Sairadelphys tocantinensis
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Ordo: Didelphimorphia
Familia: Didelphidae
Genus: Sairadelphys
Name
Sairadelphys tocantinensis Oliveira, Édison Vicente, 2011 – Wikispecies link – Pensoft Profile
- Sairadelphys tocantinensis Oliveira, Édison Vicente, 2011, Zootaxa 3041: 55-60.
Etymology
Etymology.tocantinensis after the State of Tocantins, where the paleontological site is located.
Materials Examined
Type. DGEO-UFPE 6745, incomplete left maxilla with complete M 2–4. Hypodygm. The type and DGEO-UFPE 6746, an isolated left m 1. Locality and age. Municipality of Aurora de Tocantins, cave of Gruta dos Mouras, Sate of Tocantins, Brazil (12 º 42´47 ´´S and 46 º 24´28 ´´W); Pleistocene.
Diagnosis
Diagnosis and description. Same as for the genus.
Discussion
Comments. The lower molar assigned to Sairadelphys tocantinensis is similar in morphology to that of Hyladelphys and Marmosa (e.g. M. murina Linnaeus). However, in comparison with Marmosa we noted that in DGEO- UFPE6746 the crests are less developed and the cristid oblique is most labially placed in relation to the postprotocristid notch; therefore, the cristid oblique in the new taxon runs less obliquely in relation to the anteroposterior dental axis, a feature that is compatible with the linear centrocrista described for upper molars of Sairadelphys. Another complementary occlusal relationship between the holotype and the assigned lower molar is related to the low protocone in Sairadelphys, which is compatible with lower molars with high entoconid as seen in DGEO- UFPE6746.
Description
Measurements (mm). DGEO-UFPE 6745: M 2 L =1.38, M 2 W=1.77; M 3 L=1.42, M 3 W=1.50; M 4 L= 0.73, M 4 W=0.97; DEGEO-UFPE 6746: m 1 L = 1.68, m 1 W=0.93. Comparisons. Several features of this new marsupial confidently place it in the Didelphimorphia (see below). However, the presence of plesiomorphic features in Sairadelphys tocantinensis, as exemplified by the presence of a linear centrocrista, and subequal paracone and metacone, constitute characters absent in most living didelphimorphians and, therefore, warrants comparisons with fossil and generalized forms such as Caluromyinae, Sparassocynidae, Peradectidae, Wirunodon Goin & Candela, and Microbiotheriidae. A relationship to the latter can be rejected on the basis of several characters: the trigon basin is reduced in Sairadelphys (very wide in Microbiotheriidae), the protocone is narrow (it is wide in Microbiotheriidae), and the stylar shelf is wide in relation to the talon (very reduced in Microbiotheriidae). Sairadelphys tocantinensis differs from the Peradectidae in the absence of cingula, para- and metaconule and StC, and in the preparacrista ending at the anterolabial angle of the tooth (stylar cusp A region). Furthermore, peradectids are significatively older than Sairadelphys, which was found on Pleistocene sediments (see below). The enigmatic marsupial Wirunodon, from the late Paleogene of Santa Rosa, Peru (Goin & Candela 2004) resembles Sairadelphys, with some characters such as the reduction of stylar cusps and of the protocone. However, Sairadelphys differs from Wirunodon in having subequal paracone and metacone, absence of anterior cingulum, and much less developed stylar cusps. Sparassocynid affinities of Sairadelphys can be ruled out on the basis of its absence of cingula and conules (except Hesperocynus Forasiepi, Goin & Martinelli), deep ectoflexus (mainly in M 3), absence of cutting crests, reduced postmetacrista, and in that the paracone and the metacone are similar in size.
Materials Examined
Age of material. In absence of radiometric dating for the mammal-bearing deposit, the age of the Aurora de Tocantins fauna is discussed on the basis of the marsupials and associated taxa such as the tayassuid Catagonus Ameghino, the xenarthran dasypodid Propraopus Ameghino and the glyptodontid Pachyarmatherium Downing & White (unpublished data). Although some of these taxa (e.g. Propraopus, Pachyarmatherium) are frequently found in late Pleistocene deposits in Brazil, other taxa do not permit a very accurate age (SALMA or epoch) assignment. For example, the Catagonus and Pachyarmatherium genera range from the late Pliocene to late Pleistocene of South and South/North America, respectively (Porpino et al. 2009, Gasparini et al. 2009). However, the genus Propraopus suggests a Pleistocene age because it ranges from the Ensenadan to Lujanian SALMAs (early to late Pleistocene) (Cione & Tonni 1999). The marsupial fauna include numeral isolated teeth, incomplete maxillaries and dentaries. In addition to the new taxa described here, the preliminary analysis of the remaining marsupials also suggests the presence of a probable new species of Monodelphis Burnertt. Given that none of the studied marsupial specimens can be assigned confidently to any known living species cited for in Brazil (Gardner 2008), the marsupial fauna is inconclusive in terms of age. Other mammals recovered from the same cave include numerous undescribed remains of rodents, bats, and indeterminate microvertebrates, currently under study (Avilla et al. 2010). Although we regard the fauna of Gruta dos Mouras cave as Pleistocene, we do not rule out the possibility of temporal mixing (“time-averaging”) of Pleistocene and Holocene specimens, and thus there is a chance that the newly described taxon is still a living marsupial in the study area. More field work is necessary for corroboration of this exciting possibility.
Taxon Treatment
- Oliveira, Édison Vicente; Nova, Patricia Villa; Goin, Francisco J.; Avilla, Leonardo Dos Santos; 2011: A new hyladelphine marsupial (Didelphimorphia, Didelphidae) from cave deposits of northern Brazil, Zootaxa 3041: 55-60. doi
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