clades

25 species of Crocodilia, 2 species of Sphenodontia, approximately 9,200 Squamata species, and the Testudines, with about 325 species

Question 47

Crocodilia (reptiles)

Answer 47

arose with a distinct lineage by the middle Triassic; extant species include alligators, crocodiles, and caimans

live throughout the tropics and subtropics of Africa, South America, Southern Florida, Asia, and Australia

freshwater, saltwater, and brackish habitats

Some species are able to move on land due to their semi-erect posture

Question 48

Sphenodontia (reptiles)

Answer 48

arose in the Mesozoic era and includes only one living genus, Tuatara, comprising two species that are found in New Zealand

Tuataras measure up to 80 centimeters and weigh about 1 kilogram

unique features of the skull and jaws clearly define them and distinguish the group from the squamates

Question 49

Squamata (reptiles)

Answer 49

arose in the late Permian

extant species include lizards and snakes

found on all continents except Antarctica

most closely related to tuataras, both groups having evolved from a lepidosaurian ancestor

largest extant clade of reptiles

Most lizards differ from snakes by having four limbs, although these have been variously lost or significantly reduced in at least 60 lineages

Snakes lack eyelids and external ears, which are present in lizards

Lizard species range in size from chameleons and geckos, which are a few centimeters in length, to the Komodo dragon, which is about 3 meters in length

Most lizards are carnivorous, but some large species, such as iguanas, are herbivores

Snakes are thought to have descended from either burrowing lizards or aquatic lizards over 100 million years ago

Snakes comprise about 3,000 species

range in size from 10 centimeter-long thread snakes to 10 meter-long pythons and anacondas

All snakes are carnivorous and eat small animals, birds, eggs, fish, and insects

specializations all point to snakes having evolved to feed on relatively large prey (even though some current species have reversed this trend)

most snakes have a skull that is very flexible, involving eight rotational joints

having mandibles (lower jaws) without either bony or ligamentous attachment anteriorly–> connection via skin and muscle

great expansion of the gape and independent motion of the two sides—both advantages in swallowing big items

Question 50

Testudines (reptiles)

Answer 50

Turtles

characterized by a bony or cartilaginous shell

shell consists of the ventral surface called the plastron and the dorsal surface called the carapace, which develops from the ribs

plastron is made of scutes or plates
–>the scutes can be used to differentiate species of turtles

two clades of turtles are most easily recognized by how they retract their necks

dominant group, which includes all North American species, retracts its neck in a vertical S-curve. Turtles in the less speciose clade retract the neck with a horizontal curve

arose approximately 200 million years ago predating crocodiles lizards and snakes

are ectotherms

lay eggs on land, although many species live in or near water

None exhibit parental care

Turtles range in size from the speckled padloper tortoise at 8 centimeters to the leatherback sea turtle at 200 centimeters

Question 51

Characteristics of Birds

Answer 51

endothermic, and because they fly, they require large amounts of energy, necessitating a high metabolic rate

have an insulating covering that keeps heat in the body: feathers

down feathers are especially insulating, trapping air in spaces between each feather to decrease the rate of heat loss

Certain parts of a bird’s body are covered in down feathers, and the base of other feathers have a downy portion, whereas newly hatched birds are covered in down

feathers allow for flight, enabling the lift and thrust necessary to become airborne

feathers on a wing are flexible, so the collective feathers move and separate as air moves through them, reducing the drag on the wing

Flight feathers are asymmetrical, which affects airflow over them and provides some of the lifting and thrusting force required for flight

Two types of flight feathers
- primary feathers –> located at the tip of the wing and provide thrust
- secondary feathers –> located closer to the body, attach to the forearm portion of the wing and provide lift

Contour feathers are the feathers found on the body, and they help reduce drag produced by wind resistance during flight

flapping of wings caused by chest muscles–> the pectoralis and the supracoracoideus

highly developed in birds account for higher percentage of body mass than in most mammals

These attach to a blade-shaped keel, like that of a boat, located on the sternum

sternum of birds larger than that of other vertebrates, which accommodates the large muscles required to generate enough upward force to generate lift with the flapping of the wings

