Rats! – (or where Mickey Mouse diverged from Walt Disney)

We don’t talk about mammals much, but as reptiles they (we) do qualify as subjects to be covered by ReptileEvolution.com.

A new online study by Wu et al. (2012) finds evidence for a post-Cretaceous origin for rodents. Rodents (everything from porcupines and guinea pigs to squirrels and mice) are related to rabbits (lagomorphs) which are related to primates (including readers of this blog and lemurs) which all were derived from arboreal carnivores like Vulpavus.

The Wu et al 2012 study on rodents and their post-Cretaceous appearance.

The Wu et al 2012 study on rodents and their post-Cretaceous appearance.

How are they all related? 
Near (but not at) the base of the primates is an interesting set of taxa known as tree shrews. Essentially they are micro lemurs with shifted teeth.

Tupaia, the large tree shrew,

Figure 1. Tupaia, the large tree shrew, a living taxon close to the base of rabbits and rodents with origins in the Paleocene, just following the Cretaceous. Click to learn more.

The most common one, Tupaia (Raffles 1821) was found to be basal to the equally arboreal Plesiadapis (Fig. 3) and by extension to the terrestrial rabbits, and by further extension to rodents (keeping on topic), like the porcupine. It’s worthwhile to see the porcupine skull and how close it resembles that of Plesiadapis.

Plesiadapis

Figure 3. Plesiadapis, formerly considered a basal primate, is here considered a basal arboreal lagomorph (rabbit ancestor).

The other arboreal tree shrew, Ptilocercus, was found to be basal to bats and colugos (flying lemurs), all three with relatives extending back to the Paleocene (post-Cretaceous).

Ptilocercus, pen-tailed tree shrew

Figure 2. Ptilocercus, pen-tailed tree shrew, a living relative to the ancestor of bats and colugos.

I don’t know much about rodents, but given what I do know about the initial appearance of their outgroups, the Wu et al. (2012) study makes perfect sense in the present context!

References
Wu S, Wu W, Zhang Z, Ye J, Ni X, Sun J, Edwards SV, Meng J and Organ CL 2012. Molecular and Paleontological Evidence for a Post-Cretaceous Origin of Rodents. PLoS ONE 7(10): e46445. doi:10.1371/journal.pone.0046445
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0046445

2 thoughts on “Rats! – (or where Mickey Mouse diverged from Walt Disney)

  1. Except that molecular studies like Janecka et al.’s (2007) ” Molecular and Genomic Data Identify the Closest Living Relative of Primates” show that Ptilocercus is closer to Tupaia than colugos, and all molecular analyses agree bats are laurasiatheres with no particular relation to euarchontoglires.

    • I’ve seen molecular studies that support morphological studies and others that do not. Ultimately you have to go with morphological studies, and these can change as more fossils come to the fore, as they have with whales, for instance.

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