Badania nad niedźwiedziami plioceńskimi

• Autorzy: Ryziewicz Z.

Warianty tytułu

EN

Studies on Pliocene bears

RU

Issledowanija pliocenovykh medvedejj

• Języki publikacji: PL

Abstrakty

PL

W pracy przedstawiono opis czaszki Ursus wenzensis Stach i porównano ją z czaszkami U. arctos L., U. (Thalarctos) maritimus Phipps i U. etruscus Cuv. Zbadano rozwój żuchw i ich uzębienia u osobników młodocianych i porównano je z żuchwami osobników dorosłych i ich uzębieniem. Przeanalizowano uzębienie U. wenzensis Stach i U. boeckhi Schlosser i porównano je z uzębieniem innych niedźwiedzi kopalnych (U. ruscinensis Deperet, U. arvernensis Cr. & J., U. etruscus Cuv., U. (Plionarctos) stehlini Kretzoi) oraz współczesnych (U. (Helarctos) malayanus Raffles i in.). W rezultacie tych badań autor doszedł do wniosku, że U. boeckhi Schlosser i U. ruscinensis Depéret są najpierwotniejszymi przedstawicielami plioceńskich niedźwiedzi rodzaju Ursus. Pochodzą one przypuszczalnie od wspólnego przodka, którym prawdopodobnie był Ursavus brevirhinus Hofmann, wykazują jednak różne kierunki zmienności, mimo że znajdują się na jednakowym szczeblu ewolucyjnym. Potomkiem U. boeckhi Schlosser jest przypuszczalnie U. wenzensis Stach, który spośród niedźwiedzi współczesnych pod względem uzębienia nawiązuje najbardziej do U. (Helarctos) malayanus Raffles. U. wenzensis Stach znajduje się na tym samym szczeblu ewolucyjnym, co U. etruscus Cuv. czy U. arvernensis Cr. & J., lecz gatunki te realizują inne kierunki rozwojowe.