Another skeletal modification found in most birds is the fusion of the two clavicles (collarbones), forming the furcula or wishbone. The furcula is flexible enough to bend and provide support to the shoulder girdle during flapping

low body weight is important for flight:
-1)Pneumatic bones are bones that are hollow, rather than filled with tissue, contain air spaces that are sometimes connected to air sacs, and they have struts of bone to provide structural reinforcement
- not found in all birds, more extensive in large than in small birds
- Not all bones of the skeleton are pneumatic, although the skulls of almost all birds are
-2) lack of a urinary bladder
- possess a cloaca, a structure that allows water to be reabsorbed from waste back into the bloodstream. Uric acid is not expelled as a liquid but is concentrated into urate salts, which are expelled along with fecal matter
- 3) only possess one ovary rather than two

largest living bird is the ostrich, and while it is much smaller than the largest mammals, it is flightless

air sacs that extend into bones to form pneumatic bones also join with the lungs and function in respiration–> airflow through bird lungs travels in one direction, Air sacs allow for this unidirectional airflow, which also creates a cross-current exchange system with the blood. In a cross-current or counter-current system, the air flows in one direction and the blood flows in the opposite direction, creating a very efficient means of gas exchange

Question 52

Evolution of Birds

Answer 52

somewhat unclear

fragility of bird bones, they do not fossilize as well as other vertebrates

Birds are diapsids, meaning they have two fenestrations or openings in their skulls

belong to a group of diapsids called the archosaurs, which also includes crocodiles and dinosaurs

Dinosaurs (including birds) are further subdivided into two groups>
- the Saurischia (“lizard like”) –> Saurischia diverged into two groups: One included the long-necked herbivorous dinosaurs, such as Apatosaurus. The second group, bipedal predators called theropods, includes birds.
- the Ornithischia (“bird like”)

This course of evolution is suggested by similarities between theropod fossils and birds, specifically in the structure of the hip and wrist bones, as well as the presence of the wishbone, formed by the fusing of the clavicles

Archaeopteryx, from the Jurassic period

important in establishing the relationship between birds and dinosaurs, because it is an intermediate fossil, meaning it has characteristics of both dinosaurs and birds

and it had teeth whereas birds do not, but it also had feathers modified for flight, a trait associated only with birds among modern animals

Fossils of older feathered dinosaurs exist, but the feathers do not have the characteristics of flight feathers

unclear exactly how flight evolved in birds

Two theories:
- arboreal (“tree”) hypothesis
- terrestrial (“land”) hypothesis

the question of how endothermy evolved in birds still is unanswered

Feathers provide insulation, but this is only beneficial if body heat is being produced internally. Similarly, internal heat production is only viable if insulation is present to retain that heat. It has been suggested that one or the other—feathers or endothermy—evolved in response to some other selective pressure

During the Cretaceous period, a group known as the Enantiornithes was the dominant bird type

certain bones of the feet are joined differently than the way the bones are joined in modern birds, they did not survive past the Cretaceous

Along with the Enantiornithes, Ornithurae birds (the evolutionary line that includes modern birds) were also present in the Cretaceous

After the extinction of Enantiornithes, modern birds became the dominant bird, with a large radiation occurring during the Cenozoic Era.

Referred to as Neornithes (“new birds”), modern birds are now classified into two groups:
- the Paleognathae (“old jaw”) or ratites, a group of flightless birds including ostriches, emus, rheas, and kiwis
- the Neognathae (“new jaw”), which includes all other birds

Question 53

arboreal hypothesis (birds)

Answer 53

The arboreal hypothesis posits that tree-dwelling precursors to modern birds jumped from branch to branch using their feathers for gliding before becoming fully capable of flapping flight.

Question 54

terrestrial hypothesis

Answer 54

the terrestrial hypothesis holds that running was the stimulus for flight, as wings could be used to improve running and then became used for flapping flight.

Question 55

Mammals

Answer 55

Mammals are vertebrates that possess hair and mammary glands. Several other characteristics are distinctive to mammals, including
- certain features of the jaw
- skeleton
- integument
- internal anatomy

Modern mammals belong to three clades:
- monotremes
- marsupials
- eutherians (or placental mammals)

Question 56

Characteristics of Mammals

Answer 56

presence of hair–>not very extensive on certain species, such as whales, hair has many important functions for mammals
- provides insulation to retain metabolic heat (they are endothermic)
- sensory mechanism–> speciallized hair called vibrissae (whiskers), attach to nerves that transmit information about sensation, which is particularly useful to nocturnal or burrowing mammals
- can provide coloration or be part of social signaling

Mammalian integument, or skin, includes secretory glands with various functions
- Sebaceous glands: produce a lipid mixture called sebum that is secreted onto the hair and skin for water resistance and lubrication, Sebaceous glands are located over most of the body
- Eccrine glands produce sweat, or perspiration–>mainly composed of wate, In most mammals, limited to certain areas of the body,some do not possess them at all. However, in primates, especially humans, sweat figures prominently in thermoregulation, regulating the body through evaporative cooling. Sweat glands are located over most of the body surface in primates.
- Apocrine glands (or scent glands): secrete substances that are used for chemical communication, such as in skunks
- Mammary glands: produce milk that is used to feed newborns. While male monotremes and eutherians possess mammary glands, male marsupials do not. Mammary glands likely are modified sebaceous or eccrine glands, but their evolutionary origin is not entirely clear

skeletal system of mammals possesses many unique features

lower jaw consists of only one bone, the dentary

joins the skull at the squamosal bone, while in other vertebrates, the quadrate bone of the jaw joins with the articular bone of the skull–> These bones are present in mammals, but they have been modified to function in hearing and form bones in the middle ear

