Lutra lutra groissii Heller, 1983

Marciszak, Adrian, Hilpert, Brigitte & Ambros, Dieta, 2024, The remarkable record of mustelids from Hunas (Bavaria, Germany), Comptes Rendus Palevol 23 (23), pp. 339-383 : 344-347

Lutra lutra groissii Heller, 1983

( Fig. 4A )

Lutra lutra groissii Heller, 1983: 211 ; pl. 8/1. – Groiss 1983: 354; table 48. – Koenigswald & Heinrich 1999: 96. – Ambros 2006: 54. – Rosendahl, Ambros, Hilpert, Hambach, Alt, Knipping, Reisch & Kaulich 2011: 19; table 3/2.

Lutra lutra Ambros, 2006: 37 ; fig. 43; table 18. – Baumann 2011: 8.

REFERRED MATERIAL. — Maxilla with P4-M1 and phalanx 1 .

DESCRIPTION

Both teeth are unworn and belonged to a relatively young animal. In the occlusal view, P4 has a rectangular triangle outline ( Fig. 4 ). The crown is divided into two morphologically distinct parts, the trigon extending buccally and the talon lingually. All margins are rounded, with two considerable concaves. The mesial concave is situated on the median part, on the border between the parastyle and protocone. The buccal concavity is placed almost exactly in the medium of this margin. The elongated and large parastyle is a crescent, low cusp. Its apex and the mesial wall of the paracone are connected by a distinct, low, thick crest, which does not extend to the paracone apex. The high, conical paracone is oriented almost vertically. It is separated from the protocone by a wide, not very deep, V-shaped valley. This distinct cusp has three crests, two mesial and one distal. The first mesial crest, low and flat, runs mesio-lingually from the top. The second, much thicker and stronger crest runs mesially toward a parastyle in the mesio-buccal margin of the crown as part of the mesial cingulum. The distal crest is orientated oblique-longitudinally, running from the top toward the metacone. The elongated and enlarged parastyle is pointed mesially and narrows distally. Its internal, broad surface forms an elongated, triangular, shallow basin, slightly deeper in the middle. The whole protocone is collared by a thick, high cingulum, especially strong on the mesial and mesio-lingual margins. The talon is mesio-distally enlarged and broad, and its distal margin does not reach the distal margin of the metacone in the occlusal view. The metacone is lower than the paracone and the crest that connects the two cusps is curved lingually. On the buccal wall of the talon a flat and relatively deep surface in the form of a concave meniscus is present. A stronger cingulum is present only on the disto-lingual margin ( Fig. 4 ).

M1 has a bean-shaped occlusal outline, and the crown is oriented disto-lingually ( Fig. 4 ). In relation to P4, it is situated more disto-lingually. There are two considerable concavities, buccal and distal. The buccal one is situated in the median part between the paracone and the metacone. The distal depression is located on the border between the trigon and talon. In the lateral view, the crown is strongly concave in the median part. The depression is a wide, flat, U-shaped valley, which runs transversally through the whole crown length. The trigon is slightly shorter than the talon, with two well developed, main cusps. Both cusps are relatively high and spherical, and the paracone is slightly higher and larger than the metacone. Both cusps are separated by a wide, not very deep, V-shaped valley. The elongated talon is broad, with rounded margins. The protocone is elongated and well developed, connected to the paracone by a strong and thin crest. The hypocone is on the disto-lingual corner of the talon and is crest-like. The central, extensive basin of the talon is concave, shallow and smooth. The moderately developed cingulum is placed only on the disto-lingual margin of the talon ( Fig. 4 ).

REMARKS

The unique find of the otter from Hunas was studied by Heller (1983d, e). He compared the find with various lutrinae species and determined it as L. lutra . He also found some differences like an enlarged protocone of P4 and an M1 with a shallower median depression and less marked median, buccal concavity and talon oriented less disto-lingually. This allowed him to classify the Hunas otter as a new subspecies called Lutra lutra groissii ( Heller 1983d, e). Potentially, three lutrinae species can be considered: L. lutra , Lutra simplicidens Thenius, 1965 and Cyrnaonyx antiqua (de Blainville, 1841) . The differences between them are mostly in the premolars and molars. Morphologically, the Hunas otter considerably stood out from the dentition of C. antiqua . In the occlusal view, the P4 from Hunas is a rectangular triangle, while the P4 of C. antiqua is an irregular quadratic ( Fig. 4 ). The parastyle is smaller and less distinct in the Hunas specimen.

