Néstor Toledo

Eucholoeops Ameghino, 1887 (Xenarthra, Tardigrada, Megalonychidae) from the Santa Cruz Formation, Argentine Patagonia: implications for the systematics of Santacrucian sloths

ABSTRACT New well-preserved remains of the megalonychid sloth Eucholoeops Ameghino, 1887 recovered under strict stratigraphic control from late Early Miocene Santa Cruz Formation (c. 19 to 14 Ma; Santacrucian Age), together with analysis of older collections, consideration of intraspecific variation in extinct and extant sloths, and assessment of the validity of the early literature on Santacrucian sloths, permit revision of the status of the numerous species erected for this genus. The current contribution deals with the systematics of E. ingens Ameghino, 1887, but its methodology provides a basis for revision of other Eucholoeops species, as well as other sloth genera recovered from the Santa Cruz Formation. The failure to make progress on the systematics of the Santacrucian taxa since their first description is shown to be due mainly to a combination of the poor quality of many of the specimens, which are often fragmented and incomplete and from older collections, as well as inadequate stratigraphic and geographic control of their recovery, an overly rigid reliance on the early literature that accompanied their descriptions, and lack of consideration for intraspecific variation. A neotype is designated for E. ingens, as the original specimen is no longer available. The species E. latirostris Ameghino, 1891, E. externus Ameghino, 1891, and E. curtus Ameghino, 1894 are considered as junior synonyms of E. ingens.

Muscular reconstruction and functional morphology of the hind limb of santacrucian (Early Miocene) sloths (Xenarthra, Folivora) of Patagonia

This article presents a morphofunctional analysis of the hind limb of Santacrucian (Early Miocene) sloths from southernmost Patagonia (Argentina). These fossil sloths were mid sized to large animals, ranging from 40 to 120 kg, and their postcranial skeleton was markedly different in shape compared with that of extant tree sloths, which vary from 2 to 10 kg. The functional anatomy of the hind limb of Santacrucian sloths was compared with that of living xenarthrans (tree sloths, anteaters, and armadillos), which involved reconstruction of the hind limb musculature and comparative and qualitative morphofunctional analyses, and hypotheses on the biological role of the hind limb in terms of preferences in substrate, posture, and strategies of locomotion were formulated. The hind limb of Santacrucian sloths bears strong resemblances to that of living South American anteaters in stoutness of skeletal elements, form of the characteristics related to muscular and ligamentous attachments, and conservative, pentadactylous strong‐clawed pes. The musculature was very well developed, allowing powerful forces, principally in entire limb adduction, crus flexion and extension, pes extension, and toe prehension. These functional features, together with those of the forelimb, are congruent with climbing behavior, and support the hypothesis that Santacrucian sloths were good but slow climbing mammals. However, their climbing strategies were limited, owing principally to their comparatively large body size, and they relied to a large extent on their powerful musculature and curved manual and pedal unguals for both moving and standing on the arboreal supports. Anat Rec, 298:842–864, 2015.

Paleobiological Integration of Santacrucian Sloths (Early Miocene of Patagonia)

Abstract. Paleobiological integration proceeds from descriptive morphology and paleosynecological reconstruction. This integration is achieved through modeling of function, inference of faculties, performance and resource use to hypothesize about fundamental niche. Environmental information is then incorporated to discuss biological roles and realized niche. Herein, paleobiological integration of Santacrucian (early Miocene of Patagonia) sloths is analyzed as a study case. Santacrucian sloths comprise a diversity of approximately 11 genera ranging from 40 kg to 120 kg in body mass and characterized by being morphologically different from any living relatives. In this study, the realized niche of each taxon is reconstructed via integration of three paleoecological attributes: body size, dietary habits and substrate preference. An ecomorphological approach is applied using Principal Components Analysis to explore the correlation between postcranial linear dimensions and substrate preference together with classical functional indices. Integration of these results with previous studies indicates that the mid-sized Hapalops, Pelecyodon, Schismotherium and Analcimorphus (stem Megatherioidea) and Eucholoeops (Megalonychidae) are members of the arboreal folivore paleoguild. In contrast, the mylodonts Analcitherium and Nematherium, marked by their greater size, may have been semiarboreal consumers of leaves, fruits and tubers due to their digging capabilities. Prepotherium (Megatheriidae), the largest and most terrestrial Santacrucian sloth, was also a folivore. Only the latter three genera competed for trophic resources with other coexistent mammalian herbivores. Their body size, strength and claws made Santacrucian sloths subject of predation solely for the largest Santacrucian carnivores, borhyaenoids marsupials and phorusrhacoid birds. Finally, the absence of modern analogues of these heavy-sized arboreal and semiarboreal herbivore diversity is discussed.