EN

Previous studies (Stach, 1953) on Ursus wenzensis Stach from bone breccia of Węże near Działoszyn were based on a scanty material (a crushed skull of a young individual and a few teeth). A further preparation of the breccia supplied a rich material consisting of an almost complete skull of an adult individual, a cranium, a dozen or so lower jaws with teeth and some scores of detached teeth. Ursus boeckhi Schlosser from Barót-Köpec, described by Schlosser (1899), and another, more abundant material (two halves of upper jaws with a complete dentition, part of a lower jaw with molars and a few detached teeth) of this species, described by Maier v. Mayerfels (1928), were not exhaustively characterized. Consequently, both bears were, despite a difference in geological age, i. e. U. wenzensis Stach - Upper Pliocene, and U. boeckhi Schlosser - Middle Pliocene (Lower Levant), erroneously assigned (for instance, by Thenius, 1959) to the same species. The present writer’s study of the remaine of both bears has allowed him to show beyond doubt that these were two different species. The following results were obtained by the studies of skulls of U. wenzensis, i.e. both the holotype described by Stach (1953) and a complete skull of the cotype, as well as by comparing them with the skulls of Recent bears U. arctos L. and U. (Thalarctos) maritimus Phipps. The dimensions of the skull of U. wenzensis are contained within the range of variability of the skulls of U. arctos. The studies on the shape of the skull of U. wenzensis have shown that although it is somewhat similar to the skull of U. arctos, at the same time it also displays many differences. These differences are particularly great as compared with U. (Thalarctos) maritimus. In these comparisons, the present writer took into account not only an absolute magnitude of measurements, but also and primarily their ratio to the length of the cranium base (basion-prosthion). In front (over M¹), the face in U. wenzensis is narrower than in U. arctos, but somewhat higher, whereas in the orbital and postorbital regions it is much the same in height but wider. The cranium is identical in width but lower. On the other hand, the profile of the skull is different from that in U. arctos, but similar to that in U. etruscus Cuv. As regards the proportions of the cranium to the face, the cranium in U. wenzensis is somewhat longer (54.9 mm) than in U. arctos (51.3 and 51.0 mm), but shorter than in U. (Thalarctos) maritimus (58.0 and 58.8), and the facial part in U. wenzensis is shorter (45.0) than in U. arctos (48.7 and 49.0), but longer than in U. (Thalarctos) maritimus (42.7 and 41.5). The palate of U. wenzensis is somewhat longer. The length of the P⁴-M² tooth row, as compared with the basal length of the skull is smaller (21.6) than in U. arctos (24.3 and 23.5), but larger than in U. (Thalarctos) maritimus (18.3 and 18.6). In U. wenzensis, the occipital surface is relatively smaller than in U. arctos, i.e. lower (24.5; in U. arctos 32.2 and 29.4) and narrower (spacing of processus mastoidei 45.8, of processus jugulares 31.9, and of condyli occipitales 20.5, in U. arctos respectively: 59.9 and 48.1; 38.8 and 33.5; 22.0 and 24.2). Comparison of skulls of V. wenzensis, U. etruscus and U. arctos The skull of U. etruscus is larger than averagely large skulls of Recent U. arctos (although it does not equal in size the skulls of subfossil individuals) and much larger than that of U. wenzensis. In shape, width and height its skull is more similar to that of U. arctos than that of U. wenzensis. On the other hand, the length of cranium (in relation to the total length of the skull, i.e. acrocranion-prosthion) in U. etruscus is somewhat larger (58.1) than in U. arctos (57.8 and 54.6) and almost identical with that of U. wenzensis (58.1 in cotype and 56.7 in holotype), whereas the face is somewhat shorter (48.0) than in U. arctos (48.3 and 52.9) and in U. wenzensis (50.5 and 47.8). In this respect, the skull of U. etruscus is more similar to that of U. wenzensis than that of U. arctos. Likewise, its profile is also more similar to that in U. wenzensis. Dentition The most characteristic teeth with best marked primitive features (or more or less specialized characters) were taken into account for the purposes of comparison. This allows one to ascertain an approximate level of their evolutionary development. Carnassial teeth P⁴ and M₁, as well as M² are such teeth. Characteristic are also the P⁴/M² and M₁/M₂ ratios, as well as a percentage of length of individual teeth in the row of teeth, both upper and lower. In P⁴, primitive characters are: 1) a relatively larger length of a carnassial tooth as compared with the length of this tooth in other species and as compared with other teeth, primarily with M²; 2) a situation of deuterocone in relation to para- and metacone; the situation of deuterocone before an incision which separates these cusps, or in front of such incision is a primitive character, whereas a more posterior situation of deuterocone is a specialized character; 3) a lack of accessory cusps. In M², shorter and wider teeth are more primitive. In M₁: 1) the most