Other vertebrates possess only one middle ear bone, the stapes

Mammals have three: the malleus, incus, and stapes

malleus originated from the articular bone, whereas the incus originated from the quadrate bone. This arrangement of jaw and ear bones aids in distinguishing fossil mammals from fossils of other synapsids

adductor muscle that closes the jaw is composed of two muscles in mammals: the temporalis and the masseter–> side-to-side movement, making chewing possible, which is unique to mammals

have heterodont teeth, meaning that they have different types and shapes of teeth rather than just one type and shape of tooth

diphyodonts, meaning that they have two sets of teeth in their lifetime: deciduous or “baby” teeth, and permanent teeth

Other vertebrates are polyphyodonts, that is, their teeth are replaced throughout their entire life

possess a four-chambered heart

specialized group of cardiac fibers located in the walls of their right atrium called the sinoatrial node, or pacemaker, which determines the rate at which the heart beats

Mammalian erythrocytes (red blood cells) do not have nuclei, whereas the erythrocytes of other vertebrates are nucleated

kidneys of mammals have a portion of the nephron called the loop of Henle or nephritic loop, which allows mammals to produce urine with a high concentration of solutes, higher than that of the blood

lack a renal portal system, which is a system of veins that moves blood from the hind or lower limbs and region of the tail to the kidneys, it exists in all other vertabrates except jawless fish

urinary bladder

in some the cerebral cortex, the outermost part of the cerebrum, is highly folded, allowing for a greater surface area than is possible with a smooth cortex

optic lobes, located in the midbrain, are divided into two parts in mammals,

whereas other vertebrates possess a single, undivided lobe

Eutherian mammals also possess a specialized structure that links the two cerebral hemispheres, called the corpus callosum

Question 57

Evolution of Mammals

Answer 57

synapsids, meaning they have a single opening in the skull

only living synapsids, as earlier forms became extinct by the Jurassic period

early non-mammalian synapsids can be divided into two groups:
-the pelycosaurs
- therapsids
–>Within the therapsids, a group called the cynodonts are thought to be the ancestors of mammals

key characteristic of synapsids is endothermy

increased metabolic rate required to internally modify body temperature went hand in hand with changes to certain skeletal structures

later synapsids, which had more evolved characteristics unique to mammals, possess cheeks for holding food and heterodont teeth, which are specialized for chewing, mechanically breaking down food to speed digestion and releasing the energy needed to produce heat

Chewing also requires the ability to chew and breathe at the same time–> facilitated by the presence of a secondary palate. A secondary palate separates the area of the mouth where chewing occurs from the area above where respiration occurs, allowing breathing to proceed uninterrupted during chewing.

A secondary palate is not found in pelycosaurs but is present in cynodonts and mammals

jawbone also shows changes from early synapsids to later ones

The zygomatic arch, or cheekbone, is present in mammals and advanced therapsids such as cynodonts, but is not present in pelycosaurs

The presence of the zygomatic arch suggests the presence of the masseter muscle, which closes the jaw and functions in chewing

In the appendicular skeleton, the shoulder girdle of therian mammals is modified from that of other vertebrates in that it does not possess a procoracoid bone or an interclavicle, and the scapula is the dominant bone

evolved from therapsids in the late Triassic period, as the earliest known mammal fossils are from the early Jurassic period, some 205 million years ago.

Early mammals were small

diversify in the Mesozoic Era

from the Jurassic to the Cretaceous periods, although most of these mammals were extinct by the end of the Mesozoic.

During the Cretaceous period, another radiation of mammals began and continued through the Cenozoic Era, about 65 million years ago

Question 58

Living Mammals

Answer 58

eutherians, or placental mammals, and the marsupials together comprise the clade of therian mammals.
Monotremes, or metatherians, form their sister clade

Question 59

monotremes (sister clade of mammals)

Answer 59

three living species of monotremes:
platypusand two species of echidnas, or spiny anteaters

leathery-beaked platypus belongs to the family Ornithorhynchidae (“bird beak”), whereas echidnas belong to the family Tachyglossidae (“sticky tongue”)

The platypus and one species of echidna are found in Australia, and the other species of echidna is found in New Guinea

Monotremes are unique among mammals as they lay eggs, rather than giving birth to live young. The shells of their eggs are not like the hard shells of birds, but are a leathery shell, similar to the shells of reptile eggs. Monotremes have no teeth

Question 60

Marsupials (sisterclade of mammals)

Answer 60

found primarily in Australia, though the opossum is found in North America.

