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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
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