Evolution of Vertebrae

Question 1

Shared Derived Features of all Chordates

Answer 1

Perforated pharynx, post-anal tail, dorsal hollow nerve chord, notocord. Chordates display these as adults or as larvae.

Question 2

Tunicata

Answer 2

Sea squirts-adults are sessile filter feeders. Have a reduced musculature and nervous system, and an enlarged perforated pharynx. Larvae display all shared derived features of chordates.

Question 3

Cephalochordates

Answer 3

Lancelets-have very simple heads, like simplified fish, filter feeders, water pumped through pharynx, food particles filtered out.

Question 4

Craniates

Answer 4

Chordates with skeletal elements around brain and sense organs-have jawed and jawless clades (agnaths and gnathostomes).

Question 5

“Agnaths”

Answer 5

Jawless. Not natural grouping-hagfish, highly modified basal craniates (no lower jaw, no vertebrae).

Question 6

Lampreys

Answer 6

Modern ones are blood feeders, use toothed tongue to scrape skin of host fish, then drink blood and fluids. Also jawless.

Question 7

Gnathostomes

Answer 7

Jaws and paired limbs, includes “fish,” amphibians, “reptiles,” mammals, and birds. Inclusive group of vertebrates.

Question 8

Key Innovations of Gnathostomes

Answer 8

Jaws-likely evolved from 3rd and 4th pairs of gill elements in jawless form. Allows biting.
Paired fins-allowed high-speed swimming and manoeuvrability.

Question 9

“Fish”- Chondrichthyes

Answer 9

Sharks and rays, enamel and dentine teeth, but skeleton is cartilaginous- bone secondarily lost (low metabolic rates), each pair of gills have separate opening, scales are enamel.

Question 10

“Fish”- Ray-finned Fish

Answer 10

Majority of modern fish species, bony skeleton, swim bladder derived from gut-homologous to lung (used to maintain buoyancy) Gills shielded under single operculum.

Question 11

“Fish”- Lobe finned fish

Answer 11

Lungfish and coelacanths-lungs, homologous to tetrapod lungs, fins are fleshy, elements homologous to tetrapod limbs.

Question 12

Tetrapods

Answer 12

Sister group to lobe-finned fish, group inclusive of all four legged vertebrates, only vertebrates to effectively exploit terrestrial environment.

Question 13

Initial adaptive radiation

Answer 13

Result of adaptations made to life in shallow water, allowing increasing exploitation of shore-modification of fore and hindlimb, increase in lung development.

Question 14

Amphibians

Answer 14

Frogs, salamanders, caecilians, only modern survivors of initial tetrapod radiation, skin acts as auxiliary respiratory organs, must be kept moist, favour aquatic or damp terrestrial environments. Most lay eggs in water, non-amniotic eggs, larvae hatch and live as gill breathing aquatic forms with lateral line organs. In metamorphisis, gills, fins, and lateral line organs atrophy, lungs and limbs develop.

Question 15

Amniotes

Answer 15

Evolutionary radiation of terrestrial tetrapods. Key innovations were the amniotic egg, dessication resistant chamber, extraembryonic membranes, nutrient supply. Allowed amniotes to breed independently of water, colonize most terrestrial habitats. Two main lineages are mammals and “reptiles”.

Question 16

“Reptiles”

Answer 16

Turtles, lizards, snakes and tuataras. Not all descendents of unique common ancestor-birds, crocodiles, dinosaurs. Unified by shared ancestral features-amniotic egg, scales, ectothermic (cold blooded).

Question 17

Dinosaurs

Answer 17

Crocodiles, dinosaurs and birds are classed together as Archosauria. Bridged transition from scaled ectotherms to feathered endotherms.

Question 18

Birds

Answer 18

Sister group of some dinosaurs-theropods shown to have feathers or proto-feathers. Earliest birds were like feathered dinosaurs, feathers evolved initially for insulation and later co-opted for flight. Shared derived features-endothermy, air-sac system feathers?

Question 19

Mammals

Answer 19

Shared derived features-hair, mammary glands, three middle ear bones, heterodont dentition (different teeth), endothermic, big brained, active. 3 groups- monotremes (5 species), Marsupials (324 species), and Eutherians (placental mammels, 5010 species).

Question 20

Marsupials vs Mammals

Answer 20

Shorter embryonic develipment in uterus, completes development in mothers pouch which makes for rapid reproduction.