Midterm

Question 1

What are the derived characteristics of the chordates?

What do these characteristics reflect selection for?

Answer 1

• A generalized nonvertebrate chordate:
  
  • Notochord
  • Dorsal hollow nerve cord
  • Myomeres (v-shaped)
  • Postanal tail
  • Pharyngeal slits and bars (“gill slits” - supporting bars of collagen-like material) - mostly for filter feeding (minimal gas exchange)
  • Endostyle (may have developed into thyroid)
• Reflects selection for enhanced locomotion and feeding

Question 2

What are the defining synapomorphies of the Subphylum Craniata?

Answer 2

• Cephalization (many synapomorphies associated with this)
• Splanchnocranium or visceral skeleton
• Chondrocranium
• Complex, W-shaped myomeres
• Excretory function (extretory tubules in hagfishes or kidneys)
• Three-chambered heart
• Prominent tail fin with fin rays
• Closed circulatory
• RBCs, haemoglobin

Question 3

What are the synapomorphies associated with cephalization?

Answer 3

1. Distinct head with cranium, tripartite brain, and sensory organs
   
   • Paired lateral eyes
   • Single olfactory tract
   • Inner ears with one or more semicircular canals (orientation in 3D space; balance)
   • Lateral line system - movement in water (pressure)
2. Cartilaginous pharyngeal (gill) arches
   
   • Support respiratory gills
3. Pharynx and gut is muscularized
   
   • Aids in respiration and suction feeding (pharynx)
   • Peristalsis (in gut) - increases efficiency

Question 4

What are the two key developmental and genetic changes involved in the origin of craniates?

Answer 4

1. Evolution of neural crest cells and ectodermal placodes
2. New developmental and regulatory genes (Hox genes and regulatory micro RNAs)

Question 5

What are neural crest cells?

What can they differentiate into?

Which outgroup to the hagfish and lampreys may have had neural crest cells?

Answer 5

• Embryonic ectodermal cells
• Form along the neural tube and migrate throughout the body
• Control development
• Differentiate into many different cell types (define cellular differentiation in many different parts of the body)
  
  • Splachnocranium (pharyngeal arches and pouches)
  • Teeth, nasal area of skull, jaws, middle ear
  • Peripheral nervous system
  • Endocrine organs
  • Epidermal pigment cells
• The Urochordates may have had neural crest-like genes

Question 6

What are ectodermal placodes?

What do they differentiate into?

Ectodermal placodes and neural crest cells interact with each other to form what?

Answer 6

• Thickening of the anterior ectoderm near the neural tube - highly neurogenic (caused by, controlled by, or arising in the nervous system)
• Placodes differentiate into (think sensory!):
  
  • Olfactory region
  • Taste receptors
  • Eye lens
  • Inner ears
  • Lateral line system
  • Electroreceptors
  • Cranial nerves
• Interact with neural crest cells to form most of the vertebrate head

Question 7

What are Hox genes?

What do their duplications lead to?

Answer 7

• Duplicate/multiple genes work in concert to code for more complex body parts during development
  
  • Non-craniate animals = Single Hox cluster
  • Jawless craniates = Two Hox clusters
  • Jawed craniates = Four Hox clusters

Question 8

What is the function of regulatory micro RNAs?

Answer 8

• Regulate RNAs that code for proteins
• Attach to mRNA and block translation
• Regulate development of many complex vertebrate structures

Question 9

What are the different ways that the “Cyclostomes” or “Agnathans” can be grouped? (i.e., in what ways can they be grouped as either monopyletic or paraphyletic?)

Answer 9

• Based on morphology (no jaws, no bone, single nasal opening)
  
  • Hagfish = outgroup to the lampreys and gnathostomes
  • “Paraphyletic”
• Based on molecular evidence (micro RNAs and genes)
  
  • Hagfish and lampreys are monophyletic outgroup to the gnathostomes

Question 10

What are the characteristics of the Hagfishes (the Myxinoidea)?

Answer 10

• Around 40 species, worldwide, marine
• Fibrous cranium
• No vertebrae
• One semicircular canal
• Rudimentary lateral line
• Rudimentary kidneys = osmoconformer (all body fluid is at the same solute concentration as salt water)
• Reduced eyes, no pineal
• Caudal fin only
• Deep sea scavangers

Question 11

What are the characteristics of the Lampreys (the Petromyzontoidea)?

