Sarcopterygii - Lobe-Finned Fishes and Tetrapods The lobe-finned fishes include such "living fossils" as

These are the closest living relatives of the four-legged vertebrates, tetrapods.


Tetrapods

Tetrapods are the four-legged, primarily terrestrial vertebrates, derived from a specialized group of shallow-water fishes that probably resembled living (extant) lobe-finned fishes.

Tetrapoda includes


Let's meet the non-avian Diapsids: The Reptiles

Recall that the study of birds is known as Ornithology.

The study of reptiles (and amphibians) is known as Herpetology from the Greek herpeton, meaning "crawling". Typical reptile characteristics include...


Crocodilia - First Cousins of Birds Crocodilians include the crocodiles, alligators, caimans and the gharial.
There are 23 extant species of crocodilians.

Evolutionary relationships are still not fully clear. Most data suggest that they are most closely related to birds. However, a molecular study published in 1999 suggested that crocodilians may be more closely related to turtles than birds.

The jury is still out.

There are three Crocodilian families:


Chelonia - Turtles and their relatives (Anapsida) Members of Order Chelonia are of uncertain evolutionary affinity. It is possible that these shelled reptiles comprise a polyphyletic group (i.e., they have more than one ancestral origin).

How did such an odd body form evolve? Here is one hypothetical scenario:


Tuataras

The only extant species of Tuatara (Sphenodon punctatus) lives in New Zealand, and nowhere else. Although it resembles a typical lizard, it belongs to a distinct and very ancient lineage, Rhynchocephalia.

(The basic "lizard shape" was very common among early amniotes. But not all of those early amniotes gave rise to what we now know as "lizards". The earliest known fossil reptile, Hylonomus, was shaped like a lizard. Therefore, lizard shape can be considered a basal amniote characteristic.)

Rhynchocephalia can serve as an outgroup for the Squamata, the order containing lizards and snakes.

The word tuatara means "peaks on the back" in the Maori language. Let's let the Kiwis tell you about tuataras themselves.

Primitive characteristics of Tuataras: