Midterm I

Question 1

Describe simplisiomorphy and give an example

Answer 1

Shared primitive trait

Ex. When talking about mammalia, vertebrae are a shared primitive trait

Question 2

Describe synapomorphy and give an example

Answer 2

Shared derived trait; Found among two or more taxa and their most recent common ancestor, whose own ancestor does not possess that trait.
Ex. Ray finned fishes and bony-finned fishes both have a jaw, just like their ancestor, sharks, but the ancestor of sharks (lamprey) do not have jaws

Question 3

Define parsimony

Answer 3

The most parsiminious cladogram is the one that requires the least amount of changes to reach the end result

Question 4

Describe a monophyletic group

Answer 4

An organism and all of its descendants

Question 5

Describe a polyphletic group

Answer 5

A polyphyletic group consists of two or more organisms and no common ancestor
Ex. a depiction of birds and bats (both have wings) not including a common ancestor

Question 6

Describe a paraphyletic group

Answer 6

Some descendant groups not included

Ex. A cladogram depicting the relationship between birds and mammals but omitting other animals within Reptilia

Question 7

What do echinoderms and Chordates have in common?

Answer 7

Echinoderms and chordates are both deuterostomes, meaning that they share certain embryonic similarities

Question 8

What are the five traits of chordates? Describe each

Answer 8

1. Dorsal, hollow nerve chord
2. Notochord - gives rise to spine
3. Post-anal muscular tail
4. Pharyngeal pouches - become gills
5. Iodine-concentrating organ - Endostyle or thyroid

Question 9

Name the three subphyla within Chordata and give common names/representative organisms of each

Answer 9

Urochordates - Tunicates most common (otherwise known as ascidians), sister group of vertebrata
Cephalochordates - Amphioxus most common
Vertebrata - Fish, amphibians, reptiles, humans, the list goes on

Question 10

Briefly compare and contrast deuterostomes and protostomes

Answer 10

Deuterostomes include echinoderms and chordates. The name indicates cleavage in the early embryo (radial and indeterminate).
Protostomes include annelida, arthropoda, and molluscs. Cleavage is spiral and terminate

Question 11

Describe hemichordates (including their chordate characteristics) and their primary representative organism and how it lives

Answer 11

Hemichordates are not considered to be actual chordates, though they do have gill slits and a stomochord (made of chitinous material).
The Acorn Worms have three parts, a proboscis, collar, and trunk, and they live in U-shaped burrows. They gulp water into their coelom to move back and forth in their burrow

Question 12

Which two groups are considered “protochordates” or “lower chordates”?

Answer 12

Urochordata and cephalochordata

Question 13

What chordate characteristics do larval ascidians have? Adults?

Answer 13

Larval: All 5!
Adults: Endostyle, gill slits

Question 14

Describe, in detail, the feeding systems in adult ascidians

Answer 14

Food and water go into the pharynx via the incurrent syphon. The endostyle creates mucous strands that line the pharynx and pick up food particles which are moved by cilia into the digestive system. The excess water is pushed out of the outcurrent syphon via the gill slits.

Question 15

Why is the larval ascidian significant?

Answer 15

The larval ascidian has all chordate characteristics, and was thought to have given rise to cephalochordates, given that we now know that the sessile adult form is derived. Now it is thought that the cephalochordates arose from the few motile adult urochordates.

Question 16

Name the subgroups of urochordata and briefly describe the lifestyle, feeding habits, and locomotion

Answer 16

Ascidians - Tunicates: Motile larval form with all chordate characteristics. Adults are sessile and filter feed.
Thalaecians - Salps live in colonial and solitary forms, canreproduce asexually or sexually, and filter feed. Pyrosoma don’t move much, are bioluminescent and colonial. Filter feed also.
Appendicularians - Tiny little motile animals that secrete a large mucous house around themselves with the most complicated filtration system in the world

Question 17

What are the chordate characteristics of cephalochordates? What about vertebrate characteristics? What is the name of the best known cephalochordate?