Australian marsupials include the kangaroo, koala, bandicoot, Tasmanian devil and several other species.

Most species of marsupials possess a pouch in which the very premature young reside after birth, receiving milk and continuing to develop.

Marsupials differ from eutherians in that there is a less complex placental connection: The young are born at an extremely early age and latch onto the nipple within the pouch.

Question 61

Eutherians ( sister clade mammals)

Answer 61

Eutherians are the most widespread of the mammals, occurring throughout the world.

There are 18 to 20 orders of placental mammals.

Some examples are Insectivora, the insect eaters; Edentata, the toothless anteaters; Rodentia, the rodents; Cetacea, the aquatic mammals including whales; Carnivora, carnivorous mammals including dogs, cats, and bears; and Primates, which includes humans.

Eutherian mammals are sometimes called placental mammals because all species possess a complex placenta that connects a fetus to the mother, allowing for gas, fluid, and nutrient exchange.

While other mammals possess a less complex placenta or briefly have a placenta, all eutherians possess a complex placenta during gestation.

Question 62

primates

Answer 62

Order Primates of class Mammalia includes lemurs, tarsiers, monkeys, apes, and humans

Non-human primates live primarily in the tropical or subtropical regions of South America, Africa, and Asia

Question 63

Characteristics of Primates

Answer 63

All primate species possess adaptations for climbing trees, as they all descended from tree-dwellers

resulted in hands and feet that are adapted for brachiation, or climbing and swinging through trees

These adaptations include, but are not limited to:
1) a rotating shoulder joint,
2) a big toe that is widely separated from the other toes and thumbs, which are widely separated from fingers (except humans), which allow for gripping branches,
3) stereoscopic vision, two overlapping fields of vision from the eyes, which allows for the perception of depth and gauging distance.

Other characteristics of primates are>
brains that are larger than those of most other mammals,
claws that have been modified into flattened nails, typically only one offspring per pregnancy,
and a trend toward holding the body upright

Order Primates is divided into two groups: prosimians and anthropoids

Prosimians include the bush babies of Africa, the lemurs of Madagascar, and the lorises, pottos, and tarsiers of Southeast Asia

Anthropoids include monkeys, apes, and humans. In general, prosimians tend to be nocturnal (in contrast to diurnal anthropoids) and exhibit a smaller size and smaller brain than anthropoids.

Question 64

Evolution of Primates

Answer 64

first primate-like mammals are referred to as proto-primates.

roughly similar to squirrels

misterious since not a lot of evidencs

oldest known primate-like mammals with a relatively robust fossil record is Plesiadapis

Fossils of this primate have been dated to approximately 55 million years ago.

teeth and skeleton in common with true primates. They were found in North America and Europe in the Cenozoic and went extinct by the end of the Eocene.

first true primates were found in North America, Europe, Asia, and Africa in the Eocene Epoch

resembled present-day prosimians such as lemurs

evolution continued–> larger brains and eyes, and smaller muzzles being the trend

By the end of the Eocene Epoch, many of the early prosimian species went extinct due either to cooler temperatures or competition from the first monkeys

Anthropoid monkeys evolved from prosimians during the Oligocene Epoch

40 million years ago, evidence indicates that monkeys were present in the New World (South America) and the Old World (Africa and Asia)

New World monkeys are also called Platyrrhini—a reference to their broad noses

Old World monkeys are called Catarrhini—a reference to their narrow noses.

it is thought that monkeys arose in the Old World and reached the New World either by drifting on log rafts or by crossing land bridges

reproductive isolation–> seperate adaptive radiations

new world monkeys all aboral, old world monkeys aboral and ground-dwelling

Apes evolved from the catarrhines in Africa midway through the Cenozoic, approximately 25 million years ago

• generally larger than monkeys
• do not possess a tail
• All apes are capable of moving through trees
• many species spend most their time on the ground
• Apes are more intelligent than monkeys, and they have relatively larger brains proportionate to body size

divided into two groups.
The lesser apes comprise the family Hylobatidae, including gibbons and siamangs
The great apes include the genera Pan (chimpanzees and bonobos)

Gorilla (gorillas), Pongo (orangutans), and Homo (humans)

The very arboreal gibbons are smaller than the great apes; they have low sexual dimorphism (that is, the sexes are not markedly different in size); and they have relatively longer arms used for swinging through trees

