Ursus savini rossicus BORISSIAK , 1930

Spassov, Nikolai, Hristova, Latinka, Ivanova, Stefanka & Georgiev, Ivan, 2017, First Record Of The “ Small Cave Bear ” In Bulgaria And The Taxonomic Status Of Bears Of The Ursus Savini Andrews - Ursus Rossicus Borissiak Group, Fossil Imprint 73 (3 - 4), pp. 275-291 : 276-282

Ursus savini rossicus BORISSIAK, 1930

E m e n d e d d i a g n o s i s.A spelaeoid bear with small sized but very robust skull: extremely short and broad in the zygomatic arches. The skull (especially in males) bulges significantly in the frontal region, and has a relatively high neurocranium. The muzzle is very short. The frontal sinuses extend backward significantly. The occipital is very deep in the area of the external occipital protuberance. The lingual morphology of P4 is simple, the protocone positioned in the central part of the tooth or very slightly further back. The p4 with 2–3 relatively high supplementary cuspids; rear presence of P3 and/or of p1/2. The first lower molar is only slightly constricted in the area between the trigonid and the talonid; its entoconid has 1–3 cuspids in close proximity to each other, their size increases in a backward direction. The mandibular corpus is very deep; the coronoid process of the mandible is vertical.

Description of the Bulgarian bear m a t e r i a l f r o m M i s h i n K a m i k. The MK bone sample exhibits an impressive robustness. All the skulls are from very old individuals, the teeth extremely worn, and canines absent. The skulls are robust and very wide, with massive zygomatic arches ( Tab. 1); with a strongly domed and bilobated frontal portion, especially in males ( Text-fig. 1 ); the temporal crests are prominent and the sagittal crest is deep. In most cases the sagittal crest (as in many other cave bears) seems longitudinally split (or double) because of the not fully fused temporal lines on its dorsal surface from which the crest is formed (Pl. 1, Figs 1–3). The choanae are narrow, the muzzle is rather short, the palate is concave in the area of M2; the nasal aperture is oblique in lateral view; the rostral end of the nasal bones is at the level of the mesial surface of P4. The glabella of the MK specimens is deep – varying from 7.85 to 15.4 mm (11.41 mean).

Two of the skulls (Nos. FM 3111, FM 3385) have a less domed (more oblique) frontal profile, practically without bilobation; frontals with weaker zygomatic processes and respectively a slightly narrower frontal width; weaker sagittal and transversal crests and less pronounced postorbital constriction. One of them (No. FM 3111) is the smallest of all the skulls from this location (Pl. 1, Fig. 3). We consider these two skulls to be from females.

The tooth morphology remains rather unclear due to the degree of wear. Nevertheless, when considering the P4 outlines it is possible to state that the protocone is placed relatively centrally, close to the paracone-metacone border and that the paracone and metacone are in line and not at an angle with respect to each other (Pl. 2, Fig. 6); these features could also be observed in some better preserved isolated teeth. Only one isolated M1 has a preserved occlusal morphology (Pl. 2, Fig. 7). It is archaic, with a limited number of swellings and cusplets, the middle longitudinal valley is narrow, wider only on the talonid. The mesocone is single; the cingulum is developed on the labial side from the protocone to the distal end of the hypocone. Two M2 have a preserved occlusal surface. Each of them has different morphology – one with a more complex morphology and with well-developed cingulum, the other with more simple morphology and without a cingulum (Pl. 2, Figs 8, 9). The hemi-mandibles are well preserved in the MK sample (Pl. 2, Figs 1–5, Tab. 2). Only one hemi-mandible has an alveolus for p2; another has molars only (FM 3331; Pl. 2, Fig. 3), p4 is not developed at all, and this must be an anomaly. Some of the hemi-mandibles have a preserved p4 and it is possible to observe its morphology (Pl. 2, Figs 11a–15b). All of the specimens have a paraconid and metaconid more or less of a similar size, situated close to each other. In some cases, there is an additional cuspid of the same size behind them, and all p4 have smaller additional cusplets (morphotypes D2, D2/D3 after Rabeder 1989, Rabeder and Tsoukala 1990). The rather simple m1 morphology is without constriction between the talonid and the trigonid and with relatively more archaic entoconid (Pl. 2, Fig. 10). On the mandibles the preserved m1 are excessively worn, but in all cases the archaic outline is clearly visible. For all teeth measurements see Table 3.

