Chalicomys jaegeri Kaup, 1832

Sen, Sevket, 2016, Rodents, lagomorphs and insectivores, Geodiversitas 38 (2), pp. 299-314 : 302-308

Chalicomys jaegeri Kaup, 1832

( Figs 3 , 4 , 5 )

TYPE LOCALITY. — Eppelsheim, Rhineland-Palatinate, Germany, MN 9|10.

MATERIAL. — From Küçükçekmece East (ITU collections) two upper incisors, one P4, two M1 or M2, one lower incisor, one m3 and two astragali, numbered as KÇ501 to KÇ509. From Küçükçekmece West (MNHN collections) 10 upper incisor fragments, five P4, nine M1 or M2, six M3, 14 lover incisor fragments, one mandible fragment with p4-m1, 17 p4, 12 m1 or m2, and five m3, numbered as MNHN.F.TRQ788 to TRQ866.

MEASUREMENTS. — See Table 1. Measurements of the length and width of cheek teeth are the maximum values that can be measured on teeth, often taken close to the base of the crown. Indeed, the cheek teeth, in particular when the attrition is not advanced, have occlusal surface shorter and narrower than near the base of the crown (see in particular Figures 3 and 4 ). In other words, in lateral and lingual views, the crown enlarges towards the root. Some authors provide measurements at the occlusal surface ( Aldana Carrasco 1992; Apoltsev & Neofitny 2015) or occlusal surface and when possible largest dimensions of cheek teeth ( Stefen 2009; Mörs & Stefen 2010). Largest dimensions are given here since the length and width of the occlusal surface generally increase with attrition.

DESCRIPTION

As shown in Figures 3 and 4 , and Table 1, the specimens from Küçükçekmece display some size variation, in particular for incisors and p4, the larger teeth being 20 to 25% larger than the smaller ones. However, the Küçükçekmece material does not show any size grouping, and the morphology of incisors and cheek teeth generally does not distinguish different species. Such a size variation has been observed in several other localities, when a sufficient number of specimens is available, as for the type locality of Chalicomys jaegeri, Eppelsheim (e.g., Stefen 2009: table 1). Size variation in castorids is explained by Hugueney (1999: 283) as being due “to the fact that castorid individual growth lasts during a long time (at least four years and perhaps all along the life, in extant Castor ), so that size variation is very large”.

The upper incisor has a wear facet 1.4 to 1.5 times longer than the width of the anterior face. The enamel is smooth and slightly convex. The section is rather rounded.

All cheek teeth have flexi/ids filled with cement, and in some teeth, the cement covers parts of or even all faces of the crown (e.g., Fig. 4F, G ). The root is open in young individuals, but closed with cement layers in older ones. Upper cheek teeth are strongly convex lingually and twisted distally, while lower cheek teeth are slightly convex labially and curved mesially. The crown is high; the maximum crown heights measured on fresh teeth are 21.8 mm for a p4 (MNHN.F.TRQ843) and 24.3 mm for a P4 (TRQ830).

On the P4, the hypoflexus is strongly directed forward and penetrates deep inside the occlusal surface; in one P4 (MNHN.F.TRQ830, Fig. 3B ) it is connected with the paraflexus. On other P4s these two flexi face each other. The metaflexus is labially closed in very early stage of wear, and in one specimen it has a distal extension (TRQ829, Fig. 3A ). The mesoflexus is arc-shaped and remains lingually open, as does the paraflexus, until late stages of wear. In lingual view, the depth of the hypostria is somewhat variable: in 1/3 of P4s it reaches the base of the crown ( Fig. 3B ), while in the others its ends far from the base of the crown. In labial view, the depth of strii increases from metastria to parastria ( Fig. 3B ”), although the metastria disappears in very early stages of wear, while the mesostria and parastria are preserved quite late; their depth does not exceed half of the crown height in unworn specimens. Crown height is three times more than the length in unworn or moderately worn specimens.

The M1 and M2 are much smaller than the P4. Their occlusal outline is roughly square. The hypoflexus is strongly directed forward, and it ends in front of the paraflexus, which is an island in all specimens. The mesoflexus remains open quite late in wear, while the metaflexus becomes closed in moderately worn teeth. The hypostria does not reach the base of the crown; it ends about 7-8 mm above it. On two fresh M1-2, (MNHN.F.TRQ817 and 819), its depth is about 2/3 of the crown height. The mesostria and metastria are equally deep ( Fig. 3D ”, F”), but they disappear in moderately worn specimens.

The M3 is similar in size to M1-2 or slightly smaller. The crown is twisted lingually and distally, more than in the other upper cheek teeth. The other characters are similar to that of M1-2.

The lower incisor has a wear facet much longer than that of the upper incisor, and its length is twice its anterior enamel width. The enamel of the anterior face is smooth and rather flat. The section is triangular.

