Durlstotherium newmani, Sweetman & Smith & Martill, 2017
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publication ID |
https://doi.org/ 10.4202/app.00408.2017 |
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persistent identifier |
https://treatment.plazi.org/id/03A07060-2768-7212-FCA6-CB1C2672F928 |
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treatment provided by |
Felipe |
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scientific name |
Durlstotherium newmani |
| status |
sp. nov. |
Durlstotherium newmani sp. nov.
Figs. 3–6 View Fig View Fig View Fig View Fig .
Etymology: In honour of Charlie Newman, recognising his intimate local knowledge, willingly shared, and his help in the field.
L C2 L*
A-W * A-W
B
D
Holotype: NHMUK PV M 99991, a well preserved upper right distal-most (M3) tooth lacking only the labial roots, Figs. 3 View Fig , 4A View Fig , 5A View Fig , 6A View Fig .
Type locality: Durlston Bay, Dorset, southern England, at British National Grid Reference SZ 03673 78377 ( Fig. 1 View Fig ).
Type horizon: A beach-level exposure of bed DB 83 ( Clements 1993) of the Lower Cretaceous, Berriasian ( Ogg et al. 1994; Hunt 2004), Purbeck Group. ( Fig. 2 View Fig ).
Diagnosis.—Monotypic tribosphenic mammal with a unique combination of derived dental characters. Differs from stem therians including Juramaia and Acristatherium , from the Oxfordian and Barremian of China respectively, but resembles Late Cretaceous eutherians, particularly asioryctitheres, cimolestids, and gypsonictopsids in: height and expansion of the protocone relative to labial cusps; possession of conules placed labially immediately adjacent to the paracone and metacone with sharp internal cristae and distance between conules as a percentage of total tooth length>31% <50% (44%) ( Luo et al. 2003, 2011). Differs from Prokennalestes from the Aptian–Albian of Mongolia in the presence of a pre- and postcingulum. Resembles Gypsonictops from the Late Cretaceous of North America in the presence of strong cingula but differs from it in lack of a hypocone. Also differs from it in having a more connate paracone. Resembles members of Asioryctidae in the presence of a transversely elongate crown but differs from them in presence of strongly developed cingula. Also differs from Asioryctes from the Late Cretaceous of Mongolia in presence of a metaconule. Resembles members of Kennalestidae in the presence of cingula but differs from them in the presence of a preparastyle. Resembles members of Cimolestidae , which possess anteroposteriorly short and transversely broad upper molars with an anteroposteriorly compresed protocone and a paracone that is much taller than the metacone, but differs in the presence of a pre- and postcingulum which are either weak or lacking in members of Cimolestidae .
Description.—NHMUK PV M 99991 is an upper molar lacking only the labial roots. It is otherwise well preserved although substantially worn as a result of occlusion with the lower dentition and dietary attrition. It is a distal-most upper right molar (M3), identified as such on the basis of its general outline in occlusal view, the lack of a metastylar lobe and the expanded parastylar wing as defined by Kielan-Jaworowska et al. (2004; see also Figs. 3 View Fig , 4A View Fig , 5A View Fig , 6A View Fig ). Measurements are shown in Fig. 3 View Fig .