Answer 11

• 40 species, north waters, marine and fresh water
• Cartilaginous cranium (stiff, fibrous material)
• Cartilaginous “arcualia” (cartilaginous vertebrae)
• Two semicircular canals
• Well developed lateral line
• Well developed kidneys
• Well developed eyes, pineal
• Caudal and dorsal fin
• Many are external parasites

Question 12

What are the two major extinct jawless vertebrate groups?

Answer 12

• The Conodonts
• The “Ostracoderms”

Question 13

What are the key features of the conodonts?

Answer 13

• Mineralized pharyngeal teeth (first record of mineralized tissue!)
  
  • Unique vertebrate mineral of hydroxyapatite (Ca, P) bound to collagen fibers
• Similar to vertebrate tooth dentine and enamel (but independent evolution)
• But no jaws!

Question 14

What are the key features of the “Ostracoderms”?

What kind of bone do they have?

What are the selective advantages to having this type of bone?

Answer 14

• Paraphyletic group with an uncertain phylogeny
• Mineralized exoskeleton (armour-like or scale-like)
• Most with cartilaginous endoskeleton
• First known vertebrates with bone
  
  • ​This is dermal bone (external hardening around connective tissue)
    
    • Dentine (from neural crest cells)
    • Acellular bone (not heavily bound to collagen) under tooth-like dentine projections called “odontodes”
    • Assumed homologous to chondrichthyan scales and teeth
• Selective advantage to dermal bone?
  
  • Protection
  • Mineral storage
  • Enhanced sensory reception

Question 15

What is the major group of derived “Ostracoderms”?

What are their derived bony characteristics?

What key changes do they exhibit from the “ostracoderms”?

Answer 15

• The “cephalaspids” (extinct)
• Complex dermal bone and bony endoskeleton (unlike cartilaginous endoskeleton in “ostracoderms”)
• Derived bony characteristics (from “ostracoderms”)
  
  • Dermal bone is cellular (rather than acellular in “ostradocerms”) - stronger
  • Endoskeleton has mineralized cartilage and perichondral bone
• Paired pectoral fins
• Heterocercal tail

Question 16

What are the two major synapomorphies of the Gnathostomata?

What controls the development of these synapomorphies?

Answer 16

• Jaws with teeth
  
  • Development controlled by neural crest cells
• **Two sets of paired appendages **
  
  • Development controlled by Hox genes

Question 17

Which group are considered to be stem gnathostomes?

What are some key differences between this group and the eugnathostomata?

Answer 17

• The Placoderms
• Thick jointed dermal bone on head and trunk
• Have jaws!
• Differences from eugnathostomata:
  
  • No deep rooted or replacement teeth
  • Pelvic fins (?)
  • Autostylic jaw suspension - hyomandibula does not support jaw (nothing supports jaw - top part of jaw is attached to chondrocranium)
  • Weakly developed myomeres

Question 18

What are the characteristics in the eugnathostomata that are not seen in the placoderms?

Answer 18

• Deep rooted teeth and/or with replacement
• Amphistylic jaw suspension
  
  • Hyomandibula does support jaw (stronger)
• Complex myomeres with epaxial and hypaxial elements
• Overall, more complex

Question 19

Name nine generalized gnathostome synapomorphies

Answer 19

1. Jaws with replacement teeth (stem group placoderms lack replacement teeth)
2. Branchial (and visceral) skeleton with jointed arches and gill rakers
3. Hypobranchial musculature
4. Two olfactory bulbs and paired nostrils
5. Spiracle
6. Three semicircular canals in the inner ear
7. Conus arteriosis (anterior heart chamber; “four-chambered” heart with sinus venosus, atrium, ventricle)
8. Complex axial muscles with epaxial and hypaxial portions, with lateral line in between (weakly developed in stem group placoderms)
9. Vertebra with neural and haemal arches, and centrum elements around or replacing the notochord

Question 20

Describe the differences between an early chordate, early craniate, and gnathostome heart/aortic arches.

Answer 20

• Early chordate
  
  • 6 arches (non-respiratory)
  • Sinus venosus only
  • Blood is all deoxygenated
• Early craniate
  
  • 6 respiratory arches
  • Atrium + ventricle + sinus venosus = three-chambered heart
  • Deoxygenated blood flows through heart and up through respiratory arches, then becomes oxygenated blood
• Gnathostome
  
  • Five respiratory arches (sixth is lost)
  • Subclavian and iliac arteries
  • Conus arteriosis + sinus venosus + atrium + ventricle = four-chambered heart
  • The conus arteriosis decreases turbulent blood flow from other chambers

Question 21

How did the mandibular arch form in early gnathostomes?

