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Monotreme-like spalacothere (today's Nature)




The Yixian Formation coughs up another furball. This one is named _Akidolestes cifellii_, and is based on a nearly complete skeleton with fur impressions.


Gang Li and Zhe-Xi Luo (2006). A Cretaceous symmetrodont therian with some monotreme-like postcranial features. Nature 439: 195-200.

Abstract: "A new spalacotheriid mammal preserved with a complete postcranium and a partial skull has been discovered from the Yixian Formation of Liaoning, China. Spalacotheroid symmetrodonts are relatives to modern therians (combined group of marsupials and placentals) and are characterized by many skeletal apomorphies of therians. But unlike the closely related spalacotheroids and living therians, this new mammal revealed some surprisingly convergent features to monotremes in the lumbar vertebrae, pelvis and hindlimb. These peculiar features may have developed as functional convergence to locomotory features of monotremes, or the presence of lumbar ribs in this newly discovered mammal and their absence in its close relatives might be due to evolutionary developmental homoplasy. Analysis including this new taxon suggests that spalacotheroids evolved earlier in Eurasia and then dispersed to North America, in concordance with prevailing geodispersal patterns of several common mammalian groups during the Early Cretaceous period."

"Etymology. _Akidolestes_: akido- (Greek) for point, for the pointed rostrum of this new mammal; -lestes (Greek), for thief, a common suffix for the name of fossil mammals; cifellii, in honour of Richard L. Cifelli, for his pioneering studies of symmetrodont mammals."

From the Editor: "The Yixian Formation in China has yielded some of the most
important mammalian fossils of the past decade - notably a series of feathered dinosaurs - and continues to produce fossils that challenge conventional wisdom about the evolution of early mammals. The latest is a well preserved 'spalacotheroid symmetrodont', a relative of the modern therians (the marsupials and placentals). Parts of its skeleton are very un-therian like: from lumbar vertebrae down to the ankle, this mammal is very like the platypus, perhaps as a result of functional convergence. This new fossil is also of interest from the palaeobiogeography perspective. Like many other mammals in the Early Cretaceous, spalacotheroids seem to have evolved initially in Eurasia and then to have dispersed to North America."

Cheers

Tim