Magnatalpa fumamons, Oberg & Samuels, 2022

Oberg, Danielle E. & Samuels, Joshua X., 2022, Fossil moles from the Gray Fossil Site (Tennessee): Implications for diversification and evolution of North American Talpidae, Palaeontologia Electronica (a 33) 25 (3), pp. 1-39 : 6-10

Magnatalpa fumamons sp. nov.

Figure 3A - J

zoobank.org/ 9A3A7163-408A-4159-857B-A0AAA50D56A0

Type material. ETMNH 9664 - right m2.

Paratypes. ETMNH 20747 - left M1 ; ETMNH 20779 - right M1 ; ETMNH 21077 - right partial edentulous dentary .

Type locality. Gray Fossil Site, TN, USA.

Etymology. Genus Magnatalpa translates into large mole, as this dental material represents a mole that was much larger than all North American extant moles, fossil moles and desmans, and comparable in size to extant desmans ( Table 3). The species is named M. fumamons due to the material’s proximity to the Smoky Mountains.

Diagnosis. Large size; anteroposteriorly elongated lower molar; m2 lacking anterior, posterior, and lingual cingulids; m2 cristid obliqua joins metaconid; upper molars with continuous mesostyle; M1 lingual border with distinct, lingually projecting, protoconule and metaconule, either larger than or equal in size to the protocone.

Differential diagnosis. Magnatalpa fumamons lacks a divided mesostyle on the M1, a character unique to all true and extant desmans. Magnatalpa fumamons m2 lacks an anterolabial cingulum and a small cuspule on the cingulum in the re-entrant valley, differentiating it from all nine species of Archaeodesmana . Magnatalpa fumamons m2 has similarly sized trigonid and talonid as well as separate metaconid and entoconid, differentiating it from all species of Asthenoscapter . Magnatalpa fumamons m2 has a cristid obliqua that joins at the metaconid and has a large re-entrechat valley, differentiating it from all species of Mygalea . Magnatalpa fumamons teeth are substantially larger than those of Mygalinia hungarica ( Table 3). Magnatalpa fumamons m2 has a wider re-entrechat valley than all fossil species of Desmana .

Description. The holotype m2, ETMNH 9664, is a very large tooth for a talpid ( Figure 3A - C , Table 3). The cusps are relatively worn. The talonid is about the same length as the trigonid, but substantially wider. The entire tooth is anterioposteriorly elongate. The talonid and trigonid are both very open. There is a large reentrant valley between the trigonid and talonid. The cristid obliqua joins with the metaconid. There are no anterior, posterior, or lingual cingulids. The paraconid, metaconid, and entoconid are much lower than protoconid and hypoconid. The metaconid and entoconid are about the same size, but the metaconid is a little larger. The entoconid shows signs of heavy wear. The entostylid is large and triangular. The paraconid has an extra bladed notch along the posterior aspect.

ETMNH 20747 and 20779 both resemble a typical talpid M1, but are large ( Figure 3D - G , Table 3). They have a lopsided triangular outline due to the great difference in the morphology of the labial cusps and have pre- and post-cingula. The paracone and metacone are crescentic in shape and relatively similar in size, but the paracone is slightly smaller. The protocone is also large and centrally placed. The teeth are very open; the paracone and metacone are well separated. There is a large paraconule about the same size as the paracone. The mesostyle is not divided. The protoconule and the metaconule are well developed and influence the lingual outline of the crown causing the antero- and posterolingual side to bulge outwards. The protoconule is closely appressed to the anterior margin of the protocone. A deep basin lies between the protocone, paracone, and metacone.

ETMNH 21077 is a partial right edentulous dentary. The dentary is broken at the fourth antemolar. There are alveoli for four antemolars, m1, m2, and m3 ( Figure 3H - J ). There are two alveoli per molar for two roots. The alveoli for m2 are the largest, while m3 are the smallest. Each antemolar has only one alveolus and they decrease in size anteriorly. The total length of the partial dentary is 17.46 mm, and it is 2.68 mm deep at the m2 anterior alveolus. The ascending ramus and mandibular angle are broken off, but a portion of the masseteric fossa is preserved.

Discussion. The formal systematic classification of desmans has been debated for quite some time. This group was previously classified as a subfamily (Barabasch-Nikiforow, 1975; Hutchison, 1974; Rümke, 1985) called Desmaninae . Some researchers thought there was enough morphological distinction between desmans and other talpids to warrant a family-level designation; however, recent genetic work (Shinohara et al., 2003; Shinohara et al., 2004; He et al., 2014, 2016) shows that this group falls within the subfamily Talpinae and should be classified as a tribe.