important is the development of metaconide, i.e. a metaconide in the form of a single small and pointed cone without accessory cusps is more primitive, whereas a laterally flattened metaconide with accessory cusps indicates specialization; 2) a tooth, whose talonid is less widened than trigonid, is more primitive. In addition, a higher degree of primitivity is shown in all teeth by: 1) pointed, conical cusps without accessory cusps, and 2) corrugated enamel. Comparison of dentition in U. wenzensis and in other bears (Tables 21-24) 1) In addition to a certain similarity to U. wenzensis, U. boeckhi Schlosser displays fundamental differences. The upper and lower canine teeth of U. boeckhi are much more powerful and flattened, whereas three crests on enamel, running from the apex, are distributed in a much the same way. All the three premolars (P¹-P³ and P₁-P₃) occur in both species, but P¹ and P₁ are the largest (in U. boeckhi lower premolars are unknown). P⁴ displays considerable differences. In U. boeckhi it is larger, i.e. relatively longer (26.0, as opposed to 23.6) and slightly wider (67.7 to 66.6). Deuterocone is situated before the incision separating para- from metaconid. In U. wenzensis, these proportions are not settled, but on the whole they are similar. In U. boeckhi, M² is shorter (41.7) and wider (64.8) and in U. wenzensis resp. 43.8 and 57.2. In U. boeckhi, M₁ has metaconide in the form of a single, small, pointed cone which looks as if it was mounted on the internal slope of protoconide and somewhat posteriorly of its apex, whereas in U. wenzensis metaconide is slightly larger, laterally flattened and has accessory cusps. In U. boeckhi, however, the tooth itself is posteriorly more strongly widened than in U. wenzensis, which represents a certain specialization. The P⁴/M² index of length also differs in the species compared. In U. boeckhi it amounts to 62.4 and in U. wenzensis to 54.3; the M²/M¹ index amounts in the former to 128.6 and in the latter to 134.7. A certain regularity is observed in all bears, both fossil and Recent ones. The shortening of P⁴ in the P⁴-M² tooth row is accompanied by the extension and narrowing of M² (Text-fig. 21, Table 20). This phenomenon makes up a certain trend in evolutionary changes which, in bears, are related with passing from predominant carnivorousness to omnivorousness with a steadily increasing predominance of herbivorousness. These changes probably occur in different species of bears in different time and to a varying extent. 2) Ursus ruscinensis Depéret: only its lower jaw with teeth are known. The most characteristic is M₁ whose metaconide occurs in the form of a single, small, conical cusp, similar to that in U. boeckhi. This indicates that U. ruscinensis has reached a similar evolutionary level as that of U. boeckhi and, therefore, is more primitive than U. wenzensis. This is in conformity with the time of occurrence. U. ruscinensis, the same as U. boeckhi, is a Middle Pliocene animal. In addition, in U. ruscinensis M₁ is wider (52.1) than in U. wenzensis (43.8), but not so strongly extended posteriorly (52.1-45.8 = 6.3; Table 23) as M₁ in U. wenzensis (43.8-36.9 = 6.9). The absolute length of teeth is larger and, as regards their length as a percentage, M₁ is shorter (37.2 as compared with 38.6) and M₂ much longer (28.7 as compared with 25.4). The M₁/M₂ index is also larger (109.1 as compared with 107.3 in XJ. wenzensis). 3) U. arvernensis has, on the whole, both upper (P⁴, M¹ and M²) and lower (M₁, M₂, M₃) teeth slightly longer, as expressed in absolute measurements, whereas their width is different: P⁴ is slightly narrower (62.3 as compared with 66.6 in U. wenzensis), M¹ and M² are similar in width and lower teeth are wider (M₁ = 51.3 as compared with 43.8, and M₂ = 81.7 as compared with 75.8). M₁, a lower carnassial tooth, has metaconide with an accessory cusp and, therefore, its level of evolution is similar to that in U. wenzensis. Talonid is slightly more extended (7.1 as compared with 6.9). The P⁴/M² index is slightly lower (53.2 as compared to 54.3) and the M₁/M₂ index slightly higher (109.9 as compared with 107.3). 4) U. etruscus has both upper and lower teeth much more powerful. It is revealed by the percentage ratio of lengths that if P⁴ is almost equal in length (23.8 as compared with 23.6), M² is much longer (45.0 as compared with 43.8) and the P⁴/M² ratio amounts to 53.1 (in U. wenzensis 54.3). Lower teeth display similar ratios: M₁ is slightly shorter, M₂ almost identical in length and M₃ is longer. The M₁/M₂ ratio = 103.8. In U. etruscus M₁ has a metaconide consisting of two cusps and, therefore, its level of evolution is identical with that of U. wenzensis and U. arvernensis. The posterior extension of M₁ is much stronger (10.0 as compared with 6.9 in U. wenzensis). The remark occurs that U. etruscus, U. arvernensis and U. wenzensis make up a group of very similar bears which, however, belong to different species with different trends in their evolutionary variability. 