The p4 is by far the largest cheek tooth. Its occlusal surface tapers mesially in young individuals, but becomes rounded in adult ones. The hypoflexid is strongly distally oblique and does not reach the metaflexid. Its depth increases with wear progress.The paraflexid is mesially twisted and bifurcated into two branches.The mesoflexid and metaflexid are slightly oblique mesially or rather transverse. On some fresh specimens, such as the p4 MNHN.F.TRQ813 ( Fig. 4E ), there is a remnant of proparafossettid which becomes an enamel island with a little wear; this is also seen in some lower molars ( Fig. 4J, K ). In labial view, the hypostriid reaches the base of the crown in all specimens. In lingual view, the depth of the three striids increases posteriorly, the deepest being the metastriid, which reaches half of the crown height in fresh p4s (see Fig. 4E ”).

m1 and m2 are smaller and in particular shorter than p4. The occlusal pattern is similar to that of p4, except that the paraflexid and mesoflexid are rather transverse and gently curved. Contrary to p4, the metaflexid becomes closed earlier than the other flexids. In labial view, the hypostriid reaches or may not reach the base of the crown. In lingual view, the deepest striid is the mesostriid, while the metastriid is the shorter.

The m3 has a similar occlusal pattern to m1 and m2, except that the hypostriid is less oblique. In all m3s, the hypostriid reaches the base of the crown. In lingual view, the height of mesostriid and parastriid is similar, but the metastriid is shorter.

The ITU collection also includes two astragali of beaver from Küçükçekmece East ( Fig. 5A, B ). They are complete, well preserved and may belong to the same individual. Their dimensions in mm are as follows (left – right): maximum length = 21.2-21.2; maximum width = 18.6-18.5; maximum width of trochlea = 13.3-13.5; maximum width of the head = 11.0-10.5.

The size and proportions of these astragali are similar to those of Castor fiber ( Fig. 5 ). In dorsal view, the trochlea is faintly and asymmetrically convex. Its lateral condyle is sharper than the medial condyle. The cotylar fossa is rather shallow. These characters are also seen in C. fiber . The lateral condyle extends distally up to the neck, like an U-shaped tongue, while the facet of the medial condyle is much larger and shorter. In C. fiber , the lateral and medial articular facets of the trochlea are V-shaped, and consequently the interarticular rugose area has an arrow shape that penetrates the trochlea. This area is ∩-shaped on the astragali of Küçükçekmece due to the parallel borders of the distolateral and distomedial articular facets of the trochlea. The head is short and the navicular facet appears crescent-shaped along its distal margin.

In plantar view, the ectal facet extends more medially than in C. fiber , and its medial margin is more rounded than in this species. The trochlear facet and sustentacular facet (for calcaneus) are separated on the Küçükçekmece astragali by a rugose area, while in C. fiber these two facets are connected and their limit is marked by a roughly mediolateral ridge. In C. fiber the sustentacular facet is constricted at the level of the neck, while this constriction is tenuous on the Küçükçekmece astragali. Distally, the sustentacular facet joins the cuboid facet of the head on our samples. In C. fiber , these two facets are partly separated by a lateral notch that penetrates the distal face to form a sulcus between these facets. In summary, the astragali of Küçükçekmece and C. fiber are similar in size and in their proportions, but different in the shape and connections of articular facets.

As far as I know from the literature, the astragalus of Chalicomys is undescribed to date. The astragalus from Sansan ( France, MN6), described by Hugueney & Duranton (2012) and referred to Euroxenomys minutus , has similar proportions but is notably smaller than the Küçükçekmece astragali. In plantar view, the shape of the ectal facet is similar, but the sustentacular facet occupies more space on the head, and its outline is different compared to that of Küçükçekmece. The same differences are also observed with the astragalus of E. minutus from Aumeister near Munich (MN9, Stromer 1928: pl. 2, fig. 19). Hugueney & Duranton (2012) also illustrated an astragalus of Steneofiber castorinus from St Gérand Le Puy ( France, MN2; see also Stefen 2011 for the systematic status of this species). This astragalus (max. L × W = 16 × 11.5 mm) is also smaller than that of Küçükçekmece, and the head is proportionally elongated. These characters and many other detailed morphological differences prevent any reliable comparison with the Küçükçekmece astragali.

DISCUSSION

Malik & Nafiz (1933) described Steneofiber sp. from the locality Küçükçekmece East based on four lower jaws, about twenty isolated cheek teeth and ten incisors. They illustrated one lower jaw with p4-m3 ( Fig. 5A ). Most of the fossils from Küçükçekmece East were lost during the fire that devoured Geological Institute of Istanbul University on February 28, 1942 ( Sen 2016). The remaining specimens, which are housed now at the ITU collection, do not contain any mandible but only isolated teeth and two astragali. We do not know how much of this material is inherited from the initial collection of Malik & Nafiz (1933).

