Monotreme ears (Science)

[Tim Williams <twilliams_alpha@hotmail.com>]

My apologies if this has already been forwarded to the list...

Thomas H. Rich, James A. Hopson, Anne M. Musser, Timothy F. Flannery, 
Patricia Vickers-Rich (2005).  Independent Origins of Middle Ear Bones in 
Monotremes and Therians.  Science 307: 910-914.

ABSTRACT: A dentary of the oldest known monotreme, the Early Cretaceous 
_Teinolophos trusleri_, has an internal mandibular trough, which in 
outgroups to mammals houses accessory jaw bones, and probable contact facets 
for angular, coronoid, and splenial bones. Certain of these accessory bones 
were detached from the mandible to become middle ear bones in mammals. 
Evidence that the angular (homologous with the mammalian ectotympanic) and 
the articular and prearticular (homologous with the mammalian malleus) bones 
retained attachment to the lower jaw in a basal monotreme indicates that the 
definitive mammalian middle ear evolved independently in living monotremes 
and therians (marsupials and placentals).