5) U. (Plionarctos) stehlini Kretzoi has lower canine teeth smaller than those in U. wenzensis. Its P₄ is somewhat longer (11.3) and thicker (55.6), M₁ shorter (20.3) and wider (46.5) and the tooth itself is posteriorly much less extended (46.5-40.5 = 6.0). Metaconide has two cusps. The percentage ratio of length indicates a strongly specialized type with a much shorter M₁ (35.7), much longer M₃ (28.2) and the M₁/M₂ index amounting to 99. U. (Plionarctos) stehlini is at the same evolutionary level as U. wenzensis, but is much more specialized than the latter species. 6) Of all Recent bears, U. (Helarctos) malayanus Raffles is to the greatest extent similar in dentition to U. wenzensis. It is marked by powerful upper and lower canine teeth, equal to or even larger than those in U. wenzensis, but less flattened. All other teeth are much smaller (shorter), but wider. As regards the percentage ratio of length of particular teeth in the upper and lower row, they are very similar to the teeth of U. wenzensis (see table below), but more primitive. The upper carnassial tooth has a deuterocone, which mostly is vestigial and, even if more strongly developed, it is situated opposite the incision, separating the para- from metacone, or slightly more anteriorly. As regards percentage, M₁ is identical in length, extends more strongly (8.9) than M₁ of U. wenzensis (6.9) and its metaconide consists of two almost identical cusps or, sometimes, may be also single. U. (Helarctos) malayanus displays several characters which are more archaic than those in U. wenzensis but, at the same time, it is more specialized than the latter species. These two species of bears are much more closely related to each other than to any other Recent bears. Comparison of U. boeckhi with other species of bears 1) U. ruscinensis was probably much bigger than U. boeckhi as indicated by the length of the mandibulary tooth row (M₁-M₂ in U. ruscinensis - 64.5, in U. boeckhi - 52.8). However, the percentage ratio of their length shows a less primitive character of their dentition, M₁ (37.2) and M₂ (34.1) being shorter and M₃ (28.7) much longer. On the other hand, the M₁/M₂ index is higher (109.1) than that in U. wenzensis (107.3). As compared with their length, all teeth are wider, except for M₃ which is narrower (70.3). The posterior extension of M₁ is much smaller (6.3) and the structure of metaconide, a small, single cusp, is similar. On the basis of these facts, we may assume that U. ruscinensis is at the same evolutionary level as U. boeckhi, but display a somewhat different trend in specialization. It is quite likely that both these species derive from a common ancestor which was Ursavus brevirhinus Hofmann. 2) Of two species of bears, U. ruscinensis and U. pyrenaicus described by Depéret (1890, 1892), the latter was considered by Thenius (1947, 1958) as identical with U. boeckhi. Erdbrink (1953) erroneously believed U. boeckhi to be a synonym of U. ruscinensis. The present writer inclines to agree with his view but only as regards the upper jaw dentition. The mandible did not belong to the same individual and, moreover, we may even doubt if it belong to the same species. The differences in the absolute size are probably contained within the range of the ontogenetic variability: 3) U. arvernensis differs from U. wenzensis in both its upper and lower dentition: its P⁴ being relatively much shorter (24.2) and M² much longer (45.4). M₁ has a metaconide consisting of two cusps like that in U. etruscus. 4) The present author does not agree with the view of Thenius (1947), who believed that the M₁ tooth, found in Liang-chia-ho (Shansi), belonged to the U. sinomalayanus species, erected by him, but agrees with Zdansky (1927) who determined this tooth as that of U. cf. boeckhi. Comparison of skulls of U. wenzensis, U. etruscus and U. arctos As results from this comparison, the skull of U. etruscus is much the same in size as those of large U. arctos, while the skull of U. wenzensis is much smaller. Although the face of U. etruscus is more similar to that of U. arctos, than to that of U. wenzensis, the percentage ratio of length of the cranium and the face (i.e. to the total length of the skull), as well as the profile of the skull in U. etruscus are, however, more similar to those in U. wenzensis. Likewise, the ratio of the length of the P⁴-M² tooth row to the total length of the skull is also more similar to that in U. wenzensis, than to that in U. arctos. Although the absolute dimensions of the upper dentition in U. etruscus are larger (teeth are longer and wider), but the percentage size of individual teeth in the row, despite certain differences, differs to a smaller extent from those in U. wenzensis, than from those in U. arctos. This is also true of the M²/P⁴ index and of the lower teeth (Tables 21-24). Because of these facts, the present writer believes that U. etruscus is more similar to U. wenzensis than to U. arctos both in the structure of the skull and in dentition, and should be placed in a similar stage of evolutionary changes. The differences displayed by these species are, however, sufficiently important as to prevent the identification of U. etruscus with U. wenzensis. On the other hand, these differences are smaller than those occurring between U. wenzensis and U. boeckhi.

