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)