Juan Abella

Evidence for an African-Iberian mammal dispersal during the pre-evaporitic Messinian

The accurate timing of biogeographic dispersal can be determined by examining the age of fossiliferous strata on either side of a physical barrier. Here we show that African mammals migrated to Iberia and European mammals migrated to North Africa at the same time before isolation of the Mediterranean Sea during the Messinian. The fossil site of Venta del Moro (Spain) exhibits western Europe’s most complete vertebrate fauna for the latest Miocene. Its uniquely cosmopolitan assemblage is evidence of faunal dispersals from Africa and Asia to Europe during the latest Miocene glaciation. A preliminary paleomagnetic study suggested an age of 5.8 Ma for this site, but our expanded magnetostratigraphy dates the site at 6.23 Ma. In addition, we recalibrated the paleomagnetic age of the Librilla site (Spain) and the North Africa site of Afoud-1 (Morocco) using the Astronomical Tuned Neogene Time Scale. Our results show a two-way African-Iberian mammal dispersal just before 6.2 Ma. These new ages indicate that an ephemeral land corridor existed between the two continents 250 k.y. before the onset of the Messinian Salinity Crisis, reflecting a tentative initial isolation of the Mediterranean Sea. This corridor developed after tectonics closed the Betic Seaway at 6.3 Ma and during the intensification of the latest Miocene glaciation at 6.26 Ma, when water circulation in the Mediterranean became very restricted.

Kretzoiarctos gen. nov., the Oldest Member of the Giant Panda Clade

The phylogenetic position of the giant panda, Ailuropoda melanoleuca (Carnivora: Ursidae: Ailuropodinae), has been one of the most hotly debated topics by mammalian biologists and paleontologists during the last century. Based on molecular data, it is currently recognized as a true ursid, sister-taxon of the remaining extant bears, from which it would have diverged by the Early Miocene. However, from a paleobiogeographic and chronological perspective, the origin of the giant panda lineage has remained elusive due to the scarcity of the available Miocene fossil record. Until recently, the genus Ailurarctos from the Late Miocene of China (ca. 8–7 mya) was recognized as the oldest undoubted member of the Ailuropodinae, suggesting that the panda lineage might have originated from an Ursavus ancestor. The role of the purported ailuropodine Agriarctos, from the Miocene of Europe, in the origins of this clade has been generally dismissed due to the paucity of the available material. Here, we describe a new ailuropodine genus, Kretzoiarctos gen. nov., based on remains from two Middle Miocene (ca. 12–11 Ma) Spanish localities. A cladistic analysis of fossil and extant members of the Ursoidea confirms the inclusion of the new genus into the Ailuropodinae. Moreover, Kretzoiarctos precedes in time the previously-known, Late Miocene members of the giant panda clade from Eurasia (Agriarctos and Ailurarctos). The former can be therefore considered the oldest recorded member of the giant panda lineage, which has significant implications for understanding the origins of this clade from a paleobiogeographic viewpoint.

Eucyon debonisi n. sp., a new Canidae (Mammalia, Carnivora) from the latest Miocene of Venta del Moro (Valencia, Spain)

ABSTRACT A new species of canid (Eucyon debonisi n. sp.) is described from the late Miocene of Venta del Moro (Valencia, Spain). The new species is smaller than all the other Eucyon species, excepting E. intrepidus from the late Miocene of Lukeino (Kenya). Eucyon debonisi n. sp. is characterized by the greater size of the M2 in relation with the M1, showing comparable morphology with E. monticinensis, but this new species has a stronger parastyle, a less developed lingual cingulum and a more closed valley in the talon of the M1. Besides, it has a more slender dentition and mandible than E. monticinensis and possesses a diastema between p1 and p2 and between p2 and p3. Excepting the problematic Cants cipio from the middle Turolian locality of Concud (Spain), E. debonisi n. sp. represents the first modern canid that reached western Europe.

Complete description of the skull and mandible of the giant mustelid Eomellivora piveteaui Ozansoy, 1965 (Mammalia, Carnivora, Mustelidae), from Batallones (MN10), late Miocene (Madrid, Spain)

ABSTRACT We describe cranial, mandibular, and dental remains of five individuals of the giant mustelid Eomellivora piveteaui Ozansoy, 1965, from the late Miocene (MN10) site of Cerro de los Batallones (Madrid, Spain)—the first complete cranial remains recorded for this species and the most complete remains of the genus. This new sample enables a review of the systematic status of Eomellivora, leading us to accept as valid the species E. piveteaui Ozansoy, 1965, E. wimani Zdansky, 1924, E. ursogulo (Orlov, 1948), and E. hungarica Kretzoi, 1942. Our phylogenetic hypothesis indicates that Eomellivora is the sister taxon of the extant Mellivora capensis and E. piveteaui had a common ancestor within the crown group E. wimani—E. ursogulo. Eomellivora piveteaui was specialized for a more hypercarnivorous diet than the largest extant terrestrial mustelids, although it also had some derived bone-crushing adaptations. Eomellivora piveteaui had an active predatory role in the late Miocene carnivore faunas, exploiting both small and relatively large prey.

