Evolution and Diversity of Vertebrates

Question 1

what is a homologous structure?

Answer 1

inherited from a common ancestor.

Question 2

what is an analogous structure?

Answer 2

similar function, different evolutionary origins.

Question 3

what is the difference between primitive and derivative traits?

Answer 3

Primitive traits: ancestral; Derived traits: evolved more recently.

Question 4

what are the characteristics of an animal?

Answer 4

• Feeds on organic matter (heterotrophic),
• Lacks cell walls,
• Has specialised sense organs and nervous systems for rapid response,
• Is motile (at least at some stage),
• Typically reproduces sexually and has a blastula embryonic stage.

Question 5

what is the difference in Deuterostomes and Protostomes in terms of the blastopore

Answer 5

Deuterostomes: blastopore becomes the anus.
Protostomes: blastopore becomes the mouth.

Question 6

What 4 things do all Chordates share at some point of development?

Answer 6

1. Notochord,
2. Dorsal, hollow nerve cord,
3. Pharyngeal slits,
4. Post-anal tail.

Question 7

what are the two non-vertebrate chordate groups

Answer 7

Tunicates (subphylum Urochordata)

Lancelets (Cephalochordata)

marine filter feeders and chordate features often only in larvae

Question 8

why are vertebrates studied?

Answer 8

o Culturally significant and highly visible.
o Well-studied due to human bias—we are vertebrates too.
o Compared to invertebrates, only arthropods rival vertebrates in diversity, and only cephalopods in cognition and size

Question 9

7 Major Vertebrate Groups

Answer 9

1. Jawless fish
2. Cartilaginous fish
3. Bony fish
4. Amphibians
5. Reptiles
6. Birds
7. Mammals

Question 10

what % of vertebrate species are threatened with extinction?

Answer 10

• Over 20%

o Cartilaginous fish (32%)
o Amphibians (35%)
o Mammals (22%)
o Birds (13%)
o Reptiles (18%)
o Bony fish (13%)

Question 11

why is conservation awareness not evenly distributed? (Davies et al. 2018) what has this led to?

Answer 11

public interest is disproportionately skewed towards mammals and birds. overshadowing more threatened but less “charismatic” groups like amphibians and fish.

has led to a mismatch in funding and conservation efforts, where visibility—not extinction risk—drives investment

Question 12

do terrestrial or aquatic clades show higher diversification rates?

Answer 12

terrestrial (birds, mammals, reptiles) showing the key factor is habitat. (Wiens, 2015)

• Diversification is strongly correlated with the proportion of terrestrial species in a clade.

Question 13

why do terrestrial clades diversify more?

Answer 13

Terrestrial environments offer:
Greater niche availability,
Higher ecological barriers (promoting speciation),
Possibly lower extinction rates over time.

Question 14

what is allopatric speciation?

Answer 14

barriers separating species into different populations and Founder effect may lead to faster speciation.

Question 15

what are the two types of allopatry?

Answer 15

Contiguous allopatry – ranges of 2 populations meet but without interbreeding

Disjunct allopatry – 2 population are separated spatially or temporally

Question 16

what are the 5 key features of vertebrates

Answer 16

1. Cranium
2. Vertebral Column
3. Vertebrae
4. Neural crest
5. Complexity

Question 17

function of the cranium

Answer 17

• Protects brain & sensory organs
• Some scientists use Craniata instead of Vertebrata due to hagfish

Question 18

function of the vertebral column

Answer 18

• Backbone made of vertebrae
• Replaces notochord (except in some fish)
• Hagfish often lack it, lampreys have only fragments

Question 19

function of vertebrae

Answer 19

• Articulating bones with discs = flexibility
• Body (centrum) from notochord
• Vertebral foramen = spinal cord
• Hemal arch = for blood vessels (in some)

Question 20

function of the neural crest

Answer 20

• Special embryonic cells along neural tube
• Develop into various tissues (nerves, bones, etc.)
• Sometimes called a “4th independent germ layer” (Hall, 2000)

Question 21

what makes vertebrates complex?

Answer 21

• larger vertebrates = more complex
• Developed Central Nervous System & cephalisation → complex head + 3-part brain

Question 22

what is the evidence that Tunicates came first in the ancestry of vertebrates?

Answer 22

Paedomorphosis hypothesis: larvae develop reproductive organs, sessile adult stage lost (Garstang, 1920). Tunicates are likely the closest living relatives from genomics.

