As the title says…
If we jumped back 70 million years in a time machine, what creatures and species would we be likely to see in the skies above us?
Were there are earlier species resembling modern birds in the dinosaur era? As our modern birds evolved later then what, if anything, were their airbourne precursors? If nothing, what would have dominated the skies in those times - mainly (or solely) large insects? Only the major flying reptiles? Nothing?
Thanks for any clarification.
Aro there were lots of birds around while the dinosaurs were still around. By the time of the later dinosaurs the skies would have been filed with essentially modern birds that filled every major niche filled by modern flying birds. In the late cretaceous for example you would have seen flocks of migrating geese, ducks feeding on the rivers and lakes, seagulls and petrels covering the ocean and feeding along the shores. They wouldn’t be exactly the same families as birds as they have evolved into since, but the direct ancestors of all those birds lived alongside the dinosaurs and would have been recognisable to the average person as being ducks, seagulls etc.
In addition to the waterbirds, which are over-represented in the fossil record for obvious reasons, there were also various other groups of birds filling the niches of crows, cardinals, tits and probably many other smaller types that never got fossilised. Most of those birds probably weren’t the ancestors of modern bird types, but they would have made up just as noticeable a part of the cretaceous fauna.
Really it’s only a few distinctive bird groups like parrots, penguins and owls that would have been noticeably absent from the cretaceous sky to a casual observer. Aside from that there is no reason to assume a lack of birds.
Excellent.
Thanks for that.
There were unambiguously four modern bird lineages present as of the end of the Cretaceous:
There are also ambiguous fossils for representatives of cormorants, pelicans, flamingos, and relatives of modern chickens and turkeys.
Based on inferred relationships, it is likely that there were several other groups (besides the four mentioned above) present during that time, even though we don’t have unambiguous fossils of them:
[ul][li]Paleognathae (ratites)[/li][li] Tinamiformes (tinamous)[/li][li] Galliformes (chickens, turkeys, etc.)[/li][li] Pelicaniformes (pelicans)[/li][li] Sphenisciformes (penguins)[/li][li] Podicipediformes (grebes)[/li][li] Gruiformes (cranes, coots, rails)[/li][li] Columbiformes (pigeons, etc.)[/li][li] Ciconiformes (herons, egrets, ibises)[/li][/ul]
The lineages which produced the remaining modern forms would likely also been present during the Late Cretaceous.
Note that the above is not to imply that all modern species of those lineages were present, only that the ancestors of those forms were, and that they probably looked similar to the modern forms. Nevertheless, avian diversity was quite high during the Mesozoic, and at the end of the Cretaceous in particular.
[aside]
In fact, considering Dinosauria as a whole (non-avian dinosaurs + avians), Dinosauria has always exceeded Mammalia in terms of diversity, even to this day.
[/aside]
Also note that there would be plenty of pterosaurs flying around too. I can’t remember when the earliest bat fossils date from, or when we think the earliest bats must have been around even if we don’t have fossil evidence for them.
The earliest bat fossils are from about 50 mya, but even these are fully formed, unmistakeable bats. Based on molecular analysis, it is thought that bats may have first diverged somewhere between 65-80 million years ago, possibly a bit sooner. So, it is probably a safe guess that early bats were likewise sharing the skies with birds and pterosaurs prior to the end of the Cretaceous.
[QUOTE=Blake]
Really it’s only a few distinctive bird groups like parrots, penguins and owls that would have been noticeably absent from the cretaceous sky to a casual observer.
[QUOTE]
A sky without penguins! That must have been a weird time. 
[QUOTE=Blake]
Really it’s only a few distinctive bird groups like parrots, penguins and owls that would have been noticeably absent from the cretaceous sky to a casual observer.
[QUOTE]
Notably absent would have been the small Perching Birds, or “songbirds” (Passeriformes) that make up more than half of all bird species today, an whose great expansion in diversity dates to the mid-Tertiary or so. However, even in the Creatceous there would have been many small arboreal birds that would appear similar to the casual observer.
Right. For the sake of completeness, the “lineages which produced the remaining modern forms” that I mentioned earlier - the ones which are thought to have arisen in the Tertiary, rather than the Mesozoic, are as follows:
[ul]
[li] Falconiformes (hawks, falcons, etc.)[/li][li] Strigiformes (owls)[/li][li] Caprimulgiformes (nightjars)[/li][li] Apodiformes (hummingbirds and swifts)[/li][li] Coraciiformes (kingfishers)[/li][li] Piciformes (woodpeckers, toucans)[/li][li] Passeriformes (damn-near everything else)[/li][/ul]
Each of these groups have fossil records within the Tertiary, but have none within the Mesozoic. Their ancestors, however, were most probably present during the Mesozoic. Two other groups - Psittaciformes (parrots and kin), and Cuculiformes (cuckoos, turacos, hoatzins) - were accidently excluded from my previous list; it is thought by some that their immediate ancestry (and ultimate origin) dates back to the Cretaceous, even though we have only Tertiary fossils for them.
Which niches were filled by flying reptiles? Or were they out-competed by birds?
From a phylogenetic standpoint, birds are flying reptiles (the ones that aren’t / weren’t flightless, anyway). It’s difficult to say exactly what the interaction between birds and pterosaurs was, though. To my knowledge, the two have not been found in the same sediments, so it may be possible that they never (or rarely) actually came into direct competition. And many small pterosaurs are thought to have been every bit the equal, flight-wise, of modern birds.
Pterosaurs as a group arose during the Triassic (~215 mya), and lasted until the end of the Cretaceous. Given that, as mentioned, birds were plentiful during a good portion of that period that period (the overlap is around 85 million years), I would think it unlikely that birds outcompeted pterosaurs in general.
Known pterosaurs included mostly fish-eating forms, but a few were insectivorous. None are known to have eaten fruits, seeds, or other vegetable matter as many birds do, but it’s possible some did but we have not found their remains. The insectivorous forms were mostly Jurassic; by the Cretaceous pterosaurs consisted mainly of rather large fish-eaters and perhaps some carrion eaters. At least one, however, seems to have been a filter-feeder on small aquatic life like a flamingo. None of the known forms had raptorial adapatations to prey on terrestrial vertebrates as hawks do.
Pterosaurs were probably on the whole less maneuverable than birds, an airfoil made of skin being less versatile than one made of feathers. (Although Darwin’s Finch may be correct that a few might have been the equal of some birds in flight.) Also, few if any were able to become bipedal and run on the ground at any speed. So the niches that were open to them may have been more limited than those open to birds.
It’s possible that the insectivorous pterosaurs were out-competed by birds before the start of the Cretaceous. However, the others were evidently killed off by whatever got the non-avian dinosaurs at the end of the Cretaceous, not by competition with birds.
Incidentally, a significant number of bird lineages, especially the Enantiornithes (“opposite birds,” because some of their bones are arranged in an opposite manner to those of modern birds) also became extinct at the end of the Cretaceous.
Is it safe to assume that you’re talking about the wonderfully weird Pterodaustro ?
Yes, that’s the one.