Kenomagnathus scottae, Spindler, 2020

Spindler, Frederik, 2020, A faunivorous early sphenacodontian synapsid with a diastema, Palaeontologia Electronica (a 01) 23 (1), pp. 1-9 : 2-3

Kenomagnathus scottae sp. nov.

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Etymology. To honor Diane Scott, preparator at the Reisz lab, Mississauga, University of Toronto, who greatly helped with teaching and specimen handling, and also inspired this study.

Holotype. ROM 43608 , disarticulated but associated maxilla and lacrimal ( Figures 1 , 2 ). The specimen was originally labelled as Haptodus garnettensis ( Laurin, 1993, figure 5 A). Additional preparation of the precanine margin after the re-evaluation as a distinct taxon was carried out by D. Scott in 2013.

Holotype locality. Putnam Township , Garnett, Kansas, USA ( Reisz et al., 1982).

Stratigraphic horizon and age. Carbonaceous, calcareous mudstone in the Rock Lake Shale Member of the Stanton Formation (Lansing Group), Missourian, Upper Pennsylvanian (late Carboniferous).

Description

The toothed margin of the maxilla is robust and more strongly convex than in “ Haptodus” garnettensis , with a palatine sutural surface that appears to reach further anterior than in ROM 43606 ( Spindler, 2015, figure 4.13). The canines are placed more anteriorly, resulting from the shortness of the maxilla compared to other early Haptodontiformes. There is a modest medial supracanine buttress and one even weaker in the posterior region. The anterior end of the maxilla is clearly indicated by the sutural facet to overlap the premaxilla. The antero-dorsal margin of the dorsal blade is steeply inclined. Therefore, the nostril architecture would not be the same as in “ Haptodus” garnettensis .

Regarding the tooth curvature and striation, Kenomagnathus does not differ significantly from “ Haptodus” garnettensis , although the bulb-like thickening near the tips looks rather pronounced, producing a blunter appearance. In contrast, tooth shafts are more slender in Kenomagnathus . There are two large canines or caniniforms and the bases of two broken precanines. Anterior to that, another indistinct shallow socket may reflect an additional, smaller tooth position, probably overgrown ontogenetically. Starting at this position and further anterior, a thinned ventral edge instead of a broad tooth margin indicates the presence of a diastema that covers the length of about three regular tooth positions ( Figure 3 ). As the labial side of the diastema area was embedded in the host rock until the ventral margin was freed carefully, there is neither damage nor hidden bone substance that would debate this narrow edge. No precanine step interrupts the convexity of the ventral edge. There are 11 postcanine teeth preserved, with the gaps to account for 14. In the posterior area, not much of the maxilla is missing, thus the postcanine number equals that of “ Haptodus” garnettensis , while the maxilla extends less far posteriorly.

As the type of Kenomagnathus is the only Garnett specimen exposing the medial surface of the lacrimal, no detailed comparison is possible. In the anterior region, the outlet of the lacrimal duct is visible. From an ontogenetic point of view, the type of Kenomagnathus does not appear to be a very young juvenile. The lacrimal duct exposes its anterior outlet on the medial surface, whereas the juveniles of Palaeohatteria show a laterally exposed duct due to very incomplete ossification ( Currie, 1979; Spindler, 2016).

The anterior expansion of the lacrimal would contribute to the narial rim with a tall area, resulting in a compact outline of the snout. Both the maxilla and lacrimal strongly resemble “ Haptodus” garnettensis in general morphology but imply a taller skull ( Figure 4 ). This is interpreted as reflecting a general condition of the skull, probably an adaption to a specialized diet or feeding behavior. Altogether, the short facial region, large orbits, and a maxillary diastema result also in a superficial resemblance with Tetraceratops .

Figures

FIGURE 1. ROM 43608, holotype of Kenomagnathus scottae, gen. et sp. nov. Scale bar equals 2 cm.

FIGURE 2. Interpretative drawing of ROM 43608, holotype of Kenomagnathus scottae, gen. et sp. nov., medial aspect of lacrimal and maxilla. Scale bar equals 2 cm.

FIGURE 3. ROM 43608, holotype of Kenomagnathus scottae, gen. et sp. nov., close-up of anterior maxilla in medial aspect, from latero-ventral (above) and lateral (below). Scale bars equal 2 cm.

FIGURE 4. Skull reconstructions of chosen early synapsids with initial or functional diastemata. “Haptodus” garnettensis (immature size) is combined from best-known specimens, resulting from digital reconstructions. In comparison, Kenomagnathus scottae, gen. et sp. nov., has a deeper orbit and hypothetically deeper jaw. Own data, except for Gordodon (Lucas et al., 2018). Scale bar equals 5 cm.