Friday, February 24, 2006

 

New Jurassic Mammal Found

A new fossil find has radically changed our view of early mammal development. The find is detailed in today's issue of the journal "Science". The new species resembles a river otter, but has a beaver-like tail. From the journal's summary:
Mesozoic mammals have been thought to have been small, nocturnal, and confined to a few niches on land until the demise of the dinosaurs 65 million years ago. Most are recorded by isolated jaw fragments or teeth. Ji et al. now describe a Jurassic mammal from China that breaks this mold. The fossil is well preserved, and impressions of fur can be seen on its body and scales on a broad tail (similar to a beaver overall). The animal was fairly large, approaching not quite half a meter in length, and the shape of its limbs suggest that it was adapted for swimming and burrowing. The combination of both primitive and derived features in this early mammal, and the demonstration that mammals had occupied aquatic habitats by this time, expands the evolutionary innovations of early mammals.

The fossil is 164 million years old and pushes back the mammalian expansion into water by 100 million years. From an AP article on the find:
It's the first evidence that some ancient mammals were semi-aquatic, indicating a greater diversification than previously thought, the researchers said. Modern semi-aquatic mammals such as beavers and otters and aquatic mammals like whales did not appear until between 55 million years ago and 25 million years ago, according to the researchers. The new animal is not related to modern beavers or otters but has features similar to them.

The find means that mammals took to the water much earlier than previously expected. Rather than merely living in dinosaurs' shadows, as previously thought, it appears that mammals were actually thriving alongside them (and probably getting eaten by them) for millions of years.

I expect many more finds like this to come out of China in the next few years. There are some pristine fossil sites in China that will produce some amazing stuff.

I have a photo of the actual fossil find and I am working on getting an electronic copy (being friends with the State Paleontologist for Utah is helpful). The closest I could find online was a drawing of the fossil within an article. What's really striking about the skeleton is the size of the vertebrae in the tail; they are as big as the dorsal vertebrae (backbone). Typical mammals have much smaller vertebrae in their tails. You can also see the imprint of the body fur and the scales on the tail (much like a beaver's tail) in the fossil. If I can get an electronic copy of the photo, I'll post it here.

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