Storchodon cingulatus, Martin & Averianov & Jäger & Schwermann & Oliver & Wings, 2019

Martin, Thomas, Averianov, Alexander O., Jäger, Kai R. K., Schwermann, Achim H. & Wings, Oliver, 2019, A Large Morganucodontan Mammaliaform From The Late Jurassic Of Germany, Fossil Imprint 75 (3 - 4), pp. 504-509 : 505-507

Storchodon cingulatus sp. nov.

Text-figs 2 , 3

H o l o t y p e. NLMH 105654, a right upper molar.

E t y m o l o g y. The species name refers to the welldeveloped cingulum around the crown.

R e f e r r e d s p e c i m e n s. Holotype only.

T y p e l o c a l i t y a n d h o r i z o n. Langenberg Quarry near the town of Goslar, Lower Saxony, northern Germany (N 51° 54.110′, E 10° 30.500′). Bed 83 (after Fischer 1991). The sample was collected in a temporarily exposed dark grey lens of marl within the normally light grey-greenish marly limestone bed. It belongs to the Süntel Formation, Late Jurassic (late Kimmeridgian) age .

D i f f e r e n t i a l d i a g n o s i s.As for the genus.

D e s c r i p t i o n. The presence of a continuous cingulum around the crown identifies the tooth as an upper molar ( Text-fig. 2 ); in lower molars of Morganucodonta the buccal cingulid is absent ( Kielan-Jaworowska et al. 2004). The three main cusps A, B, and C are aligned serially. Cusp D is set off this line and sits more lingually compared to cusp C. Thus, the line A-B-C-D is slightly convexly curved in a lingual direction. Cusp A is not completely preserved; its base is only slightly larger than that of cusp C. Cusp A was probably only little higher than cusp C and vertically directed, whereas cusp C is slightly distally oriented. Cusp B has about two thirds the size of cusp C and is slightly mesially directed. The main cusps are connected by a sharp crest which extends to their apices (incompletely preserved on cusp A). This crest is extended on the mesial side of cusp B, as well as on the distal side of cusp C and on both sides of cusp D. The crown is surrounded by a continuous cingulum bearing numerous cusps. There is a distinct valley between the cingulum and the bases of the main cusps on the buccal, lingual, and mesial sides of the crown. Cusp D (incomplete) is more distally directed than cusp C. Cusp D is not part of the cingulum (a unique character of the new taxon within Morganucodonta ), but is connected distally with a rather large cingular cusp. Only in Erythrotherium and in some individuals of Morganucodon is cusp D equally prominent ( Text-fig. 3 ). A relatively large cingular cusp is situated on the mesial end of the crown; it is separated by a groove from cusp B. This mesial cingular cusp possibly corresponds to cusp E of other morganucodontans. Two large cingular cusps are located on the buccal cingulum opposite to cusp C. Distally and mesially to these cusps, the size of the cingular cusps decreases. Altogether there are 13 cusps on the buccal cingulumandatleast 14 cuspsonthepreservedlingualportion of the cingulum (part of the lingual cingulum between cusps B and A is missing due to dental wear). The size variation between the lingual cingular cusps is smaller than that of the buccal cingular cusps. The lingual cingulum is elevated opposite to cusp A and between cusps A and C, similar to the “protocone” in the “symmetrodontan” mammal Yermackia from the Early Cretaceous of West Siberia ( Averianov and Lopatin 2008). The mesial and distal sides of the crown are rhomboidal with pointed ends. This, and the lack of mesial cingular cusps E and F with an embayment between them, indicates that the new taxon lacked an upper molar interlock between cusps D and E-F, which is also seen in Indotherium , Indozostrodon and Bridetherium ( Prasad and Manhas 1997, Datta and Das 2001, Clemens 2011). The molar contact in the maxilla was likely imbricating. The tips of cusps B and C have small apical abrasion facets, but otherwise the cusps are unworn. There is a large wear facet on the lingual side between cusps A and B which was caused by cusp a of the lower antagonist, and a small facet between cusps A and C (caused by cusp c of the antagonist). According to Mills (1971), the cingulum wears rapidly on the lingual side in Morganucodon . The insignificant apical wear and the only partially worn lingual cingulum suggest that NLMH 105654 was only recently erupted. This occlusal mode is identical with the one described for Morganucodon ( Crompton and Jenkins 1968) . There are two roots connected basally by an interradical crest ( Text-fig. 2d ). The mesial root has a normal position while the distal root is set obliquely to the longitudinal axis of the crown. This apparently reflects an oblique position of cusp D relative to cusp C (both cusps are supported by the distal root). The pulp cavity of the distal root is smaller compared with that of the mesial root. The distal root is oval in cross section, with the mesiodistal diameter being larger than the buccolingual one.

M e a s u r e m e n t s. Length 3.07 mm, width 1.44 mm.

Figures

Text-fig. 2. Storchodon cingulatus gen. et sp. nov., NLMH 105654, holotype, right upper molar, in buccal (a), occlusal (b, b’ stereopair), lingual (c), and basal (d) views. Langenberg Quarry, Lower Saxony, Germany; Süntel Formation, Late Jurassic (late Kimmeridgian) age. Abbreviations: A, B, C and D, main cusps of the crown; ic, interradical crest.

Text-fig. 3. Right upper molars of Morganucodon watsoni KÜHNE, 1949, UMZC_Eo.M(Ur).27 (cast) (a) and Storchodon cingulatus gen. et sp. nov., NLMH 105654, holotype (b) in lingual and occlusal views. Abbreviations: A, B, C, D, E and F, main cusps of the crown. Specimens to scale.