Deccanolestes Prasad and Sahni, 1988

Rana, Rajendra S. & Wilson, Gregory P., 2003, New Late Cretaceous mammals from the Intertrappean beds of Rangapur, India and paleobiogeographic framework, Acta Palaeontologica Polonica 48 (3), pp. 331-348 : 333-337

Genus Deccanolestes Prasad and Sahni, 1988

Type species: Deccanolestes hislopi Prasad and Sahni, 1988 . Late Cretaceous (Maastrichtian) of Naskal, Andhra Pradesh, India .

Deccanolestes cf. hislopi Prasad and Sahni, 1988 Tables 1, 2; Fig. 3.

Material.—ITV/ R /Mm−2, right M2; ITV/ R /Mm−7, right m1 or m2; ITV/ R /Mm−10, right m1 or m2; ITV/ R /Mm−11, left m3; ITV/ R /Mm−12, right m3.

Distribution.—Late Cretaceous (Maastrichtian) Intertrappean beds of Naskal and Rangapur, Andhra Pradesh, India.

Description.— Upper dentition ( Fig. 3C): Specimen ITV/ R / Mm−2 is identified as an isolated right upper molar, most likely M2. Labial roots are missing, but a lingual root remains. The crown has no breaks and little natural wear on the cusps, but bears some surface pitting. It is transversely wide (anterior width to buccal length ratio; Table 1). The metacone is nearly equal in height to the paracone, and the protocone is slightly shorter than both. The apices of the two labial cusps are well separated from each other. Compared to the metacone, the base of the paracone has greater girth and is more lingually expanded. Centrocristae are absent. The labial cusps are fused at their bases, but not extending much above the stylar shelf (moderate zalambdodonty; sensu Gheerbrant 1992). Rather, the fused cusps form a wide valley that is visible in labial view ( Fig. 3C 3). The labial aspect of these cusps is flat and contacts the stylar shelf at a steep slope. This flat to valley−like shelf rises labially to a weak ectocingulum. The ectoflexus is deep. Accessory cusps are not present on the stylar shelf, and there is no indication of wear or breakage. There is no parastylar hook. The metastylar region is somewhat larger than the parastylar region, and both regions extend slightly beyond the anterior and posterior limits of the main labial cusps. The preparacrista is more distinct than the postmetacrista. Both follow the steep gradient of the labial cusps and trend labially with very little anterior or posterior components. The postmetacrista blends with the posterolabial margin of the tooth, whereas the preparacrista does not quite form the anterolabial margin of the tooth.

The metaconule is taller than the paraconule and is positioned just lingual to the base of the metacone. It has a weak but distinct premetaconule crista that forms a step above the trigon basin. The postmetaconule crista is also distinct but basin and is positioned closer to the metaconid than to the terminates at the posterolingual base of the metacone. The protoconid. A paracristid is not evident. A strong anterior paraconule is closer to the protocone than to the paracone and buccal cingulid extends from the base of the crown below the shifted anteriorly relative to both cusps. The postparaconule protoconid toward the paraconid. An anterior lingual cuspule crista is weak labially and absent lingually. It forms a short is not present. The contact between the posterior face of the step above the trigon basin. The preparaconule crista flares to trigonid and the talonid is slightly oblique.

produce a wide paracingulum that bows around the anterior The cristid obliqua is strong and contacts the trigonid beaspect of the paracone before blending with the anterior mar− low the protocristid notch. A faint trace of a distal metacristid gin of the crown. The trigon basin is deep, with the deepest is present. The hypoconid is the largest of the talonid cusps, part closer to the protocone than to the labial cusps. In followed by the hypoconulid and a slightly smaller entoocclusal outline, there is slight anteroposterior waisting at the conid. The talonid cusps are positioned posteriorly on the posterior margin of the crown in the conular region ( Fig. 3C 1, talonid except a slight anterolabial shift for the hypoconid. C 2). The apex of the protocone is high and anterolabially de− The cristid obliqua forms a fairly deep hypoflexid. The flected, whereas the base is lingually and somewhat antero− hypoconid is connected to the hypoconulid via a high postposteriorly expanded. hypocristid, whereas the entoconid is separated from the Lower dentition ( Fig. 3A, B, D, E): Two lower molars hypoconulid by a small notch. The hypoconulid is slightly ( ITV / R /Mm−7, ITV/ R /Mm−10) are identified as either m1 or closer to the entoconid than it is to the hypoconid. The m2. ITV/ R /Mm−7 ( Fig. 3A) is a right lower molar. Roots are entocristid runs anteroventrally toward the trigonid to form a not preserved, and there is a small hole that has been eroded deep talonid notch that just encloses the talonid basin. The at the anterolingual base of the crown. The trigonid is slightly talonid basin is deep and slopes downward in an anterowider and more than one−and−a−half times taller than the lingual direction. In posterior view, the labial margins of the talonid ( Table 2). In occlusal view, the trigonid appears talonid and protoconid are convex. A postcingulid is absent.

