Some more information on fawn-footed mosaic-tailed rats…

Fig. 1. Me and Duff at Kewarra Beach

Moving swiftly into August and Blog 8, it’s hard to believe that we’ve made it this far into 2019! I am back in sunny Cairns (Figure 1), which is quite a change from the bustling metropolis of Chicago. I’m going to continue with our discussion on the native Australian fawn-footed mosaic-tailed rat Melomys cervinipes (Figure 2), still keeping the focus quite general at this point.

Fig. 2. Fawn-footed mosaic-tailed rat M. cervinipes

I didn’t mention this in the last blog, but I thought I should just quickly enlighten you all as to what being a murid actually means. To start with, murids fall into the sub-order Myomopha. To distinguish this sub-order from the Sciuromorpha (squirrels and relatives) and the Hystricomorpha (porcupines and relatives), we look at the zygomasseteric system – basically, the muscles in the face. In Myomorphs, the medial and lateral masseter muscles are displaced forward, and the medial masseter muscle passes through the eye socket (Figure 3).

Fig. 3. Myomorph skull (http://users.tamuk.edu)

The Muridae is a family of rodents. It is the largest family, with typical representatives being mice, rats, jirds and gerbils (Figure 4). Again, we can use the skull to distinguish murids from other rodents. Specifically, murids have an enlarged infraorbital foramen that has a keyhole shape. They have a broad zygomatic plate, and lack a postorbital process. The maxilla and mandible each house a pair of unrooted incisors and no premolars. In the mandible, the angular process and the incisors begin in the same area.

Fig. 4. Mongolian gerbil Meriones unguiculatus (Photo: Alastair Rae) https://commons.wikimedia.org/wiki/File:Meriones_unguiculatus_(wild).jpg

The first definitive recording of a member of the genus Melomys occurs in the fossil record of the late Pleistocene, around 33000 – 15450 years old. These fossils were found in the Pyramids cave about 6.5km north east of Buchan, Victoria. Fawn-footed mosaic-tailed rats are endemic to Australia, and can be found in the coastal and subcoastal regions from northern New South Wales to Queensland (Figure 5). It has been recorded at locations at sea level, as well as Mount Elliot (1221m.a.s.l), and even all the way to 1600m.

Fig. 5. Distribution of M. cervinipes (Callaway et al. 2018)

Fig. 6. M. cervinipes skull (Photo: David Wilson; Callaway et al. 2018)

If we take a closer look at the form and function of fawn-footed mosaic-tailed rats, the skull (Figure 6) is typical murid, bearing a pair of incisors, no canines or premolars and three pairs of molars on each of the upper and lower jaws, a total of 16 teeth in total. The incisors are opisthodont. The first and second pair of molars shows four distinctive roots, while the third pair of molars show three roots. The alveolar length of the first molar ranges from 3.1-3.7mm.

In the next blog, I’ll continue talking about mosaic-tailed rats.

You can read more about my research in my publications, listed on my blog. You can also find me on ResearchGate, the James Cook University website and Twitter.