9, 11, 13-14: Chordata, Vertebrata, Tetrapoda, Amphibia

Question 1

Name the main groups that are within Deuterostomia, but NOT Chordata

Answer 1

Ambulacrania - a group containing Echinodermata (e.g., starfish) and Hemichordata (e.g., Acorn Worms!)

Question 2

Name the main groups that are within Chordata, but NOT Vertebrata

Answer 2

Cephalochordata (30 sp.) e.g., Amphioxus and Tunicata (formerly Urochordata, 2000 sp.)

Note: Vertebrata = 70,000 sp. (mostly fishes)

Question 3

Describe the common anatomical features of chordates

Answer 3

Notochord (of course) - a stiff rod along the dorsal axis of the body, mechanically important

Pharyngeal Gill Slits
Endostyle
V-shaped Myomeres
Dorsal Nerve Cord (i.e. more dorsal than the gut)
Post-anal tail

Question 4

What is Amphioxus?

Answer 4

A small, filter-feeding Cephalochordate with simple morphology - often interpreted as the Archetypal Chordate

Question 5

Describe the Tunicates

Answer 5

All juveniles (and adult larvaceans) have notochord, nerve cord, brain, muscular post-anal tail

Adult forms can be larvaceans, salps or Sea Squirts

Sea Squirts undergo metamorphosis from a mobile stage to a sessile stage - pedomorphosis

Question 6

What are the defining features of VERTEBRATES?

Answer 6

1. Developed brain
2. Paired sensory structures
3. Branchial arches
4. (MOST) some sort of vertebral column

Question 7

What has changed fairly recently about our understanding of Chordate phylogeny?

Answer 7

Previously, it was assumed that Tunicates were sister taxon to other chordates, and that Cephalochordates were the closest relatives of Vertebrata (based on Neuroanatomy, Metameric Segmentation and Molecular Data)

Now, taking into account LBA of the Tunicates, it is thought that Cephalochordates are sister taxon and Tunicates are closest relatives of the Vertebrata [Grouped together as Olfactores]

Question 8

What are some key anatomical differences between the general anatomy of plesiomorphic Chordates and Vertebrates?

Answer 8

Vertebrates have W-SHAPED Myomeres (not V)

Vertebrates have a muscular pharynx with fewer gill slits

Vertebrates have a brain and paired sense organs

Vertebrates have a NEURAL CREST - a migratory population of multipotent cells that form around the developing Neural Tube, and give rise to many important cell types, allowing the formation of important vertebrate characters (e.g., teeth, heart, nerves, etc.)

Question 9

What is the interesting feature about Vertebrate Genomes?

Answer 9

There appears to have been TWO Whole Genome Duplication events in early vertebrate evolution - one between amphioxus and the jawless vertebrate ancestor, and another one since

Question 10

Describe the Jawless Vertebrates in terms of morphology and lifestyle

Answer 10

Main 2 groups - Lampreys and Hagfish

Lampreys: Eel-like morphology with an oral sucker and keratinous teeth, no bones or fins; parasitic blood-sucking lifestyle

Hagfish: Soft, blind, worm-like morphology, no bones or fins; slime as defense mechanisms and “tie themselves in knots”

Question 11

Describe the jawless vertebrates in terms of anatomy

Answer 11

Both have a CAARTILAGINOUS SKULL (very different from out own) and just one nostril

Lampreys: Single median nostril, Cranial Cartilages, Branchial Cartilages, Arcualia (which MAY be homologous with our backbone despite not being bone)

Hagfish: Single terminal nostril, Slime Glands, MANY gill openings, Cranial Cartilages, NO SORT OF BACKBONE (unusual for vertebrates)

Question 12

Describe the jawless vertebrates in terms of Development

Answer 12

Lampreys undergo Metamorphosis: juvenile stage (ammocoete) lacks eyes or oral sucker (similar to Amphioxus)

Hagfish: development very difficult to study but eventually neural crest was confirmed, as well as similarity to lamprey cranio-facial development

Question 13

What are the key differences between Cyclostomata and GNATHOSTOMATA

Answer 13

GNATHOSTOMATA (Jawed vertebrates - Cartilaginous Fishes, Boney Fishes, Lobe Finned Fishes, Tetrapods) have:

Paired Nostrils
Hinged Jaws
Vertebrae
Bone
Adaptive Immune System

Question 14

Describe the debate/discussion surrounding the phylogeny of the jawless vertebrates

Answer 14

The Traditional View: Jawless Vertebrates as their own clade, Cyclostomata (Based on feeding apparatus and nasohypophysial opening)

Challenger Hypothesis: Jawless Vertebrate Paraphyly - Lampreys may be more closely related to Gnathostomata based on Vertebrae, Dorsal Fins, Camera Eyes, Closed Circulation

Conclusion based on MicroRNA Genetic Data - Traditional View was actually correct. Cyclostomata are monophyletic [Also, character losses in Hagfish were confirmed, because a stem hagfish fossil was found to have eyes with melasomes and melanin!]

