|Pen-tailed tree shrew (Ptilocercus lowii) |
By Joseph Wolf (1820 – 1899) [Public domain] via Wikimedia Commons
Just how troublesome tree shrews have become is highlighted by a new paper on mammalian evolution by Tarver et al. (here).
|Alternative roots to the mammalian tree from Mess & Carter (here)|
Tarver et al. attempted to resolve this using a huge amount of genomic data and more sophisticated modelling techniques. They argue convincingly for the hypothesis at the top of the diagram where Afrotheria and Xenarthra are sister groups in a clade called Atlantogenata.
But once again tree shrews caused trouble. In a consensus tree based on protein-coding genes, tree shrews were basal to Glires (rodents and lagomorphs). This is in agreement with another recent study (here). But in a separate data set based on genes for microRNA tree shrews were basal to all the other orders in Euarchontoglires. So much so that the clade itself collapsed as a valid taxon. Naughty tree shrews!
Placentation in several species of tree shrew was studied by Luckett (here) and later in Tupaia glis by Kaufmann (here and here). The placenta is labyrinthine and endotheliochorial. So far nobody has looked at a placenta from the pen-tailed tree shrew (pictured above). It occupies its own family and a new paper (here) characterizes it as a living fossil that has undergone little change since the Oligocene.
Incidentally, pen-tailed tree shrews have a large intake of fermented nectar from the bertram palm (described here); see this blog for "boozing tree shrews."