Answer 21

• From the first visceral arch
• Dorsal portion = the palatoquadrate cartilage
  
  • The posterior portion of this becomes the quadrate bone
• Ventral portion = the mandibular (Meckel’s) cartilage
  
  • The posterior portion of this becomes the articular bone
• The quadrate and articular bones ossify (endochondral bone) and become the jaw joint (same in all gnathostomes (except mammals))
• The rest of the jaw is covered in dermal bone

Question 22

How did the hyoid arch form in early gnathostomes?

Answer 22

• From the second visceral arch
• Dorsal portion = the hyomandibula
  
  • Functions to support the palatoquadrate
• Ventral portion = the ventral arch
  
  • Functions to support the floor of the pharynx and mouth

Question 23

What does the spiracle form from in gnathostomes?

What is derived from the spiracle and hyomandibula in tetrapods?

Answer 23

• From first pharyngeal pouch (retained in some fish for water passage)
• In tetrapods, eustachian tube is derived from spiracle
  
  • Stapes derived from hyomandibula

Question 24

What would be the advantage of a transitional stage in the origin of jaws?

What is Mallatt’s hypothesis with respect to the function of jaws in early gnathostomes?

Answer 24

• Advantage of transitional stage:
  
  • Powerful hypobranchial muscles attach to internal arches and jaws
  • This would aid in gill ventilation and opens jaws
• Mallatt’s hypothesis
  
  • First function of jaws was muscle attachment for gill ventilation
  • Secondarily modified for feeding/jaws

Question 25

What are the four different jaw suspension systems?

Answer 25

* Ancestral autostylic (placoderms) * Amphistylic (early gnathostomes) * Hyostylic (modern fishes) * Gives jaw mobility * Secondary autostylic (ratfishes, lungfishes, tetrapods)

Question 26

What kind of teeth do all crown gnathostomes have? What type of teeth to chondrichthyes have? What kind of teeth do osteichthyes have?

Answer 26

* Replaceable teeth with enamel (ectoderm) and dentine (neural crest cells) * Chondrichthyes * Non-rooted teeth develop deep within skin as "tooth whorls" * Osteichthyes * Teeth develop beneath skin (rooted) * Embedded in dermal bone (homologous to dermal bone and chondrichthyan scales)

Question 27

What are some generalized chondrichthyan synapomorphies?

Answer 27

* Calcified cartilaginous endoskeleton * Loss of dermal skeleton * Tooth whorls * Placoid scales * Unsegmented fin rays (ceratotrichia) * Claspers on male pelvic fins

Question 28

What type of scales do chondrichthyes have? What type of scales do ostracoderms have?

Answer 28

* Chondrichthyes * _Placoid_ scales * Dentine surrounded by "enameloid" (ectodermal and mesodermal elements) * Reduces drag * Reduced or absent in some bottom-dwelling skates and rays * Osteichthyes * _Ganoid_ scales are ancestral (heavy enamel over inflexible bone) * E.g., sturgeons, Acanthodians, bichirs, gars * _Elasmoid_ scales are derived (loss of enamel, dentine, and inflexible bone) * Flexible bone with thin (or no) enamel

Question 29

What does the picture below represent? In what orders of clades would you find each of these?

Answer 29

* Mineralized **endoskeleton** structures 1. Cartilage (found in hagfish, lampreys, and the early ostracoderms) 2. Mineralized cartilage and perichondral bone (found in the derived ostracoderms, placoderms, and acanthodians) 3. Calcified cartilage and remnant perichondral bone (found in the chondrichthyes) 4. Perichondral and endochondral bone (found in the osteichthyes)

Question 30

What are the differences between fin rays on the chondrichthyes and the osteichthyes?

Answer 30

* **Chondrichthyes** * **​**Ceratotrichia = horny rays that develop from unsegmented, keratinized rods * Epidermal * Some have spines from modified placoid scales (e.g., sting rays) * **Osteichthyes (bony fish)** * **​​**Lepidotrichia = scale rays developed from bony scales * Many are segmented with paired bony eleents * Very flexible (although some have inflexible spines which may be poisonous - selection for this depends on predation)

Question 31

What types of teeth are these and which vertebrates would you expect to find them in? In most vertebrates, what are the main categories of teeth? What about in mammals?

Answer 31

1. Pleurodont = Ancestral condition. Some fish, amphibians, and lizards 2. Acrodont = Most fish and lizards 3. Thecodont = Crocodiles and mammals * Most vertebrate teeth are: * Homodont (similar and simple cones) * Polyphyodont (continuously replaced) * In mammals, teeth are: * Heterodont (variable structure and function) * Diphyodont (two sets of teeth)

Question 32

What are some generalized elasmobranch characteristics?