Question 15

Describe the rate of evolution seen over the course of vertebrate history

Answer 15

Extremely rapid early vertebrate evolution with lots of innovation, and increasing complexity of development and anatomy (based on phylogenetic data, but limited fossils); slower evolution later on

Question 16

What are the oldest (potentially) Chordate fossils?

Answer 16

• Pikaia from Burgess Shale (Cambrian)
• Metaspringgia (possible Cambrian Vertebrate) has muscle bands, paired eyes and gill arches
• Cambrian Chordates of China - Haikouichtyhes, Yunnanozoan, Cathamyrus

Question 17

Why is chordate phylogeny so hard to resolve for groups before the Gnathostomata?

Answer 17

Gnathostomata is the only clade with Skeletal Hard Tissues - before this, animals were entirely soft bodied -> significant decay

The “Cambrian Chordates of China” (H, Y, C) and Haikouella could be seen as stem deuterostomes, chordates or even vertebrates

Question 18

What is taphonomy?

Answer 18

The study of the process of decay and preservation, to help interpret fossils more accurately and see which characters decay fast or slow

Question 19

What is meant by the phrase “stem-ward slippage”?

Answer 19

Organisms tend to lose synapomorphies as they decay, and so appear more primitive, or stem-like; therefore, they risk being classified as more “stemward” than they actually were

E.g., Cathamyrus only has decay resistant characters, so may be more advanced than it appears -> Potentially Any Chordate

Haikouichthys has SOME decay-prone vertebrate characters, but NO SKULL, so it probably really did lack a skull and was a true stem-vertebrate

Question 20

Define the difference between Agnatha and Cyclostoma

Answer 20

Cyclostoma refers to the EXTANT jawless fishes (Lampreys and Hagfish)

Agnatha refers to ALL jawless vertebrates, including extinct groups such as the Anaspids, Conodonts and Ostracoderms

Question 21

Describe the main sub-groups of Cyclostoma and Gnathostoma

Answer 21

Cyclostoma:
- Lampreys (Blood-sucking “vampire-eel-like fish” with keratinous teeth and oral sucker)
- Hagfish (Slimy, blind “eel-like fish” with rasping keratinous teeth

Gnathostoma:
- Chondrichthyes (Cartilaginous fishes, e.g. sharks and rays)
- Actinopterygii (Bony fishes - most diverse group)
- Sarcopterygii (lobe-finned fish and tetrapods)

Question 22

Describe some of the key features of Gnathostomata

Answer 22

• Opposing Jaws with True Teeth
• Most have paired appendages (e.g., pelvic and pectoral fins, arms, legs, wings, etc)
• Fossil record shows stepwise acquisition of Gnathostome characters among stem-Gnathostomes (e.g., Placoderms)

Question 23

Describe the Ostracoderms and name some of their groups

Answer 23

The Ostracoderms are an extinct, paraphyletic group of jawless fossil fishes, ranging from the Ordovician to the Devonian, including the Anaspids, Thelodonts, Galeaspids, Osteostracans, etc.

They may show the first evidence of Biomineralisation:
Some Anaspids have a mineralised dermoskeleton

Question 24

Describe the Conodonts

Answer 24

Early jawless fish, more stemward than the Ostracoderms

Appear to have “mineralised teeth” that may have been homologous with ours - now thought to be convergent

Question 25

Name 4 Ostracoderm Groups and describe their features

Answer 25

1. Sacamambapsis - armoured head and tail; two nostrils; widespread in Ordovician 2. Heterostracans - diverse head shield shapes, composed of multiple plates; single gill opening, no paired fins 3. Galeaspids - heavily armoured headshield; unique sensory line system (2 sensory lines going towards 1 nostril - possible step towards Gnathostome trait) 4. Osteostracans - BONY SHELLS (but still no jaws); complex paired fins and advanced bone; advanced nervous system and sense organs