The most noticeable two features distinguishing the Hunas otter from C. antiqua are the shape of the protocone and the talon of P4. The protocone of C. antiqua is extremely large, long and broad, with a deep, crescent inner surface. It is collared, as the rest of the crown (except the buccal margin) by a very thick and strong cingulum wall. Secondly, the buccal median concavity is much more strongly developed, the talon is oriented particularly disto-buccally, far beyond the main axis of the tooth. Both features in the Hunas otter are less developed ( Fig. 4 ). Also, the M1 of the Hunas otter differs from that of C. antiqua . In this species the joint paraconemetacone is developed as a wide, blunt, medio-distal crest. The protocone is a flat, narrow, longitudinally elongated cusp, connected mesially with the paraconule. The distinct lingual and distal cingulum includes a blunt metaconule on the disto-lingual crown margin. A distinct cingulum developed on the buccal side of the tooth forms a marked mesio-buccal parastyle near the paracone. The central part of the crown consists of a shallow depression separating the buccal cusps and crests from the lingual ones.

If the Hunas otter cannot be assigned to C. antiqua , maybe it is L. simplicidens . Admittedly, the youngest records of this species are dated to 400-350 kya, however, the relict survival of this otter, as many other Eurasian carnivores, cannot be entirely rule out. Compared the Hunas maxilla with the material of L. simplicidens from Voigtstedt (800-700 kya; Cherin 2017), we found some similarities in the build of P4, which differed from the extant L. lutra . When comparing the P4s of the Hunas and Voigtstedt individuals with extant L. lutra , teeth of both fossil specimens have proportionally larger, semilunar parastyles, much longer and broader protocones, which is oriented noticeably more mesio-lingually and stronger developed paracone crests ( Fig. 4 ).

The Hunas otter differs from Voigtstedt in a longer protocone with shallower internal basin and less expanded mesio-ligually, stronger buccal, median concavity and weak cingulum. The metacone of the P4 of L. lutra is a small blunt cusp in the disto-buccal crown margin. It is separated from the paracone on the buccal side by a distinct valley. A low protocone is included in the mesio-lingual margin of the crown as a crest-like wall running from the protocone toward the metacone. It forms the lingual border of one or two shallow depressions situated between the protocone, paracone and metacone. The depressions are separated from each other by a transverse wall. The external margin of the crown consists of a low cingulum visible in the buccal view. Also, an indistinct cingulum is situated below the parastyle ( Fig. 4 ). Morphologically, the P4 from Hunas most closely resembles the P4 of L. lutra from Hoxne ( Willemsen 1992; Mecozzi et al. 2022). Both teeth hold many morphological similarities like large, crescent parastyle, considerable buccal, median concavity, particularly enlarged protocone and weak cingulum.

When comparing the M1 of the Hunas otter with the L. simplicidens from Voigtstedt, it was found that they differ considerably ( Fig. 4 ). The occlusal outline of both teeth is different. In the M1 from Hunas the crown curved considerably, with the distal walls of the trigon and talon directed strongly distally. In the M1 from Voigtstedt the main axis of the crown running from disto-buccally to the mesio-lingual side, with almost straight trigon and talon in the occlusal view. In relation to P4, it is pushed more buccally ( Fig. 4 ).

In the Voigtstedt M1 the trigon and talon are of similar length, while in Hunas the talon is longer. The median concavity on the buccal margin of the trigon is stronger developed in Hunas M1. While in the Hunas otter the paracone is only slightly higher and larger than the metacone, in the Voigtstedt M1 the paracone is considerably larger and higher than the metacone. The transversal depression running through the whole crown length and separated trigon from the talon in Hunas M1 is much broader and shallower. The protocone and hypocone constriction is lower and shorter, ending on the mesial margin of the talon. In the Voigtstedt otter this structure is much longer, thicker and curved, reaching the central point of the internal talon basin ( Fig. 4 ). The internal basin of the Hunas otter is more elongated, narrower and shallower than in the Voigtstedt otter. The lingual cingulum is more strongly developed.

