DIDYMOCONIDAE, Kretzoi, 1943

Ting, Suyin, Wang, Xiaoming & Meng, Jin, 2023, Cranial And Postcranial Morphology Of The Insectivoran-Grade Mammals Hsiangolestes And Naranius (Mammalia, Eutheria) With Analyses Of Their Phylogenetic Relationships, Bulletin of the American Museum of Natural History 2023 (463), pp. 1-129 : 95-98

? DIDYMOCONIDAE

Figures 53–54 ; tables 1, 2

Specimen IVPP V7441 (? Insectivora gen. et sp. uncertain, of Ting, 1995) is an anterior part of a skull. It has four right and two left fragmentary teeth and two alveoli on the right side and one alveolus on the left side after the fourth tooth (field number: 76003) (fig. 53).

A round root represents the canine. It is single rooted and strong. There are four fragmentary teeth preserved on the right side behind the canine (figs. 53A, 54B). The lingual part of the first two teeth is preserved. They are close together, two rooted with simple major cusps and a small heel, and are strongly compressed transversely. The crown of the third tooth is better preserved and separated from the second one by a short diastema. It is larger and wider than the first two teeth, compressed transversely, and has two roots, a large major cusp, and a basin-shaped posterior edge. Its lingual cingulum is distinct, situated at the posterior half of the tooth, and the labial cingulum is much shorter than the lingual one and situated at the posterior end of the tooth. The most lingual part of the fourth tooth is preserved on both left and right side. The fourth tooth is closely positioned behind the third and is triangular. It has a conical, low protocone and a large inflated parastyle. Two crests extend from the protocone toward the labial edge of the tooth. The protoconule and the metaconule are distinct and situated on the crests. Based on the broken middle and labial part of the tooth, it should have a large cusp at the middle of the tooth. Well-preserved right and left alveoli behind the fourth tooth indicate that there is definitely another tooth behind the fourth tooth. There is a partial lingual ridge behind the fifth tooth on the right side, which indicates that the sixth tooth may occur in V7441. The portion of the maxilla posterior to the last alveolus is very thin.

In dorsal view, the nasal is narrow, extending posteriorly at the level above the alveolus of the fifth tooth (figs. 53B, 54A). The nasal-maxillary suture is simple and straight. Posteriorly, it contacts the frontal in a V-shaped suture with the apex of the V pointing posteriorly. The maxilla is large and broad (figs, 53B, C, 54A–C). It contacts the frontal in a short, curved suture. The orbital foramen is large and round, situated above the posterior edge of the third tooth. In ventral view, the maxilla occupies about two-thirds the length of the palatal area. It is narrow and straight, and extends from the canine to the posterior edge of the second tooth and laterally to the fourth tooth. The maxilla contacts the palatine in a V-shaped suture, with the apex of the V at about the level between the third and fourth teeth. The surface of the maxilla is flat and smooth. The palatine is long, narrow, and irregular in shape, and has a flat and smooth surface. On the left side of the palatine, there are three palatine foramina: one situated at the level of the anterior edge of the third tooth, one at the level of the posterior edge of the fourth tooth that is paired with its left counterpart, and one at the level of the fifth tooth. The postpalatine torus is well developed and has a ridgelike anterior edge. In lateral view, the maxilla occupies a large area of the orbital region, and extends ventrally, almost reaching the ventral border of the medial wall of the orbital fossa (figs. 53C, 54C). It contacts the lacrimal at its anterior aspect. The maxilla-lacrimal suture is not well preserved. The maxilla contacts the palatine in a zigzag suture ventrally and the frontal in a wide-open V-shaped suture posteriorly. Its ventral posterior end contacts the orbitosphenoid in a simple and straight line. Posterior to the maxilla-orbital suture is the orbitosphenoid. It contacts the frontal dorsally, the alisphenoid posteriorly, and the palatine ventrally. The frontal extends about one third ventrally in the medial wall of the temporal fossa, and is triangular. The alisphenoid is large and rectangular. It contacts the squamosal posteriorly with an oblique suture. A small ethmoid foramen is situated at the dorsal anterior aspect of the orbitosphenoid. The optic foramen is large, situated at the dorsal edge of the frontal, and covered by a well-developed ridge dorsally. A partial squamosal is preserved behind the alisphenoidsquamosal suture. The lacrimal is large and irregular in shape, and its surface is smooth and curved. The lacrimal foramen is small and separated from the posterior opening of the orbital foramen by a strong ridge, so that the lacrimal foramen seems situated in a small fossa above the orbital foramen. The palatine occupies most of the ventral border of the orbit and temporal fossa (figs. 53A, 54B). The anterior part of the palatine extends dorsally, occupying about half the medial wall of the orbital fossa and contacting the maxilla. The sphenopalatine foramen is large and round, situated at the level above the sixth tooth. Posterior to the sphenopalatine foramen is the dorsal palatine foramen. It is smaller than the sphenopalatine foramen, narrow, oval, and extending anteroposteriorly.

IVPP V7441 is much smaller than Archaeoryctes notialis ( Zheng, 1979) , and about the size of Hunanictis inexpectatus ( Li et al., 1979) or slightly larger. The first three teeth behind the canine of IVPP V7441 are two-rooted premolars. The morphology of the third tooth is somewhat similar to that of the P3 of Archaeoryctes notialis , but differs from the later in being more compressed and having no lingual projection of the tooth. It differs from Hunanictis inexpectatus in having a less-developed protocone. The morphology of the fourth tooth is similar to the P4 of Archaeoryctes notialis in its triangular shape and its strongly developed paracone situated in the middle part of the crown, protocone situated slightly anteriorly, and well-developed parastyle and metastyle. It differs from the later in that it is less molarized. It differs from Hunanictis inexpectatus in having a less-developed protocone. If the fourth tooth is P4, it means that IVPP V7441 had four premolars with a two-rooted P1. The very thin portion of the maxilla after the last alveolus indicates that V7441 may have had only two teeth after the fourth tooth. Based on the two alveoli after the fourth tooth and morphology, it is likely that V7441 had four premolars and two molars, which means it probably represents a new didymoconid with unmolarized P1–3 and submolarized P4. The classification of IVPP V7441 remains uncertain until better material is found.

Figures

FIG. 53. Anterior part of skull of?Didymoconidae, IVPP V7441: A. ventral, B. dorsal, and C. left lateral views.

FIG. 54. Drawing of anterior part of skull of?Didymoconidae: A. dorsal, B. ventral, and C. left lateral views (based on IVPP V7441).