The postcranials are also robust (Pl. 4, Figs 1–9, Tabs 4 –8). The lateral epicondyle of the humerus is enlarged, the lateral condyle of the femur distally protruding, the distal segments of the limbs (ulna, radius and especially the tibia) very shortened. The postcranials of males and females could be distinguished because of the different sizes.

Comparison of the Bulgarian bear material from Mishin Kamik

Compared to Ursus arctos , the MK bear differs in the robustness of the skull, by the completely different proportions, by the strongly domed frontals, the massive zygomatic arches and the better developped temporal crests, the larger muzzle with very wide surface for the incisors, much deeper palatal bone; visibly narrower choanae, the more complex cheek teeth morphology, absence of upper and lower anterior premolars (they very rarely persist, and are reduced in size). The nasal aperture is more oblique in lateral view and the nasal bones are more caudally situated: their rostral end is at the level of the mesial surface of P4 (in U. arctos it is normally at the level between I3 and C1). The postcranial elements are also more robust, the distal segments of the limbs are significantly shortened.

The noted features, as well as the extremely speleoid morphology of p4 (see Wagner and Čermák 2012) separate the bears from Mishin Kamik from the arctoid lineage and place them in the cave bear lineage.

The tooth morphology demonstrates a number of archaic features (see description). In this respect the Mishin Kamik bear is more similar to U. deningeri than to the large and more evolved cave bears from the U. spelaeus-U. ingressus group. This similarity is expressed also by the more or less similar size (length) of the skulls of some U. deningeri populations (SH and PTR for example) ( Text-figs 2–4 ); the mean glabella depth is similar to that of U. deningeri from SH and PTR ( García et al. 2007, Santos et. al. 2014). A comparison with U. deningeri suessenbornensis (considered by some authors, especially in older works, as a separate species) is practically impossible, as the type material is extremely scarce (see Baryshnikov 2007).

180 300 350 400 450 500

Condylobasal length

300 350 400 450 500 Condylobasal length

On the other hand the skull shape and proportions differs from U. deningeri s. str. from the early Middle Pleistocene. In

general, U. deningeri has a less wide (with some exceptions) skull ( Text-fig. 2 ). The MK bear has abruptly and strongly

elevated frontals and demonstrates the evolved profile of the U. spelaeus-U. ingressus group: The stepped forehead

forms a well developed dome, with a slight depression on the

parasagittal line. The CT scan comparison (Pl. 3) revealed

several specific profile peculiarities of the Mishin Kamik

skulls (Pl. 3, Figs 3, 4), the features and the intraspecific

variability in the development of the frontal sinuses as well

as the thickness of the skull bones. The sinuses are large, they

significantly extend backward and may occupy more than half

of the brain cavity to about 2/3 of its length (Pl. 3, Figs 3,

4). The occipital region in the area of the external occipital protuberance is very thick. In this respect the MK skulls show similarity with the scanned specimens of U. spelaeus from Spain ( García et al. 2006, 2007, Santos et al. 2014) (Pl. 3, Figs 1, 2). The basioccipital is also thick (7.6 mm and 8.1 mm respectively) and most probably pneumatized as in U. spelaeus . In spite of its clearly smaller size, in width the MK skulls may measure the same or even exceed the relative width of the skulls of the U. spelaeus-ingressus gr. On the other hand their tooth morphology is less evolved (see description).

Comparison with U. spelaeus ladinicus RABEDER et al., 2004

The skull of this small, high alpine cave bear U. s. ladinicus or U. ladinicus from Conturines cave, is similar in skull size ( Rabeder et al. 2004) to the MK bears. But all other proportions are clearly different: the zygomatic width is much larger in the MK sample, while the check teeth length is shorter ( Text-figs 2 , 4 ) and the mandibles are deeper ( Text-fig. 5 ).

Comparison with Ursus deningeroides MOTTL, 1964 and other taxa from large cave bear group

This bear from the Repolust cave in Austria was described by Mottl (1964) as a very primitive and small U. spelaeus . The locality is from the late Middle Pleistocene, with an estimated age of about 200 ka (ca. 223 ka for the lowermost level) ( Döppes and Rosendahl 2009). The skulls are considerably larger and relatively narrower than in the MK bears ( Text-fig. 6a ). They are however as significantly

70 300 350 400 450 500 550 Maximal SNƲOO length

U. spelaeus ZLH U. deningeri PTR Regression line

U. s. ladinicus CT U. sa. rossicus KRD U.spelaeus ZLH U. deningeri MOS U. spelaeus PTR U. sa. rossicus MK U.spelaeus PTR U. sa. rossicus KRD MK

