11 May 2006

Meet a Spalacotheroid called Akidolestes


What the...? Well, a Spalacotheroid is kind of mammal-like but in the absence of definite lactation can’t validly be called a mammal — so mammaliaforme (Mammal-shaped) Akido remains.

Aki’s official species name is castorocauda lutrasimilis and (s)he is casually described as “a swimming mammal”. I say “casually” because it ain’t really a mammal (beaver-like tail, seal-like teeth array, digging-type front legs, “perfect” swimming back legs, dual-layered waterproof hair, etc) and the fossil was found (Aki was nearish Nanjing, China) amongst dinosaur fossils in Middle Jurassic strata.

So...

Dr. [Zhe-Xi; (approximately “shji-zie” to us limited Angloes)] Luo notes that the new fossil of Akidolestes is a challenge to the conventional wisdom about how therians split from monotremes in the early mammalian evolutionary history. Its unusual combination of advanced therian features and the primitive monotreme features can be the consequence of convergence, in which the hind-limb of Akidolestes has re-developed the monotreme-like features.
“Metaphorically, this newly discovered fossil mammal has a forelimb posture and gaits like those of a squirrel, with elbows tucked under its body, but its hind-limb would be sprawling with a posture that is similar to a lizard,” said Dr. Luo. “It is quite unusual that this mammal re-acquired some primitive hind-limb feature.“

Sounds almost distinctly Australian (think Platypus) in uniqueness, but apparently emigrated from near China to near North America (hence involvement from CMNH).

Akido-ish looks more interesting than a rat or cavy, but also a bit of a chore to find a home and food for here in generally-parched Western Australia. Wouldn’t do too well in many parts of WA — like the parts of the Pilbara (a little east of the coast) where rain falls only every few years or so.

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