Manuscript Click here to download Manuscript: JOMM-D-14-00001R2.doc Click here to view linked References Gema Siliceo, Manuel J. Salesa, Mauricio Antón, Juan F. Pastor, Jorge Morales 1 2 3 4 5 Comparative anatomy of the shoulder region in the late Miocene 6 7 8 amphicyonid Magericyon anceps (Carnivora): functional and 9 10 11 paleoecological inferences 12 13 14 15 16 Gema Siliceo 17 18 19 Departamento de Paleobiología, Museo Nacional de Ciencias Naturales-CSIC, C/José 20 21 Gutiérrez Abascal, 2. 28006 Madrid, Spain 22 23 24 25 26 Manuel J. Salesa (corresponding author) 27 28 Departamento de Paleobiología, Museo Nacional de Ciencias Naturales-CSIC, C/José 29 30 31 Gutiérrez Abascal, 2. 28006 Madrid, Spain 32 33 34 35 36 Mauricio Antón 37 38 Departamento de Paleobiología, Museo Nacional de Ciencias Naturales-CSIC, C/José 39 40 Gutiérrez Abascal, 2. 28006 Madrid, Spain 41 42 43 44 45 Juan F. Pastor 46 47 48 Departamento de Anatomía, Facultad de Medicina, Universidad de Valladolid, C/ Ramón y 49 50 Cajal 7, 47005 Valladolid, Spain 51 52 53 54 55 Jorge Morales 56 57 58 Departamento de Paleobiología, Museo Nacional de Ciencias Naturales-CSIC, C/José 59 60 Gutiérrez Abascal, 2. 28006 Madrid, Spain 61 62 63 1 64 65 1 2 E-mail: [email protected]; telephone number: +34 915668979; fax number: +34 3 4 5 915668960 6 7 8 9 10 11 12 Abstract We describe and discuss several aspects of the functional anatomy of the shoulder 13 14 of the Miocene amphicyonid Magericyon anceps, focusing on the scapula and proximal half 15 16 17 of the humerus. This species, only known from the late Miocene (Vallesian, MN 10) site of 18 19 Batallones-1 (Madrid, Spain), is the last amphicyonid known in the fossil record of Western 20 21 22 Europe. Magericyon anceps combines a more hypercarnivorous dentition than previous 23 24 amphicyonids (including relatively more flattened canines) with primitive features on its 25 26 27 shoulder region: its scapulo-humeral region shows a reduced caudoventral projection of the 28 29 acromion, the postscapular fossa, and the teres major process, suggesting some differentiation 30 31 32 from the two morphotypes exhibited by other derived amphicyonids, and showing similarities 33 34 with primitive, generalized, medium-sized species of this family. This unique combination of 35 36 a derived dentition and a relatively generalized shoulder region points towards M. anceps 37 38 39 being a different ecological morphotype from that showed by other amphicyonids such as the 40 41 larger, bear-like amphicyonines from the European middle Miocene and the markedly 42 43 44 cursorial North American temnocyonines and daphoenines. 45 46 47 48 49 Keywords Anatomy; Amphicyonidae; Carnivora; Miocene; shoulder; locomotion; 50 51 Magericyon anceps 52 53 54 55 56 57 58 59 60 61 62 63 2 64 65 Introduction 1 2 3 4 5 The Amphicyonidae is a very diverse and geographically widespread family of 6 7 Arctoid carnivorans known from the late Eocene to the late Miocene of North America and 8 9 10 Eurasia, which attained its greatest diversification during the Oligocene and early-middle 11 12 Miocene. Its diversity was reduced in the late Miocene, with only a few taxa surviving in the 13 14 Vallesian or earliest Turolian, around 8 Ma (Hunt 1998). The dentition of this group is 15 16 17 relatively homogeneous, and a diet varying from omnivorous to hyper-carnivorous has been 18 19 inferred depending on the species (Viranta 1996; Hunt 1998; Peigné et al. 2008). On the 20 21 22 contrary, the overall morphology of the postcranial skeleton of amphicyonids shows a mosaic 23 24 of features not seen together in any other group of extant carnivorans, although some of these 25 26 27 traits are observed separately in ursids, canids, or even in felids (Olsen 1960; Ginsburg 1961; 28 29 Bergounioux and Crouzel 1973; Viranta 1996; Hunt 1998, 2009; Argot 2010). In general, 30 31 32 amphicyonids show a more generalized postcranial skeleton than that of extant large 33 34 carnivorans, although some taxa (e. g., Borocyon) have features indicative of a cursorial 35 36 specialization, similar to that of extant canids, and they were probably pursuit predators (Hunt 37 38 39 1998, 2009, 2011). Most other amphicyonids show less specialization for running, and they 40 41 probably possessed an ambulatory locomotion with certain climbing abilities, resembling in 42 43 44 some ways modern ursids (Hunt 1998, 2001, 2002, 2003; Sorkin 2006; Argot 2010). 