The morphology and size of these three molars are reminiscent of extant desmans, but these teeth do not represent either of the two extant genera. The GFS specimens are comparable in size to Desmana moschata (Russian desman) but are larger than Galemys pyrenaicus (Pyrenees desman) ( Table 3). The M1 of extant desmans resembles that of other talpids in occlusal shape and generalized morphology. However, extant desman upper molars always have a divided mesostyle (also referred to as distinctly twinned mesostyle) and a strongly developed lingual part featuring a protoconule, a protocone, a metaconule and often a small tubercle on the posterocrista of the protocone (Miller, 1912; Schreuder, 1940; Hugueney, 1972; Rümke, 1985). These cuspules act like additional cusps and increase the food processing surface area on the tooth, aiding in efficient food processing (Rümke, 1985).

An important feature that has been used as an apomorphy for defining the tribe Desmanini is the cristid obliqua of the lower molars ends either 1) against the tip of the metaconid, or 2) against the protoconid-metaconid crest (Miller, 1912; Schreuder, 1940; Hugueney, 1972; Rümke, 1985). Specifically looking at the m2, a strong entostylid is always present in extant desmans. It can be either a bulge formed by the posterior cingulum or a rounded or elliptical tubercle situated near the enamel-dentine boundary. The shape and size of the cusps, as well as the position of cristid obliqua are highly variable. The teeth can be heavy with sturdy obtuse cusps and high connecting ridges, or more slender with sharp cusps and low crests. The cristid obliqua may be short or long, ending either against the protoconid-metaconid crest or near the tip of the metaconid (Rümke, 1985).

The teeth of extant desmans are most morphologically similar to extant shrew moles, but are larger (Schreuder, 1940; Rümke, 1985). In lower molars, the talonid is v-shaped like all talpids, not u-shaped like soricids. In the upper molars, accessory cuspules along the lingual boarder in desmans’ functions like the hypocone in shrew moles (Schreuder, 1940; Hutchison, 1974; Palmeirim and Hoffmann, 1983; Carraway and Verts, 1991). The cusps on upper and lower molars tend to be brachydont, when compared to other extant talpids, and more bulbous because the diet of extant desmans consists of benthic invertebrates (Palmeirim and Hoffmann, 1983; Rümke, 1985).

The two isolated upper teeth from GFS share characteristics of both Lemoynea and Mystipterus . Lemoynea is a basal desmanine talpid known from the early late Miocene (Clarendonian) of Nebraska ( Bown, 1980), which is the oldest confirmed desman in North America. The molars of Lemoynea are reminiscent of extant desmans: they are relatively large in size ( Table 3), all three upper molars have a divided mesostyle, and there are lingual cuspules on the occlusal surface of the upper molars (Brown, 1980; Gunnell et al., 2008). The GFS teeth look very much like the teeth of Lemoynea , but they lack the divided mesostyle, which is considered a derived feature of the tribe. Mystipterus is a basal talpid ( Uropsilinae ) known from the late Oligocene to late Miocene (Arikareean to Clarendonian) of the Great Plains and Oregon ( Gunnell et al., 2008). It looks more shrew-like than other talpids: there is a large hypocone flaring off the posterior aspect of the upper molars, it does not have a divided mesostyle, and it does not have accessory lingual cuspules on the occlusal surface (Hutchison, 1968). The GFS teeth have the continuous mesostyle like Mystipterus and other basal talpids but lack the same generalized occlusal morphology and presence of a hypocone.

