#daalseth

[kathrynsower]

[alphynix]

A thought as I was cracking eggs for breakfast. Bird eggshells are hard and brittle. As we were taught in school reptile eggs are flexible and leathery. How far back do hard shell eggs go?

We know non-avian dinosaurs laid hard-shelled eggs. Crocodilians also lay hard eggs, with a slightly more “primitive” shell structure, which suggests that rigid shells could go back at least to the common ancestors of the archosaurs.

Pterosaurs do seem to have had more leathery eggs, but if hard shells were ancestral they could have secondarily lost them.

Some turtles lay hard-shelled eggs, too, and that could possibly be a deeper evolutionary link since they’re probably archosauromorphs. But it’s hard to say for certain -- it could be convergent evolution, since hard shells have also evolved independently at least once in lepidosaurs(specifically gekkonids).

[kathrynsower]

[alphynix]

@daalseth replied to your photo: Unsolved Paleo Mysteries Month #10 – Ambiguous...

Crazy blue sky idea: Suppose it was the immature form of Anomalcaris? Two appendages at the front. vestigial winglike structures. A larval form that hadn’t developed a hard shell yet.

A larval form of some other creature is another possibility!

Obviously without more information we can’t make a definite link to anything -- it could even be an as-yet-undiscovered animal -- but something like an anomalocarid is at least a very tempting speculative idea...

[alphynix]

taggthewanderer reblogged your photo: Unsolved Paleo Mysteries Month #08 ...

And then they went extinct afterwards, somehow, which might be the even bigger mystery.

Well, the diversification of archosaurs in the Early-Mid Triassic probably had something to do with it... But we don’t really know why the archosaurs were able to take over and outcompete most of the surviving synapsids so successfully, either.

daalseth replied to your photo: Unsolved Paleo Mysteries Month #08 ...

   This just in, a paper theorizing that the first part of the Great Dying was a sharp, short, ice age: sciencedaily.com/release…   

Another new theory! Sure, let’s throw an ice age into that huge mess, too.

[kathrynsower]

Doug, I want to see Marsha, please let her know.

Thanks,

Suzie

[alphynix]

@daalseth replied to your post:if Crocodilia are related to birds, then are they...

Mosasaurs were Lepidosaurs and so were related to lizards. Plesiosaurs were Sauropterygians. Where would they fall on this Cladogram?

Plesiosaurs would be within the turtle branch of that cladogram -- they’re currently considered to be stem-turtles as part of the pantestudine clade.