Thursday 5 November 2015

Possible sexual dimorphism in a Late Miocene Red Panda.

Pristinailurus bristoli is a Late Miocene Ailurid Mammal (a group that includes the modern Red Panda as its only living relative) from the Gray Fossil Site in northeast Tennessee. It was first described in 2004 from a mature individual estimated to have weighed about 8.25 kg in life. In 2011 a second specimen was described from the same site. This second specimen was much larger than the original, reconstructed as having weighed about 15 kg, but the individual appeared to be younger than the original specimen, which had very badly worn down teeth, usually accepted as a sign of age. This raises the possibility that the species may have been sexually dimorphic (i.e. adults of the two sexes may have been different sizes), though this is difficult to assert from only two specimens, and does not fit with the biology of the living Red Panda, in which both sexes tend to be the same size.

In a paper published in the journal Palaeontologica Electronica in September 2015, Ethan Fulwood of the Department of Anthropology at the University of Tennessee, Knoxville and the Department of Evolutionary Anthropology at Duke University and Steven Wallace of the Department of Geosciences and Don Sundquist Center of Excellence in Paleontology at East Tennessee State University publish a morphometric analysis of the skeletons of modern Red Pandas, Ailurus fulgens, which they believe supports the presence of sexual dimorphism within the Ailurid group as a whole.

Size differences between Ailurus fulgens (1) and the two known skeletons of Pristinailurus bristoli (2) and (3). Shaded bones represent recovered elements from the two fossil skeletons. Fulwood & Wallace (2015).

Modern Red Pandas have an unusual reproductive strategy for Carnivorans, being non-competative and promiscuous, with conflict between males being extremely rare. This gives no reason for males to be larger than females (or vice versa) and the two sexes are roughly the same size. However sexual dimorphism tends to be a conserved trait within Carnivorans, existing or not across whole groups of species regardless of the mating behaviour of individual species. Therefore it would be expected that if mate-competition and sexual dimorphism were historically found within the Ailurids then traces of it would be likely to be retained in modern Red Pandas, even if this no longer conferred any ecological advantage.

Fulwood and Wallace took 23 measurements of the bones and teeth of 22 Red Panda specimens in museum collections (11 males and 11 females). In almost all of these measurements the two sexes were identical, however the surface area of the lower canine teeth of the males were found to be consistently larger than in female specimens. Canines teeth are often strongly dimorphic in Carnivoran species where male-male conflict is the rule, and Fulwood and Wallace speculate that this may reflect the presence of such conflict in the ancestors of modern Red Pandas, supporting the idea that the Ailurids may have exhibited sexual dimorphism.

See also... new species of Olingo from the cloud forests of Colombia and Ecuador.             Olingos, Bassaricyon, are small members of the Racoon family, Procyonidae, found in Central and South America. They are not well understood, as they live in the canopy of dense forests where they are not easily observed, and are easily mistaken for the related Kinkajou, Potos flavus. of scavenging on a Pliocene Argentinean Glyptodont.                                                       Glyptondonts were large, heavily armored mammals related to Armadillos that evolved first appeared in South America in the Miocene, spread to North America in the Pliocene and became extinct at about the same time as the earliest humans entered the Americas (this is,,.

Follow Sciency Thoughts on Facebook.