The beaver remains from both Küçükçekmece localities cannot be referred to Steneofiber . The largest species of this genus S. depereti has cheek teeth as large as or somewhat smaller than the Küçükçekmece specimens (see diagrams in Mörs & Stefen 2010: fig. 7). In morphology, the cheek teeth of S. depereti are characterized by shorter hypostriae/ iids, the lack of labial striae/iids except mesostria/iid, and the absence of substantial cement. As described above, the beaver of Küçükçekmece has hypsodont cheek teeth (height three time more than length) with tetralophodont occlusal pattern, occurrence of pro-parafossettid on fresh teeth, hypostria/iid reaching or ending close to the base of the crown, abundant cement in striae/iids or even outside and long para- and mesostriae/iids. In all these characters, and also in size, the beaver of Küçükçekmece resembles Chalicomys jaegeri . Stefen (2009) restudied the type material from Eppelsheim. The size of premolars and molars, their occlusal pattern, as well as the length of striae and striids are very similar, and there is not any substantial difference between the assemblages of Steinheim and Küçükçekmece. Consequently, the material from Küçükçekmece is identified as C. jaegeri .

In her review of European castorids, Hugueney (1999) retained three species of Chalicomys : the type species C. jaegeri , C. subpyrenaicus ( Lartet, 1851) from Villefranche d’Astarac ( France, MN7) and C. plassi Storch, 1975 (in Franzen & Storch 1975) from Dorn-Dürkheim ( Germany, MN11). Casanovas-Vilar et al. (2008) added two more species from Spain: C. catalaunicus (Bataller, 1938) from Trinxera del Ferrocarril in Sant Quirze (MN7/8) and a new species C. batalleri from Abocador de Can Mata (MN7/8). Stefen (2009) and Mörs & Stefen (2010) suggest that the specimens from Abocador de Can Mata should rather be referred to Steneofiber than to Chalicomys , because the crenulations of enamel and the labiomesially open paraflexid in lower cheek teeth are indicative of the juvenile state in Steneofiber . Further, in this Spanish species, the hypostriid does not reach the base of the crown, and the size of the specimens from Abocador de Can Mata falls within the size range of S. depereti . For Hugueney (1999) C. catalaunicus should be included in Eucastor Leidy, 1858 or Schreuderia Aldana Carrasco, 1992 , while for Stefen (2009), the systematic status of this species needs re-examination, and its assignment to the genus Steneofiber seems more appropriate. Casanovas-Vilar & Alba (2011) refuted the assignment of these two Spanish species to any other genus than Chalicomys , arguing that in these species, the cheek teeth are four lophed, the hypostriae/iids of P4 and p4 approach the base of the crown, the striae/iids are filled with cement, and the P4 has three moderately developed striae on the labial side of the crown (only the mesostria is present in S. depereti ). Chalicomys plassi from Dorn-Dürkheim is poorly documented, and the dimensions of the unique p4 are in the lower size range of C. jaegeri . Casanovas-Vilar et al. (2008) follow Hugueney (1999) in accepting C. subpyrenaicus as a separate species of Chalicomys . Mörs & Stefen (2010) also discussed the characters and systematic status of C. subpyrenaicus , and they concluded that the size of this species overlaps with Steneofiber depereti Mayet, 1908 , and the morphology of its cheek teeth is quite similar in having a short hypostriid and only a mesostriid on lower cheek teeth, which are characters shared with Steneofiber species. They suggest maintaining it as a distinct species of Steneofiber pending the revision of the material referred to it by Lartet (1851), Gervais (1859) and Hugueney (1999). As seen from this short review, the systematic status of several species referred to the genus Chalicomys is debated, and there is no agreement on their attribution to Chalicomys and affiliation with the type species C. jaegeri .

Castorids are known in Turkey in localities ranging in age from Oligocene to Pleistocene. Saraç (2003) mentioned their occurrence in at least 30 localities inTurkey, referred to the genera Dipoides , Trogontherium , Euroxenomys , Steneofiber , Chalicomys and Castor . However, the castorid remains from most of these localities are not described, except for that of Erenköy ( Calvert & Neumayr 1880), Küçükçekmece East ( Malik & Nafiz 1933), Bayraktepe 1 and 2 ( Ünay 1976, 1981), Çatakbagyaka ( Ünay 1977), Manisa-Develi ( Ozansoy, 1961), Paşalar( Flynn& Jacobs 1990) and Emirkaya 2( Montuire et al. 1994).The material from the first four localities can be securely referred to Chalicomys . The fragmentary remains from Çatakbagyaka (MN7/8) are described as a new subspecies, Trogontherium minutus ozansoyi ( Ünay 1977) , and Ozansoy (1961) described a new species of Dipoides , D.anatolicus from Manisa-Develi (MN13).The unique M3 from Paşalar (MN5; Flynn & Jacobs 1990) was referred to cf. Chalicomys jaegeri because of its relatively large size (5.5 × 5.5, h = 14 mm) and the presence of a long hypostria that ends 5 mm above the base of the crown. Such characters are not sufficient for a reliable identification of the Paşalar castorid. Castor fiber was reported from the Emirkaya 2 fissure filling, correlated to the Middle Pleistocene ( Montuire et al. 1994). The cheek teeth from Küçükçekmece are similar in size and morphology to those of Erenköy, Bayraktepe 1 and Bayraktepe 2. Bayraktepe 1 is correlated to latest middle Miocene (MN7/8) while the others to early late Miocene (MN9/10) ( Ünay 1981; Saraç 2003; Ünay et al. 2003).

