A new species of recently extinct rice rat (Megalomys) from Barbados

Abstract

a b s t r a c tRecently extinct insular populations of oryzomyine rice rats (Cricetidae: Sigmodontinae) are known from across the Lesser Antilles, but most remain undescribed. Historical records of a possible now-extinct endemic rodent from Barbados are supported by presence of oryzomyine remains in Late Quaternary sites on the island, including several pre-Columbian Holocene archaeological sites. The Barbados oryzomyine is described as Megalomys georginae sp. nov., and is most closely related to species from the nearby islands of Martinique and St. Lucia, M. desmarestii and M. luciae. These species all display a zygomatic plate with its posterior margin level with the alveolus of M1, a divided anterocone on M1, and distinct anterolophids and metaflexids on m2 and m3, and are recovered as a monophyletic clade in morphological-molecular and morphology-only analyses. The new species differs from other Megalomys species in having the labial accessory root of M1 absent, a reduced anteromedian flexus on M1, two roots on m2 and m3, a supratrochlear foramen on the humerus, and in its much smaller body size. Other extinct Caribbean oryzomyines are not recovered in a monophyletic clade with Megalomys.

Unexpected evolutionary diversity in a recently extinct Caribbean mammal radiation

“…Bayesian phylogenetic analyses of our aDNA data combined with modern data from 26 extant sigmodontine genera from continental Central and South America and the Galápagos Islands (electronic supplementary material, table S2) clearly identified two distinct colonization events of the main Windward–Leeward island chain north of St Vincent ( figure 2 ). The endemic Antillean taxa Megalomys (Martinique, St Lucia) and Pennatomys (Nevis, St Eustatius, St Kitts) are demonstrated to be sister genera, in contrast to the conclusions of previous morphology-only phylogenetic analyses [ 19 , 20 ]. The monophyletic Megalomys – Pennatomys clade is distributed widely across the Lesser Antilles, and is most closely related to a clade containing representatives from both the mainland Neotropics (Trans-Andean South America and Central America; Aegialomys , Melanomys , Sigmodontomys ) and the Galápagos Islands ( Aegialomys , Nesoryzomys ).…”

“…Infrageneric diversification in Antillomys , Megalomys and Pennatomys is estimated to have occurred considerably later, during the Middle–Late Pleistocene: Antillomys = 0.097 Ma (95% HPD, 0.001–0.235 Ma), Megalomys = 0.127 Ma (95% HPD, 0.009–0.276 Ma) and Pennatomys = 1.209 Ma (95% HPD, 0.584–1.907 Ma). Notably, diversification within Pennatomys pre-dates the divergence of Megalomys populations on Martinique and St Lucia; as these Megalomys populations are recognized as morphologically distinct species ( M. desmarestii and M. luciae ) that vary in body mass as well as both craniodental and soft-tissue characteristics [ 18 – 20 ], this provides further support for likely species-level differentiation between the morphologically more poorly understood Pennatomys populations on the St Kitts Bank. Conversely, diversification within Antillomys is very recent and post-dates divergence of other Antillean oryzomyine lineages, consistent with a lack of morphological differentiation between Antillomys populations on different islands (electronic supplementary material, appendix, systematic paleontology).…”

“…Although abundant in the Late Quaternary fossil record and in Holocene pre-Columbian archaeological sites throughout the main Windward–Leeward island chain ( figure 1 ), Caribbean oryzomyine diversity remains unclear. Around 20 separate insular populations, some of which reached the size of small cats [ 18 ], have been recorded from different islands between Grenada and the Anegada Passage [ 19 , 20 ]. All of these populations are now extinct, probably as a result of European-era introduction of invasive mammals or agricultural habitat conversion [ 18 ]; this dramatic level of extinction is equivalent in magnitude to the much more widely known major historical-era loss of marsupials and rodents in Australia [ 9 , 11 ].…”

“…All of these populations are now extinct, probably as a result of European-era introduction of invasive mammals or agricultural habitat conversion [ 18 ]; this dramatic level of extinction is equivalent in magnitude to the much more widely known major historical-era loss of marsupials and rodents in Australia [ 9 , 11 ]. However, only six oryzomyine species (including two endemic genera, Megalomys and Pennatomys , and a representative of the mainland Neotropical genus Oligoryzomys on the southern island of St Vincent) have so far been formally described from the Windward–Leeward island chain [ 19 , 20 ].

Figure 1.

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Systematics and distribution of the giant fossil barn owls of the West Indies (Aves: Strigiformes: Tytonidae)

“…In the Lesser Antilles it is known so far only from Barbuda (T. "neddi") where its main prey would have been the extinct giant rice rat Megalomys audreyae Hopwood. Several species of giant rice rats (Sigmodontinae: Orizomyini) are known from fossil and archeological deposits throughout the Lesser Antilles, including Barbados, and they were also known historically from Martinique and St. Lucia, although there is as yet no evidence of rice rats on Dominica (Turvey et al 2010(Turvey et al , 2012. The islands from St. Vincent through Grenada are exceptional as much smaller rice rats (Oligoryzomys Bangs) once occurred there along with the diminutive Lesser Antillean Barn Owl Tyto insularis Pelzeln (Olson & Suárez unpub.…”