CHAPTER 35 Flashcards
Phylum Chordata
Chordates are deuterostome coelomates
Nearest relatives are echinoderms (the only other deuterostomes)
Fishes, amphibians, reptiles, birds, and mammals
4 Features
Dorsal, hollow nerve cord Notochord May be replaced by vertebral column Pharyngeal slits Pharyngeal pouches present in all vertebrate embryos Postanal tail
All chordates have all four of these characteristics at some time in their lives
Other characteristics also distinguish chordates
Chordate muscles are arranged in segmented blocks called somites
Most chordates have an internal skeleton against which the muscles work
Phylum Chordata can be divided into three subphyla
- Urochordata
- Cephalochordata
- Vertebrata
Subphylum Urochordata
Tunicates and salps are marine animals
Larvae are tadpolelike and have notochord and nerve cord
Are free-swimming but do not feed
Adults typically lose the tail and notochord
Are immobile filter-feeders
Many secrete a tunic (cellulose sac) that surrounds the animal
Subphylum Cephalochordata
Lancelets are scaleless chordates
Notochord persists throughout animal’s life
Spend most of their time partly buried
Have no distinguishable head
Feed on plankton using cilia-generated currents
Closest relatives to vertebrates
Subphylum Vertebrata
Vertebrates are chordates with a VERTEBRAL column
Distinguished from nonvertebrates by
Vertebral column—bony or cartilagenous – Encloses and protects the dorsal nerve cord
Head – Distinct and well-differentiated possessing sensory organs
Vertebrates also have
Neural crest – unique group of embryonic cells that forms many vertebrate structures
Internal organs – liver, kidneys, endocrine glands, heart, and closed circulatory system
Endoskeleton – made of cartilage or bone—living tissue that is strong but not brittle
Makes possible great size and extraordinary movement
The first vertebrates appeared in the oceans about 545 MYA
Mouth at one end, fin at the other
Jawed fishes soon became dominant
Amphibians invaded the land
Reptiles replaced them as the dominant land vertebrates
Birds and mammals became dominant after Cretaceous mass extinction
Fishes
Most diverse vertebrate group
Over half of all vertebrates
Provided the evolutionary base for invasion of land by amphibians
Fishes have the following characteristics
Vertebral column
Hagfish exception and lamprey rudamentary vertebrae of cartilage
Jaws and paired appendages
Hagfish and lamprey exceptions
Internal gills
Single-loop blood circulation
Nutritional deficiencies
Inability has been inherited by all their vertebrate descendants—cannot synthesize certain amino acids—must get them in their food.
HR
History of the Fishes
The first fishes had mouths with no jaws
Agnatha extant as hagfish (class Myxini) and lampreys (class Cephalaspidomorphi)
Ostracoderms (jawless) are now extinct—first vertebrates
The development of jaws occurred in the late Silurian period
Jaws evolved from the anterior gill arches that were made of cartilage
Armored fishes (placoderms) and some spiny fishes (Acanthodians) both had jaws
Spiny fish were common during early Devonian – replacing ostracoderms
Cartilage skeleton but skin had small plates of bone
Extinct at close of Permian
Placoderms became common in late Devonian
Jaw more improved than spiny fishes’
Upper jaw fused to the skull and the skull hinged on the shoulder
Extinct by end of period
At the end of the Devonian period, essentially all of these pioneer vertebrates disappeared, replaced by sharks and bony fishes in one of several mass extinctions
Sharks and bony fishes first evolved in the early Devonian, 400 MYA
Jaw was improved even further allowing the mouth to open much wider than was previously possible
Class Chondrichthyes
Sharks, skates, rays
Became the dominant sea predators in the Carboniferous period (360–280 MYA)
Cartilage skeleton “calcified” with granules of calcium carbonate
Light, strong skeleton
No swim bladder
Sharks were among the first vertebrates to develop teeth
Evolved from rough scales on mouth’s skin
Not set into the jaw so easily lost but continuously replaced
Sharks (and bony fishes) have a fully developed lateral line system
Series of sensory organs under the skin that detects changes in pressure waves
Reproduction in sharks differs from that of other fishes
Eggs are fertilized internally
Most pups are born alive
A few species do lay fertilized eggs
Sharks have long gestation periods and relatively few offspring
Therefore, are not able to recover quickly from population declines
Bony fishes
Evolved at the same time as sharks about 400 MYA
However, they adopted a heavy internal skeleton made completely of bone
Bony fishes are the most species-rich group of all vertebrates (> 30,000 living species)
Significant adaptations include swim bladder and gill cover
Swim bladder
Gas-filled sac that allows bony fishes to regulate their buoyant density
In most modern fish, filled and drained with gases internally
Gill cover
Hard plate, the operculum, covers gills
Flexing plate permits water pumping over gills