According to Hugueney (1999), the earliest occurrence of Chalicomys is at the locality of Riedern in Switzerland, correlated to MN6, and its latest occurrence is at Polgárdi 4 in Hungary correlated to the early part of MN13. However, Mörs & Stefen (2010) noted that occasional occurrence of some characters of Chalicomys jaegeri in individuals of MN5- MN6 beaver populations do not confirm their attribution to Chalicomys . Some individual teeth of S. depereti from Hambach and Eggingen−Mittelhart show an elongated hypostriid and cement filling of synclines. They concluded ( Mörs & Stefen (2010: 196) that “the occasional occurrence of single C. jaegeri features in MN5 populations of S. depereti supports the European lineage from S. depereti to C. jaegeri ”. Chalicomys jaegeri is frequently recorded in European localities with wet environmental conditions dated to the latest middle Miocene and late Miocene, c. between 12-6.5 Ma.

Order LAGOMORPHA Brandt, 1855 Family OCHOTONIDAE Thomas, 1897

Figures

FIG. 3. — Chalicomys jaegeri Kaup, 1832 from Küçükçekmece West.Upper incisors and cheek teeth. A, right P4 (MNHN.F.TRQ829) in occlusal (A), lingual (A’) and labial (A”) views; B, left P4 (TRQ830) in occlusal (B), lingual (B’) and labial (B”) views; C, right P4 (TRQ831) in occlusal (C), lingual (C’) and labial (C”) views; D, left M1 or M2 (TRQ822) in occlusal (D), lingual (D’) and labial (D”) views; E, left M1 or M2 (TRQ819) in occlusal (E) and lingual (E’) views; F, left M1 or M2 (TRQ817) in occlusal (F), lingual (F’) and labial (F”) views; G, left M3 (TRQ834) in occlusal (G) and lingual (G’) views; H, right upper incisor fragment (TRQ791) in lateral view; I, left upper incisor fragment (TRQ801) in lateral view. Scale bar: occlusal view of cheek teeth, 10 mm; lingual and labial views of cheek teeth and incisors, 5 mm.

FIG. 4. — Chalicomys jaegeri Kaup, 1832 from Küçükçekmece West. Lower incisors and cheek teeth. A, left lower incisor fragment in lateral view (MNHN.F.TRQ790); B, right lower incisor fragment in lateral view (TRQ797); C left mandible fragment with p4-m1 (TRQ846) in occlusal (C) and labial (C’) views; D, right p4 (TRQ845) in occlusal (D), labial (D’) and lingual (D”) views; E, left p4 (TRQ813) in occlusal (E), labial (E’) and lingual (E”) views; F, right p4 (TRQ843) in occlusal (F), labial (F’) and lingual (F”) views;G, right mandible fragment with p4 (TRQ864) in occlusal (G), labial (G’) and lingual (G”) views; H, right m1 or m2 (TRQ857) in occlusal (H) and labial (H’) views; I, right m1 or m2 (TRQ855) in occlusal (I), labial (I’) and lingual (I”) views; J, right m3 (TRQ860) in occlusal (J), labial (J’) and lingual (J”) views; K, right m3 (TRQ837) in occlusal (K), labial (K’) and lingual (K”) views.Scale bar:occlusal view of cheek teeth, 10 mm; lingual and labial views of cheek teeth and incisors,5 mm.

FIG. 5. — Chalicomys jaegeri Kaup, 1832 from Küçükçekmece East and an astragalus of Castor fiber for comparison: A, right mandible with p4-m3 in occlusal view, as illustrated by Malik & Nafiz 1933, pl. XII, fig. 8; B, left astragalus (KÇ 118) in dorsal (B1) and plantar (B2) views; C, right astragalus (KÇ 117) in dorsal (C1) and plantar (C2) views; D, right astragalus of extant C. fiber in dorsal (D1) and plantar (D2) views (MNHN.F, no number). Scale bar: 10 mm.