Question 23

what is the evidence Lancelets may be first in ancestry of vertebrates?

Answer 23

show cephalisation and brain-like structures but no true neural crest Holland & Holland, 1999.

Question 24

what was the first chordates and how many years ago?

Answer 24

Cathaymyrus diadexus (530 mya)

Question 25

what was the next chordate at 520mya?

Answer 25

Pikaia gracilens - a cephalochordate, muscle blocks (myomeres), antenna-like tentacles on head

Question 26

what were the first 2 vertebrates and when was it?

Answer 26

Myllokunmingia (Hagfish like with gill-slits) Haikouichthys (Lamprey-like with dorsal find and fin radials) (530 mya): jawless, cranium, myomeres

Question 27

describe Ostracoderms (470-450 mya)

Answer 27

* Bony armor, no jaws, cartilaginous endoskeleton * Sister group to hagfish and lampreys * Extinct by Devonian

Question 28

Describe the evolutionary milestone of Jaws and what it has enabled.

Answer 28

* Jawless fish were/are filter feeders, scavengers or ectoparasites * From anterior pharyngeal arches * Enabled predation, chewing, herbivory, and more * Also used in courtship, combat etc.

Question 29

who evolved lungs? what was evolved afterwards to replace?

Answer 29

evolved in bony fish → adapted for low oxygen in stagnant water * Some fish retained lungs and others evolved swim bladder for buoyancy

Question 30

what did lobed fins evolve into and lead to?

Answer 30

muscular, became limbs Led to tetrapods (land vertebrates)

Question 31

when did amphibians evolve?

Answer 31

* Amphibians evolved during Devonian (fluctuating environments) where the ability to move between pools and breathe air was critical

Question 32

what is an amniotic egg and why did it evolve?

Answer 32

* Shell + membranes protect embryo on land and allow gas exchange * Allowed full terrestrial life

Question 33

what purpose did feathers evolve for first?

Answer 33

insulation first, then flight.

Question 34

what is the purpose of hair?

Answer 34

insulation

Question 35

what did milk production evolve from?

Answer 35

modified sweat glands.

Question 36

why does the current vertebrae diversity estimates vary?

Answer 36

* Numbers change due to new discoveries, taxonomic debates, and extinctions

Question 37

what are 3 examples of expeditions that made new discoveries?

Answer 37

* In the Mekong, 91 new species of vertebrate were discovered in 2021-2022. * Over 14 new vertebrate species found in an expedition in Peru in 2024 * Even a new Tapanuli orangutan described in 2017 (Nater et al. 2017).

Question 38

what does functional diversity mean?

Answer 38

traits and ecological roles each species has for the community and ecosystem

Question 39

what may functional diversity better reflect?

Answer 39

ecosystem health

Question 40

describe Hagfish (Myxini) morphology and anthropogenic use

Answer 40

* No vertebrae, cranium only * Marine scavengers, knotting, slime for defence and lubrication * No paired fins, keratin “teeth”, sensory tentacles * Absorb nutrients through skin * Used for leather and occasionally eaten

Question 41

describe lampreys (Cephalaspidomorphi/Hyperoartia) morphology and anthropogenic use?

Answer 41

* Cartilage segments, true vertebrates, no paired fins * Oral disc ‘teeth’ (keratin), parasitic species feed on host blood, secreting anticoagulants * Ecological & economic impact (Great Lakes) * Widely eaten and used as bait

Question 42

what are Gnathostomes?

Answer 42

an infraphylum of vertebrates - all jawed mouths

Question 43

when did Gnathostomes appear and diversity?

Answer 43

* Appeared ~440 mya (Acanthodii – “spiny sharks”) * Diversified in Devonian (~400 mya)

Question 44

what are the 3 groups of fish?

Answer 44

Cartilaginous (Chondrichthyes) Ray-finned Fish (Actinopterygii) Lobe-finned Fish (Sarcopterygii)

Question 45

describe cartilaginous fish, origins and what species it includes

Answer 45

* Sharks, rays, chimaeras * Origins around Ordovician * Cartilage skeleton, placoid scales * Internal fertilization, various reproductive modes

Question 46

what are the two subgroups of cartilaginous fish? what are the differences?