Efficient bellows system when stationary
Gases are taken from the blood, and the gas gland secretes the gases into the swim bladder; gas is released from the bladder by a muscular valve, the oval body
Two Major Groups of Bony Fishes
Ray-finned fishes (class Actinopterygii)
Parallel bony rays support and stiffen each fin
There are no muscles within the fins
Lobe-finned fishes (class Sarcopterygii)
Have paired fins that consist of a long fleshy muscular lobe
Supported by central core of bones with fully articulated joints—muscles can move fin rays
Almost certainly the amphibian ancesto
Class Amphibia
First vertebrates to walk on land but tied to water for reproduction
Direct descendants of fishes
5 distinguishing amphibian features
Legs – adaptation to life on land
Lungs
Cutaneous respiration – supplement lungs
Pulmonary veins – separate pulmonary circuit allows higher pressure blood to tissues lungshearttissue
Partially divided heart – improves separation of pulmonary and systemic circuits—atria have separation but not ventricles—3 chambered heart
Amphibia means “double life”
Successful invasion of land by vertebrates required several adaptations
Legs to support body’s weight
Lungs to extract oxygen from air
Redesigned heart and circulatory system to drive larger muscles
Reproduction still in water to prevent egg drying
System to prevent whole body desiccation—skin glands, lungs deep in body
Amphibians evolved from lobe-finned fish
Ichthyostega was one of the first amphibians
3 Modern Amphibian groups
5,670 species in 37 different families Order Anura (“without tail”) Order Caudata (“visible tail”) Order Apoda (“without legs”)
Order Anura (frogs and toads)
Frogs have smooth, moist skin and long legs
Most live in or near water, aquatic tadpole stage before metamorphosis into adult
Toads have bumpy, dry skin and short legs
Most live in dry environments
Not a monophyletic group—some toads are more closely related to frogs than they are other toads
Eggs laid in water – lack watertight membranes
Eggs fertilized externally
Tadpole – swimming larval form
Gradual metamorphosis into adult form
Order Caudata (salamanders)
Have long bodies, tails, and smooth, moist skin
Live in moist places
Eggs are fertilized internally – females pick up male’s sperm packet
Larvae similar to adults
Order Apoda (caecilians)
Tropical, burrowing amphibians
Legless with small eyes and jaws with teeth
Fertilization is internal
JACK
Class Reptilia
Over 7000 living species
All living reptiles exhibit three key features
Amniotic eggs, which are watertight; have yolk that is a food source
Dry skin and scales which cover body and prevents water loss
Thoracic breathing (moving rib cage), which increases lung capacity
Reptiles, birds, and mammals are amniotes The amniotic egg has four membranes Chorion Outermost layer, allows gas exchange Amnion Encases embryo in fluid-filled cavity Yolk sac Provides food Allantois Contains excreted wastes from embryo
Reptiles dominated earth for 250 million years
Reptiles are distinguished by the number of holes on side of the skull behind eye orbit
0 (anapsids), 1 (synapsids), 2 (diapsids)
The synapsids rose to dominance first Pelycosaurs First land vertebrates to kill beasts their own size Therapsids Replaced them about 250 MYA May have been endotherms “Mammal-like reptile Most became extinct 170 MYA One group survived and has living descendants today – the mammals
HEY
Modern reptiles developed two important characteristics
Internal fertilization
Sperm fertilizes egg before protective membranes are formed
Improved circulation
Oxygen is provided to the body more efficiently
Septum in heart extended to create partial wall between the ventricles
Crocodiles, birds, and mammals have completely divided 4-chambered heart
All living reptiles are ectothermic
Obtain heat from external sources
Regulate body temperature by moving in and out of sunlight
Compare to endothermic animals that generate their own heat internally
There are four surviving orders of reptiles
Chelonia (turtles and tortoises)
Rhynchocephalia (tuataras)
Squamata (lizards and snakes)
Crocodylia (crocodiles and alligators)
About 7000 species
Reptiles occur worldwide except in the coldest regions, where it is impossible for ectotherms to survive
Order Chelonia__Differ from all other reptiles because their bodies are encased within a protective shell
Carapace (dorsal) and plastron (ventral)
Tortoises are terrestrial while turtles are mostly aquatic
Both lack teeth but have sharp beaks
Marine turtles must return to land to lay eggs
Order Rhynchocephalia___Contains only two species of tuataras
Large, lizardlike animals about half a meter long
Only found on islands near New Zealand
Parietal eye
Eye with lens and retina concealed under layer of scales on top of head
Order Squamata—–A characteristic of this order is the presence of paired copulatory organs in the male
Snakes – 3000 species
Lack limbs (but evolved from a lizard with limbs), movable eyelids, and external ears
Lizards – 3800 species
