Reptile evolution
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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.

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Reptile evolution

Reptile Evolution

Origin of derivatives

A brief look at Classification

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

phyletic patterns.

  • 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 characteristics

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

Skull is anapsid = no hole characteristics

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.

Lepidosaurs: snakes, lizards on land to lay eggs probably.

Start out diapsid (two holes behind the eye on land to lay eggs probably.

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

Archosaurs = major dinosaur groups on land to lay eggs probably.

Plus crocodiles, and bird ancestry.

Allometry: changes in proportion with growth. known to be social, etc.

Means young often considered different species from adults.

Stegosaurus; plate back known to be social, etc.