45 46 Four subfamilies are traditionally recognized within Amphicyonidae: Amphicyoninae, 47 48 49 Haplocyoninae, Daphoeninae and Temnocyoninae, the two later restricted to North America, 50 51 whereas Haplocyoninae is only present in the European faunas and Amphicyoninae is found 52 53 in Eurasia, North America, and Africa (Hunt 1998). This last subfamily includes the late 54 55 56 Miocene Magericyon anceps, the last amphicyonid of the Western European record. The most 57 58 common genera of European amphicyonines (Amphicyon, Cynelos, Ysengrinia) appear 59 60 61 62 63 3 64 65 abruptly at various moments in the Miocene of North America and these appearances are 1 2 interpreted as migration events (Hunt 1998, 2002, 2003). Thus, those North American middle 3 4 5 and upper Miocene amphicyonids would derive from immigrant Eurasian species (Hunt 6 7 1998). The estimated body size of amphicyonids ranges from few kilograms for the smallest 8 9 10 species up to 550 kg for Amphicyon ingens (Viranta 1996; Hunt 2001, 2003; Sorkin 2006; 11 12 Figueirido et al. 2011). Given this wide size range, Figueirido et al. (2011) proposed the 13 14 existence of three different size categories within Amphicyonidae that these authors relate to 15 16 17 different ecomorphs of extant carnivorans: small daphoenines would fit within the ecomorph 18 19 of living foxes, jackals, and coyotes; mid-sized daphoenines would be similar to pack-hunting 20 21 22 canids (Canis lupus or Lycaon pictus), and the largest amphicyonines would be the ecological 23 24 equivalent to extant large bears. 25 26 27 The Cerro de los Batallones is a low hill located 30 km south of the city of Madrid 28 29 (Spain) that has been exploited as an opencast mine of sepiolite since 1974. In July 1991, 30 31 32 during mining works, the mechanical diggers discovered a rich accumulation of fossils of 33 34 Carnivora within a lens of greenish marls intercalated between the levels of sepiolite. The site 35 36 was named Batallones-1 and it was the first of a series of nine fossil sites discovered in the 37 38 39 hill over the following years. The sites were formed during the late Miocene due to a 40 41 geological process of piping, which consisted in the erosion of the sepiolite levels by water 42 43 44 flowing along fractures, causing collapses and the development of a karst-like (‘pseudokarst’) 45 46 topography (Pozo et al. 2004; Calvo et al. 2013). This process finally led to the formation of 47 48 49 irregular cavities within the sepiolite levels, up to 15 m deep, later filled with greenish clay. 50 51 These cavities acted as a natural trap for many animals inhabiting the area, probably due to 52 53 the fact that when the sepiolite is wet, its surface becomes slippery, which would make escape 54 55 56 from the trap almost impossible. Concerning Batallones-1, a remarkable 98% of all the 57 58 macro-mammal bones recovered from the site corresponds to members of the order 59 60 61 62 63 4 64 65 Carnivora, which were probably trapped while attempting to scavenge (Antón and Morales 1 2 2000). This carnivoran assemblage includes the ailurid Simocyon batalleri, two species of 3 4 5 mustelids (Sabadellictis sp. and Proputorius sp.), the primitive hyaenid Protictitherium 6 7 crassum, the machairodont felids Machairodus aphanistus and Promegantereon ogygia, two 8 9 10 species of felines, Styriofelis vallesiensis and an undetermined, larger species, and the 11 12 amphicyonid Magericyon anceps. This impressive sample has allowed several systematic, 13 14 paleoecological and functional studies on the carnivoran fauna (Morales et al. 2000, 2004; 15 16 17 Antón and Morales 2000; Antón et al. 2004; Peigné et al. 2005, 2008; Salesa et al. 2005, 18 19 2006a, b, 2008, 2010a, b, 2012). The fossils of M. anceps from Batallones-1 represent one of 20 21 22 the best samples of Amphicyonidae in Eurasia, with at least 12 individuals represented, 23 24 including juveniles, young adults, and adults, in a fair state of preservation (Peigné et al. 25 26 27 2008). 28 29 The study of the cranial remains of M. anceps revealed a set of hypercarnivorous 30 31 32 features that pointed towards a more specialized hunting technique than that of other 33 34 amphicyonids (Peigné et al. 2008), with moderately flattened upper canines with weakly 35 36 serrated margins, and absence or strong reduction of some teeth; these features suggest a 37 38 39 reduced importance of the crushing function in the dentition, and a greater proportion of meat 40 41 in its diet compared with other amphicyonines (Peigné et al. 2008), placing the genus 42 43 44 Magericyon in a separate clade from other, less derived amphicyonids (Fig. 1). Although the 45 46 derived dental morphology of M. anceps suggests that it was a hypercarnivorous predator, its 47 48 49 postcranial skeleton has remained unstudied, and the present work is the first functional 50 51 analysis on the locomotor adaptations of this species. Among large carnivorans, 52 53 hypercarnivorous dentitions are in some cases associated with a cursorial or sub-cursorial 54 55 56 postcranial skeleton, as is the case in some canids, hyaenids, or felids, which use sprint or 57 58 sustained pursuit to catch their prey.