Storchictis, Bonis, 2020

Bonis, Louis de, 2020, New Genus Of Amphicyonid Carnivoran (Mammalia, Carnivora, Amphicyonidae) From The Phosphorites Of Quercy (France), Fossil Imprint 76 (1), pp. 201-208 : 202-203

Storchictis miacinus ( TEILHARD DE CHARDIN, 1915)

1915 Cynodon miacinus ; Teilhard de Chardin, pp. 17–18, 53, pl. 1, fig. 8.

1965 « Amphicynodon » miacinus ; Beaumont, p. 28.

H o l o t y p e. Hemimandible MNHN 1903-20 with p2,

p4–m2 ( Text-fig. 1 ).

E m e n d e d d i a g n o s i s. Smallest known European Amphicyonidae ; gracile mandible, one mental foramen, top of ascending ramus semi-circular with an acute distally directed process, elongate angular process, p2 and p4 higher than the paraconid of m1 with a small basined talonid, large height difference between m1 protoconid and paraconid, the former relatively short, metaconid of m1 is well developed and higher than paraconid, deep V-shaped talonid valley of m1 with entoconid slightly higher than hypoconid, complete and relatively high trigonid of m2 with talonid similar to that of m1.

D i f f e r e n t i a l d i a g n o s i s. Amphicynodon differs greatly from Storchictis by the presence of two mental foramina on the mandible, the rounded ascending ramus top, the thicker and low lower premolars, the thicker m1 with a lower trigonid with a smaller difference in height between the protoconid and paraconid and a basined talonid; in m2, the trigonid is low, the protoconid is equal to or smaller than the metaconid and the talonid is shallow and basined.

Cynodictis differs from Storchictis by the presence of two mental foramina on the mandible, the axe-shaped ascending ramus, the relatively lower p2 and p4, the longer mesio-distally protoconid of m1, the smaller difference in height between the protoconid and paraconid of m1, the slightly lower trigonid of m2.

Ty p e l o c a l i t y. Precise locality unknown, Quercy phosphorites, France.

G e o l o g i c a l a g e. Unknown, possibly middle or late Eocene.

D e s c r i p t i o n. All the teeth are unworn except a small wear on the top of the paraconid of m1 which does not take on the height of the cuspid. The enamel has small pits due to weathering in the fossilisation process.

The mandible is small (p2–m2 = 23mm; Teilhard de Chardin gives 39mm for i3–m3) and bears p2, p4–m2 and alveoli of the canine, p1, p3, and m3, the latter being very small. The corpus is shallow, elongate, the lower border being convex from the cranial extremity to the level of the ascending ramus where it goes up and is slightly concave. There is only one mental foramen below the root of p1. The ascending ramus is high with a semi-rounded top and an acute distally pointed process. The masseter fossa is wide, extending cranially to m3, but not so deep; it is reinforced by a strong rim along the cranial border. The articular condyle is broad (8.7 mm) and below there is a well-developed angular caudal process which constitutes a good lever for the muscle pterigoideus medialis. The anterior part of the dentary tapers off and the symphysis is very oblique. The alveolus for p1 is oval and separated from the canine alveolus by about 2.6 mm. After a small diastema (1.4 mm), p2 is higher than the paraconid of m1, sharp and bucco-lingually compressed; the crown is asymmetrical, the distal part being longer that the mesial one; there is a thin cristid along the mesial face and another one along the distal one; a cingulid surrounds the base and, distally, gives rise to a small talonid with a shallow minute basin. The p4, less asymmetrical than p2, is also higher than the paraconid of m1, pointed, and bucco-lingually compressed; there are also mesial and distal cristids, the latter with a trenchant, although step-like, posterior accessory cuspid. The step-like accessory cuspid is considered to be a derived amphicyonid feature ( Tomiya and Tseng 2016). Here the cingulid forms a small mesial stylid and, distally, a slightly hollow talonid. The carnassial m1 is characterised by a great height difference between the protoconid and paraconid. The former displays a relatively short buccal face and an almost triangular basal section; the paraconid is far lower and moderately oblique relative to the sagittal plane. The metaconid is slightly higher than the paraconid and is nearly pyramidal with its almost flat buccal and distal faces while the lingual one is convex; it is not much reduced and it is not distally displaced, it does not appear in buccal view of the tooth and it closes the trigonid valley. The talonid is shaped by an entocristid that is slightly higher than the hypoconid, the latter being thicker with a cristid obliqua joining the middle of the base of the protoconid, and a V-shaped large valley; there is no trace of the hypoconulid and the valley is distally open. A cingulid surrounds the crown. The second molar is almost rectangular, although the talonid is slightly narrower than the trigonid ( Tab. 1); the latter is complete and high relative to the talonid. The protoconid is higher, while the paraconid and metaconid are lower but well-developed, the former being a low ridge without pointed apex. The talonid is similar to that of m1 except for the cristid obliqua which is parallel to the sagittal plane. There is an oval alveolus for m3.

c – occlusal view. Scale bar = 10 mm.

Figures

Text-fig. 1. Storchictis n. gen. miacinus (TEILHARD DE CHARDIN, 1915). Left hemimandible. a – buccal view, b – lingual view,