Macrotarsomys cf. bastardi Milne-Edwards and G. Grandidier, 1898

Denys, Christiane, Gabriel, Nadine W., Lalis, Aude & Jenkins, Paulina, 2024, Subfossil rodents and tenrecs of Children’s Cave, Madagascar, Journal of Natural History 58 (25 - 28), pp. 796-839 : 806

Macrotarsomys cf. bastardi Milne-Edwards and G. Grandidier, 1898

The Children’s Cave specimens have been attributed to M. cf. bastardi based on the following characters that allow differentiation from M. koopmani :

● Long incisive foramen ending after the prelobe of M1

● m3 elongated and narrow with no median longitudinal crest between the first and the second lobe of m3 ( Figure 4 ) but presence of an oblique crest ending on the lingual side of the molar.

Attributed material: all from the Upper Stratum: 8 maxillaries; 15 mandibular rami; see Appendix.

The specimens of Children’s Cave display the bunodont molar morphology of Macrotarsomys with round alternate cusps connected medially by a longitudinal crest ( Figure 4d,e,g–i ). Their m3 allows clear differentiation from M. koopmani because there is never any trace of a longitudinal median link connecting the first and the second lobes. They display some variability in size but compared to the three modern species they correspond to the smallest species, M. bastardi . However, the Children’s Cave specimens display a slight size difference to the modern representatives of this species. The fossil specimens of Children’s Cave are clearly smaller than the larger M. cf. petteri of Andrahomana site ( Table 2 ). There is overlap with Monticolomys koopmani which displays small molars ( Figure 5 ). The few Children’s Cave remains attributed to M. cf. bastardi may belong to a yet undescribed subfossil species, but further revisions of the dental morphology of this species are still needed.

Figures

Figure 4. Rodent dental material from Childrens’s Cave.(a) Left upper molar row of B. betsileoensis NHMUK PV M 105365; (b) Right lower molar row B. betsileoensis NHMUK PV M 105196; (c) Right upper molar row R. rattus NHMUK PV M 105616; (d) Left upper molar row of M. cf. bastardi NHMUK PV M 102315; (e) Left upper molar row of M. cf. bastardi NHMUK PV M 102316;(f) Right lower molar row of Mus musculus NHMUK PV M 105164-sequence; (g) Right lower molar row M. cf. bastardi NHMUK PV M 105123; (h) Left m1 M. cf. bastardi NHMUK PV M 104879; (i) Left m1 and m3 M. cf. bastardi NHMUK PV M 105124.

Figure 5. Scatter diagram of modern Macrotarsomys spp. and Monticolomys koopmani molars and Children’s Cave M. cf. bastardi plus other fossil specimens. Top: LS13: length of the upper molar row, WM1: width of M1. Measurements in mm. Bottom: abcissa: length of the mandible (LMDB), ordinate: L13: length of the lower molar row.