Monotreme-like spalacothere (today's Nature)

[Tim Williams <twilliams_alpha@hotmail.com>]

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