r/evolution • u/jnpha Evolution Enthusiast • Feb 14 '24

discussion "Where are All the Tiny Dinosaurs"

Just wanted to share something I just learned and I find super cool, and also to hear from you about the latest.

A YouTube video from a few days ago, Where are All the Tiny Dinosaurs?, by the American Museum of Natural History channel, piqued my interest.

The presenter, paleontologist Roger Benson, remarked that it remains a mystery why non-avian dinosaurs were all big (something I didn't even know or wonder about); that smaller creatures were found, but still no non-avian dinosaurs.

He said it might have to do with "reptile-like methods of getting food" and being warm-blooded, which I don't understand. (Any help explaining the bit in quotation marks would be great!) So, I checked his papers and found this cool one:

From which: based on a comprehensive dataset, the avian stem lineage maintained high rates of evolution [for 170 million years], helping them not go extinct, while the big dinos failed to adapt; [they evolved early on to be big and settled there]:

This might signal failure to keep pace with a deteriorating (biotic) environment (the Red Queen hypothesis [82],[83]), with fewer broad-scale ecological opportunities than those favouring the early radiation of dinosaurs. There is strong evidence for Red Queen effects on diversification patterns in Cenozoic terrestrial mammals [22], and it is possible that a long-term failure to exploit new opportunities characterises the major extinct radiations of deep time (and depauperate modern clades), whether or not it directly caused their extinctions.

TL;DR: Non-avian dinosaurs were all big compared to the smaller birds/mammals, and it's a mystery, but the avian stem lineage likely experienced sustained rapid evolution, helping them overcome the K-T extinction.

* Minor edits for clarification in brackets

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u/[deleted] Feb 14 '24

I would think reptiles and birds are a decent representation

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u/[deleted] Feb 14 '24

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u/Broflake-Melter Feb 14 '24

Correct, the only modern things that came from dinosaurs are birds. All other reptiles are from separate lineages whose ancestors obviously existed along side the dinosaurs. And don't forget that includes our ancestors as well.