Answer 32

* Multiple gill openings * Pectoral fin elements * Hyostylic jaw suspension * Pectoral fin support * Vertebral centra * Ventral mouth * Changes in nervous system, cranium, and gill arches

Question 33

What are the holocephali? What are some general synapomorphies of the holocephali?

Answer 33

* The chimeras, ratfishes (or rabbitfishes) * Have a fleshy operculum over four gills (one gill opening is visible) * Loss of spiracle and absence/reduction of scales * Loss of tooth whorls (have broad crushing tooth plates = "durophagous" dentition) * Secondary autostylic jaw suspension (called _holostylic​_)

Question 34

What are the neoselachii? What are their generalized characteristics? What are the three main groups?

Answer 34

* The extant elasmobranchs * Have multiple lateral gill openings * Ventral mouth * Hyostylic jaw suspension * Three main groups: * Galeomorphi * Squalomorphi * Batoidea

Question 35

What are the main differences between the galeomorphi and the squalomorphi?

Answer 35

* **Galeomorphi** * _Anal fins_ * Open water * Large sharks, active predators * Around 400 species * **Squalomorphi** * **​**_No anal fin_ * Benthic * Around 160 species * E.g., dogfish, angel shark etc.

Question 36

What are the characteristics of the batoidea?

Answer 36

* Skates and rays * Ventral gill openings * Dorso-ventrally flattened * Durophagous dentition * No anal fin * Reduced scales * Benthic and pelagic * **Skates** * **​**Thick tail with dorsal and caudal fin * _Oviparous_ (egg layers) * **Rays** * **​**Whiplike tail with bars instead of fins * _Viviparous_ (live birth)

Question 37

What characteristics of the chondrichthyes are associated with their predaceous lifestyle?

Answer 37

* Hyostylic jaw suspension, replacement teeth * Fusiform or terete shape * Heterocercal tail * Placoid scales to reduce drag * "Ball-bearing" notochord and calcified vertebrae (powerful swimming) * Buoyancy from oil-filled liver and urea in tissues (no swim bladder)

Question 38

What are the four major chondrichthyan sensory systems?

Answer 38

1. Chemoreception * Very large olfactory organ 2. Lateral line system (mechanoreception) * Detects water disturbance and directionality of its source * Based on neuromast organs (hair cells embedded in cupula (gel) that are displaced with water movement, causes a nerve discharge) 3. Vision * Cones * Tapetum lucidum for low light (reflective crystal layer behind retina) * Nictitating membrane (obscures vision just before contact with prey) 4. Electroreception * Based on ampullae of Lorenzini (conductive gel-filled canals ending in modified hair cells of lateral line) * Detect minute changes in electric fields (and temperature and salinity)

Question 39

What are the six different types of maternal investment in chondrichthyan reproduction?

Answer 39

1. Oviparity = egg-laying * Ancestral (in 45% of species) * **Lecitrophy** (all nutrients from egg/yolk sac) 2. Yolk-sac viviparity * Viviparity = live birth * Thin shelled eggs retained in uterus until developed * Nutrients from yolk sac 3. Uterine viviparity * Hatch internally early in development * Nutrients are from the mother via extensions of oviducts or gut 4. Oophagy * Mom supplies unfertilized eggs to developing embryos 5. Embryopagy * First to hatch in oviduct eats siblings * Mom supplies unfertilized eggs * Seen in sand tiger shark * Often occurs in animals with high mobility 6. Placental viviparity * Yolk sac develops into vascularized placenta * Maternal nutrients via bloodstream * **Matrotrophy** = high level of maternal investment, occurs in viviparous species

Question 40

What are the generalized Osteichthyan characteristics?

Answer 40

* Endochondral endoskeleton * Lung/swim bladder * Segmented fin rays (lepidotrichia) * Terminal dermal mouth bones (premaxilla, maxilla, dentary) with rooted teeth * _Teleostomi_ (ignore this group and consider these to be generalized Osteichthyan characteristics) * Party ossified endoskeleton * Terminal mouth opening * Bony operculum with branchiostegal rays * Bony ganoid scales * Otoliths in inner ear

Question 41

What are the two major classes of Osteichthyans? What are their characteristics?