RU

В настоящей работе представлено строение черепа Ursus wenzensis Stach и проведено его сравнение с черепами современных медведей: U. arctos L. и U. (Thalarctos) martimus Phipps и ископаемого U. etruscus Cuv. Отмечены сходство и различия на основании измерений и коэффициентов. Череп U. wenzensis имеет некоторое сходство с U. etruscus и U. arctos, однако череп U. etruscus более сходен с U. arctos. В дальнейшем автором представлены описание морфологии и абсолютные размеры отдельных зубов U. wenzensis и U. boeckhi Schlosser, а также их относительная длина в ряду. При анализе строения зубной системы приняты во внимание, главным образом, верхние и нижние хищные зубы: в верхних хищных Р⁴ расположение деутерокона по отношению к пара- и метакону в нижних хищных зубах М₁ строение метаконида и степень расширения коронки в заднем направлении. Автор сравнивает размеры зубной системы этих двух медведей с другими ископаемыми (U. ruscinensis Dep., U. arvernensis Cr. & J., U. etruscus Cuv., U. (Plionarctos stehlini Kretzoi) и современными медведями (U. (Helarctos) malayanus Raffles, U. (Thalarctos) maritimus Phipps, U. (Selenarctos) thibetanus Cuv., U. arctos L.). На основании проведенного анализа автор пришел к выводу, что U. boeckhi является представителем очень примитивных медведей, эволюционный уровень которого такой же, как у U. ruscinensis, особенно в отношении строения верхнего хищного зуба Р⁴ и метаконида в нижнем хищном зубе М₁, который у этих двух видов является единичным бугорком. Разница в длине зубов также свидетельствует о том, что U. ruscinensis был более приспособлен к всеядности. Предполагается, что зубная система верхней челюсти U. „pyrenaicus” Dep. очень сходна с таковой у U. boeckhi, так что обе формы можно считать конспецифичными. Однако можно принять, что U. wenzensis, в отношении степени эволюционного развития, близок к U. arvernensis и U. etruscus (метаконид нижнего хищного зуба построен из главного и добавочных бугорков, M₁ тоже расширенный в заднем направлении), но это иные направления эволюции. То самое относится к U. (Plionarctos) stehlini. Среди современных медведей более тесную связь с U. wenzensis обнаруживает U. (Helarctos) malayanus, но это тоже иной тип специализации.

Słowa kluczowe

PL

paleontologia; pliocen; niedzwiedzie; czaszka; Ursus wenzensis; uzebienie; zuchwa; analiza porownawcza; Ursus arctos; Ursus ruscinensis; Ursus brevirhinus; Ursus boeckhi

• Wydawca: -
• Czasopismo: Acta Palaeontologica Polonica
• Rocznik: 1969
• Tom: 14
• Numer: 2
• Opis fizyczny: s.199-243,rys.,tab.,fot.,bibliogr.

Twórcy

autor

Ryziewicz Z.

Bibliografia

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