230 250 270 290 310 330 350 Maximal mandibular length

domed as in MK, but with a clearly slanting caudally neurocranial profile (see Mottl 1964: pl. 2, fig. 1 and pl. 3, fig. 1). The muzzles are longer in general ( Text-fig. 6b ). About 60% of specimens retain anterior premolars (P3/p3 and P1–2/p1–2) and m1 is to some degree more archaic than in MK. The mandible length of the Repolust cave bears are between 245–313 mm, and the depth under p4 varies from 50–71 mm. The MK mandibles are shorter (with maximal value 294 mm), while the depth under p4 varies from 54.29– 71.7 mm, indicating a greater depth. The mandible depth between m2 and m3 is also greater in MK – 64–78 versus 50–75 mm for the Repolust cave bears.

A cave bear of small size is described from Einhornhöhle (Middle Pleistocene, Germany). There are only mandibles, no skulls are preserved ( Schütt 1968); the p4 and m1 morphology is similar to that in the MK sample. The main difference in m1 morphology is the more complex metaconid and more acute paraconid in MK (sensu Grandal d’Angle and López-González 2004). The MK mandibles (with maximal length from 240 to 294 mm and mean value 269 mm) are smaller on the whole in relation to the Einhornhöhle specimens (260–319 mm, mean 280 mm). At the same time they are deeper: the depth under p4 varies from 54.29 to 71.7 mm (mean 62.8 mm) for MK and for the Einhornhöhle bears from 46 to 75 mm (mean 58 mm).

A small cave bear ( Ursus spelaeus parvilatipedis TORRES, 1991 ) was described from the Late Pleistocene of Troskaeta cave, Spain ( Torres et al. 1991). The mean value for the maximal mandibular length is 280.9 mm vs. mean

270

260

width 250

Zygomatic 240

230

220 300 320 340 360 380 400 a Basilar legnth

190

180

170 length 160

Rostral 150 140

130

120 300 320 340 360 380 400 b Basilar length

value of the height behind m 1 – 65.2 mm. These mean values are similar in size to the MK bears (267 mm vs. 63 mm respectively), but more data are necessary for a reliable comparison and conclusions.

In comparison with Ursus kudarensis praekudarensis ( BARYSHNIKOV, 1998) from the Middle Pleistocene of the Southern Caucasus ( Baryshnikov 1998), the skulls from MK are smaller ( Text-figs 3 , 4 ), but their teeth morphology is more complicated; in U. d. praekudarensis p4 are narrower and more archaic; the m1 is also more archaic.

Ursus kudarensis kudarensis BARYSHNIKOV, 1985 from the Late Pleistocene (see Baryshnikov 1998) exhibit significantly larger skulls than those in the MK sample ( Text-figs 1–3 ), but the teeth (P4, p4, m1) have a number of similarities (protocone on P4 is placed more mesially; developed paraconid and metaconids on p4, see in Kudaro III, layer 3–4; in m1, the junction between the trigonid and talonid is equal or slightly wider than the width of the trigonid, the metaconid is separated on two or more denticles, the entoconid consists of two or three cusps). Some DNA investigations put this bear phylogenetically somewhat apart from the clades of U. deningeri VON REICHENAU, 1904 and U. ingressus-U. spelaeus (see Knapp et al. 2009, Dabney et al. 2013).

Comparison with Ursus rossicus BORISSIAK, 1930

The bear from MK is very similar to Ursus rossicus (U. sa. rossicus ) from the type locality, Krasnodar ( Borissiak 1930, 1932), with a probable age at the very end of the

85 290 340 390 440 490 Maximal length

width

Distal

30 250 300 350 400 450 Maximal length 200 220 240 260 280 300 320 340 360 Maximal length

Middle Pleistocene or the Eemian ( Baryshnikov 2007). The skulls from Krasnodar are robust, clearly domed ( Borissiak 1932, Baryshnikov 2007) and similar to the MK bear in proportions. Their zygomatic width is large, similar to the sample from MK ( Text-fig. 2 ). On P4 the protocone is in a central position between the labial cusps, but the tooth is to some extent more evolved than in U. deningeri , as it also seems to be in the MK sample. The lower teeth morphology are also similar: p4 has a well-developed paraconid and metaconid, and many additional cusplets; m1 is archaic with a very weak constriction only at the middle part. The postcranials are smaller, about the size of the female specimens from MK ( Text-figs 8–10 ). Some small differences could however be seen: the upper cheek teeth row is shorter ( Text-fig. 3 ). The mandibles have a slightly shorter depth than in the MK sample but the sample of U. sa. rossicus is very limited in number ( Text-fig. 6 ).