Answer 41

1. Actinopterygians * "Ray-fin" fishes * Fan-like fin rays from base of fins * Single dorsal fin * Ganoine (enamel) scales * Unique forebrain development 2. Sarcopterygians * Fins with bones (humerus, femur) for support * Two dorsal fins * Cosmine (dentine) scales

Question 42

What are seven extant clades of the Osteichthyans? Provide some examples of fish found in each

Answer 42

* Polypteriformes (e.g., bichirs and reedfish) * Acipensiformes (e.g., sturgeons and paddlefish) * Neopterygii * Lepisosteiformes (e.g., gars) * Halecomorphi * Amiiformes (e.g., bowfins) * **Teleostei** (most derived group)

Question 43

What are the four main Teleost clades? Provide some examples of each

Answer 43

1. Osteoglossomorpha * Bony tongues and mooneyes 2. Elopomorpha * Eels and tarpons 3. Ostarioclupeomorpha * Ostariophysi (8000 species) = "bony bladders" * Catfish and minnows * Clupeomorphs (360 species) = herrings and anchovies 4. Euteleostei ("true final bony fish") * Protacanthopterygii * Esocids * Salmonids * Paracanthopterygii * Acanthopterygii (13500 species - "spiny rays") * Percaforms and others

Question 44

What are the four major teleost synapomorphies?

Answer 44

1. Highly mobile maxilla and premaxilla 2. Swim bladder for buyoancy 3. Homocercal tail 4. Thin, overlapping, flexible elasmoid scales

Question 45

What is the jaw system in the acipenseriformes (the sturgeons and paddlefish)?

Answer 45

* Amphistylic (maxilla and premaxilla are attached to the cranium) * Maxilla is the main jaw bone * Jaw is protrusible in sturgeons, but this is independent evolution

Question 46

What is the jaw suspension system in the early Neopterygians (Amiiformes)?

Answer 46

* Some cranial and jaw kinesis (_hyostyly_) from openings in dermal skull roof * The mobile maxilla is reduced, while the premaxilla is enlarged * Both the maxilla and the premaxilla have teeth * More dermal opercular bones form the branchiostegal rays

Question 47

Describe the evolution and function of the hyostylic jaw suspension in the teleost Actinopterygians

Answer 47

* Independently evolved many times in teleost (especially cods, perches, minnows) * Protrusible and mobile, with mobile pharyngeal jaws * This is important in the adaptive radiation of the group * Functions: * Maxilla and premaxilla highly mobile * The premaxilla is dominant, unattached, and often toothed * The maxilla is toothless and swings to lever the premaxilla * Opercular bones are mobile and open the lower jaw * Increases the opercular cavity * Suction and ventilation - This creates negative pressure to suck prey in and increase attack speed

Question 48

Name the following jaw suspension systems (clockwise from top left)

Answer 48

* Ancestral autostylic * Amphistylic * Secondary autostylic * Hyostylic

Question 49

What is the hypothesis on the evolution of the swim bladder?

Answer 49

* Evolved from evagination of the gut (likely originally for respiration) * Modified to be used for neutral buoyancy (shifts density to equilibriate with water pressure) * Hypothesis (assuming one origin): * Ventral respiratory * Dorsal respiratory --\> dorsal respiratory and buyoancy --\> dorsal buoyancy (swim bladders in teleosts) * Ventral respiratory --\> lungfishes lung and tetrapods

Question 50

Which types of fish have dorsal respiratory/buoyancy swim bladders? Which have ventral repiratory/buoyancy swim bladders?

Answer 50

* Ventral respiratory: * Sarcopterygians * Tetrapods * **Bichirs** * **​**Dorsal buoyancy and respiratory: * Gars * Bowfins * Dorsal buoyancy: * Teleostei * Sturgeons

Question 51

Describe physostomous swim bladders

Answer 51

* Primitive * Gulp air, swallow water * Found in osteoglossids, pike, eels, catfish, salmonids

Question 52

Describe physoclistous swim bladders

Answer 52

* Most derived (eu)teleosts * Gas glands only

Question 53

Describe the "Bohr effect"

Answer 53

* When pH is low, hemoglobin releases oxygen * Oxygen leaves the blood * Increases pressure * Goes into bladder

Question 54

Describe how a fish adjusts buoyancy in a physoclistous swim bladder when ascending or descending

Answer 54

* When fish is going up: * Decrease depth --\> decrease pressure --\> bladder expands --\> less gas needed in bladder for buoyancy * When going up, gas is relased through a valve (ovale) into the capillaries * When fish is going down: * Increase depth --\> increase pressure --\> bladder compresses --\> more gas needed in bladder for buoyancy * Gland secretes lactic acid and carbon dioxide --\> decreases pH --\> Bohr effect --\> Hb releases oxygen --\> goes into gas gland * Rete mirabile moves gas from the blood to the gas bladder * Extracts oxygen from the blood and releases it into the swim bladder * This is a countercurrent system (retains oxygen and builds pressure)

Question 55

What is the purpose of a homocercal tail in teleosts? How does the homocercal tail differ in gars and bowfins compared to the rest of the teleosts?