Answer 17

Cephalochordates have all 5 chordate characteristics. The main vertebrate characteristic they have is myomeres and myosepta, but they also have vertebrate-like tail and circulatory system. Amphioxus is the common name

Question 18

Describe the feeding habits and locomotion of cephalochordates

Answer 18

Feeding: Cephalochordates use gill slits to feed. They move water into the gill slits using cilia and the wheel organ.
Locomotion: They move around by contracting their myomeres against the flexible notochord

Question 19

Which group of “lower chordates” is considered to be the sister group of vertebrates? Explain why.

Answer 19

Urochordates were placed as the sister group to vertebrates relatively recently based on molecular analysis. For the longest time people though that cephalochordates were the sister group. This new information helped us to determine that some urochordates’ sessile adult nature is derived

Question 20

What are the defining features of osteichthyes?

Answer 20

Dermal head skeleton including tooth-bearing dermal jaw palatal bones, bony operculum, branchiostegal rays (dermal bone covering ventral gills), a gas-filled structure (like a lung) to regulate respiration or buoyancy

Question 21

What are the three Cambrian chordates?

Answer 21

Haikouella, Pikaia, vetucolians

Question 22

What chordate characteristics are present in the three Cambrian Chordates Hoikouella, pikaia and vetucolians?

Answer 22

Pikaia - Has an obvious notochord, no gills, and straight myomeres
Haikouella - Has myomeres, notochord, pharynx, as well as vertebrate-like derived features: large brain, eyes, branchial bars, and an upper lip
Vetucolians - Have gills slits, so many think they are stem deuterostomes

Question 23

What would be the differences between cephalochordates and a hypothetical primitive vertebrate?

Answer 23

A hypothetical primitive vertebrate would need a cranium, a tripartite brain, w-shaped myomeres, thyroid, gill slits/gill arches, three-chambered heart, liver, kidney with archinephric duct, pancreatic tissue, caudal fin

Question 24

List the following organisms in order of their evolution. Know how to construct a cladogram of these groups. Tunicates, hemichordates, cephalochordates, placoderms, Haikouicthys, lamprey, ostracoderms

Answer 24

Hemichordates, cephalochordates, tunicates, (vertebrata) haikouichthyes, hagfishes, lampreys, (dermal bone head shield) placoderms within ostracoderms

Question 25

Describe Haikouichthyes and myllokumingia

Answer 25

They were both found in Chengjiang fauna. There was evidence of a cranium and w-shaped myomeres, but no evidence of bone.
Newly found specimens suggest the presence of arcualia, branchial bars and paired eyes.

Question 26

List and describe the synapomorphies of vertebrates

Answer 26

1. Vertebral column
2. Cranium (structures that enclose brain: can be bone, cartilage, fibrous materials)
3. Expanded tripartite brain and complex sense organs (includes forebrain, midbrain, hindbrain, as well as organs of sight, smell, etc.)
4. Muscular pharynx (uses branchiomeric musculature)
5. Duplicated HOX genes
6. Neural crest cells in the embryo

Question 27

Compare and contrast the extant Agnathans in terms of their anatomy, lifestyles, reproduction and feeding behaviour.

Answer 27

Agnatha means “no jaws”.
Hagfish are elongated organisms with mouth tentacles, a primitive eye, 12 gill slits and mucous glands. They secrete a thick mucous to clog up the gills of predators. Hagfish feed on decaying bodies using kerotinized plates on their tongue which are projected out of the mouth, to pull flesh inward. They knot their bodies up to pull food inward. Have a low reproductive rate.
Lamprey are elongated as well and feed on blood and body fluids of cold animals. They do so using their highly developed buccal funnel mouth. Eggs are laid in gravel and larva travel downstream. They bury themselves in the mud for 5+ years, metamorphosis and migration occur. Larval lamprey are called ammocoetes, and they filter feed using an endostyle and have a muscular pharynx.

Question 28

What are the germ layers? Describe each

Answer 28

Ectoderm: Gives rise to nervous system and skin
Mesoderm: Gives rise to muscles
Endoderm: Gives rise to gut, mostly
Neural crest: Migrates all over the body and gives rise to many bones and muscles of the face, visceral skeleton (near the gills), PNS, Schwann cells (wrapped around axons of motor neurons), pigment cells

Question 29

Which living agnathans are the most primitve? support your answer

Answer 29

Hagfish are the most primitive agnathan. They are jawless, have a single nostril, pronephros (type of kidney), 1 semicircular canal, isotonic body fluids

Question 30

What are conodonts? Where do they fit into vertebrate phylogeny?

