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Body mass estimation in amphicyonid carnivoran mammals: A multiple regression approach from skull & skeleton.; Figueirido; et al. (2011). Acta Palaeontologica Polonica. 56 (2): 225–246. doi:10.4202/app.2010.0005
Topic Started: Jan 21 2017, 03:00 PM (718 Views)
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Journal Reference:
Figueirido; et al. (2011). "Body mass estimation in amphicyonid carnivoran mammals: A multiple regression approach from the skull and skeleton." (PDF). Acta Palaeontologica Polonica. 56 (2): 225–246. doi:10.4202/app.2010.0005

ABSTRACT
The body masses of sixteen species of amphicyonids (Mammalia, Carnivora, Amphicyonidae) from the New and Old World were estimated on the basis of 86 osteological variables measured from the craniodental (N = 44) and postcranial (N = 42) skeleton of living species of Canidae and Ursidae. Given the absence of complete and well preserved skeletons of amphicyonids in the fossil record, multiple regression functions were derived separately from measurements taken from the mandible, the cranium and the major limb bones. The accuracy of the regression functions was evaluated using the percentage prediction error and the percentage standard error of the estimates. Mass values were calculated with these equations using measurements taken in adult individuals from a number of daphoenine and amphicyonine species. Results obtained show that three distinct size classes of amphicyonids emerged through the evolutionary history of the “beardog” family and that these size classes correlate with presumably different ecomorphs. Quantitative estimates of body size of amphicyonids are critical for deciphering the paleobiology of this poorly understood family of large fissiped carnivorans and can be used for placing it within a broader ecological context.




Body mass estimates for amphicyonids.

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We calculated the mass of the giant beardog Amphicyon ingens as ca. 547 kg, which is in accordance with previous estimates obtained by Sorkin (2006), who provided a figure of ca. 550 kg based on the proportions of the femur. It is worth noting that this value is intermediate between those obtained with the functions derived by Van Valkenburgh (1990) and Anyonge (1993) for the craniodental and postcranial skeleton (706 and 378 kg, respectively; see Table 6). This result indicates that, along with the Pleistocene lion Panthera atrox, the Kodiak Island Ursus arctos, the Mio−Pliocene Agriotherium and the Pleistocene Arctodus simus (a species that is hypothesized to have behaved more as an omnivore than as an active predator, Figueirido et al. 2010), A. ingens was one of the largest mammalian carnivores ever known. In fact, the body masses of these three species are probably close to the upper limit for a mammalian terrestrial predator (Carbone et al. 2007).
The other North American species of Amphicyon included in the analysis are clearly smaller than A. ingens. Specifically, the mass of A. galushai was calculated at ca. 187 kg, a value which clearly agrees with the ones obtained with the functions of Van Valkenburgh (1990) and Anyonge (1993), and the estimate for A. frendens was ca. 432 kg. These values reach the size of a grizzly bear and a Polar Bear, respectively. The few remains of the European A. major analyzed in this study provide lower mass estimates (ca. 223 kg) than those obtained from the New World specimens.
Concerning North American Pseudocyon sp., the only material included in this paper consists of two mandibles and a cranium from different individuals collected from different sites. The mass estimate derived from a mandible collected from the Santa Fe Group (New Mexico) was ca. 773 kg. This mandible (F:AM 49247) is of medial Barstovian age and clearly represents a very large individual of Pseudocyon. However, the mass estimate for another mandible (F:AM54209) is ca. 370 kg, a figure in agreement with the one provided by a skull of ca. 396 kg (F:AM 25144), both remains collected from the early Clarendonian of Nebraska. It is also worth noting that the mass estimate obtained with the function of Van Valkenburgh (1990) for the specimen F:AM 25144 is 331 kg, a value in agreement with our results. Also, the mass of Pseudocyon sansaniensis from Europe (ca. 245 kg) is close to the estimate derived from the North American specimens. These different body mass estimations of Pseudocyon could be attributed to a marked sexual dimorphism in this extinct species, because the fossils most probably represent a single lineage.
We calculated the mass of the beardog Ysengrinia americana as ca. 173 kg, but the mass obtained from the best individual function estimate (BIFE, derived from the diameter of the femur at the midshaft) yields a higher estimate (ca. 231kg). In fact, a broad range in the estimates derived from postcranial bones occurs for this species (Table 6). The variability in the masses obtained for Y. americana may result from several biases which are difficult to avoid in those extinct species with no living analogues (e.g., amphicyonids). Such biases may arise from anatomical differences related to inter or intrapopulational variation (e.g., sexual dimorphism and ecogeographic variations). The postcranial bones of Y. americana included in the database belong to a number of individuals of early Miocene age (late Arikareean, North American Land Mammal Ages) that were preserved together in a waterhole at Harper Quarry, Sioux County, Nebraska (USA). However, it is clear that the geometric mean of the mass estimates for Y. americana lies within the range of values (145–211 kg) obtained with the functions of Van Valkenburgh (1990) and Anyonge (1993). A similarly−sized beardog was Pliocyon medius, with a mean mass estimated at ca. 128 kg (ca. 145 kg with the function of Van Valkenburgh 1990).
The mass of Ischyrocyon gidleyi was estimated at ca. 235 kg for the Barstovian specimens and ca. 546 kg for the individuals from the Clarendonian. Despite this divergence in body size, I. gidleyi apparently represents a single lineage during its time span (14–9 Ma) and could be split into two species, one comprising the smaller forms of the Barstow (California) and Valentine Formations (Nebraska), and the other the huge individuals from the Clarendon Beds (Texas). In any case, a systematic revision of the genus is necessary for corroborating such a possibility.
Our results show that Daphoenodon contains mid−sized to large amphicyonids, represented in this work by three North American species: D. skinneri, D. falkenbachi, and D. neomexicanus. Among them, D. skinneri was estimated to be the smallest, with a mass of ca. 40 kg (derived from the regression function adjusted with the variables of the mandible), whereas D. neomexicanus and D. falkenbachi were considerably larger, with estimates of 79 kg and 137 kg, respectively. D. neomexicanus is represented in our database by only the skull of a single individual and is the size of a large male wolf. It is worth noting that mass estimate obtained for D. neomexicanus with the function of Van Valkenburgh (1990), adjusted for the craniodental skeleton using a much wider sample of carnivorans, was ca. 79 kg (see table 6). Concerning Adilophontes brachykolos, its body mass was estimated to be ca. 125 kg.
The genus Daphoenus includes small−sized amphicyonids with a generalized postcranial skeleton (Hunt 1998). The mass estimate for D. vetus is ca. 25 kg and the one for D. hartshornianus ca. 11 kg. However, these species are not the smallest amphicyonids, as the estimate for Paradaphoenus cuspigerus is only ca. 4 kg. This result agrees with the suggestion that Paradaphoenus includes some of the smallest New World amphicyonids, never exceeding 3–4 kg (Hunt 2001).
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Attached File Body_mass_estimation_in_amphicyonid_carnivoran_mammals.pdf (631.37 KB)
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Claudiu Constantin Nicolaescu
Heterotrophic Organism
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The family Amphicyonidae included great mammals! Too bad they all went extinct! I would like to see them back in the wild again!
Edited by Claudiu Constantin Nicolaescu, Jan 24 2017, 06:08 AM.
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