M. Susana Bargo

Limb bone proportions, strength and digging in some Lujanian (Late Pleistocene-Early Holocene) mylodontid ground sloths (Mammalia, Xenarthra)

Abstract The mylodontid ground sloths (Xenarthra, Tardigrada) are among the most intriguing components of the Lujanian (Late Pleistocene-Early Holocene) fauna of the Pampean region in South America. Limb proportions and resistance to bending forces were studied in Scelidotherium, Glossotherium and Lestodon to infer their locomotory abilities. Body masses were estimated using scale and computer-generated geometric models. Allometric equations were calculated from humeri, ulnae, radii, femora, tibiae, and the pes, and were used to predict linear dimensions from body mass. Slopes and intercepts were obtained using Model I and II regressions. An indicator of strength was calculated for humeri and femora. Body masses of approximately 850, 1,500 and 4,100 kg were estimated from scale models for Scelidotherium, Glossotherium and Lestodon, respectively. The proportions and capacity to resist bending forces of the limb bones of Scelidotherium and Glossotherium indicate that they were well adapted for strenuous activities in which force is enhanced over velocity, such as digging. We consider these taxa as possible builders of the large Late Cenozoic burrows present in the Pampean region. Although limb proportions of Lestodon are comparable to those of the others, its low strength indicator suggests that its limbs were not as well designed to perform such strenuous activity.

Predominance of Orthal Masticatory Movements in the Early Miocene Eucholaeops (Mammalia, Xenarthra, Tardigrada, Megalonychidae) and Other Megatherioid Sloths

ABSTRACT The megatherioid sloths from the Santa Cruz Formation (Santacrucian Age; early-middle Miocene, Patagonia, southernmost South America) occupy basal positions in the most recent phylogenetic schemes. The cranial morphology of Eucholaeops, particularly of the teeth, suggests interesting functional features that shed light on the type of food it was capable of processing, and thus on the diet. A detailed morphofunctional analysis of the jaw apparatus was performed, and the results briefly compared with other contemporary megatherioid sloths. Comprehensive descriptions of the teeth of Eucholaeops allow us to generate a nomenclature for describing the inferred occlusal pattern analogous to that applied to other mammals. Based on examination and mapping of occlusal wear facets, we reconstruct two distinct jaw movements during the power stroke. One corresponds to the basic therian pattern equivalent to Phase I: the working side mandibular corpus is moved dorsally, mainly orthally but also anteriorly and slightly medially; the result is puncturing, tearing and shearing of food. The second is a distinct and unrelated movement of the working side corpus dorsally, mainly orthally, but also posteriorly and slightly medially; the dominant result is to produce shearing of food. The analysis of the tooth wear facets, combined with the shape of the temporomandibular joint, the presence of a fused mandibular symphysis, and a well-developed temporalis muscle, indicates that the orthal component was predominant during mastication. Eucholaeops, and probably nearly all other Miocene megatherioids, were most likely leaf eaters and the primary method of food reduction must have been by shearing or cutting.

Early Miocene paleobiology in Patagonia : high-latitude paleocommunities of the Santa Cruz Formation