Answer 30

Conodonts are mysterious microfossils found to be homologous to vertebrate teeth (similar in structure to dentine). The discovery of fossilized animals with these conodont elements as well as vertebrate features (notochord, cranium, myomeres, large eyes), implying that they are full vertebrates.

Question 31

Describe the characteristics of the paleozoic jawless vertebrates.

Answer 31

Paleozoic jawless vertebrates were covered in an armored shell (carapace). They had no jaws, but some had movable mouth plates. There were thwo classes: pteraspids (ostracoderms) and myopterygii (cephalaspids)

Question 32

Which group is considered the sister group of the gnathostomes?

Answer 32

The cephalaspid Osteostracans

Question 33

Describe the anatomical trends of the paleozoic jawless vertebrates from primitive to more derived forms

Answer 33

Pteraspids “ostracoderms” - Head shield formed from 2 bony plates, paired nasal openings, two semicircular canals
Myopterygii “cephalaspids”:
Anaspids - no large head shields, more adapted to open water swimming
Osteostracans - single nasal opening, head shield shows brain impression, single olfactory tract, distinct cerebellum, evidence of lateral line, 2 semicircular canals and pectoral fins
In general, more ancestral ostracoderms had some sort of midline dorsal fin, others as well had some sort of paired, anterior finlike projections, and the most derived had true pectoral fins

Question 34

What factors may have reduced competition between ostracoderms and gnathostomes for 50 million years?

Answer 34

Likely the two types of organisms exploited very different resources. Mass reductions in ostracoderm diversity during the devonian are most likely because of lowering global sea levels.

Question 35

What makes gnathostomes more derived than agnathans, other than the presence of jaws?

Answer 35

Jaws caused new food to become available (allowing gnathostomes to become bigger), allowed for manipulation of objects, allowed better gill ventilation. They have two sets of paired fins, teeth, and a second duplication of HOX genes.

Question 36

What are the shared derived characters of the gnathostomes?

Answer 36

1. Jaws
2. Gill skeleton (branchial arches and gill rakers)
3. Hypobranchial musculature for suction
4. Two distinct olfactory tracts and nostrils
5. Original first gill slit becomes spiracle (between mandibular and hyoid arches)
6. 3 semicircular canals
7. Conus arteriosus in the heart
8. Horizontal septum dividing muscle into epaxial and hypaxial
9. Vertebrae now have centra and ribs

Question 37

Completely and concisely discuss the evolution of jaws including the mechanism by which they evolved, evidence based on evo-devo and embryology, the advantage jaws gave early vertebrates, and the selective value of an early proto-jaw stage

Answer 37

Jaws evolved from the gill arches, and are basically another gill arch in the front (in most fishes, the jaw is supported by the 2nd gill arch, the hyoid arch).
Jaws and pharyngeal arches arise in series and both originate from neural crest cells. Nerves going to the jaws (V) and hyoid arch (VII) resemble cranial nerves (IX, X) to gill arches. Jaw musculature and gill arch musculature are homologous.
Jaws allowed for new feeding behaviours: grasping/biting prey, pursuit of prey, and herbivory as well as defense against predators, manipulation of objects.
Proto-jaws allow for strong mouth closing to squeeze water out of gills and strong mouth opening to suck in water.

Question 38

Describe the problems that have arisen in research pertaining to the evolution of jaws from the gill arches

Answer 38

Problem #1: Gill arches are arrange in the opposite direction in lamprey than in jawed fishes (gill arches are external to gill tissue). It was found that this is caused by when the gill supports start to develop in the womb, with Hox and Dlx genes contributing to these changes.
Problem #2: Why would the first gill arch enlarge?
It improves gill ventilation, increased activity. Once enlarged it can help in sucking in and squeezing out water

Question 39

Describe the placoderms and acanthodians in terms of their anatomy, feeding, lifestyle and reproduction. Which group is more derived?

