Uromys caudimaculatus (Krefft, 1867)

Cramb, Jonathan, Hocknull, Scott A. & Price, Gilbert J., 2020, Fossil Uromys (Rodentia: Murinae) from Central Queensland, with a Description of a New Middle Pleistocene Species, Records of the Australian Museum (Rec. Aust. Mus.) 72 (5), pp. 175-191 : 179-180

Uromys caudimaculatus (Krefft, 1867)

Fig. 3A, 3B

Material examined. QML 1456: spit 142–147 cm: QMF 60126 right M 1, QMF 60127 left M 1, QMF 60128 right M 1, QMF 60129 left M 2, QMF 60130 left M 1, QMF 60131 right M 2. Additional specimens were also recovered from spits 152–157 cm, and 177–182 cm.

Remarks. Isolated molars of this species are distinguished by a combination of characters including very large size; crescentic lophs on M 1–2; deep posterior indent present on M 1–2; long, variably bifurcated lingual root on M 1–2; crescentic lophids on M 1–2; lingual root present on M 1; large posteroconid on M 1–2; and a relatively shallow cleft between the antero-buccal cuspid and protoconid on M 1.

Uromys caudimaculatus was previously considered to include U. sherrini , so it is pertinent to include a list of characters that distinguish these species. These are: the margins of the interorbital area above the orbits, which are almost parallel in U. sherrini but divergent in U. caudimaculatus ( Thomas, 1923a) ; the anterior palatal foramina are commonly broader in U. sherrini ; the M 1–2 of U. sherrini have shallower posterior indents on the T8–9 complex; the posterior loph on M 3 / 3 is commonly narrower; the nasals are shorter, not projecting anterior of the premaxillae as in U. caudimaculatus ; the anterior edge of the zygomatic plate is directed antero-lingually in dorsal or ventral outline, while that of U. caudimaculatus is deflected, making it parallel with the rostrum ( Fig. 4 ).

Specimens of U. caudimaculatus from QML1456 have only slightly worn tooth crowns, indicating that the owls thought to be the accumulating agents of the deposit were preying on young individuals. The excavation spit that yielded the stratigraphically youngest U. caudimaculatus specimens (i.e., 142–147 cm) is probably slightly younger than 50 kyr (see Price et al., 2015 for a full discussion of the age of the deposit). The older spits (i.e., 152–157 cm and 177–182 cm) are undated, but are likely to be Late Pleistocene (c. 80–60 ka) based on the age model presented in Price et al. (2015). Deposition in QML1456 is thought to have been continuous during the late Quaternary, with no evidence of depositional hiatuses.

Figures

Figure 3. Succession of Uromys spp. in the Mt Etna area. (A–B) Uromys caudimaculatus, (A) QMF60126 right M1, QML1456 spit 142–147, c. 50 ka; (B) QMF60127 left M1, deposit and age as for A. (C–D) Uromys aplini, (C) QMF55340 left M1, QML1312, 205–170 ka; (D) QMF60125 right M1, QML1311 H,> 450 ka. Scale bar = 1 mm.

Figure 4. Comparison of skulls of Uromys sherrini and U. caudimaculatus in ventral outline. (A) U. sherrini (CM10822); (B) U. caudimaculatus (CM705). The larger degree of deflection in the zygomatic plate, seen in U. caudimaculatus, is indicated with an arrow. Scale bar = 5 mm.