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Re: Fwd: Dinogeorge Digest special edition (long)



Dinogeorge wrote

>There were almost certainly no small non-avian dinosaurs left at the end of
>the Cretaceous. By then they had all evolved into birds. The Cretaceous is by
>far the best sampled of the three Mesozoic periods, yet small, bird-size
>(total length about 50 cm) non-avian dinosaurs are rare to non-existent. I
>claim they had been slowly replaced in their niches by placental mammals,
>whose fossils become increasingly abundant in the later stages of the
>Cretaceous. Small non-avian dinosaurs, thus, weren't at the K-T boundary,
>where they might have had a good chance of surviving to repopulate the planet
>with a new radiation of larger dinosaurs following the extinction. Instead,
>the planet was repopulated by larger mammals and, to a lesser extent, larger
>birds.

I'm curious what proportion of known dinosaur taxa were small at different
periods. Preservation biases will throw the ratio off, of course, but was
there a steady decline in the fraction of small _non-avian_ dinosaurs?

That also raises another question: were all small dinosaurs members of the
theropod/bird lineage?

And finally an observation -- birds also appear to have replaced the
smaller pterosaurs through the Cretaceous, so by the end of the Cretaceous
the only known pterosaurs were the supergiants.

-- Jeff Hecht