Mass estimation of Santacrucian sloths from the Early Miocene Santa Cruz Formation of Patagonia, Argentina

Miocene deposits of the Santa Cruz Formation, Patagonia, comprise a diverse and excellently preserved vertebrate fauna, allowing detailed paleobiological and paleoecological studies based on three ecological parameters: body mass, diet, and substrate preference. In contrast to the small and arboreal extant sloths, Bradypus and Choloepus, Santacrucian sloths were much more diverse and larger, and comprised 11 genera previously characterized as arboreal or climbing forms. Here, we focus on body mass estimation based on measurements of postcranial elements. We present a morphometric database comprising 64 linear, base-ten logged variables applied to Santacrucian sloths and a wide sample of extant mammals, as well as the body mass of the extant taxa as reported in the literature. To detect any potential phylogenetical bias, we performed a variance decomposition test on our sample of extant mammals. Based on four orthogram statistics, logged body mass was found not to be dependent on phylogenetic tree topology. Predictive equations for the body mass of extant mammals were generated through multiple regression analysis, using weighting procedures to avoid taxonomic biases and stepwise analysis to discard redundant variables. Using this procedure, we derived separate equations for the scapula, humerus, radius, ulna, pelvis, femur, tibia plus fibula, astragalus, and calcaneum. These equations were then applied to estimate the body mass of our sample of Santacrucian sloths. We obtained an average body mass of about 70 kg for the megalonychid Eucholoeops. Among stem megatherioids, Hapalops ranged between 30 and 80 kg, Analcimorphus was estimated at 67 kg, and Schismotherium at 44 kg. Larger genera included the megatheriid Prepotherium (∼123 kg), and the mylodontids Analcitherium (∼88 kg) and Nematherium (∼89 kg). The medium to large body size of Santacrucian sloths imposed constraints on their climbing abilities. Megalonychids and stem megatherioids were likely unable to access the finest branches, while megatheriids and mylodonts were more terrestrial forms.

THE BASICRANIUM AND ORBITAL REGION OF THE EARLY MIOCENE EUCHOLOEOPS INGENS AMEGHINO, (XENARTHRA, PILOSA, MEGALONYCHIDAE)

Abstract. New, exceptionally well preserved skulls of the basal megalonychid ground sloth Eucholoeops ingens Ameghino have been recovered through recent field work in the late early Miocene Santa Cruz Formation of southern Argentina (Patagonia, Santacrucian SALMA). These specimens have permitted detailed description of the anatomy of the basicranium, endocranium, and orbital wall, including descriptions of the morphology and sutural relationships of the bones from this portion of the skull, and their associated cranial foramina. Comparisons are made to other megalonychid and megatherioid sloths, including the extant two-toed sloth Choloepus Illiger (Megalonychidae). As the descriptions are based on multiple specimens of E. ingens, we have been able to examine intraspecific variation in the features described, and have found marked differences among individual specimens in sutural patterns (e.g., the bones that surround the foramen ovale aperture), cranial foramina (e.g., the presence/absence of a postglenoid foramen), and bony morphology (e.g., fusion of the alae of the vomer). The basicranial and orbital morphology of Eucholoeops ingens is shown to possess numerous plesiomorphic aspects, including the presence of a descending lamina of the pterygoid that is hemispherical in outline, and the absence of an alisphenoid/parietal contact, no doubt due to its position as the oldest megalonychid known from relatively complete material. The presence of distinct grooves on the promontorial surface directed toward the fenestra ovalis suggest that Eucholoeops ingens may be the only known xenarthran to have retained a functional stapedial artery Into adulthood.

LOS RESTOS TEGUMENTARIOS DE PEREZOSOS TERRESTRES (XENARTHRA, FOLIVORA) DE ÚLTIMA ESPERANZA (CHILE). CRONOLOGÍA DE LOS REPORTES, ORIGEN Y UBICACIÓN ACTUAL