Comparison with U. savini ANDREWS, 1922 from Bacton

Wagner and Čermák (2012) include in U. savini only the specimens from Bacton s. str. (Forest Bed locality). The exact provenance of the only known skull is unclear. The size and proportions of the MK sample compared to the Bacton mandibular material are very similar ( Text-fig. 10 ), while some differences exist in the tooth morphology. In the MK sample the p4 morphology is more evolved to some extent, with a well-developed metaconid and paraconid and with many additional cusplets and swellings; m1 is similar in morphology, but with a better developed enthypoconid (sensu Rabeder 1999) and with more cusplets on the talonid. The only known skull from Bacton is a larger size (maximal length is 432 mm) and has a relatively short cheek teeth row in relation to its size, but the absolute length of the cheek teeth row (length of 82.3 mm) (M. Pacher, pers. comm. in 2017) is comparable to that in the specimens from MK. It is difficult to say without more data if this skull belongs to a different species ( U. deningeri (?)) or to U. savini from the type locality. It is noteworthy, however, that the specimen had a short muzzle (considering the photo kindly sent by A. Stewart) and strongly domed frontals, which is not

diastema

the

at

Height

130 150 170 190 c1 - m3 length

Regression line 160 170 180 190 200 210 Palatal length

typical for U. deningeri , especially at such an early stage in evolution of this species.

Comparison with U. “ rossicus ” uralensis VERESHCHAGIN, 1973 from Kizel cave

The small bear from Kizel cave (Ural, Russia) has several significant similarities in skull size and proportions to the MK bear, as well as to the typical U. sa. rossicus from Krasnodar ( Text-figs 2 , 3 ; see also: Vereshchagin and Baryshnikov 2000, Baryshnikov 2007). The metric comparison (Textfig. 11; for comparison see also the photos in Vereshchagin 1973: fig. 9) shows however, that U. sa. rossicus has a wider skull, and in particular the muzzle, and that in this respect U. uralensis is similar to some extend, in our opinion, to the large cave bears of the U. spelaeus-kanivetz / ingressus group. The bear from Kizel is rather young in geologic age (around 40 000 B.P.). After several opinions it seems to be genetically related more or less to U. ingressus ( Pacher et al. 2009, Stiller et al. 2014), but new palaeogenomic data are in contradiction with this view ( Barlow 2017).

Figures

Text-fig. 1. Restoration of living appearance of U. sa. rossicus based on the fossil material from Mishin Kamik cave. Drawing by Assen Ignatov.

Text-fig. 2. Scatter diagram: condylobasal length vs. zygomatic width in skulls of different cave bear taxa. Data after Rabeder et al. 2004, Baryshnikov 2007, Santos et al. 2014.

Text-fig. 3. Scatter diagram: condylobasal length vs. length of rostrum in skulls of different cave bear taxa. Data after Baryshnikov 2007, Santos et al. 2014.

Text-fig. 4. Scatter diagram: maximal skull length vs. P4 – M2 length in skulls of different cave bear taxa. Data after Zapfe 1948, Rabeder et al. 2004, Baryshnikov 2007, Pacher (pers. comm. in 2017).

Text-fig. 5. Scatter diagram: maximal mandibular length vs. height behind m1 in different cave bear taxa. Data after Rabeder et al. 2004, Baryshnikov 2007, Baryshnikov and Tsoukala 2010.

Text-fig. 6. Scatter diagrams: a) basilar length vs. zygomatic width in skulls of U. deningeroides RH and U. sa. rossicus MK. b) basilar length vs. rostral length in skulls of U. deningeroides RH and U. sa. rossicus MK. Data after Mottl 1964 and personal observations.

Text-fig. 8. Scatter diagram: maximal length vs. distal width of ulnae in different cave bear taxa. Data after Borissiak 1932, Nagel et al. 2005, Athen 2007, Baryshnikov and Tsoukala 2010.

Text-fig. 9. Scatter diagram: maximal length vs. distal width of tibiae in different cave bear taxa. Data after Borissiak 1932, Nagel et al. 2005, Athen 2007, Baryshnikov and Tsoukala 2010.

Text-fig. 10. Scatter diagram: c1 – m3 length vs. height of mandibles in front of p4 in different cave bear taxa. Data after Baryshnikov 2007, Sher et al. 2011.