Brian Thomas writes:
Researchers in 2006 described a fossil they named Castorocauda. They found it in a sedimentary layer mixed with pterosaurs, insects, amphibians, a dinosaur, and a gastropod. It “has a broad, flattened, partly scaly tail analogous to that of modern beavers.” Maybe it was a beaver.
(“Devils, Dinosaurs, and Squirrel Fossils,” January 2015 Acts & Facts)
That’s a common idea expressed by creationists – they don’t like the fact that the organisms alive in the past were different to those around today, so wouldn’t it be great if they were actually the same? Unfortunately for the creationists, these are testable claims.
Was it a beaver? The quote Thomas gives comes from the abstract of the paper he is referencing:
A docodontan mammaliaform from the Middle Jurassic of China possesses swimming and burrowing skeletal adaptations and some dental features for aquatic feeding. It is the most primitive taxon in the mammalian lineage known to have fur and has a broad, flattened, partly scaly tail analogous to that of modern beavers. We infer that docodontans were semiaquatic, convergent to the modern platypus and many Cenozoic placentals. This fossil demonstrates that some mammaliaforms, or proximal relatives to modern mammals, developed diverse locomotory and feeding adaptations and were ecomorphologically different from the majority of generalized small terrestrial Mesozoic mammalian insectivores.
The obvious red flag here – which should be clear even in Thomas’ paragraph – is that the tail is merely analogous to that of a beaver, and only the tail. This is an extraordinarily weak basis for declaring that Castorocauda lutrasimilis (this fossil) should actually be simply Castor lutrasimilis, i.e. a type of beaver. But this weakness isn’t enough on its own for us to say Thomas is wrong – that will require looking not at what the authors of the paper wrote but what they actually found.
Jaws and teeth are great ways to distinguish between types of animals, and it just so happens that this fossil – which you can see a picture and reconstruction of here – includes them. As you can see the jaw is relatively straight and simple, as befitting a “primitive” mammal.
In stark contrast beavers are rodents, and rodent teeth are weird. You can find a picture specifically of a beaver skeleton here if you don’t believe me, but suffice to say that the skull of a Castor is very different to a Castorocauda.
While Thomas didn’t mention it – it would complicated his point – the authors also draw comparisons to the platypus, which is worth investigating. But it’s abundantly clear from the diagram above that the platypus too has very different teeth and jaws to the fossil.
So I think we can be extremely confident in saying “no, Brian, it’s not a beaver – and nor is it a platypus either, just in case that was your next thought.” We might also guess that Thomas didn’t do any of this research, contenting himself to making wild speculation without considering it important to test.
There are several other examples that Thomas gives in his article – the not-beaver is simply the most blatant. What do we make of this? Well for one, that the ICR and Brian Thomas are just as they always were. It’s good to be back.