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Putting dinosaur decline into context

It is probably safe to say that to many, the idea that dinosaurs were slowly in decline, or that they weren't 'evolving' as fast as they should have been, is an uncomfortable thought.

I thought some context will make this idea easier to appreciate.

Palaeontologists are generally happy to say that Velociraptor is a very close relative of birds. It is morphologically very similar to birds, and there is even strong evidence that it possessed secondary feathers on its forearms (Turner et al., 2007. Science 317: 1721).

Velociraptor lived during the Campanian Stage of the Late Cretaceous, 83.6 - 72.1 million years ago (Ma).
Velociraptor from Wikimedia Commons

On the other hand, the oldest bird known to date, Archaeopteryx, is known from the Tithonian Stage of the Late Jurassic, 152.1 - 147.7 Ma.
Archaropteryx as a Blue Jay
Archaeopteryx with red plumage
So that's on average about 72 million years (Myr) between these two dinosaurs, with a maximum of ~80 Myr and minimum of ~64 Myr.

We Homo sapiens are on average about 78 Myr apart from Velociraptor in time. That's about the same amount of time that separates Velociraptor from Archaeopteryx.

However, look how far mammals have come in that time from our rat-like mammal ancestors. We had less time to evolve than Velociraptor did from its last common ancestor with Archaeopteryx, yet mammals radiated into virtually every ecological niche conceivable, including flighted bats, giant terrestrial elephants, insectivorous anteaters, hypercarnivorous cats, deep-sea cetaceans, eusocial naked mole rats, bipedal tool-making humans, etc.

Compare that with Velociraptor, which basically looks just like any other big dromaeosaur, and very similar to Archaeopteryx - Velociraptor hadn't evolved much.

This goes for dinosaurs like Tyrannosaurus as well - despite its colossal size, the rate at which tyrannosaurs evolved in size is as one would expect given the amount of time they've been around (this is based on unpublished results from our lab; but also with respect to their biting performance).

So remember, the next time you talk about dinosaur evolution, keep in mind the passage of time - dinosaurs have been around for a very very long time, and what may seem like extreme specialisations can, more often than not, be explained by the passage of time.

Stratigraphy.net | Impressum

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