Paleontologists Help! - Eosuchians

[Polycarp]

Okay, I enjoy reading about paleontology -- Wonderful Life, Colbert's Evolution of the Vertebrates, and so on. And I've run into something I cannot find the answer to.

Here's the breakdown...reptiles are subdivided by the holes in their skulls -- in addition to the eye socket, they had 0, 1, or 2 additional openings on each side of their heads, which were apparently where muscles anchored. Mammals are descended from a group called synapsids which had one hole (per side) at their temple. Plesiosaurs and such had one hole further up, about where a man in the early stages of pattern baldness still has hair above the ear. Turtles and their relatives had no holes.

The ones with two holes were called diapsids, and were broken down into archosaurs and lepidosaurs. What's the difference? Nobody says. Archosaurs include crocodiles, flying reptiles, dinosaurs, and early birds, and a primitive group that died out after the Triassic and were apparently ancestors of the others. Lepidosaurs include lizards and snakes, rhynchosaurs, and eosuchians. Okay, lizards are distinguished by the idea that their temporal fenestra (the lower hole) is open at the front to allow a larger jaw gape, and snakes are distinguished from legless lizards like the "glass snake" by the upper hole being added into this jaw gape thing. Rhynchosaurs and their relatives had beaks. Eosuchians are "true diapsid lepidosaurs with the bar at the front of the temporal fenestra still present which did not have beaks." But nobody gives examples!

Eosuchians lived from the Permian into the Eocene, when they became extinct.

One book mentions champsosaurs and phytosaurs as being "false crocodiles" and says that one group were eosuchians and the other were those primitive archosaurs.

Okay, we have a group of reptiles that lived through the two biggest extinctions in Earth's history, included things that were not crocodiles, and which were not archosaurs, lizards, or rhynchosaurs.

So what the heck were they? Lots of things are not crocodiles. Birds aren't crocs. Cats aren't crocs. I would give high odds that no SDMB regulars are crocs (though some of their posts are! ;))

Anybody know what an eosuchian was? (As opposed to what they were not)

[tomndebb]

The EB provides these statements:

From "Permian Period"
Permian reptile fossils are locally common and include the protorosaurs, aquatic reptiles; the captorhinomorphs, the "stem reptiles" from which most other reptiles are thought to have evolved; the eosuchians, early ancestors of the snakes and lizards; early anapsids, ancestors of turtles; early archosaurs, ancestors of the large ruling reptiles of the Mesozoic; and the synapsids, a common and varied group of mammallike reptiles that eventually gave rise to mammals in the Mesozoic.

from "lizards"
The diapsids comprise two subclasses of reptiles: the Archosauria (crocodiles, pterosaurs, dinosaurs) and the more primitive Lepidosauria (lizards, snakes, eosuchians, and rhynchocephalians). The earliest known Lepidosaurian order (Eosuchia) appeared in the Late Permian (about 230,000,000 years ago) and almost undoubtedly was ancestral to lizards.

The only eosuchian species that I could find named (no illustration) was the youngina.


(Unless, of course, eosuchian simply means raw fish that one eats at the break of day.)

------------------
Tom~

[Nickrz]

Or that little tube that equalizes the air pressure in your ears.