The GFS teeth are distinct from European fossil desman genera: Asthenoscapter , Mygalea , Mygalinia , and Desmana . Asthenoscapter detention is morphologically more similar to Uropsilinae , especially Mystipterus , than other? Desmanini (Hutchison, 1968; 1974). The molars of Asthenoscapter are nearly morphologically identical to Mystipterus in proportion, cingulid development, relative cuspid size, and cristid arrangement. The m2s of Asthenoscapter species have a narrower trigonid than talonid and a very well-developed metacristid, which is continuous with the entocristid (Hutchinson, 1974), whereas M. fumamons has similarly sized trigonid and talonid as well as a separate metaconid and entoconid. Mygalea m2s have a cristid obliqua is directed towards the middle of the protocnid-metaconid crest but bends sharply and ends at the metaconid or metacristid and a small re-entrechat valley (Van den Hoek Ostende and Fejfar, 2006), whereas M. fumamons has a cristid obliqua that joins at the metaconid and has a large re-entrechat valley. Mygalinia m2 trigonid and talonid are more or less of the same size, the oblique cristid reaches the tip of the metaconid and the re-entrant valley is deep (Rzebik-Kowalska and Rekovets, 2016), which is morphologically similar to M. fumamons ; however, Mygalinia was a substantially smaller desman based on tooth size ( Table 3). Fossil species of Desmana m2s are typical for desmans with heavy and have sturdy obtuse cusps, cristid obliquids are long and end near the tip of the metaconid (Topachevsky, 1962). Cingulids are wide and present on anterior, buccal, and posterior sides. Unlike M. fumamons , the re-entrant valley is narrow in all fossil species of Desmana .

All three GFS teeth are distinct from the well-known fossil desman, Archaeodesmana . Archaeodesmana is known from the late Miocene to early Pliocene of Europe (Hutterer, 1995, Minwer-Barakat et al., 2020). The M1 of Archaeodesmana is morphologically similar to the extant species Galemys pyrenaicus , with a poorly developed metastyle and a divided mesostyle. On all three lower molars, the anterolabial cingulum is well developed, and sometimes there is a small cuspule on the cingulum in the re-entrant valley (Martín-Suárez et al., 2001). These characteristics are not present on any of the GFS specimens, thus excluding Archaeodesmana .

The GFS partial dentary is also morphologically distinct from other known desmans. In specimens identified as Lemoynea , the ventral border of the horizontal ramus becomes deeply inflected posteriorly beneath the m1 hypoflexid and anteriorly beneath the anterior root of p3 (Brown, 1980). The dentary is deepest beneath m 2 in Desmana moschata , Galemys pyrenaicus , and all known species of Archaeodesmana (Brown, 1980; Ziegler, 2005). The GFS dentary has no inflections, nor does it deepen; the body of the dentary is smooth and continuous. Specimens of Lemoynea possess a large mental mandibular foramen situated beneath the posterior root of m1, about onethird the distance from the inferior border of the mandible to the alveolar border of the tooth row (Brown, 1980). In Archaeodesmana species, there are two mental foramina: the anterior one under the p1 or below p1/p2, and the posterior one under the trigonid of m1 or below the posterior root of p4 (Ziegler, 2005). In fossil Desmana species, tri- or quadripartite mandibular foramen are common ( Bown, 1980, Minwer-Barakat et al., 2020). In Mygalea , there are two mental foramina: a large one below the posterior root p4/anterior root m1, and the front mental foramen is smaller and lies in the upper part of the horizontal ramus under the canine (Van den Hoek Ostende and Fejfar, 2006). The GFS dentary has one large mental foramen under the posterior alveolus of p4.

The morphology of the GFS materials is unique among fossil talpids. The size of these teeth is comparable to that of extant desmans, and similar in size to the largest fossil forms ( Table 3). Though reminiscent of desmans, the upper molars ( ETMNH 20747 and ETMNH 20779 ) do not possess all the synapomorphies that have been used to define the tribe; however, all of the lower molar synapomorphies are present in the holotype m2 ( ETMNH 6994 ). Thus, these specimens are interpreted as representing a new occurrence of a stem desman, outside crown-group desmans .

Additionally, the holotype right m2 and right M1 can occlude. The second shear facet on the posterior aspect of the M1s line up with the second shear facet on the m2 ( Figure 4 ). The holotype m2 also fits within the alveoli of the referred edentulous dentary ( ETMNH 21077 ), supporting referral of that specimen. While these specimens fit together, they were recovered from different locations, suggesting they come from two different individuals .

Figures

FIGURE 3. Magnatalpa fumamons gen. et sp. nov. dental material. ETMNH 9664, right m2 - A) occlusal, B) labial, and C) lingual views. ETMNH 20747, left M1 - D) occlusal view. ETMNH 20779, right M1 - E) occlusal, F) lingual, and G) labial views. ETMNH 21077, edentulous dentary - H) lingual, I) labial, and J) occlusal views. Scale bars equal 1 mm.

FIGURE 4. M1 (ETMNH 20779) super-positioned on top of m2 (ETMNH 6994). Scale bar equals 1 mm.