Why no aquatic/flying dinosaurs?

Factual Questions
41

Ceratopsians had both beak and teeth further back in the jaws, so not quite bird-like. Of course, this applies to a vast majority of Mesozoic birds as well (many of which didn’t even have beaks). If you draw the line at toothless beaks, you’re still left with only crown group birds.

Note that some more primitive theropods had toothless beaks, such as the ceratosaur Limusaurus, the ornithomimids, and the confuciusornithids, but these arose via convergent evolution. IIRC no ornithischians lacked teeth completely but I may be forgetting something.

ETA: Here’s a good if slightly technical diagram showing the stepwise acquisition of “bird” features among dinosaurs: GEOL 104 Theropoda III, Eumaniraptora: Dinosaurs of the Air

42

Right. This was true of many other Ornithischians, as well (I fired off that response as I was heading out the door, so didn’t have time for a more detailed response). The Ornithischian beak was largely limited to the premaxilla; but then, the upper beaks of modern birds consist of only the premaxilla and nasal bones, as well. So not entirely the same, but not entirely unlike, either.

43

From which one can see that the Confuciusornithidae, which still lacked some key characters of modern birds, had also evolved toothless beaks.

44

Yup, as mentioned above, toothless beaks evolved numerous times among coelurosaurs in general. By my count…

  1. Ornithomimidae
  2. Oviraptoridae
  3. Yandangornis
  4. Confuciusornithidae
  5. Zhongjiangornis
  6. Gobipteryx
  7. Schizooura
  8. Archaeorhynchus
  9. Aves

So that’s at most nine separate instances of tooth loss. Note some of those things might end up forming clades with each other which would reduce the number of parallel evolutionary instances. I wouldn’t be particularly surprised if Zhonjiangornis and/or *Yandangornis *turned out to fall in with the confucisuornithids, or if *Archaeorhynchus *and *Schizooura *formed a clade to the exclusion of modern birds.

45

So basically we’re not all that good at taxonomy, or rather, we don’t have it down to an exact science. I remember a good part of The Ancestors Tale was devoted to that problem, so it’s not terribly surprising.

Part of my misunderstanding was I assumed dinosaurs were warm blooded (isn’t that how the evidence is pointing?) and outsiders like pterosaurs/mosasaurs, referred to as reptiles, were cold blooded. Was I wrong in that assessment in some way?

Also a bit more reading seems to indicate that spinosaurus aegyptiacus may have spent a fair amount of its time in water fishing and came up with some unique adaptations for that… but then grizzlies fish a lot too and they’re not about to turn into sharks, so…

46

Yup.

There is a broad consensus that pteorsaurs were warm-blooded (they even had a form of “fur”).

Recent research indicates that at least some types of marine reptiles were also warm-blooded. http://www.smithsonianmag.com/science-nature/Wild-Things-Life-as-We-Know-It-201009.html

Reptile =/= cold blooded, at least not in modern classification. If it did, we’d have to remove many groups long considered reptiles to their own “classes”.

Note that at least some professional hepetological associations recently restricted “Class Reptilia” to lizards and snakes and placed crocs and turtles in their own classes. http://www.cnah.org/taxonomy.asp