Kenomagnathus: what you can do with only 2 bones

Spindler 2020
reports on a new basal pelycosaur, Kenomagnathus scottae (ROM 43608; Upper Pennsylvanian, Late Carboniferous, Garnett, KS, USA; Figs 1-3) known from a single lacrimal and maxilla (with teeth) exposed in medial view (Fig. 1).

Figure 1. Kenomagnathus in situ from Spindler 2020.

Figure 1. Kenomagnathus in situ from Spindler 2020. The halo of organic matter is interesting.

From the abstract:
“This is the oldest known diastema in synapsid evolution, and the first reported from a faunivorous member that lacks a precanine step, aside from Tetraceratops. This unique precanine morphology occurred independently from similar structures in Sphenacodontoidea.” 

See Spindler’s freehand drawing
of the ‘true diastema’ (Fig. 2). 

Figure 2. Kenomagnathus maxilla and lacrimal with the rest of the skull restored in lateral view. Note the deep jugal, as in Ophiacodon (Figs. 3, 4). Spindler's freehand drawing indicates a deeper orbit, smaller jugal.

Figure 2. Kenomagnathus maxilla and lacrimal with the rest of the skull restored in lateral view. Note the deeper jugal (cyan), though not as deep as in Ophiacodon (Figs. 3, 4). For that reason the mandible of Ophiacodon was used in this restoration. Spindler’s freehand drawing indicates a deeper orbit, shallower jugal and smaller naris along with a larger mandible.

It is worth noting
that maxillary teeth shrink toward the naris in Ophiacodon (Fig. 3). A diastema may be present in Pantelosaurus (formerly Haptodus saxonicus, Fig.3). These pertinent taxa were not illustrated in Spindler 2020.

Figure 3. Pertinent synapsid skulls to scale. The origin of the Pelycosauria + Therapsida is marked by phylogenetic miniaturization, as in so many other clade origins. Note the depth of the jugal in basal taxa here.

Figure 3. Pertinent synapsid skulls to scale. The origin of the Pelycosauria + Therapsida is marked by phylogenetic miniaturization, as in so many other clade origins. Note the depth of the jugal in basal taxa here.

Spindler’s freehand restoration
increased the size of the orbit and decreased the depth of the restored jugal. So this is yet another cautionary tale highlighting the danger in using freehand drawings in scientific studies.

The shallow jugal depth in the Spindler freehand restoration
is a key oversight. When repaired (Fig. 2) the semi-deep jugal of Kenomagnathus transitionally links deeper jugal Ophiacodon (Fig. 3) to shallower jugal Pantelosaurus and Haptodus (Fig. 3) at the base of Pelycosauria + Therapsida in the large reptile tree (LRT, 1642+ taxa). While running the risk of ‘Pulling a Larry Martin’, there are so few traits to consider here (Fig. 1) and none contradict the present hypothesis of interrelationships. All that puts Kenomagnathus in the lineage of synapsids leading to therapsids, mammals, primates and humans.


References
Spindler F 2020. A faunivorous early sphenacodontian synapsid with a diastema. Palaeontologia Electronic 23(1):a01. doi: https://doi.org/10.26879/1023
https://palaeo-electronica.org/content/2020/2905-early-sphenacodontian-diastema

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