Question 26

Describe the Placoderms

Answer 26

The Placoderms were Jawed Stem Gnathostomes - i.e. more closely related to extant Gnathostomes than Ostracoderms They were a diverse group, with simple jaws, pelvic fins and possibly teeth Include the first "mega-predators" - e.g., Dunkleostus, whose bladed jaws had 5000N biting strength, stronger than a Great White

Question 27

Summarise the stepwise acquisition of Gnathostome Characters along the Gnathostome stem

Answer 27

BONE TRANSITION: - Origin of unmineralised skeleton in Cyclostomes - Mineralised dermal skeleton in Anaspids - Armoured Head + Tail in Sacabambapsis - Multiple Plates in Heterostracans - Heavily armoured head shield in Galeaspids - Axial skeleton and Appendicular Skeleton in Crown-Gnathostomes TEETH TRANSITION: - Inside-out hypothesis -> Teeth derived from dermoskeleton migrating into the oral cavity - Stem-Gnathostomes have dermoskeletal bone, and some pharyngeal denticles - Helicoprion (a Chondrichthyan) had a buzzsaw-like mouth PAIRED APPENDAGES: - Strange paired anal fin in Devonian Euphanerops (FIRST PAIRED APPENDAGES??) - Osteostracans have paired pectoral fins with skeleton BRAIN EVOLUTION: - Development of cerebellum - Transitional brains seen in Placoderms

Question 28

Name the two main groups of Chondrichthyes

Answer 28

Elasmobranches (Sharks and Rays which grow and shed teeth) Holocephalans (Rat Fishes with tooth plate)

Question 29

Describe the key features of Chondrichthyes

Answer 29

The Cartilaginous Fish have: - Cartilaginous Skeletons with placoid scales composed of dentine and enamel (HOMOLOGOUS WITH TEETH) - Bony Teeth (and mineralised vertebral centra) - Gill openings - Closed Blood System - More Complex Brain than Placoderms - Sensory systems: Lateral Line System for water pressure changes, and Ampullae of Lorenzini for Electroreception - Sharks have claspers

Question 30

What are "Osteichthyes"

Answer 30

ALL BONY VERTEBRATES (so Actinopterygii and Sarcopterygii)

Question 31

Name the three groups of Actinopterygii

Answer 31

Chondrostei (Sturgeons, Paddlefish and Reedfish) Holostei (Bowfin and Gars) TELEOSTOMI (Hyperdiverse, Classical "Fishes")

Question 32

Describe the key anatomical features of Actinopterygii

Answer 32

- Bony Endoskeleton, including Lepidotrichia (Fin Rays) - Swim Bladder to control buoyancy - Operculum - Bony scales

Question 33

Name the main groups of Sarcopterygii

Answer 33

The Lobe-Finned Fish (Sarcopterygii) include: - Actinistia (e.g., Coelocanth) - Dipnoi (e.g., Lungfish) - TETRAPODA (ofc)

Question 34

Describe the key features of non-tetrapod Sarcopterygii

Answer 34

Specialised fleshy lobed fins Stylopod (homologus to humerus) in a single connection between fin and supportive girdle (monobasal articulation)

Question 35

What major shift in our understanding of bone evolution (may have) occurred in 2020?

Answer 35

Evidence of endochondral bone in Placoderms - meaning it first evolved far earlier than we thought, and was simply lost in Chondrichthyes, rather than being a synapomorphy of Osteichthyes

Question 36

State some examples of the different ways one could possibly define the complexity of a taxonomic group

Answer 36

Genetic complexity (e.g., WGD events) Anatomical complexity Taxonomic diversity Taxonomic longevity

Question 37

Describe some examples of the fish mating strategies discussed in the lecture

Answer 37

Sexual Dimorphism - Male and Female individuals have morphological differences, e.g. females usually larger [SEEN IN SALMON, PARROT FISH, MANY OTHERS] Hermaphroditism - Either Synchronous or Transitional, only seen in 8 orders [INCLUDING CLOWNFISH] Parthogenesis - Virgin Bonnethead sharks can give birth (rare but may be important for species that live far apart?) Sexual Parasitism (e.g., Angler Fish)

Question 38

State and define some of the Fish Rearing Strategies discussed in the lecture

Answer 38

Oviparity - internal fertilisation, external egg development (e.g., majority of Actinopterygii) Ovuliparity - External fertilisation Viviparity - Internal development of nurtured embryos (e.g., White Surf Fish, Sand Tiger Shark) Ovoviviparity - Internal development, but using resources from egg only

Question 39

What is meant by "Euryhaline" Fish?

