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The Triassic was full of creatures that look a lot like other, more modern species, even though they’re not closely related at all. The reason for this has to do with how evolution works and with the timing of the Triassic itself: when life was trapped between two mass extinctions.

Thanks to Ceri Thomas for the Drepanosaurus reconstruction. Check out more of Ceri's paleoart at   / alphynix   and http://nixillustration.com

And thanks as always to Nobumichi Tamura for allowing us to use his wonderful paleoart: http://spinops.blogspot.com/

Finally, thanks to Emilio Rolandia, Matt Celeskey, and Studio 252mya for their excellent images as well.

Produced for PBS Digital Studios.

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References:
Original description of Triopticus with a description of repeated bodyplans and lifestyles of Triassic and later Mesozoic animals http://www.cell.com/currentbiology/a...
Original description of Shringasaurus with discussion of allokotosaur evolution
https://www.nature.com/articles/s4159...
Original description of Avicranium with a discussion of drepanosaurids
http://rsos.royalsocietypublishing.or...
An earlier phylogenetic analysis of drepanosaurs with discussion of their likely habits in life
https://doi.org/10.1017/S147720190400...
A very thorough, but fairly technical discussion of adaptive radiations (including those triggered by extinctions) can be found in chapters 4, 5, and 10 of:
Stanley, SM. 1979. Macroevolution: Pattern and Process. John Hopkins University Press.
ISBN 080185735X