Answer 55

* Homocercal tails provide uniform thrust with no fin drag * Pectorals and pelvics are not needed for lift * Pelvics move anteriorally * Fins used for manoeuverability and other functions * Gars and bowfins have an abbreviated homocercal tail * Has **hypural bones** for support with **modified haemal arches** * **​**In true homocercal tails: * Unique **uroneural bone** (modified neural) * **Reduced hypurals**

Question 56

What is the difference between freshwater species and marine species with respect to reproduction in the teleosts?

Answer 56

* Freshwater species * Small clutches of large demersal (bottom dwelling) eggs * Burried in gravel, attached to rocks/plants, in nests * Eggs and young (fry) with large yolk sacs * Many provide parental care of eggs but few provide parental care after hatch * Marine species * Large clutches of small, pelagic (middle of the water column) eggs * Eggs drift in open sea for weeks/months before settling * No parental egg care * Young (larvae) with small or no yolk sac * Few marine species have demersal eggs and make nests (mostly small species, some with paternal egg care)

Question 57

What is "protandry" in anemone fish? What type of hermaphroditism is this an example of? What are simultaneous hermaphrodites?

Answer 57

* Exampe of "sequential hermaphrodites" * Switch male to female (largest size is the most advantageous in females - bigger clutch - therefore largest individual is always female) * Monogamous pair at anemone * If female dies, male changes to female, attracts new small male * Simultaneous hermaphrodites * Occurs in 20 families * One self-fertilizing species

Question 58

What are the two groups of living, non-tetrapod sacropterygians? What are their general synapomorphies (general sarcopterygian synapomorphies)? What are the synapomorphies specific to each group?

Answer 58

* General synapomorphies: * Skeletal fin support * Cosmine (dentine) scales * Two dorsal fins * The Actinistia (the Coelacanths): * Electroreceptive rostral organ * **Muscular lobed fins with skeletal support** * Three lobed tail (diphycercal) * Moves paired fins like tetrapod gait * The Dipnoi (the lungfishes): * Secondary autostylic jaw suspension with durophagous dentition * Obligate or facultative air breathers with lungs and gills * Paired nostrils: one external, _one internal_ (ancestral to internal nostrils ("choanae") of tetrapods?)

Question 59

What types of lungs do the Neoceratodus have? What types of lungs do the Lepidosiren and Protopterus have? (Both Dipnoi)

Answer 59

* Neoceratodus * Gills and ventral unpaired lungs * Lepidosiren and Protopterus * Reduced gills * Paired ventral lungs * Obligate air breathers * Can estivate ("hibernate") for months

Question 60

What are the Rhipidistia? What are their synapomorphies?

Answer 60

* Clade of lobe-finned fishes including the lungfishes (dipnoi) and the tetrapods 1. Molecular support 2. Heart with separated pulmonary and systemic circulation * Pulmonary vein goes into separated atrium * Also partly separated ventricle and conus arteriosis (with spiral valve) * Keeps oxygenated blood separate from deoxygenated blood

Question 61

What are the two major groups of Tetrapodomorphs (the Choanata)? Are they extinct of extant? What are their synapomorphies?

Answer 61

* Both groups are extinct * "Osteolepiformes" (paraphyletic!) * True choana * Autostylic jaw suspension * Many pectoral limb elements * Glenoid fossa on pectoral girdle * Paired vertebrae with dorsal ribs * Labyrinthodont teeth (infolded dentine * Elpistostegidae (derived osteolepiformes) * Flattened skull with dorsal eyes * Loss of dorsal and anal fin * Vertebrae with ventral ribs * Well-developed pectoral limb * Large ulnare bone and no digits (but in a CT scan of intact pectoral, ulnare appears to be many distal radials - digits derived from distal elements of fin)

Question 62

What was the key Elpistostegid discovery?