Answer 39

Those that are exposed to a wide range of salinity due to migration

Question 40

What is the difference between Iteroparity and Semelparity?

Answer 40

Iteroparity = continuous breeding Semelparity = single mass breeding event (e.g., Pacific Salmon)

Question 41

How does each fish in a school behave, leading to overall complex swarming behaviour?

Answer 41

Rules: - Same direction as neighbour - Stable distance from neighbour - Avoid collisions

Question 42

What are the Teleostei and what is believed to have contributed to their hyperdiversity?

Answer 42

An extremely diverse group of fishes within the Actinopterygii (essentially all bony fish excluding Chondrostei such as Sturgeons and Holostei such as Bowfins) Whole Genome Duplication event in their stem lineage

Question 43

What are two key features of Teleost anatomy?

Answer 43

Mobile Premaxilla for protrusion feeding (remember video of expanding jaw and sucking in prey) - protrusion has gradually increased since the Late Cretaceous Homocercal Tail - spinal column ends at caudal peduncle, allowing fins beyond to take a wide range of forms

Question 44

What are the Acanthomorphs, and name a couple of examples of both Acanthomorphs and Non-Acanthomorphs

Answer 44

Acanthomorpha are an extremely diverse group within the Teleosts, making up a third of extant vertebrate species (over 14000) Acanthomorpha include Tuna, Mackerel, Sunfish, Anglerfish, Seahorses, Clownfish, etc. etc. Non-Acanthomorpha include Eels, Herrings, Carp and Salmon

Question 45

Describe the two mechanisms used by fish for Buoyancy

Answer 45

Swim Bladder - Oesteichthyes control their buoyancy via gaseous exchange in and out of the swim bladder Oily Liver - Chondrichthyes have a large oily liver that provides buoyancy (oil is more buoyant than air), BUT less control, so must control depth using orientation

Question 46

Name the four broad swimming morphologies (and an example of each), from most head movement to least What are the advantages/disadvantages?

Answer 46

Anguilliform (Eels) -> Subcarangiform (e.g., Salmon) -> Carangiform (e.g., Mackerel) -> Thunniform (e.g., Tuna) Anguilliform allows the most rapid acceleration, while Thunniform allows the most efficient cruising ALSO NOTE: Ostraciiform allows highest manoeuvrability

Question 47

Name some niches that have been filled almost identically by both extinct and extant groups

Answer 47

Rapid accelerators, High Manoeuvrability, Sustained Swimming [Examples for most of these among Palaeozoic Chondrostei, Mesozoic Actinops AND Modern Teleosts] Also Mega-Planktivores (Giant Filter Feeders) currently filled by Chondricthyes, but has previously been filled by Actinops (in Mesozoic), Placoderms (in Palaeozoic) and Anomalocaridids (in Cambrian)

Question 48

What is meant by "Morphometrics"?

Answer 48

It is a way of quantifying morphological disparity by plotting "landmarks" to give geometry to fish fossils

Question 49

When did the Acanthomorpha radiate most rapidly?

Answer 49

After the Cretaceous mass extinction event - they evolved into many niches that were previously occupied before the extinction

Question 50

Which group within Osteichthyes did Tetrapods arise from, and in what period did they make the transition to land?

Answer 50

From Sarcopterygians (Lobe-finned fish) and they are thought to have made the transition in the Devonian (around 390 mya)

Question 51

Why (fundamentally) did tetrapods make the transition to land, and what are some key evolutionary events that made this possible?

Answer 51

There was available space and a niche to occupy - they needed terrestrial locomotion, air breathing, structural support and reproductive strategies

Question 52

Describe the main anatomical evidence for the evolution of amphibians from lobe-finned fish

Answer 52

1. Arrangement and development of bones in the skull 2. The amphibian limb appears to be derived from fin structure 3. Labyrinthodont tooth structure (ridges on outside and folded structure) 4. Lobe-finned fish have an opening to the nostrils inside the mouth - this feature is found in ALL LAND VERTEBRATES

Question 53

Name some of the "key player" lobe finned fish and describe the features that make them notable in piecing together the evolution of amphibians

Answer 53

Glyptolepis (385 mya) - distinct loose scales, perhaps early progenitor Eusthenopteron (385 mya) - internal nostrils and distinct fin endoskeleton, first evidence of body support in fins Panderichthys (385 mya) - lacks anal and dorsal fins, tail and shoulder more closely resemble tetrapod features, but still fish-like front fins Acanthostega (365 mya) - early tetrapod, longer snout with fewer bones, lacks opercular bones, interlocking vertebrae, larger pelvis, separation of skull from shoulder Icthyostega, Balanerpeton = Fully tetrapods

Question 54

What are the major general differences in characteristics between fish and amphibians?