somewhat anteroposteriorly compressed ( Fig. 3A 1, A 2). In Another right lower molar ( ITV / R /Mm−10; Fig. 3B) is also lingual view, it is tipped forward relative to the talonid (Fig. identified as either m1 or m2. Preservation of the crown and 3A 3). The protoconid is slightly taller than the metaconid, both roots is good. The crown length and trigonid width are which exceeds the very reduced, crest−like paraconid. The larger than those of ITV/ R /Mm−7. The arrangement of the paraconid is anteriorly projecting and labially positioned rel− trigonid is very similar to the latter ( ITV / R /Mm−7), except it ative to the mesiodistal line formed by the metaconid and shows little to no anteroposterior compression. The paraconid entoconid. The metaconid is positioned slightly posterior rel− is not quite as small nor as crest−like, labially positioned, and ative to the protoconid, and its apex is lingually deflected. anteriorly projecting as in ITV/ R /Mm−7. The protocristid is The protocristid notch rises above the level of the trigonid slightly higher and there is a very low paracristid.

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With very few exceptions, the talonid morphology of ITV/ R /Mm−10 is as described for ITV/ R /Mm−7. Differences relate to an anteroposterior shortening of the talonid, in which the hypoconid is slightly more anterolabially shifted, the hypoflexid is not well excavated, and the talonid basin is deep but not anterolingually sloped.

Two lower molars ( ITV / R /Mm−11, ITV/ R /Mm−12; Fig. 3D, E) are identified as m3’s. Roots are preserved on both specimens, but there is pitting on the crowns. The protoconid on ITV/ R /Mm−12 is broken at the base. The paraconid on ITV/ R /Mm−11 was chipped after description but prior to imaging. The trigonid morphology for these specimens is very similar to that described for the other lower molars ( ITV / R /Mm−7, ITV/ R /Mm−10). The paraconids are small and positioned slightly labially. There is very little to no anteroposterior compression of the trigonids. Prominent anterior buccal cingulids are present on both specimens. Furthermore, the posterior faces of the trigonids contact the talonids at a slightly oblique angle.

As expected for m3’s, the greatest morphological differences with the other lower molars exist on the talonids. The talonid basins are shallow and encroached by inflated talonid cusps. The cristid obliqua and other talonid cristids are rounded and poorly defined. The hypoflexids and talonid notches are shallow. The talonid lengths are increased by posteriorly expanded hypoconulids, but the talonid widths are somewhat reduced.

Discussion.—Prasad and others (1994) described an upper molar ( VPL /JU/ NKIM /15) that they referred with uncertainty to D. hislopi . They suggested that the differences with the holotypic specimen of D. hislopi ( VPL /JU/ NKIM /10) may be due to tooth locus but admitted more specimens are needed. We agree that the variation they discussed is commonly found between the M1 and M2 of eutherian mammals (see Lillegraven 1969; Clemens 1973; Archibald 1982; Kielan−Jaworowska and Dashzeveg 1989). Because similar variation exists between ITV/ R /Mm−2 and the holotype of D. hislopi ( VPL /JU/ NKIM /10), we suggest that the former may be an M2 of D. hislopi . Similarities between ITV/ R /Mm−2 and the holotype include a transversely wide crown with a moderately wide stylar shelf, moderate zalambdodont structure, and a well−developed protocone and metacone. Differences between ITV/ R /Mm−2 and the holotype include a greater transverse width, a larger and more lingually placed paraconule, and a bowed paracingulum. ITV/ R /Mm−2 further differs from the holotype and a referred specimen ( VPL /JU/ NKIM /15) in that the parastylar region is less developed than the metastylar region, stylar cusps are absent, and the metacrista is not high and blade−like.