Answer 62

* Discovery of Tiktaalik in Canadian Arctic in 2006 * Pectoral with fin rays but flexible elbow and wrist joint * Loss of opercular and pectoral girdle elements - pectoral girdle is free of the skull * Loss of opercular dermal bones * Post-opercular bones incorporated into girdle or lost * First fish with a neck! * Robust axial skeleton * Capable of supporting body on land * Has a developed pelvic girdle * Robust pelvis with transitional features * Pubis, ilium, acetabulum (no ischium) * Not attached to sacral ribs * **Tiktaalik clearly "transitional" to stem tetrapods**

Question 63

What are the general characteristics of the "Stem (Devonian) Tetrapods"?

Answer 63

* Limbs with carpels (or tarsals) and digits * Acanthostega (basal early tetrapod) * 6-8 digits (fin-like forelimb) * Dendrerpeton (more derived early tetrapod) * 5 or fewer digits * Pelvic girdle attached to sacral vertebrae via ilium * Vertebrae with zygapophyses

Question 64

How does hearing differ in early tetrapods? E.g., Panderiichthys and Tiktaalik Acanthostega Early crown group tetrapods Derived tetrapods

Answer 64

* Panderiichthys and Tiktaalik * Widened spiracle and shortened hyomandibula * Acanthostega * Small hyomandibula --\> "columella" or "stapes" --\> in spiracle tract * Stapes abuts against cranium --\> support only (no hearing role?) * Early crown group tetrapods * Stapes abuts against quadrate and fenestra ovalis in otic capsule * Hearing function (low frequency) * Derived tetrapods * Stapes modified to more dorsal position * More specialized for hearing

Question 65

What are the Lissamphibia? What are their synapomorphies?

Answer 65

* The recent (extant) amphibians * Synapomorphies (modified, reduced, or lost in some groups): 1. Skin characteristics * Thin and scaleless * Cutaneous respiration (obligate in some) 2. Unique retinal cells (green rods) and levator bulbi muscle to elevate eyes * Large buccal cavity (capable of cutaneous respiration) * Aids in feeding and lung respiration 3. Bicuspid pedicellate teeth * Mostly dentine; 2 parts * Loss of ancestral labryinthodont teeth * Eyes and teeth possible from paedomorphosis 4. Occipital condyles = two (convergent in mammals) 5. Middle ear with two-way sound connection 6. Metamorphosis * Free living aquatic larva develops into terrestrial/semiaquatic adult

Question 66

Describe the middle ear in amphibians What are tympanic and opercular hearing?

Answer 66

* Middle ear with two-way sound connection * Tympanic hearing * Tympanum - stapes - oval window * **High frequencies** to _papilla basilaris_ in inner ear (as in other tetrapods) * E.g., mating calls * Absent in adult salamanders * Opercular hearing * Operculum unique middle ear ossicle --\> sound from pectoral girdle to operculum via opercular muscle * Uses unique _papilla amphiborium_ in inner ear * **Sensitive to low frequencies** * Reduced in caecilians and some adult salamanders

Question 67

What are the synapomorphies of the Gymnophiona?

Answer 67

* Caecilians * Aquatic and terrestrial * Loss of legs, girdles, and tail * Eyes and ears - loss of green rods, reduced papilla amphiorium, operculum, and tympanum * Small jaw adductors and small head for burrowing but strong jaws for excavation and carnivory

Question 68

Describe caecilian reproduction

Answer 68

* **Internal fertilization** with protrusible "phallodeum" (cloacal wall) * Most species viviparous and matrotrophic * Fetuses have large filamentous gill that is resorbed after birth * Larvae also have caudal fins and a lateral line system * Some fetus/larva eat walls of mom's oviduct or her skin with specialized teeth

Question 69

What are the main synapomorphies of the Urodela?

Answer 69

* Salamanders/caudata * Main synapomorphies are skull and appendicular characteristics * Opercular system with papilla amphiborium most prominent * Lack middle ear and tympanum * Stapes is fused to skull * Stapes basilaris reduced or absent * Low frequency sensitivity * Most with both girdles and limbs (reduced or lost in some (e.g., reduced in amphipiumidae; lost in sirenidae)

Question 70

Describe Urodele reproduction

Answer 70

* **Oviparous** in most * Transfer of spermatophore (**internal fertilization**) * One parent attends eggs in around 70 species, no other parental care * Some newts with **yolk-sac viviparity** or **uterine viviparity**

Question 71

Describe metamorphosis in the Urodela

Answer 71

* Larval stages * External gills, lateral line, tail fins * Limbs develop, skeleton ossifies early * Carnivorous, like adults * Metamorphosis is relatively simple: * Resorb gills, gill slits, tail fin * Develop eyelids and tongue, choanae, and lungs

Question 72

Describe urodele paedomorphosis What is it? What are the two pathways?

