Reptile Evolution

Origin of derivatives

Ancestral reptile = anapsid , small, legs out to sides.

A brief look at Classification

“Old view” = Amphibians give rise to reptiles, reptiles give rise to birds and mammals

phyletic patterns.

Major radiation into all ways of life; terrestrial, aquatic, aerial.

New View of Taxonomy = Cladistics common derived characteristics

Problem with reptiles = heart structure.

• fossil reptiles that give rise to mammals appear early in

reptile history and leave no descendents

modern reptiles heart structure is different from mammal structure, so cant derive modern mammals from modern reptiles.

so in Cladistics, kick mammal ancestors out of the reptiles

(if it looks like a lizard, it is a lizard???)

Living anapsids = chelonia, the turtles

Shoulder girdle inside shell, which is ribs and vertebrae!!

Skull is anapsid = no hole

But has a notch at back which serves the same purpose, accommodate the jaw muscles.

Ichthyosaurs: fully aquatic, but air breathing. A reptile equivalent to whales or porpoises. Mostly fish eating.

Plesiosaurs; snake neck strung through a turtle body. Came on land to lay eggs probably.

Lepidosaurs: snakes, lizards

Start out diapsid (two holes behind the eye

In snakes, one opening, and extra hinges in jaw.

Archosaurs = major dinosaur groups

Plus crocodiles, and bird ancestry.

A very diverse and complex group. - die out at Cretaceous boundary = meteor?

Pterosaurs = hang glider wings.

Archosaurs: wide variety, carnivorous, plant eaters, now known to be social, etc.

Allometry: changes in proportion with growth.

Means young often considered different species from adults.

Stegosaurus; plate back

Functions:?

courtship

thermoregulation?

Crocodiles; surviving archosaurs, in past many terrestrial.