Many have ability to regenerate lost tails
Order Crocodylia_)__25 species of large, primarily aquatic carnivorous reptiles
Crocodiles
Typically nocturnal
Tropical and subtropical regions
Alligators – only 2 species
Bodies well adapted to stealth hunting
Eyes on top of head, nostrils on top of snout, enormous mouth, strong necks
JACK
Class Aves___Birds are the most diverse of all terrestrial vertebrates
28 orders, 166 families, about 8600 species
Success lies in unique structure – feather
Birds still retain many reptilian traits Amniotic eggs and scales on legs Lack teeth and tails of reptiles Two major distinguishing traits Feathers Modified scales of keratin Provide lift for flight and conserve heat Flight skeleton Bones are thin and hollow Many are fused for rigidity – anchor strong flight muscles
Feathers developed from reptile scales
Linked structures provide continuous surface and a sturdy but flexible shape
Keel-shaped sternum
Archaeopteryx is the first known bird
Had skull with teeth, long reptilian tail
Feathers on wings and tail
Forelimbs nearly identical to those of theropods (dinosaur)
Feather probably evolved for insulation
Modern Birds
Adaptations for flight–physiology
Efficient respiration
Air passes all the way through lungs in a single direction via air sacs
Efficient circulation
4-chambered heart so muscles receive fully oxygenated blood
Rapid heartbeat
Endothermy
Body temperature (40–42oC) permits higher metabolic rate
Class Mammalia——-2 fundamentally mammalian traits
Hair
Long, keratin-rich filaments that extend from hair follicles
Insulation, camouflage, sensory structure
Mammary glands
Females possess mammary glands that secrete milk
Other notable features of mammals
Endothermy depends on higher metabolic rate
4-chambered heart
Respiration using diaphragm
Placenta in most mammals
Specialized organ that brings fetal and maternal blood into close contact
The mammalian lineage also gave rise to several adaptations in some groups
Specialized teeth
Different types of teeth are highly specialized to match particular eating habits
Contrast carnivore teeth to herbivore teeth
Digestion of plants Herbivorous mammals rely on mutualistic partnerships with bacteria for cellulose breakdown Development of hooves and horns Hooves are specialized keratin pads Horns are bone surrounded by keratin Antlers are made of bone, not keratin
Flying mammals: Bats
Only mammals capable of powered flight
Wing is a leathery membrane of skin and muscle stretched over 4 finger bones
Navigate in the dark by echolocation
HEY
History of Mammals
Mammals have been around since the time of the dinosaurs, about 220 MYA
Tiny, shrewlike, insect-eating, tree-dwelling creatures
May have been nocturnal – large eye sockets
Mammals reached their maximum diversity in the Tertiary period (65–2 MYA)
After mass extinction of dinosaurs
Decline in the total number of mammalian species over last 15 million years
2 Subclasses of Mammals
Prototheria (most primitive) Lay shelled eggs Only living group is the monotremes Theria Viviparous – young are born alive Two living groups Marsupials or pouched mammals Placental mammals
Evolution of Primates
Primates are the mammals that gave rise to our own species
Evolved two features that allowed them to succeed in an arboreal environment
Grasping fingers and toes
First digit (thumb) is opposable in many
Binocular vision
Eyes are shifted toward the front of the face
Lets brain judge distances precisely
About 40 MYA, the earliest primates split into two groups Prosimians Only a few survive today Lemurs, lorises and tarsiers Large eyes with increased visual acuity Most are nocturnal Anthropoids
Anthropoids
Include monkeys, apes, and humans
Almost all diurnal
Changes in eye design include color vision
Expanded brain
Live in groups with complex social interactions
Care for young for extended period
Long period of learning and brain development
30 MYA
New World monkeys migrated to South America
All arboreal; many have prehensile tail
Old World monkeys and hominids remained in Africa
No prehensile tails
Hominoids include
Apes
Gibbon, orangutan, gorilla, and chimpanzee
Larger brains than monkeys and lack tails
Paraphyletic group – some more closely related to hominids
Hominids
Humans
Soon after the gorilla lineage diverged, the common ancestor of all hominids split off from the chimpanzee line to begin the evolutionary journey leading to humans
Apes vs. Hominids
The common ancestor of apes and hominids is thought to have been an arboreal climber
Hominids became bipedal, walking upright
Apes evolved knuckle-walking
Differences related to bipedal locomotion
Human vertebral column is more curved
Spinal cord exits from bottom of skull
Humans carry much of the body’s weight on the lower limbs
Modern Humans
Modern humans first appeared in Africa about 600,000 years ago Three species are thought to have evolved Homo heidelbergensis (oldest) Coexisted with H. erectus Homo neanderthalensis Shorter and stockier than modern humans Homo sapiens (“wise man”) Some lump all 3 into H. sapiens