Answer 54

Most relate to locomotion (moving in water vs on land requires skeletal changes, especially limbs, shoulder, vertebrae and pelvis) Others relate to skull structure (breathing and feeding) - general trend is that tetrapods have FEWER skull bones (consolidation) and lost the opercular bones, which are completely gone in Tiktaalik and Acathostega

Question 55

Describe the specific skeletal changes between Fish and Amphibians (and discuss the reasons why)

Answer 55

Pelvis and Shoulder Girdle: Attached to Vertebral Column in Amph, but NOT in fish Brain Case and Notochord: Notochord replaced by bone in modern adult tetrapods, and no longer runs into brain case Gill Arches: Reduced in number and size Bone that supports gill arches was redeployed in formation of tongue support + musculature Hip is attached to vertebrae in tetrapods, but NOT in fish Also, amphibians GAINED A NECK which fish lack All generally because neck flexibility important for feeding and breathing on land

Question 56

Describe specifically the change in shoulder structure between fish and amphibians and the importance of this

Answer 56

In fish, the shoulder (pectoral) girdle is attached to the skull (for hydrodynamics) In tetrapods, the shoulder girdle is attached firmly to the backbone, and is separated from the skull (it consists of an enlarged scapulocoracoid and clavicle) This allows force transduction and more flexible head movement when walking on land

Question 57

What factors in the Late Silurian and Devonian may have contributed to the eventual appearance of lungs and terrestrial life?

Answer 57

Fluctuations in rainfall, drying of bodies of fresh water, water temperature increases, O2 levels decrease -> All of this makes gills less useful as O2 falls, so animals with the strongest "limbs" are selected for

Question 58

Describe the problems with evolving air breathing from gills

Answer 58

Breathing in air via external gills would result in massive water loss through evaporation from moist respiratory surfaces -> therefore, need INVAGINATED LUNGS and FOLDED vascularised tissue bathed in fluid HOWEVER, all lungs must use a tidal flow (bidirectional) system, which is not as efficient as unidirectional through-flow due to dead space -> therefore, needs an EFFICIENT PUMP

Question 59

Describe some of the novel adaptations that helped tetrapods to overcome the problems with air breathing

Answer 59

More efficient pumps: - Amphibians use a MODIFIED form of the BUCCAL PUMP (the system used by some air-breathing fishes, in which the mouth makes the pressure changes necessary to move water), in which the AXIAL muscles are used for expiration - Amniotes use an ASPIRATION PUMP, in which the axial muscles are used for both inspiration and expiration Within the amniotes, various specialisations include uncinate processes, pelvic aspiration, hepatic pistons and gular pumping -> possible BR ;)

Question 60

Explain the significance of the fin structure seen in Eusthenopteron

Answer 60

Its forefins contain bones that appear to be homologous with the humerus, ulna and radius Its pelvic fins contain bones that appear to be homologous with the femur, tibia and fibula

Question 61

Describe the changes in the backbone between fish and amphibians

Answer 61

The vertebrae in amphibians are INTERLOCKING (go from just neural arch to NEURAL SPINE + ARCH), fuse with Centrum Elements(?) This makes the backbone less flexible, but stronger, allowing the organism to support its own weight on land

Question 62

Name some of the key traits in the complex web of interconnected characteristics that had to evolve together in the transition to land

Answer 62

Grasping Feeding, Skull, Jaw, Olfaction Substrate Locomotion, Robust Limbs, Shoulder Girdle, Flexible Neck, Intervertebral Articulations, Ribs, Pulmonary Ventilation Many more, but these are some of the key connections

Question 63

When were the most dominant land animals amphibians, and when did they split from the group that would become the Amniotes?

Answer 63

Dominant in the late Carboniferous and early Permian periods (around 310-250mya?) Amniote branch split off around 300 mya

Question 64

Describe the key ecological features of Amphibians

Answer 64

They lay eggs in water, and newborn amphibians live underwater, before metamorphosing into adult forms, which often live on land. Their moist skin functions in gas exchange

Question 65

What were the advantages of moving onto land for the first terrestrial vertebrates?

