The oldest known record of a ground sloth (Mammalia, Xenarthra, Folivora) from Hispaniola: evolutionary and paleobiogeographical implications

Sloths were among the most diverse groups of land vertebrates that inhabited the Greater Antilles until their extinction in the middle-late Holocene following the arrival of humans to the islands. Although the fossil record of the group is well known from Quaternary deposits in Cuba, Hispaniola, and Puerto Rico, remains from older units are scarce, limiting our understanding of their evolution and biogeographic history. Here we report the oldest known fossil ground sloth from Hispaniola, represented by an unassociated partial tibia and scapula that are recognized as a single taxon from the late Miocene-early Pliocene of the Dominican Republic. The combination of characters observed on the tibia suggests a close relationship with Megalocnus, otherwise only known from the Pleistocene–Holocene of Cuba. These fossils fill a temporal gap between those previously known from the early Miocene of Cuba and those from Pleistocene–Holocene deposits in the region and provide additional support for a continuous presence of the group in the Greater Antilles since the Oligocene.

Isotope data from amino acids indicate Darwin’s ground sloth was not an herbivore

Fossil sloths are regarded as obligate herbivores for reasons including peculiarities of their craniodental morphology and that all living sloths feed exclusively on plants. We challenge this view based on isotopic analyses of nitrogen of specific amino acids, which show that Darwin’s ground sloth Mylodon darwinii was an opportunistic omnivore. This direct evidence of omnivory in an ancient sloth requires reevaluation of the ecological structure of South American Cenozoic mammalian communities, as sloths represented a major component of these ecosystems across the past 34 Myr. Furthermore, by analyzing modern mammals with known diets, we provide a basis for reliable interpretation of nitrogen isotopes of amino acids of fossils. We argue that a widely used equation to determine trophic position is unnecessary, and that the relative isotopic values of the amino acids glutamate and phenylalanine alone permit reliable reconstructions of trophic positions of extant and extinct mammals.

New species of the ground sloth Parocnus from the late Pleistocene-early Holocene of Hispaniola

Parocnus dominicanus sp. nov. represents a new species of megalonychid ground sloth from theAltagracia Province of southeastern Dominican Republic. Specimens of multiple individuals, including oneassociated partial skeleton, were recovered from two separate underwater caves in the Parque Nacional delEste through collaborations with museums and cave divers between 2009–2013. Parocnus dominicanus sp.nov. is distinguished by its small size compared to that of P. serus, with percent differences in limb elementlengths ranging from 13−24%. Numerous cranial and post-cranial elements also exhibit morphological characterstates that are not attributable to size variations. The recovery of multiple individuals within each localitydemonstrates a size dimorphism, possibly sexual, which parallels patterns exhibited by P. serus. The twospecies are also geographically distinct, with no examples of co-occurrence at any localities to date. Parocnusdominicanus sp. nov. and P. serus share character states that are distinct from those of the Cuban species, P.browni, and which suggest differential usage of the forelimb. The exact age of the specimens described here isunknown, however, Parocnus has been dated to the Holocene in Haiti.http://zoobank.org/urn:lsid:zoobank.org:pub:12E495D3-E261-4522-9854-D3B4C2D5FFB8