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.

Let’s talk about rats … cute native Australian ones …

Fig. 1. Chicago from the John Hancock building (Photo: T. Rymer)

 

Moving on to Blog 7, we’ll be taking a different view from this month of July. We’re more than half way through the year right now, and I’m writing this from the gangster-ridden, speak-easy city of Chicago! (Figure 1). I thought I would take a bit of time to talk about some of the work we’ve been doing on native Australian fawn-footed mosaic-tailed rats Melomys cervinipes (Figure 2). There will hopefully be lots more of this to come in the future.

For starters, I thought I’d take a bit of time to introduce you to this little rat. I coordinated a group of postgraduate and honours students to collate data from a variety of studies into a single work representing the biology, ecology and life history of this species, which we published as a species account in the journal Mammalian Species. We presented a taxonomic account at the species level, providing a species diagnosis and general characters description. We also provided notes on the distribution and fossil record accounts. Finally, we collated information on the form and function, ontogeny and reproduction, ecology, behaviour, genetics and conservation of the species.

Fig. 2. Female fawn-footed mosaic-tailed rat (Photo: T. Rymer)

The species belongs to order Rodentia, family Muridae, sub-family Murinae, tribe Uryomyini. The species was first described by Gould in 1852, and placed in the genus Mus. The specimen was a female, and it is the designated lectotype. The type locality was named as Stradbrook Island (Figure 3) in Moreton Bay, Queensland, Australia. The first occurrence of the current name combination is recorded by Thomas in 1922. The genus Melomys comprises 21 species, of which three are native to Australia. A 4^th species, Melomys rubicola was declared extinct in 2014. No subspecies are recognised within M. cervinipes. The generic name, Melomys is derived from the English Melanesia, indicating the wide distribution of species from this genus, and the Greek mys for mouse. The species name cervinipes is from the Latin cerv for deer or fawn and pes for foot, referring to the light colouring (fawn) of the feet.

Fig. 3. Stradbroke Island, Australia

Melomys cervinipes is small, light grey-brown to russet brown (Figure 2), although colour is highly variable and can change with age, with a white to cream ventral surface, a brown to black tail, and light fawn-coloured feet. Young animals are often a uniform light grey. The fur is soft, fine, and long, and dark whiskers are conspicuous on the muzzle. The ears are short, rounded, and dark grey to black, and the eyes bulge conspicuously. The tail is naked, with the scales arranged in a mosaic-like pattern, interlocking with little overlap, with short hairs, and is approximately equal to the head–body length. The tail is partially prehensile, with the tip capable of curving round objects to potentially provide support. The hind feet are long and wide. Average body mass is 72.9 ± 12 g, average head–body length is 133.5 ± 12.7 mm, average tail length is 142.6 ± 10.9 mm, average hind foot length is 27.5 ± 0.8 mm and average ear length is 18.3 ± 1.6 mm.

Distinguishing this species from its sister taxon Melomys burtoni in the field is challenging. However, some techniques have been used, including counting the number of tail scale rows (13 vs. 14-15), and length of 1^st and 5^th inter-digital pads (1^st = > 2.3mm; 5^th = > 1.7mm indicating M. cervinipes). Dentition provides a more accurate estimate, but is not possible for living wild animals.

In the next blog, I’ll continue to describe the basic biology of this fascinating little rat.

 

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.