Answer 65

It opens up new niches and terrestrial prey options It allows for more diverse locomotive ability It reduces competition or predation from other aquatic species It facilitates selection of an increase in body temperature, which increases rates of digestion, development and other physiological processes

Question 66

What is meant by the "amphibian gap" and what are some possible reasons for it?

Answer 66

The distinct lack of fossils for a clear ancestor of any of the modern amphibian groups, prior to the early Jurassic - we only have a good record of the archaic amphibians and the stereospondyls Taphonomy can help explain this: Amphibians have a reduced skeleton, lots of soft, delicate body parts, and many are burrowing species in a fertile environment -> all of these factors reduce their chances of being preserved Fortunately, shared features at least provide confidence in monophyly of the three crown groups, although very little fossil evidence of their ancestors until Cretaceous (one or two Salamander ancestors from Jurassic)

Question 67

What were the stereospondyli?

Answer 67

A group of extinct amphibians that appeared in the Late Permian - two families survived into the Triassic They had a distinct anatomy (simple backbones and weak vertebral structure, suggesting an aquatic lifestyle) -> none are a likely ancestor for any modern amphibians

Question 68

What are the three main theories for the origin of amphibians, and what two features provide reasonably strong evidence for one of these hypotheses?

Answer 68

1. Lepospondyl hypothesis (Lepospondyli are sister to all Lissamphibia) 2. Temnospondyl hypothesis (all modern amphibians are closely related to dissorophoid temnospondyls) 3. Different groups of Lissamphibians evolved from different groups of early tetrapods or lobe-finned fish A phylogenetic analysis from Sigurdsen and Greene (2011) supports the second hypothesis, as does the shared rare feature of Pedicellate Teeth among all modern amphibians, and the Lissamphibian Elbow Joint

Question 69

Name the three groups of modern amphibians, and the period in which they likely underwent radiation

Answer 69

Anurans (Frogs), Caecilians and Salamanders (Early-Mid) Carboniferous

Question 70

Describe some of the key anatomical features of Amphibians

Answer 70

Circulatory System: They have a 2-chambered heart (unlike the partially- or fully separated hearts seen in reptiles and mammals) Limbs: 4 limbs and 4 digits (except Caecilians) - limbs can support body weight unlike lobe-finned fish, but humerus much less developed than in reptiles Skull: Consolidation of skull parts compared to fish, reduction of opercular bone and loss of posterior skull bones

Question 71

Describe the ecology of Salamanders

Answer 71

- Many show a classic amphibious lifestyle (aquatic larvae and terrestrial adults, others more neotonic) - Carnivorous - worms, arthropods and molluscs - Paedomorphosis (e.g., Axolotls) - Capture prey using prehension of sticky tongue (rapid projection and retraction)

Question 72

Describe the anatomy of Salamanders and their different groups

Answer 72

- Limbs at right angle to gait (SPRAWLING) - Anatomy varies with ecology - aquatic and burrowing groups have reduced limbs, while terrestrial and metamorphosing genera have short bodies and stout limbs

Question 73

Describe the features of Caecilians (and briefly describe their fossil record)

Answer 73

- Unique among modern amphibians in their (secondary) lack of girdles and limbs -> have a "kink" where pelvis used to be - Elongated body with small scales, good burrowers using INTERNAL CONCERTINA locomotion - Eat worms and small invertebrates - Young have special dentition to eat layers of mother's modified skin (possible intermediate step in evolution of viviparity) Fossil record ranges from Lower Jurassic to Upper Paleocene (though only 3 are well-preserved enough to have been named)

Question 74

Describe the fossil record of Anurans (Frogs)

Answer 74

Frog fossil record dates back to Jurassic (Prosalirus bitis), but most (e.g., Gerobetrachus) are quite morphologically similar to modern Anurans -> this is useful for showing how long ago the modern form appeared, but less useful for determining what transitional forms were like Prosalirus bitis has uncinate processes on ribs and was capable of jumping

Question 75

Describe the characteristics of modern Anurans

Answer 75

- REPRODUCTION: Aquatic reproduction, tailed larval form, with gills - Adults lack tails and have lungs, and are specialised for jumping - Extreme skeletal changes, including lots of fusion of bones (e.g., post-sacral vertebrae into urostyle, tibiofibula, radioulna) - Evidence of gliding ability (likely did not evolve flight because they are ectothermic, and that niche was already filled by pterosaurs and then birds)