Question 65

Human Evolution

Answer 65

family Hominidae of order Primates includes the hominoids: the great apes

comparison of human and chimpanzee DNA suggests that humans and chimpanzees diverged from a common hominoid ancestor approximately 6 million years ago

Several species evolved from the evolutionary branch that includes humans, although our species is the only surviving member

hominin is used to refer to those species that evolved after this split of the primate line, thereby designating species that are more closely related to humans than to chimpanzees

Hominins were predominantly bipedal and include those groups that likely gave rise to our species—including Australopithecus, Homo habilis, and Homo erectus—and those non-ancestral groups that can be considered “cousins” of modern humans, such as Neanderthals

there was often more than one species alive at any one time and that many of the fossils found (and species named) represent hominin species that died out and are not ancestral to modern humans

Question 66

Very Early Hominins

Answer 66

Three species of very early hominids

oldest of these, Sahelanthropus tchadensis, has been dated to nearly 7 million years ago

a single specimen of this genus, a skull that was a surface find in Chad.

The fossil, informally called “Toumai,” is a mosaic of primitive and evolved characteristics, and it is unclear how this fossil fits with the picture given by molecular data,

namely that the line leading to modern humans and modern chimpanzees apparently bifurcated about 6 million years ago.

second, younger species, Orrorin tugenensis, is also a relatively recent discovery, found in 2000

not known whether Orrorin was a human ancestor, but this possibility has not been ruled out

Some features of Orrorin are more similar to those of modern humans than are the australopiths, although Orrorin is much older

third genus, Ardipithecus, was discovered in the 1990s,

and the scientists who discovered the first fossil found that some other scientists did not believe the organism to be a biped (thus, it would not be considered a hominid).

In the intervening years, several more specimens of Ardipithecus, classified as two different species, demonstrated that the organism was bipedal. Again, the status of this genus as a human ancestor is uncertain.

Question 67

Early Hominins: Genus Australopithecus

Answer 67

genus of hominin that evolved in eastern Africa approximately 4 million years ago and went extinct about 2 million years ago

it is thought that our genus, genus Homo, evolved from a common ancestor shared with Australopithecus about 2 million years ago

number of characteristics that were more similar to the great apes than to modern humans

sexual dimorphism was more exaggerated than in modern humans. Males were up to 50 percent larger than females, a ratio that is similar to that seen in modern gorillas and orangutans

modern human males are approximately 15 to 20 percent larger than females

The brain size of Australopithecus relative to its body mass was also smaller than modern humans

common with modern humans was bipedalism, although it is likely that Australopithecus also spent time in trees

Hominin footprints, similar to those of modern humans, were found in Laetoli, Tanzania and dated to 3.6 million years ago

number of Australopithecus species, which are often referred to as australopiths

Australopithecus anamensis lived about 4.2 million years ago

More is known about another early species, Australopithecus afarensis, which lived between 3.9 and 2.9 million years ago

This species demonstrates a trend in human evolution: the reduction of the dentition and jaw in size

A. afarensis had smaller canines and molars compared to apes, but these were larger than those of modern humans.

Its brain size was 380–450 cubic centimeters, approximately the size of a modern chimpanzee brain

also had prognathic jaws, which is a relatively longer jaw than that of modern humans

fossil, which is informally called “Lucy,” is significant because it was the most complete australopith fossil found, with 40 percent of the skeleton recovered

Australopithecus africanus lived between 2 and 3 million years ago.

It had a slender build and was bipedal, but had robust arm bones and, like other early hominids, may have spent significant time in trees

brain was larger than that of A. afarensis at 500 cubic centimeters which is slightly less than one-third the size of modern human brains.

Two other species, Australopithecus bahrelghazali and Australopithecus garhi, have been added to the roster of australopiths in recent years.

Question 68

A Dead End: Genus Paranthropus

Answer 68

australopiths had a relatively slender build and teeth that were suited for soft food.

In the past several years, fossils of hominids of a different body type have been found and dated to approximately 2.5 million years ago.

These hominids, of the genus Paranthropus, were muscular, stood 1.3-1.4 meters tall, and had large grinding teeth. Their molars showed heavy wear, suggesting that they had a coarse and fibrous vegetarian diet as opposed to the partially carnivorous diet of the australopiths.

Paranthropus includes Paranthropus robustus of South Africa, and Paranthropus aethiopicus and Paranthropus boisei of East Africa.

The hominids in this genus went extinct more than 1 million years ago and are not thought to be ancestral to modern humans, but rather members of an evolutionary branch on the hominin tree that left no descendants

Question 69

Early Hominins: Genus Homo

Answer 69

human genus, Homo, first appeared between 2.5 and 3 million years ago

h.habilis were the oldest examples in the genus Homo, but in 2010, a new species called Homo gautengensis was discovered and may be older

Compared to A. africanus, H. habilis had a number of features more similar to modern humans:
- jaw that was less prognathic than the australopiths
- a larger brain, at 600–750 cubic centimeters

However, H. habilis retained some features of older hominin species, such as long arms.

