Myxomygale gracilis, Ziegler, 2003

Ziegler, Reinhard, 2003, Moles (Talpidae) from the late Middle Miocene of South Germany, Acta Palaeontologica Polonica 48 (4), pp. 617-648 : 635-637

Myxomygale gracilis sp. nov.

Fig. 9 .

Etymology: From Latin gracilis ,slender,lank; becauseof thegracilehumerus.

Holotype: Right humerus, P10−615/2, fig. 9D.

Measurementsoftheholotype: GL (8.05), Bp (3.50), BpwT (3.15), DS (1.30), Bd (3.92), BdwE (3.46), Bp*100/GL (43.5).

Type locality: Petersbuch 10 (details see p. 618).

Age :UppermostpartoftheMiddleMiocene(MN7/8, Rummel 2000).

Paratypes and measurements.—Petersbuch 10: CRW P10−614/1, left dentary fragment with m1–m2; m1 (1.47× 0.89×1.07); m2 (1.69×1.09×–); NHMA P10−614 /2, right dentary fragment with m2–m3; m2 (1.64×1.15×1.04); m3 (1.35×0.88×0.6) ; NHMA P10−614 /3, right dentary fragment with m2–m3; m2 (1.65×1.09 ×0.97), m3 (1.37×0.84×0.60) ; NHMA P10−614 /4, left maxilla fragment with M1, M1 (2.10×1.84); CRW P10−614/5, right M1 (2.03×1.77); CRW P10−615.1, left humerus fragment, DS (1.44), Bd (ca. 4.1), BdwE (3.40) .

Diagnosis.—Small−sized Myxomygale characterised a mental foramen situated under the protoconid of m1, an oblique cristid, extending labially in m1, joining a marked metacristid in m2 and m3. M1 without parastyle and preparacrista, with deeply divided mesostyle. The humerus is urotrichine and slender with long ledge−like teres tubercle and a pectoral tubercle situated laterally.

Description of the holotype

Only the deltoid process and the epicondylar spines are broken off. In anterior view the humerus shows a long teres tubercle with a proximal end hidden by the marked pectoral ridge. The pointed pectoral tubercle extends further distally than the teres tubercle and is situated on the lateral margin of the shaft. It is visible in posterior view. The brachialis fossa is moderately deep. The sulcus between head and major tubercle is a narrow groove. There is a large, pocketed supratrochlear fossa, between trochlea and the fossa m. flexor digitorum profundus ligament a deep, concave notch. The posterior face shows the shallow olecranon fossa and the head with a long axis slightly directed disto−laterally. The ridge between head and lesser tubercle is short and tapers towards the lesser tubercle.

Description of the paratypes

Dentary.—Among the 4 short fragments of the horizontal ramus two show the posterior mental foramen beneath the trigonid of m1. The specimens yield no information concerning the antemolar dentition.

Lower molars.—The size relation is m2>m1>m3. In the m1 the oblique cristid runs rather bucally, extending to the posterior base of the protoconid. There is no metacristid. The precingulid does not extend to below the paraconid but is continuous with the ectocingulid. There is only a weak postcingulid hidden by the marked precingulid of the m2. The entostylid is broken off. In the m2 the protoconid is more elevated than in the m1 and the trigonid is distinctly narrower. The oblique cristid joins the marked metacristid. The precingulid is more marked than in the m1. The m3 differs from the m 2 in the smaller size and in the reduced talonid without entostylid.

Maxilla.—One fragment with M1 shows the lacrimal foramen above the anterior root of M1.

M1.—There are neither preparacrista nor parastyle. The mesostyle is deeply divided. Para− and metaconule are only moderately differentiated. The preparaconuluscrista is continuous with the precingulum, which extends to the buccal margin. The postmetaconuluscrista joins the metacingulum which itself tapers in its mid part and ends in a marked short crest above the metastyle.

Humerus.—In addition to the type specimen there is one humerus with the proximal third and the point of the pectoral tubercle broken off. It yields no further information.

Comparisons

There are five species of Myxomygale known thus far most of which are only scarcely represented. They are listed in ascending order with respect to their stratigraphic range: the type species Myxomygale antiqua Filhol, 1890 from the Quercy (Oligocene), Myxomygale vauclusensis Crochet, 1995 from Saint−Martin−de−Castillon (Oligocene, MP 23, figures and measurements in Hugueney 1972: 53 f), Myxomygaleminor Ziegler, 1990 from Ulm−Westtangente (Lower Miocene, MN 2a), Myxomygale hutchisoni ( Ziegler, 1985) from Petersbuch 2 (Lower Miocene, MN 4), Myxomygale engesseri Doukas, 1986 from Aliveri in Greece (Lower Miocene, MN 4). The humerus is known, i. e. published, described and figured, only from M. hutchisoni ( Ziegler 1985: fig. 8, tab. 3). Crochet (1995: 56) also mentions the humerus in the revised genus diagnosis of Myxomygale . However, it is not known to which species he refers. As much as is known from published evidence, the humerus is only preserved in M. hutchisoni . Perhaps Crochet knows unpublished humeri from M. antiqua .