Answer 72

* _Paedomorphosis:_ Larvae becomes sexually mature without attaining full adult form (obligate in some families, facultative in others) * Retain some larval characteristics when reproductively mature: * Bones, teeth, tail * Functional lateral line system * External gills, no eyelids * Two pathways: * _Neoteny:_ Retention of embryonic/larval characteristics past reproductive maturity (mature at "normal" age) * _Progenesis:_ Accelerated development of reproduction organs relative to somatic (mature at early age)

Question 73

What are the selective advantages of paedomorphosis?

Answer 73

* Predict paedomorphosis where and when fitness is higher in aquatic environment than terrestrial * More paedomorphic individuals when water is constant (but there are also genetic differences)

Question 74

What are the anuran characteristics?

Answer 74

* Many associated with ability to jump (saltatorial locomotion) * Reduced skull, toothless dentary * 5-9 presacral vertebrae with strong zygapophyses * Fused caudal vertebrae (_urostyle_) * Elongate pelvic girdle, hind limbs, and digits * Fused radius/ulna and tibia/fibula * Sacroiliac joint provides extra thrust * Short neck * Post-sacral vertebrae all fused * Head and mouth shape reflects diet * Body shape reflects diversity of locomotion

Question 75

Describe anuran reproduction

Answer 75

* External fertilization in most frogs * Male and female ranid in _amplexus_ (male hangs onto female - can last for weeks or months!) * No amplexus in terrestrial egg layers * "Mate guarding" * Internal fertilization in "tailed" frogs and a few others (tail = copulatory organ for transferring sperm) * Breeding can be explosive (ephemeral vernal pools) or prolonged * Egg-laying behaviour is highly variable

Question 76

In the anurans, when would you predict parental care?

Answer 76

* Most in moist tropical areas with small clutches and large young * Costs = low reproductive output and low parental survival * Benefits = enhanced offspring survival (predation, cannibalism, dessication) * Predict selection for parental care when: * Costs are high but crucial (associated with terrestrial environments and **small bodies of water**) * Costs are low (male care when multiple clutches are laid on territory, female care when output is low anyway)

Question 77

What are the major changes in anuran metamorphosis? What are the three "stages" of metamorphosis?

Answer 77

* Aquatic filter-feeding herbivore --\> terrestrial carnivore * Stages: * _Premetamorphosis_ - size increases * _Prometamorphosis_ - hind limbs * _Metamorphic climax "froglet"_ - front limbs, tail regresses (most vulnerable to predation so this is the shortest stage!) * Complete restructuring of mouth, head and gut, organs * Loss of gills/development of lungs, ossification of skeleton

Question 78

What affects variation in timing in metamorphosis in different populations?

Answer 78

* Go where conditions are most favourable for growth and survival (similar to paedomorphosis) * Selection favours attaining minimum size required for metamorphosis as fast as possible * Then, facultative development based on: 1. Food supply/larval density 2. Permanency of water/drying conditions * Poor food/high density/drying conditions --\> accelerate development rate and metamorphosis

Question 79

How does metamorphosis respond to food/density/water levels? (At the hormonal level)

Answer 79

* High larval/drying conditions --\> CRH (corticotropin releasing hormone - hypothalamus) --\> Corticosterone (adrenals) --\> TSH (thyroid stimulating hormone - pituitary) --\> **Thyroxin** (thyroid) --\> Metamorphosis

Question 80

What changes occur in the amphibians with respect to blood flow and circulation? (What happens to their gills? What happens to their arches in circulatory system?)

Answer 80

* Gills are resorbed and lungs develop in froglets * Changes to arches: * 3rd anterior to head * 4th posterior to body * 5th lost * 6th redirected to lungs and skin

Question 81

During pulmonary respiration, what occurs with the blood from the lungs?

Answer 81

* Blood from lungs --\> high pulmonary pressure * Deep into ventricle * Right side spiral valve * (Low pressure blood from skin left side spiral valve) * Oxygen to aortic arches

Question 82

During cutaneous respiration, what happens with blood from the skin? What allows the cutaneous blood through the aortic arches?

Answer 82

* Bypasses pulmonary arches and going to the lungs (because it is already oxygenated) * Blood from skin, high cutaneous pressure * Deep into ventricle * Right side spiral valve * Oxygen to aortic arches * Cutaneous blood is allowed through the aortic arches because of: * Undivided ventricle * Vascular constriction * Spiral valve