The name H. habilis means “handy man,” which is a reference to the stone tools that have been found with its remains

H. erectus appeared approximately 1.8 million years ago

originated in East Africa and was the first hominin species to migrate out of Africa

Fossils of H. erectus have been found in India, China, Java, and Europe, and were known in the past as “Java Man” or “Peking Man.”

had a number of features similar to modern humans than those of H. habilis. H. erectus
- larger in size than earlier hominins, reaching heights up to 1.85 meters and weighing up to 65 kilograms, sizes similar to those of modern humans
- degree of sexual dimorphism less than earlier species,males being 20 to 30 percent larger than females, close to the size difference seen in our species
- larger brain than earlier species at 775–1,100 cubic centimeters, which compares to the 1,130–1,260 cubic centimeters modern human brains.
- H. erectus also had a nose with downward-facing nostrils similar to modern humans, rather than the forward facing nostrils found in other primates.

Longer, downward-facing nostrils allow for the warming of cold air before it enters the lungs and may have been an adaptation to colder climates.

Artifacts found with fossils of H. erectus suggest that it was the first hominin to use fire, hunt, and have a home base. H. erectus is generally thought to have lived until about 50,000 years ago.

Question 70

Humans: Homo sapiens

Answer 70

Homo sapiens, apparently evolved from H. erectus

starting about 500,000 years ago

include Homo heidelbergensis, Homo rhodesiensis, and Homo neanderthalensis

archaic H. sapiens had a brain size similar to that of modern humans, averaging 1,200–1,400 cubic centimeters.

They differed from modern humans by having a thick skull, a prominent brow ridge, and a receding chin.

Some of these species survived until 30,000–10,000 years ago, overlapping with modern humans

debate about the origins of anatomically modern humans or Homo sapiens sapiens

H. erectus migrated out of Africa and into Asia and Europe in the first major wave of migration about 1.5 million years ago

modern humans arose in Africa from H. erectus and migrated out of Africa about 100,000 years ago in a second major migration wave.

Then, modern humans replaced H. erectus species that had migrated into Asia and Europe in the first wave

One approach to studying the origins of modern humans is to examine mitochondrial DNA (mtDNA) from populations around the world.

fetus develops from an egg containing its mother’s mitochondria (which have their own, non-nuclear DNA), mtDNA is passed entirely through the maternal line.

Mutations in mtDNA can now be used to estimate the timeline of genetic divergence.

The resulting evidence suggests that all modern humans have mtDNA inherited from a common ancestor that lived in Africa about 160,000 years ago.

Another approach to the molecular understanding of human evolution is to examine the Y chromosome, which is passed from father to son.

This evidence suggests that all men today inherited a Y chromosome from a male that lived in Africa about 140,000 years ago.

Question 71

superphzlum Ecdysozoa

Answer 71

contains two of the most diverse animal groups: phylum Nematoda (the roundworms) and Phylum Arthropoda (the arthropods)

tough external covering called the cuticle. The cuticle provides a tough, but flexible exoskeleton tht protects these animals from water loss, predators and other aspects of the external environment

periodically molt, or shed their cuticle as they grow–> secrete a new cuticle

process of molting and replacing the cuticle is called ecdysis, which is how the superphylum derived its name

Question 72

Phylum Nematoda in superphylum ecdysozoa

Answer 72

triploblastic and possess an embryonic mesoderm that is sandwiched between the ectoderm and endoderm

bilaterally symmetrical

nematodes, or roundworms, possess a pseudocoelom and consist of both free-living and parasitic forms

were all the non-nematode matter of the biosphere removed, there would remain a shadow of the former world in the form of nematodes

belong to the superphylum Ecdysozoa that is believed to be a clade consisting of all evolutionary descendants from one common ancestor

have a hard cuticle that covers their bodies, which must be periodically shed and replaced for them to increase in size

more than 28,000 species with an estimated 16,000 being parasitic in nature

includes roundworms

all habitats with a large number of individuals of each species present in each

Caenorhabditis elegans has been extensively used as a model system in laboratories

Question 73

Morphology od Nematoda in superphylum ecdysozoa

Answer 73

show a tubular morphology and circular cross-section, cylindrical molrphology

pseudocoelomates and show the presence of a complete digestive system with a distinct mouth and anus. This is in contrast with the cnidarians, where only one opening is present (an incomplete digestive system)

cuticle of Nematodes is rich in collagen and a carbohydrate-protein polymer called chitin, and forms an external “skeleton” outside the epidermis

cuticle also lines many of the organs internally, including the pharynx and rectum

