Did climate change do for the tragulids?

Lesser Mouse-deer (Tragulus kanchil) at Singapore Zoo
Photo by Bjørn Christian Tørrisen (CC)

In a previous post, on giraffe and okapi placenta, I mentioned that tragulids (chevrotains or mouse-deer) were the most abundant ruminants in the Early Miocene. They were displaced by the pecoran ruminants and today are represented by a mere handful of species.

A new paper in PLoS One re-examines the European fossil fauna and shows tragulids already were on the way out in the Oligocene (full text here). The focus of the study is on a narrow time period called MP28 (MP stands for Mammal Palaeogene zone). This was a period of global warming that led to wooded environments being replaced by more open habitats and the appearance of seasonality including a dry season.

Pecorans have an additional forestomach, the omasum, and this may have given them the edge over tragulids in exploiting new resources. 

Placenta of Lesser Mouse-deer showing binucleate cells stained with
anti-bovine lactogen. From the Benirschke web site.

Although tragulids have the binucleate trophoblast cells that are the signature feature of ruminant placentation, they differ from pecorans in lacking cotyledons (reviewed here).