The connate and slightly labiolingualy compressed paracone dominates the labial side of the crown and descends vertically. It is approximately three times the height of the metacone with a basal diameter a little over one and a half times that of the latter. The paracone is truncated by a substantial wear facet (facet 3, Fig. 6A View Fig ) resulting from dietary attrition, that extends along the distal margin and across the narrow centrocrista to the base of the metacone. A labiolingually narrow wear facet, an extension of facet 1 ( Fig. 6A View Fig ), extends from the apex to the base of the paracone on its mesial surface. The metacone is closely appressed to the paracone and is placed distal and lingual to it. It is more heavily worn than the paracone with no trace of the original apex of the cusp remaining (facet 4, Fig. 6A View Fig ). The flat, apical surface ascends towards the base of the paracone at an angle of about 45°. There is no metastylar lobe and consequently no ectoflexus. A low and apicobasally narrow ectocingulum, entirely devoid of cusps, extends from the linguobasal extremity of the metacone to the distal extremity of the parastylar wing. The latter is a prominent feature of the crown extending mesiolabially from the base of the paracone. It is strongly mesiolabially expanded with no evidence of molar interlock and bears a preparacrista that extends from the base of the paracone to the parastyle, the apex of which appears to have been substantially blunted by wear. There appears to be no stylocone but there is a minute cuspule on the anterior margin of the parastylar wing a short distance lingual to the parastyle that might be a remnant of it. A more substantial, but worn cusp taken to be the preparastyle is located lingual to this. A small labiolingually elongate and apicobasally narrow wear facet extends from the preparastyle to the lingual margin of the cuspule labial to it on the mesial margin of the parastylar wing. The substantial, labially placed paraconule is considerably worn mesially, facet 1 ( Fig. 6A View Fig ) and somewhat less so distolingually, facet 3 ( Figs. 4A View Fig , 6A View Fig ). It is pyramidal with a basal profile approximating that of an acute isosceles triangle, the long axis of which is mesiolabially inclined with the apex of the triangle at the labial end. Its labial surface ascends steeply to the base of the paracone forming with it a steep sided valley. The metaconule is also a substantial, labially placed cusp. Its labial surface ascends more steeply than that of the paraconule forming with the lingual surface of the metacone a sharply V-shaped valley. It is considerably worn mesiolingually, facet 4, but is unworn labially and distally except along the very short region originally occupied by the postmetaconule crista but now comprising the sharp edge of facet 2 ( Fig. 6A View Fig ). It is also pyramidal but unlike the paraconule its basal profile is that of an equilateral triangle the apex of which points lingually. The trigon basin occupying the area between the cusps described above has a smooth occlusal surface. It is deep and substantially worn (primarily by facet 4, Figs. 4A View Fig , 6A View Fig ).
On the lingual part of the crown the worn preprotocrista extends from the apex of the protocone to overlie the paracone mesially. The postprotocrista extends labially to the lingual extremity of the metaconule. Wear also extends across the preparaconule crista, across the apex of the paraconule and along the postparaconule crista. On the distal side it extends from the apex of the sharply pointed metaconule, down the short premetaconule and postmetaconule cristae (facet 2, Fig. 6A View Fig ). All cristae in this part of the crown form sharp shearing surfaces. The protocone is a robust cusp only slightly less elevated than the paracone. It is placed directly lingual to the paracone and mesiolingual to the metacone. The apex is mesiodistally compressed but expands basally and labially. Its apicobasal axis is tilted apicomesially. Its dorsoventral axis is mesially inclined at
A labial mesial facet 1
facet 2
facet 3
facet 4
facet 5
facet 6
broken or damaged ca. 70°. There is a well-developed precingulum which has wear facet on its mesial margin (facet 5, Fig. 6A View Fig ). In apparent continuation of this there is also a small facet at the apex of the protocone on its mesial side. The precingulum overlies the mid part of the preprotocrista for about two thirds of its length. A substantial postcingulum, lacking a hypocone, extends from the lingual margin of the postmetaconule crista to a point opposite the lingual extremity of the precingulum and is of approximately the same length. It is somewhat apicobasally broader than the precingulum and it bears a correspondingly broader wear facet (facet 6, Fig. 6A View Fig ). In contrast, however, there is no expression of this facet on the apex of the protocone on its distal margin.
The root overlying the protocone is very robust, apicobasally short and labiolingually broad. It is mesiodistally compressed with a mesiolingually projecting and expanded flange at its apex. Roots overlying the parastylar wing and the area between the paracone and metacone are broken away close to their bases. That part of the root overlying the parastylar wing is laterally compressed following the axis of the wing and is large compared to that overlying the junction between the paracone and metacone. The former is about two thirds the size in basal area of that overlying the protocone. The root occupying the area between the paracone and metacone is approximately circular in outline and is the smallest of the roots. Its diameter is approximately half the labiolingual width of its labiomesial neighbour.
Stratigraphic and geographic range. —Currently known only from the type horizon and locality.
| NHMUK |
Natural History Museum, London |
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.