Contrary to that, the M1 of the Hunas otter holds many similarities with the extant L. lutra like M1, in relations to the P4, pushed more lingually and less perpendicularly, similar size of paracone and metacone, broad and shallow depression separated trigon and talon, relatively short and low protocone and arched curved crown in the occlusal view. However, it simultaneously differs in the less arched trigon and talon, more strongly developed median concavity on the trigon buccal margin, higher para- and metacone and longer talon, with broader and more extensive internal basin, and stronger cingulum ( Fig. 4 ).

Given the above features, it can be concluded that the Hunas otter showed some intermediate characteristics between L. simplicidens and L. lutra , and can suggest one evolutionary lineage or development of similar features during the evolution.According most authors, the derivation L. lutra from L. simplicidens is hardly conceivable ( Willemsen 1992, 2006; Mecozzi et al. 2022), but cannot be entirely ruled out. Our analysis showed the Hunas otter as something like a transitional form between these two species, and a possible link between them. There are morphometric differences between the two species that provide further support for a different derivation of L. lutra . The generally accepted chronological framework is that L. lutra dispersed into Europe from Asia during the late Middle Pleistocene and replaced L. simplicidens ( Willemsen 1992, 2006; Mecozzi et al. 2022). In this scenario dated to c. 550-500 kya, otters from Cengelle, previously classified as L. lutra by Pasa (1947), with the trigonid broader than the talonid, can be re-determined as L. simplicidens ( Mecozzi et al. 2022) . This character has a high taxonomic value, which allows attribution of the Cengelle otter to L. simplicidens ( Willemsen 1992) .

The P4 from Hoxne, ascribed to Lutra sp. by Willemsen (1992), was recognised as having a strong resemblance to L. lutra . Given the absence of coeval maxillary Lutrinae material, attribution to L. simplicidens cannot be entirely ruled out. The comparison of the P4 shows slightly but significant morphological distinction between the Hoxne specimen and Voigtstedt ones. L. simplicidens has a characteristic talon profile, with a convexity along the distal margin, about half length, in the occlusal view ( Cherin 2017). In the P4 from Hoxne, the profile of the distal margin is straight, not convex, which allows us to refer it to L. lutra ( Mecozzi et al. 2022) . If not for the whole European territory, locally L. simplicidens may be ancestral to some populations of L. lutra . The present work allows us to recognise several anatomical similarities as well as distinctions of the Hunas otter between L. simplicidens and L. lutra . The presence of such multiple, intermediate features in this specimen might suggest that L. simplicidens may be part of the same clade. Unfortunately, this cannot be supported by cladistic data until sufficiently complete cranial material of L. simplicidens are discovered. The same goes for the European late Middle Pleistocene L. lutra and the revision of the material from other, so far undescribed sites. New discoveries can also help clarify the taxonomic status of some of these otters, however most of these materials would require a taxonomic revision. In light of the observed similarities with L. simplicidens , the Hunas otter and L. lutra , the possible attribution of L. simplicidens in one evolutionary lineage with L. lutra is plausible, but further discoveries are needed to test this hypothesis. In view of the uniqueness of the Hunas find and its morphological separation from extant L. lutra , we also maintain subspecific status of the otter L. l. groissii, proposed by Heller (1983d, e).

Figures

FIG. 4. — The P4-M1 of Lutra Brisson,1762 species: A, Lutra lutra groissii Heller, 1983 from Hunas (HHu 4020);B, extant Lutra lutra (Linnaeus, 1758) from Silesia; C, D, Lutra simplicidens Thenius, 1965 from Voigtstedt (C, IQW 1966/7314 (Voi. 3532); D, IQW 1966/7313 (Voi. 3525); modified after Cherin (2017: 436; fig. 2). Scale bar: 10 mm.