Resumen. En 1895, H. Eberhard descubrio un fragmento de cuero de mamifero, con pelos y osteodermos, en una caverna cercana a Puerto Consuelo (Seno de Ultima Esperanza, Chile). Los restos fueron asignados a un perezoso milodontido, nominado en 1899 Neomylodon listai por F. Ameghino. El hallazgo suscitaria numerosas publicaciones y una fuerte competencia, especialmente entre F.P. Moreno y F. Ameghino. Posteriormente al hallazgo de Eberhard, nuevos restos de tegumento fueron colectados por otros exploradores (entre ellos O. Nordenskjold y R. Hauthal). En esta contribucion presentamos una cronologia pormenorizada de los hallazgos y el derrotero de los restos de cuero desde 1895 hasta 1910 e indicamos su ubicacion actual. Se realizo una exhaustiva busqueda y revision bibliografica en publicaciones y correspondencia de la epoca. El cuero encontrado por Eberhard fue llevado por Moreno a La Plata en 1898 y de alli a Londres a comienzos de 1899 y actualmente esta depositado en la coleccion del Natural History Museum de Londres. Los restos hallados por la expedicion de R. Hauthal en 1899 estan en el Museo de La Plata, incluyendo el trozo de cuero que se encuentra en exhibicion (MLP 94-VIII-10-28). La evidencia recopilada no permite despejar dudas sobre la procedencia del material originalmente descripto por F. Ameghino, que desencadeno numerosas expediciones nacionales y extranjeras. En la actualidad existen al menos 40 restos de tegumento asignables a milodontidos provenientes de la Cueva de Ultima Esperanza distribuidas en once instituciones del mundo (Argentina, Chile, EEUU y Europa). PALABRAS CLAVE . Neomylodon listai . Grypotherium . Cueva del Milodon. Ameghino. Moreno. Osteodermos. Cuero. Abstract. HIDE REMAINS OF GROUND SLOTHS (XENARTHRA, FOLIVORA) FROM ULTIMA ESPERANZA (CHILE). CHRONOLOGY OF THE REPORTS, ORIGIN AND CURRENT LOCATION. In 1895, H. Eberhard discovered a piece of mammal hide, with hair and osteoderms, in a cavern near Puerto Consuelo (Seno de Ultima Esperanza, Chile). The remains were assigned to a mylodontid ground sloth, named in 1899 as Neomylodon listai by F. Ameghino. The finding promoted several publications and a strong competition, especially between F.P. Moreno and F. Ameghino. After Eberhard’s finding, new hide remains were collected by other explorers (among them O. Nordenskjold and R. Hauthal). In this contribution, we present a detailed chronology of the findings and the track of the hide remains, from 1895 to 1910, and their current location. In doing so, an exhaustive search and bibliographic revision of publications and letters from that epoch was performed. The hide found by Eberhard was taken to the Museo de La Plata in 1898, and then, to London in the beginning of 1899. The hide is housed at the Natural History Museum of London. The remains found by Hauthal’s expedition in 1899 are deposited in the Museo de La Plata, including the exhibited fragment of hide (MLP 94-VIII-10-28). The evidence provided here does not allow clearing up doubts on the provenance of the material originally described by F. Ameghino, which triggered numerous national and foreign expeditions. At present there are at least 40 remains of hide assignable to mylodontids, recovered from the Cave of Ultima Esperanza spread in eleven institutions world wide (Argentina, Chile, USA and Europe). KEY WORDS . Neomylodon listai . Grypotherium. Cueva del Milodon. Ameghino. Moreno. Osteoderms. Hide.

Body mass estimation for †Cyonasua (Procyonidae, Carnivora) and related taxa based on postcranial skeleton

Abstract Procyonidae were the first northern placental carnivorans that reached the Neotropics. They are represented by two extinct genera: †Cyonasua and †Chapalmalania (late Miocene – early Pleistocene). Postcranial elements are only known for †Cyonasua and related taxa (†Parahyaenodon argentinus and †Tetraprothomo argentinus). To obtain highly reliable allometric equations for body mass estimations of fossil procyonids, we performed least squares regressions (multiple and bivariate lineal models) using 51 postcranial linear measurements. The extant sample included 124 taxa corresponding to nine families of Carnivora, with body mass data from the literature. We obtained about 63 equations from diverse combinations of postcranial measurements; 14 of them were selected using several reliability indexes as criteria. Our results show that body masses calculated for †Cyonasua range between 12.63 and 28.45 kg, †P. argentinus was estimated at 14.41 kg, while †T. argentinus at 25.31 kg. Thus, the body mass of †Cyonasua would have been at least twice as high as the mean of the extant procyonid Procyon cancrivorus. †Cyonasua was probably able to fend off predators and quite capable of climbing slowly on thick-enough branches. Other palaeoecological and palaeobiological inferences are discussed.

Evolution of South American Paucituberculata (Metatheria: Marsupialia): adaptive radiation and climate changes at the Eocene- Oligocene boundary

ABSTRACT The Eocene-Oligocene boundary (EOB) marks a period of remodeling in the metatherian faunas of South America. Paucituberculata was one of the groups that successfully diversified as the climate and environment conditions changed, and they became, during the first part of the Neogene, an important component of micromammal assemblages. Among paucituberculatans, the non-pichipilid palaeothentoids (NPP) has been recognized as the clade that diversified most widely in post-EOB times. Here we explore the evolutionary response of the NPP to the climatic-environmental changes around the EOB, by analysing the temporal patterns of disparity, taxonomic diversity and body mass in a phylogenetic context. To asses the magnitude of the NPP radiation comparisons based on these macroevolutionary parameters were done with its sister-group Pichipilidae, and its next closest relative, the Caenolestidae. In all considered parameters, NPP reached values significantly higher than the remaining paucituberculatans clades. From its initial diversification in the middle Eocene, taxonomic diversity increased through time, but it was decoupled from disparity across the EOB, and from the late Oligocene to early Miocene. The Oligocene emerges as the key period in NPP evolution, which is evidenced by a significant and concordant expansion of disparity and taxonomic diversity, suggesting evolution into empty ecospace.