Spermophilinus bredai (VON MEYER, 1848)

Prieto, Jérôme, Rummel, Michael, Peláez-Campomanes, Pablo & Vasilyan, Davit, 2020, Dental Anomaly In A Middle Miocene Fossil Of The Genus Spermophilinus (Rodentia, Sciuridae) From Southern Germany, Fossil Imprint 76 (1), pp. 174-180 : 176-177

Spermophilinus bredai (VON MEYER, 1848)

Text-figs 1 , 2

M a t e r i a l a n d m e a s u r e m e n t s. Right upper jaw with (abnormal) P3, P4 and all molars (NMA-2019- 1/2352; Text-fig. 1 ). Measurements (L × W in mm): P4: 1.38 × 1.74; M1: 1.64 × 2.06; M2: 1.71 × 2.13; M3: 2.08 × 2.05.

C o m p a r a t i v e m a t e r i a l. Left upper jaw with P3–M1 from the same locality (NMA-2019-2/2352; Textfig. 2). Measurements: P3: Di: 0.54, H: ~0.38; P4: 1.44 × 1.65; M1: 1.68 × 2.05.

D e s c r i p t i o n. NMA-2019-1/2352. The fragmentary maxilla conserves the P3–M 3 in situ. The specimen is adult as shown by the wear stage of the teeth.The P3 is not recognizable as such. The crown of the tooth or teeth is/are broken. This break reflects the original condition of the specimen and does not result from damage due to, for example, screen washing of the fossil-enriched sediment. Two posteriorly-directed roots are developed in front of the P4, between the two anterior roots of the last premolar. A very small third root emerges in front of the anterolabial root of the P4. The lingual root is the strongest. The morphology of Spermophilinus molars is well known and, thus, deserves no detailed description. We only notice that the parastyle is not significantly developed in the P4. P4–M3 have a strong, crest-shaped mesostyle. It forms a bridge between the paracone and metacone (P4), or is directed rather towards the labial part of the tooth (M1, M2). The crest is observed in the M3, but included in the expanded posterior part of the tooth. The M1 differs from M2 by the metacone which is more clearly labially differentiated, the protocone which has a more central position, as well as the less well-achieved metalophid/protocone junction.

NMA-2019-2/2352. The specimen shows less trace of tooth wear. The P4 has a parastyle completely included in the anteroloph. The P3 is complete, uniradicular, posteriorly directed, and placed between the anterolabial root and lingual root of the P4. The crown of the tooth is conical and comes into contact with the P4 under the hypothetical parastyle.

R e m a r k s. The molars show the characteristics of Spermophilinus , a genus relatively common in the German middle Miocene (see details in Ziegler 2005, for instance). To be brief, four known species of Spermophilinus ( S. besana , S. bredai , S. turolensis and S. giganteus ) differ essentially in size. It has long been accepted that these species represent a lineage characterized by an increase in molar size. Bosma et al. (2018) have recently changed this view by demonstrating the presence of two coexisting species of Spermophilinus in a single site in Anatolia. It is out of the scope of this paper to review the German record in order to discuss the specific homogeneity, and we, thus, consider the Bavarian fossil populations to be monospecific in each locality.

The early and middle Miocene Spermophilinus collections from the Upper Freshwater Molasse were considered to be assigned to S. aff. bredai for the older localities while S. bredai is found in younger ones (e.g., Ziegler and Fahlbusch 1986, Kälin 1993). Ziegler (2005; following de Bruijn 1995) considered that the smaller and older species belong to S. besana . The measurements of M1 and M2 from selected localities in Switzerland and southern Germany are shown in the Text-fig. 3 . It emerges that it becomes difficult to clearly separate the species in a stratigraphic framework. The use of the average tooth size for all selected localities would certainly have added more clarity to present the evolution of the genus, but would not have allowed us to discuss in detail the size of our specimens (some molar samples are indeed too small). Pending further study of the Petersbuch 136 material, the studied specimens do not oppose a taxonomic assignment to S. bredai .

It is important to note for the following discussion that we consider the tooth shown in Text-fig. 2 as a P3 and not as a DP3 that has not been replaced.

Figures

Text-fig. 1. Spermophilinus bredai (VON MEYER, 1848): 3D models of a right upper jaw with (abnormal) P3, P4 and all molars (mirrored; NMA-2019-1/2352). a – the specimen in occlusal view showing the relative position of the three roots in place of P3 (yellow) compared to P4 (green); b – same view, with focus on P3–P4; c – lingual view; d – mesial view. Scale bars 2mm.

Text-fig. 2. Spermophilinus bredai (VON MEYER, 1848): left upper jaw with P3–M1 (NMA-2019-2/2352). a – the specimen in occlusal view; b – mesial view; c – labial view. Scale bars 1mm.

Text-fig. 3. Scatter diagram of mean L/W values of selected Spermophilinus upper first molars (M1 and M2) from Switzerland and south Germany. The crosses correspond to the minimum and maximum values of the length and width. The intersection gives the value of the mean. Comparative data are after Ziegler and Fahlbusch (1986), Bolliger (1992), Kälin (1993), Ziegler (1995, 2005), Kälin and Engesser (2001), Prieto (2007), Prieto et al. (2009, 2017), Seehuber (2009). Blue: localities younger than ~14 Ma (S. bredai); Green: localities ranging from ~14 Ma to ~15Ma (S. bredai); Red: localities ranging from ~15 Ma to ~16 Ma (S. besana); Yellow: older localities (most S. besana).