The epidermis can be either a single layer of cells or a syncytium, which is a multinucleated cell formed from the fusion of uninucleated cells

The head is radially symmetrical. A mouth opening is present at the anterior end with three or six lips as well as teeth in some species in the form of cuticle extensions

Some nematodes may present other external modifications like rings, head shields, or warts

Rings, however, do not reflect true internal body segmentation–>The mouth leads to a muscular pharynx and intestine, which leads to a rectum and anal opening at the posterior end

The muscles of nematodes differ from those of most animals: They have a longitudinal layer only, which accounts for the whip-like motion of their movement

Question 74

Excretory System of Nematoda in superphylum ecdysozoa

Answer 74

not well developed. Nitrogenous wastes may be lost by diffusion through the entire body or into the pseudocoelom (body cavity), where they are removed by specialized cells

Regulation of water and salt content of the body is achieved by renette glands, present under the pharynx in marine nematodes

Question 75

Nervous system of Nematoda in superphylum ecdysozoa

Answer 75

Most nematodes possess four longitudinal nerve cords that run along the length of the body in dorsal, ventral, and lateral positions

The ventral nerve cord is better developed than the dorsal or lateral cords

All nerve cords fuse at the anterior end, around the pharynx, to form head ganglia or the “brain” of the worm (which take the form of a ring around the pharynx) as well as at the posterior end to form the tail ganglia

In C. elegans, the nervous system accounts for nearly one-third of the total number of cells in the animal

Question 76

Reproduction of Nematoda in superphylum ecdysozoa

Answer 76

Nematodes employ a variety of reproductive strategies that range from monoecious to dioecious to parthenogenic, depending upon the species

C. elegans is a monoecious species and shows development of ova contained in a uterus as well as sperm contained in the spermatheca

The uterus has an external opening known as the vulva. The female genital pore is near the middle of the body, whereas the male’s is at the tip. Specialized structures at the tail of the male keep him in place while he deposits sperm with copulatory spicules

Fertilization is internal, and embryonic development starts very soon after fertilization

The embryo is released from the vulva during the gastrulation stage

The embryonic development stage lasts for 14 hours; development then continues through four successive larval stages with ecdysis between each stage—L1, L2, L3, and L4—leading to the development of a young male or female adult worm

Adverse environmental conditions like overcrowding and lack of food can result in the formation of an intermediate larval stage known as the dauer larva

Question 77

parasitic nematodes

Answer 77

exhibit complex lifecycles that involve multiple hosts, and they can have significant medical and veterinary impacts

Humans infected by Dracunculus medinensis, known as guinea worms, when they drink unfiltered water containing copepods

Hookworms, such as Ancyclostoma and Necator, infest intestines and feed on blood of mammals, especially in dogs, cats, and humans

Trichina worms (Trichinella) are the causal organism of trichinosis in humans, often resulting from the consumption of undercooked pork;can infect other mammalian hosts as well

Ascaris, a large intestinal roundworm, steals nutrition from its human host and may create physical blockage of the intestines

The filarial worms, such as Dirofilaria and Wuchereria, are commonly vectored by mosquitoes, which pass the infective agents among mammals through their blood-sucking activity

Dirofilaria immitis, a blood-infective parasite, is the notorious dog heartworm species

Wuchereria bancrofti infects the lymph nodes of humans, resulting in the non-lethal but deforming condition called elephantiasis, in which parts of the body become swelled to gigantic proportions due to obstruction of lymphatic drainage and inflammation of lymphatic tissues

Question 78

Superphylum Lophotrochozoa

Answer 78

are protostomes, in which the blastopore, or the point of involution of the ectoderm or outer germ layer, becomes the mouth opening to the alimentary canal. This is called protostomy or “first mouth.”

solid groups of cells split from the endoderm or inner germ layer to form a central mesodermal layer of cells. This layer multiplies into a band and then splits internally to form the coelom; this protostomic coelom is hence termed schizocoelom

possess either a lophophore or trochophore larvae:
- lophophores include groups united by the presence of the lophophore, a set of ciliated tentacles surrounding the mouth Lophophorata include the flatworms and several other phyla–> clades are upheld when RNA sequences are compared.

• Trochophore larvae are characterized by two bands of cilia around the body

triploblastic and possess an embryonic mesoderm

these phyla are also bilaterally symmetrical
–>means the beginning of cephalization, the evolution of a concentration of nervous tissues and sensory organs in the head of the organism, which is where it first encounters its environment.