Tracing the origin of the panda’s thumb

We investigate the relative development of the carnivoran radial sesamoids to untangle the evolution of this iconic structure. In the pandas (both giant and red), this ‘false thumb’ is known to perform a grasping role during bamboo feeding in both the red and giant pandas. An original locomotor role has been inferred for ailurids, but this remains to be ascertained for ursids. A large sample of radial sesamoids of Indarctos arctoides from the Miocene of Batallones-3 (Spain) indicates that this early ailuropodine bear displayed a relatively hypertrophied radial sesamoid, with a configuration more similar to that of the red panda and other carnivorans than to that of giant pandas. This false thumb is the first evidence of this feature in the Ursidae, which can be linked to a more herbivorous diet. Moreover, in the two extant pandas, the false thumb should not be interpreted as an anatomical convergence, but as an exaptive convergence regarding its use during the bamboo feeding, which changes the evolutionary view of this singular structure.

On the Socio-Sexual Behaviour of the Extinct Ursid Indarctos arctoides: An Approach Based on Its Baculum Size and Morphology

The fossil bacula, or os penis, constitutes a rare subject of study due to its scarcity in the fossil record. In the present paper we describe five bacula attributed to the bear Indarctos arctoides Depéret, 1895 from the Batallones-3 site (Madrid Basin, Spain). Both the length and morphology of this fossil bacula enabled us to make interpretative approaches to a series of ecological and ethological characters of this bear. Thus, we suggest that I. arctoides could have had prolonged periods of intromission and/or maintenance of intromission during the post-ejaculatory intervals, a multi-male mating system and large home range sizes and/or lower population density. Its size might also have helped females to choose from among the available males.

Megalictis, the Bone-Crushing Giant Mustelid (Carnivora, Mustelidae, Oligobuninae) from the Early Miocene of North America

We describe cranial and mandibular remains of three undescribed individuals of the giant mustelid Megalictis ferox Matthew, 1907 from the latest Arikareean (Ar4), Early Miocene mammal fauna of Nebraska, and Wyoming (USA) housed at the American Museum of Natural History (New York, USA). Our phylogenetic hypothesis indicates that Ar4 specimens assigned to M. ferox constitute a monophyletic group. We assign three additional species previously referred to Paroligobunis to Megalictis: M. simplicidens, M. frazieri, and “M.” petersoni. The node containing these four species of Megalictis and Oligobunis forms the Oligobuninae. We test the hypothesis that Oligobuninae (Megalictis and Oligobunis) is a stem mustelid taxon. Our results indicate that the Oligobuninae form the sister clade to the crown extant mustelids. Based on the cranium, M. ferox is a jaguar-size mustelid and the largest terrestrial mustelid known to have existed. This new material also sheds light on a new ecomorphological interpretation of M. ferox as a bone-crushing durophage (similar to hyenas), rather than a cat-like hypercarnivore, as had been previously described. The relative large size of M. ferox, together with a stout rostrum and mandible made it one of the more powerful predators of the Early Miocene of the Great Plains of North America.

New findings of Pleistocene fossil turtles (Geoemydidae, Kinosternidae and Chelydridae) from Santa Elena Province, Ecuador

New Pleistocene fossilized turtle remains from five localities of western Ecuador (Santa Elena Province) are described here. All these shell (carapace and plastron) fossil remains come from the Tablazo Formation and belong to three different lineages of cryptodires (“hidden-necked” turtles). The most abundant remains belong to geoemydids, attributed here to the genus Rhinoclemmys (indeterminate species). Less abundant in occurrence are the kinosternidids, attributed to Kinosternon (indeterminate species), and the first fossil record of chelydrids, Chelydra(indeterminate species), in the entirety of Central and South America.

A new tropical Oligocene dolphin from Montañita/Olón, Santa Elena, Ecuador

A new small probable Oligocene dolphin from Ecuador represents a new genus and species, Urkudelphis chawpipacha. The new taxon is known from a single juvenile skull and earbones; it differs from other archaic dolphins in features including widely exposed frontals at the vertex, a dorsally wide open vomer at the mesorostral groove, and a strongly projected and pointed lateral tuberosity of the periotic. Phylogenetic analysis places it toward the base of the largely-extinct clade Platanistoidea. The fossil is one of a few records of tropical fossil dolphins.

Feeding ecology and habitat preferences of top predators from two Miocene carnivore-rich assemblages

Abstract. Carnivore-rich fossil sites are uncommon in the fossil record and, accordingly, provide valuable opportunities to study predators from vantages that are rarely applied to ancient faunas. Through stable isotopes of carbon and a Bayesian mixing model, we analyze time-successive (nearly contemporaneous), late Miocene carnivoran populations from two fossil sites (Batallones-1 and Batallones-3) from central Spain. Stable isotopes of carbon in tooth enamel provide a reliable and direct methodology to track ancient diets. These two carnivoran-dominated fossil sites display differences in the composition and abundance of the carnivoran species, with some species present at both sites and some present only at one site. This disparity has been interpreted as the consequence of habitat differences between Batallones-1, the older site, and Batallones-3, the younger site. However, carbon isotope values of carnivore and herbivore tooth enamel suggest a common habitat of C3 woodland originally present at both sites. The differences in the carnivoran faunas rather may be the consequence of the dynamics of species entrance and exit from the Madrid Basin during the time elapsed between Batallones-1 and Batallones-3 and changes in population densities due to biotic factors. We infer higher levels of interspecific competition in Batallones-3 than in Batallones-1 because of the larger number of similar-sized, sympatric predators; the clear overlap in their δ13C values (except for the amphicyonid Magericyon anceps); and similarity of their preferred prey: the hipparionine horses. Finally, carbon stable isotopic composition of Indarctos arctoides teeth implies that this ursid was a carnivorous omnivore rather than a herbivorous omnivore. This work demonstrates the insights that stable isotopes can provide in characterizing the feeding ecology and trophic interactions of ancient carnivoran taxa.