Answer 39

Placoderms - Weak myomeres, initially marine but moved to FW. internal skeleton was cartilage, plates over the anterior portion of body. Some, like arthrodires, were predatory. Recently evidence was found that hints toward internal fertilization and live birth Ptyctodontids and arthrodires.
Acanthodians - Have multiple paired fins, a rounded (but streamlined) body, palagic swimmers, mainly FW, have a wide gape for filter feeding, Acanthodians most derived.

Question 40

Describe the diversity in body form of the various placoderm groups

Answer 40

Arthrodires - “jointed-neck”, most successful placoderms, include dunkleosteous, jaw muscles were inside palatoquadrate (unique among gnathostomes)
Antiarch placoderms - Mostly freshwater, heavy covering of dermal bone, jointed pectoral fins
Rhenanids - Dorsal-ventrally flattened, resembled modern skates
Ptyctodontids - “beak teeth”, armor reduced, crushing toothplate (perhaps preyed on shellfish)

Question 41

In the traditional view, placoderms are the sister group to ______ and acanthodians are the sister group to the ______. What recent evidence may challenge the traditional view?

Answer 41

Other gnathostomes, Osteichthyes.
Recently evidence has been found that the chondrocranium of acanthodians so closely reveals Chondrichthyes that they may in fact be basal Gnathostomes

Question 42

Give evidence to support paraphyly between acanthodians and placoderms

Answer 42

The chondrocranium of acanthodians is very similar to that of Chondrichthyes and placoderms. Jaw suspension of acanthodians appears to be intermediate between paleozoic condrichthyans and osteichthyans.

Question 43

List and describe the elements of the vertebrate cranium

Answer 43

1. Chondrocranium - Surrounds brain and is formed from neural crest
2. Splanchnocranium - Visceral skeleton (jaws and gill supports), formed from neural crest
3. Dermatocranium - Dermal bone within skin

Question 44

Explain the difference between the two bone types

Answer 44

Dermal bone - “Membranous bone”, always superficial, forms dermatocranium
Endochondral bone - Begins as cartilage, then ossifies (may remain cartilaginous like in sharks)

Question 45

Distinguish between axial, hypobranchial, and visceral muscle

Answer 45

Axial musculature - Segmented (myomeres), divided into epaxial and hypaxial
Hypobranchial - Muscles functioning to open the mouth located near the branchial arches
Visceral - “Branchiomeric”, attach to the splanchnocranium and are involved in feeding and gill ventilation

Question 46

Distinguish between the different basic tooth attachment types in gnathostomes

Answer 46

Tooth whorl - Teeth attached to skin (ex. Shark)
Pleurodont - Teeth set on inner side of jawbone (ex. some fishes, amphibians, some lizards)
Acrodont - Teeth fused to jawbone (ex. most bony fishes, reptiles)
Thecodont - Teeth set in sockets and held in place by peridontal ligaments (ex. archosaurian reptiles, mammals)

Question 47

Distinguish between the two major extant groups of Chondrichthyes

Answer 47

Holocephali - have a single gill opening - extant ones are ratfishes and chimaerans.
Neoselachii - have 5-7 gill openings - extant, sharks, skates, rays

Question 48

What are the shared derived characters of chondrichthyes

Answer 48

1. Prismatic (tesserate) calcified cartilaginous skeleton
2. Placoid scales - remnant of dermal skeleton
3. Unique tooth whorl
4. Inner ear opens externally via endolymphatic pores
5. Pelvic claspers

Question 49

Discuss the evolution of chondrichthyans, including descriptions of the typical forms in the three major radiations

Answer 49

Paleozoic radiation - 2m long, mainly freshwater, pelagic predators. Representative organism is cladoselache: has multi-cusped teeth, terminal mouth (at end of body), neural arches, symmetrical caudal fin, unrestricted notochord and a few placoid scales. Had amphistylic jaw and a large gape as well.
Mesozoic Radiation - Representative is Hybodus: had advanced fin structure, Heterocercal tail (both of these fin adaptations made movement easier), Heterodont dentition
Modern radiation - Neoselachii: extant sharks, skates, rays have protrusible jaw, mobile pectoral fin, stronger teeth, rostrum, subterminal mouth, calcified vertebrae and restricted notochord