Question 79

Phylum Platyhelminthes of superphylum Lophotrochozoa

Answer 79

flatworms are acoelomate organisms that include many free-living and parasitic forms.

consist of two lineages: the Catenulida and the Rhabditophora

Catenulida, or “chain worms” is a small clade of just over 100 species. These worms typically reproduce asexually by budding. However, the offspring do not fully attach from the parents and, resemble a chain in appearance

have three embryonic tissue layers that give rise to surfaces that cover tissues (from ectoderm), internal tissues (from mesoderm), and line the digestive system (from endoderm)

The epidermal tissue is a single layer cells or a layer of fused cells (syncytium) that covers a layer of circular muscle above a layer of longitudinal muscle

mesodermal tissues include mesenchymal cells that contain collagen and support secretory cells that secrete mucus and other materials at the surface. The flatworms are acoelomates, so their bodies are solid between the outer surface and the cavity of the digestive system

Question 80

Physiological Processes of Flatworms from Phylum Platyhelminthes of superphylum Lophotrochozoa

Answer 80

free-living species of flatworms are predators or scavengers

Parasitic forms feed on the tissues of their hosts

Most flatworms, such as the planarian have a gastrovascular cavity rather than a complete digestive system–>mouth=anus, some have anus

gut may be a simple sac or highly branched

Digestion is extracellular, with digested materials taken in to the cells of the gut lining by phagocytosis

One group, the cestodes, lacks a digestive system

excretory system with a network of tubules throughout the body with openings to the environment and nearby flame cells, whose cilia beat to direct waste fluids concentrated in the tubules out of the body–>regulation of dissolved salts and the excretion of nitrogenous wastes

nervous system consists of a pair of nerve cords running the length of the body with connections between them and a large ganglion or concentration of nerves at the anterior end of the worm, where there may also be a concentration of photosensory and chemosensory cells

no circulatory nor respiratory system
gas and nutrient exchange dependent on diffusion and cell-cell junctions. This necessarily limits the thickness of the body in these organisms, constraining them to be “flat” worms

Most flatworm species are monoecious, and fertilization is typically internal. Asexual reproduction is common in some groups

Question 81

Diversity of Flatworms from Phylum Platyhelminthes of superphylum Lophotrochozoa

Answer 81

four classes:
- Turbellaria
- Monogenea
- Trematoda
- Cestoda
a group that does not have a single common ancestor

Turbellaria mainly free-living, marine species, although some species live in freshwater or moist terrestrial environments

The ventral epidermis of turbellarians is ciliated and facilitates their locomotion

capable of remarkable feats of regeneration in which they may regrow the body, even from a small fragment

The monogeneans are ectoparasites, mostly of fish, simple lifecycles consist of a free-swimming larva that attaches to a fish to begin transformation to the parasitic adult form

The parasite has only one host and that host is usually only one species

The worms may produce enzymes that digest the host tissues or simply graze on surface mucus and skin particles

Most are hermaphroditic, but the male gametes develop first so cross-fertilization is quite common

The trematodes, or flukes, are internal parasites of mollusks and many other groups, including humans

have complex lifecycles that involve a primary host in which sexual reproduction occurs, and one or more secondary hosts in which asexual reproduction occurs

The primary host is almost always a mollusk

responsible for serious human diseases including schistosomiasis, a blood fluke. The disease infects an estimated 200 million people in the tropics, leading to organ damage and chronic symptoms like fatigue. Infection occurs when the human enters the water and a larva, released from the primary snail host, locates and penetrates the skin. The parasite infects various organs in the body and feeds on red blood cells before reproducing. Many of the eggs are released in feces and find their way into a waterway, where they are able to reinfect the primary snail host

cestodes, or tapeworms, are also internal parasites, mainly of vertebrates

live in the intestinal tract of the primary host and remain fixed using a sucker on the anterior end, or scolex, of the tapeworm body

The remaining body of the tapeworm is made up of a long series of units called proglottids, each of which may contain an excretory system with flame cells, but contain reproductive structures, both male and female

Tapeworms do not possess a digestive system; instead, they absorb nutrients from the food matter passing them in the host’s intestine

Proglottids are produced at the scolex and gradually migrate to the end of the tapeworm; at this point, they are “mature” and all structures except fertilized eggs have degenerated

Most reproduction occurs by cross-fertilization. The proglottid detaches from the body of the worm and is released into the feces of the organism

The eggs are eaten by an intermediate host

The juvenile worm infects the intermediate host and takes up residence, usually in muscle tissue. When the muscle tissue is eaten by the primary host, the cycle is completed

There are several tapeworm parasites of humans that are transmitted by eating uncooked or poorly cooked pork, beef, and fish.