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The Book Page
The Rise and Reign of the Mammals
Steve Brusatte
c. 2022
In round numbers:
- amphibians appear on land, 365 million years ago
- the "link" from amphibian to reptile/mammal ancestor appears: 300 million years ago
- mammal/reptile split --> direct mammalian ancestor (cynodont): 260 million years ago
- dinosaurs appear: 250 million years ago
- mammals flourish; non-dinosaur reptiles persist (birds, crocodile and their ancestors)
Amphibians --> reptile/mammal ancestor
- skull difference
- one group develops two large skull openings behind each of their eyes -->disapsids --> reptiles
- the other group: the two large skull openings fuse into one --> synapsids --> mammals
- for test-taking, how does one remember which is which?
- these large openings -- windows -- fenestrae -- that's where muscles attach
- the stronger the muscles, the more windows needed
- which have stronger jaw muscles: crocodiles or humans?
- so, crocodiles are diapsids; mammals are synapsids
- note: the synapsides in humans have anatomically closed but one can feel "functional" "windows" - the synapsid -- when opening and closing jaws
This book is c. 2022 but it's already somewhat out of date, or perhaps in period of transition
- the ancestor -- amphibian -->reptile/mammal ancestor -- has most recently been "called" a pelycosaur
- but now, pelycosaur is already falling out of favor
- pelycosaur is still used informally, as in this book, but purists in formal settings use a new term
- now, the preferred term: Eupelycosauria (Eu = true; pelycosaur)
- the term Eupelycosauria includes most pelycosaurs, but also Therapsida and Mammalia
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