Question 50

Discuss the characteristics of the three major extant groups of elasmombranchs

Answer 50

Galeoids - About 279 species, have anal fin, consists of sand tigers, basking sharks, whale sharks, great white sharks, nurse sharks, hammerhead sharks, mako sharks
Squaloids - About 124 species, deep water sharks such as dogfish, angel, cookie cutter, megamouth. Most primitive
Batoidea - skates and rays. At least 534 species. Electric rays, manta rays, stingrays skates

Question 51

What are the two types of bony fishes?

Answer 51

Actinopterygians - ray-finned fishes

Sarcopterygians - lobe-finned fishes

Question 52

Discuss the adaptations of living modern sharks for swimming, buoyancy, and prey capture.

Answer 52

Streamlining: Fusiform body shape. Skin tightly adheres to muscles below and is covered in placoid scales that reduce drag along body. They reduce drag using tiny riblits (outcroppings) on each scale.
Buoyancy: Reduced density increases buoyancy - The presence of cartilage instead of bone and the oil-filled liver both keep them quite buoyant
Sensory systems and prey systems: Lateral line system (detects water displacement), ampullae of Lorenzini (mild electrical detection), olfaction (smelling)

Question 53

Describe, in detail, the sensory systems of sharks

Answer 53

Lateral line - Detects water displacement (senses low frequency pressure waves and directional information) using units called neuromasts (hair cells with sensory cilia inside of a gelatinous cupula)
Ampullae of Lorenzini - Modified from the lateral line. Very sensitive to bioelectrical impulses. Consist of ampulla (filled with jelly) leading to pores on body. Used in prey detection and maybe even in navigation
Olfactory senses - Olfactory bulbs make up 14% of brain mass
Eyes - Shark eyes are quite similar to the eyes of other fishes, but they have one added feature: a shiny layer on the back of the eye called the tapetum lucidum which reflects light and enables better night-vision. They also have many rods in their retinas for night vision as well.
Hearing - Sharks do have an inner ear but they cannot hear nearly at the same range as humans. They can, however, hear at a lower level than humans (infrasound)
Sharks can hear up to 7 km away, can smell over 100m away, see up to 100m, feel pressure from up to 100m away, and perceive electrical impulses at up to 50cm away

Question 54

Describe the process of jaw protrusion in sharks and give the muscles involved

Answer 54

 - Expansive phase:
   - Lower jaw and hyoid depression:
     - Coracomandibular
     - Coracohyoid
   - Palatoquadrate protrusion:
     - Preorbitalis
   - Elevate cranium:
     - Epibranchials
 - Compressive phase
   - Mouth closing: 
     - Adductor mandibulae (insets on lower jaw - very strong)
   - Upper jaw retraction:
     - Levator palatoquadrati
     - Levator hyomandibulae

Question 55

Discuss the reproductive biology of Chondrichthyes. Use correct terminology for food sources for young and developmental categories

Answer 55

All sharks use internal fertilization. One of the male’s claspers rotates 90 degrees into the cloaca of the female, and the subcutaneous sac empties of water, washing the sperm in the clasper into the female’s cloaca.
Energy can be supplied to the fetus by either an egg yolk (called lecithotrophy) or using her reproductive tract (called matrotrophy).
There are three methods of babies entering the world: oviparity - baby hatches from egg, ovoviviparity - eggs are kept in mother until ready to hatch (obtain food from yolk sac) or viviparity - eggs hatch in mother (obtain food from yolk sac then mother)

Question 56

What characteristics of the life history of sharks make them highly vulnerable to fishing pressures?

Answer 56

They grow extremely slowly, have long life spans, mature at a late age (6-18 years or more), long gestation (up to two years), do not breed annually

Question 57

List the shared derived traits of neoselachii

Answer 57

1. Rostrum (and therefore, subterminal mouth)
2. Calcified vertebrae - restricted notochord
3. Stronger teeth- more enameloid
4. Protrusible upper jaw
5. Mobile pectoral fin