M. gracilis differs from M. antiqua in: – the distinctly smaller size, – the size relation between m1 and m2 (m1<m2) and the weaker ectocingulids.

M. gracilis differs from M. vauclusensis in: – the distinctly smaller size, – the more anterior position of the mental foramen, – the absence of a parastyle, the divided mesostyle and the less developed para− and metaconule of M1.

M. gracilis differs from M. minor in: – the distinctly wider M1, – the absence of a parastyle and the divided mesostyle in M1,

M. gracilis differs from M. hutchisoni in: – the absence of a parastyle and the divided mesostyle in M1, – the smaller and in particular more slender humerus, with a relatively longer teres tubercle and a less marked ridge running from the head to the lesser tubercle.

M. gracilis differs from M. engesseri in: – the wider m2, – the somewhat bigger M1 without parastyle and with continuous preparaconuluscrista and paracingulum respectively and deeply divided mesostyle.

? Urotrichusdolichochir ( Gaillard, 1899) known from the type locality La Grive (Middle Miocene, MN 7 /8) by the humerus only, and from Petersbuch 6, is rather similar, thus deserves to be mentioned .

M. gracilis differs from? U. dolichochir in: – the somewhat bigger humerus, – the longer teres tubercle hidden proximally by the pectoral ridge.

In the Petersbuch 10 fauna there is another small urotrichine, which is not determinable beyond the tribe. It is represented by a humerus and tentatively associated dentition.

M. gracilis differs from Urotrichini gen. et sp. indet. I in the: – smaller overall size, – more posterior position of the mental foramen, – m1 without metacristid and an oblique cristid running more buccally, – more gracile humerus with the longer teres tubercle, – lateral position of the pectoral tubercle, – less marked ridge running from the head and tapering towards the lesser tubercle.

The Petersbuch 31 fauna yielded a small urotrichine, represented by humeri and dentition.

M. gracilis differs from Urotrichini gen. et sp. indet. II in the: – less pronounced para− and metaconule, the absence of the parastyle and the divided mesostyle in M1, – more gracile humerus with the longer teres tubercle and a weaker and discontinuous ridge between head and lesser tubercle.

Discussion

Myxomygale gracilis is the smallest talpid in the Petersbuch 10 fauna. The association of lower teeth, upper teeth, and humerus is without alternative. However, the divided mesostyle in the M1 requires some comments on the generic allocation of the species. The upper dentition of the type species is unknown. In M. vauclusensis from Saint−Martin−de−Castillon Crochet (1995: 58, fig. 20) there are some M2 with a divided mesostyle. But Hugueney (1972: table 9b) listed a confluent mesostyle in M1 and M2 as character of this species. M.minor and M.hutchisoni has an undivided mesostyle even in unworn teeth. At last, M. engesseri has a heavily worn M1 and an unworn M2 with confluent mesostyle. Actually, I consider the shape of the mesostyle (deeply divided versus confluent) a character of generic relevance. On the other hand, I am rather convinced of the homogeneity of the sample under study. The lower dentition fits well Myxomygale and the humerus shows clear urotrichine affinities. Consequently, the generic allocation is acceptable with some reserve.

Obviously M.gracilis was a poor burrower. The genus so far was known from the sites with Oligocene to Early Miocene age. The new species extends the range to the end of the Middle Miocene. As most species are known only from small samples and as not all elements are known from all species—e.g., the humerus is known only from M. hutchisoni and M. gracilis —it is not possible to find any phylogenetic relationships between the species. The earlier species are not more primitive and the later ones not more advanced than the other at a time. Much more material and more complete dentitions are necessary.

Figures

Fig. 9. Myxomygale gracilis sp. nov., Petersbuch 10. A. Right dentary with m2–m3, NHMA P10−614/3, occlusal view; ca. × 10. B. Right dentary with m2–m3, NHMA P10−614/2, buccal view; ca. × 10. C. Left M1, NHMA P10−614/4, occlusal view; ca. × 15. D. Holotype, right humerus, NHMA P10−615/2, in anterior (D1) and posterior (D2) views; ca. × 7.5.