Previously, two lower molars of Deccanolestes were reported from Naskal ( Prasad and Sahni 1988; Prasad et al. 1994). Both were identified as m1’s—one referred to D. hislopi and the other to D. robustus . The four lower molars from Rangapur generally agree with the morphological descriptions of Deccanolestes lower molars. Similarities include a trigonid that is more than one−and−a−half times taller than the talonid, a reduced and labial paraconid, a metaconid subequal to protoconid, a tall hypoconid, and a deep talonid notch. Furthermore, ITV/ R /Mm−7 is nearly identical in size to the lower molar (m1) from the D. hislopi mandibular fragment ( VPL /JU/ NKIM /16) from Naskal ( Table 2). The other lower molars from Rangapur ( ITV / R /Mm−10, ITV/ R /Mm−11, ITV/ R /Mm−12) are larger than ITV/ R /Mm−7 and VPL /JU/

position

Tooth L TRW TAW PHL PEL PDH TAL MDH AML TAH

/ TRW

L

/

TRW

TAW AML /

TRW L

/ PDH

PHL

PEL /

L / PDH−MDH / PHL L TAH PDH /

Deccanolestes hislopi VPL /JU/NKIM/ 16 m 1 0.95 0.58 0.56 0.16 – 0.76 0.40 0.36 0.38 – 0.61 0.97 0.66 0.80 – 0.42 0.17 – Deccanolestes cf. hislopi ITV /R/Mm− 7 m 1/2 0.91 0.60 0.56 0.22 0.17 0.82 0.41 0.61 0.34 0.49 0.66 0.93 0.57 0.90 0.77 0.23 0.24 1.67 ITV/R/Mm− 10 m 1/2 1.07 0.72 0.68 0.34 0.28 1.05 0.53 0.76 0.45 0.62 0.67 0.94 0.63 0.98 0.82 0.27 0.32 1.69 ITV/R/Mm− 11 m 3 1.15 0.70 0.57 0.31 0.24 0.99 0.57 0.67 0.37 0.53 0.61 0.81 0.53 0.86 0.77 0.28 0.27 1.87 ITV/R/Mm− 12 m 3 1.13 0.68 0.58 0.36 0.29 0.82 0.56 0.67 0.42 0.51 0.60 0.85 0.62 0.73 0.81 0.13 0.32 1.61 Deccanolestes ? sp. ITV/R/Mm− 9 m 1/2 0.97 0.61 0.54 0.21 0.18 0.81 0.45 0.77 0.35 0.49 0.63 0.89 0.57 0.84 0.86 0.04 0.22 1.65 ITV/R/Mm− 8 m 1/2 1.13 0.67 0.66 0.29 0.29 0.84 0.48 0.74 0.48 0.55 0.59 0.99 0.72 0.74 1.00 0.09 0.26 1.53 Deccanolestes robustus VPL /JU/NKIM/ 14 m 1 1.48 0.94 0.84 0.41 – 1.23 0.67 0.98 0.64 – 0.64 0.89 0.68 0.83 – 0.17 0.28 – Deccanolestes cf. robustus ITV /R/Mm− 6 m 2 1.83 1.12 1.05 0.50 0.34 1.42 0.83 1.17 0.68 0.84 0.61 0.94 0.61 0.78 0.68 0.14 0.27 1.69

RANA AND WILSON—LATE CRETACEOUS MAMMALS FROM INDIA 337

NKIM/16 but within an acceptable range of variation for species (according to Kielan−Jaworowska and Dashzeveg 1989). Some morphological differences with the Naskal lower molar and among the Rangapur lower molars probably reflect typical variation due to position in the tooth row (see Lillegraven 1969; Clemens 1973; Archibald 1982; Kielan−Jaworowska and Dashzeveg 1989). This variation may include a less labially shifted paraconid, less anteroposterior compression of the trigonid, a deeper hypoflexid, a deeper talonid, or a more posteriorly produced hypoconulid. As discussed in the Appendix, the relative position of the hypoconulid and the contact of the cristid obliqua with the trigonid may represent more significant differences between the samples. Until more material is collected that clarifies variation along the tooth row, we refer the upper and lower molars described above to Deccanolestes and tentatively to the species D. hislopi .