Answer 46

o Elasmobranchii: multiple gill openings o Holocephali: single gill, benthic feeders, males have cephalic clasper

Question 47

describe ray-finned fish, 1st fossils origin etc

Answer 47

* ~30,000 species, most diverse (97% of all fish) * 1st fossils from Silurian (420 mya) * Bony skeleton, fins supported by rays * Swim bladder for buoyancy * Weird biology: hermaphrodites, male pregnancy, antifreeze

Question 48

describe lobe-finned fish

Answer 48

* Only 8 extant spp.: lungfish & coelacanths * Lobed fins with bone & muscle, teeth * Primitive lungs retained * Ancestor of all tetrapods

Question 49

describe the coelacanths species of lobe-finned fish and anthropogenic use

Answer 49

Living fossil” rediscovered in 1938 thought extinct in late cretaceous (66mya) * Genome sequenced in 2013 – closest ancestor of tetrapods * Piscivorous bottom-dwellers, odd locomotion with multiple fins * 120 spp. known * Not commercially useful (bad taste) but bycatch

Question 50

4 groups of tetrapods

Answer 50

amphibians reptiles birds mammals

Question 51

describe amphibians, origin, development type etc.

Answer 51

~7300 spp. * Evolved from lobed-finned fish (,400 mya) * Aquatic larvae → adult stage (metamorphosis) * Smooth, permeable skin (gas exchange) * Ectothermic

Question 52

what are the 3 groups of amphibians and describe their morphology.

Answer 52

o Anura: frogs, toads (most diverse, large hindlegs, large head, stout body) o Urodela: salamanders, newts (short legs, elongated body, tail) o Apoda: caecilians (burrowing, limbless)

Question 53

describe reptiles origins and morphology

Answer 53

~10,000 spp. * Evolved ~300-350 mya with 1st fossil Casineria (340 mya) * Scaly skin, leathery amniotic eggs * Ectothermic, environmental sex determination

Question 54

what are the 2 subgroup of reptiles?

Answer 54

Anapsids: turtles, tortoises Diapsids: - Lepidosauria: snakes, lizards, tuataras - Archosauria: crocs, birds, dinosaurs

Question 55

Describe Birds origins and morphology

Answer 55

~10,600 spp. * Evolved from feathered dinosaurs (1st fossl Archaeopteryx from 145 mya) * Feathers were first for insulation, then later flight evolved * Light skeleton, endothermic, oviparous * Over 50% = passerines (perching birds)

Question 56

describe mammal origins and morphology

Answer 56

~6500 spp. * Hair, mammary glands, neocortex * Endothermic, mostly viviparous * Origin: ~210 mya, with 1st placentals in Jurassic (160 mya)

Question 57

what are the 3 groups of mammals

Answer 57

Prototheria – Monotremes (1 order): lay eggs (e.g. platypus) Metatheria – Marsupials (7 orders): pouches (kangaroos) Eutheria – Placentals (19 orders): majority (rodents, primates, etc.)

Question 58

what did Brazeau and Friedman (2015) find out about the evolution of gnathostomes and what does it show?

Answer 58

originated during the Great Ordovician Biodiversification Event and diversified rapidly during the Silurian period. reveal early developments in teeth and jaws and insights into the evolution of paired fins, precursors to tetrapod limbs. jawed vertebrates were already diverse in the Silurian but geographical and environmental constraints early on reduced the diversity.

Question 59

What did Frobisch and Witzmann (2019) find for the transition from aquatic to terrestrial life?

Answer 59

Parmastega aelidae exemplifies this transition: its eye positioning, breathing structures, and habitat indicate semi-terrestrial adaptation, suggesting early tetrapods could exploit both aquatic and land resources.

Question 60

What did Vermeij (2017) find about key innovations on land?

Answer 60

after the Ordovician, land became the primary source of biological innovation. Key evolutionary traits such as herbivory, eusociality, echolocation, and aerial locomotion emerged first on land and later appeared in marine settings

Question 61

how does diversification improve functional diversity Petchey and Gaston (2006) ?

Answer 61

vertebrates adapted to new environments, especially terrestrial ones, they developed a broader range of traits and ecological functions, which increased ecosystem complexity

Question 62

What did Vogel (2018) discover with the loss of traits using suckling in monotremes?

Answer 62

Though suckling is a hallmark mammalian trait, fossil and anatomical evidence suggest that early monotremes could suckle, but lost this trait due to dietary shifts. This highlights a broader theme in evolution: traits can be lost when no longer beneficial, a reminder that evolution is not unidirectional but context-dependent.