List of contributors Preface 1. Background for a paleoecological study of the Santa Cruz Formation (late Early Miocene) on the Atlantic Coast of Patagonia Sergio F. Vizcaino, Richard F. Kay and M. Susana Bargo 2. Tephrochronology of the Santa Cruz and Pinturas Formation Michael E. Perkins, John G. Fleagle, Matt T. Heitzler, Barbara Nash, Thomas M. Bown, Adan A. Tauber and Maria T. Dozo 3. Tephrochronology and paleontology of the Santa Cruz and Pinturas Formation John G. Fleagle, Michael E. Perkins, Matt T. Heitzler, Barbara Nash, Thomas M. Bown, Adan A. Tauber, Maria T. Dozo and Marcelo F. Tejedor 4. Sedimentology and paleoenvironment of the Santa Cruz Formation Sergio Matheos and M. Sol Raigemborm 5. Oysters from the base of Santa Cruz Formation (late Early Miocene) of Patagonia Miguel Griffin and Ana Parras 6. Ichnology of the Santa Cruz Formation (late Early Miocene), at the coast between the Rio Gallegos and Rio Coyle Veronica Krapovickas 7. Fossil plant studies from late Early Miocene of the Santa Cruz Formation: paleoecology and paleoclimatology at the passive margin of Patagonia, Argentina Mariana Brea, Alejandro Zucol and Ari Iglesias 8. Amphibians and squamate reptiles from the Santa Cruz Formation (late Early Miocene), Santa Cruz Province, Argentina: paleoenvironmental and paleobiological considerations Juan Carlos Fernicola and Adriana Albino 9. Diversity and paleobiology of the Santacrucian birds Federico Degrange, Jorge I. Noriega and Juan I. Areta 10. Paleoecology of the Paucituberculata and Microbiotheria (Mammalia, Marsupialia) from the late Early Miocene of Patagonia M. Alejandra Abello, Edgardo Ortiz-Jaureguizar and Adriana M. Candela 11. Paleoecology of the mammalian carnivores (Metatheria, Sparassodonta) of the Santa Cruz Formation (late Early Miocene) Francisco Prevosti, Analia M. Forasiepi, Marcos Ercoli and Guillermo F. Turazzini 12. Paleobiology of Santacrucian glyptodonts and armadillos (Xenarthra, Cingulata) Sergio F. Vizcaino, Juan Carlos Fernicola and M. Susana Bargo 13. Paleobiology of the Santacrucian sloths and anteaters (Xenarthra, Pilosa) M. Susana Bargo, Nestor Toledo and Sergio Vizcaino 14. Paleobiology of Santacrucian native ungulates (Meridiungulata: Astrapotheria, Litopterna and Notoungulata) Guillermo H. Cassini, Esperanza Cerdeno, Amalia Villafane and Nahuel A. Munoz 15. Paleobiology of Santacrucian Caviomorph rodents: a morpho-functional approach Adriana M. Candela, Luciano L. Rasia and Maria E. Perez 16. The paleobiology of Santacrucian primates Richard F. Kay, Jonathan M. G. Perry, Michael Malinzak, Kari Allen, E. Christopher Kirk, J. Michael Plavcan and John G. Fleagle 17. A review of the paleoenvironment and paleoecology of the Miocene Santa Cruz Formation Richard F. Kay, Sergio F. Vizcaino and M. Susana Bargo Index.

Early Miocene Paleobiology in Patagonia: Background for a paleoecological study of the Santa Cruz Formation (late Early Miocene) on the Atlantic Coast of Patagonia

For more than 120 years, the coastal exposures of the Santa Cruz Formation have been fertile ground for recovery of vertebrates from the late Early Miocene (~18 to 16 million years ago, Ma). As long ago as the 1840s, Captain Bartholomew Sulivan collected fossils from this region and sent them to Charles Darwin, who passed them to Richard Owen. Carlos Ameghino undertook several explorations of the region starting in the late 1880s. Carlos’ specimens were described by his brother Florentino, who believed that many of the species were more ancient than now understood and represented the ancestors of many Holarctic mammalian orders. Ameghino’s novel claims prompted William B. Scott to organize fossil collecting expeditions in the Santa Cruz beds led by John B. Hatcher. The fossils were described in a series of exhaustive monographs with the conclusion that the fauna was much younger than Ameghino thought. Several brief expeditions took place during the twentieth century, led by researchers from different institutions. Since 2003, we have undertaken the collection of over 1600 specimens, including large series of relatively complete skeletons. In this edited volume we have gathered together a group of researchers to study the coastal Santa Cruz Formation and its associated flora and fauna to provide a paleobiological reconstruction of the Santacrucian vertebrate community and to place it in its biotic and physical environment.

Muscular Reconstruction and Functional Morphology of the Forelimb of Early Miocene Sloths (Xenarthra, Folivora) of Patagonia

Early Miocene sloths are represented by a diversity of forms ranging from 38 to 95 kg, being registered mainly from Santacrucian Age deposits in southern‐most shores of Patagonia, Argentina. Their postcranial skeleton differs markedly in shape from those of their closest living relatives (arboreal forms of less than 10 kg), Bradypus and Choloepus. In order to gain insight on functional properties of the Santacrucian sloths forelimb, musculature was reconstructed and a comparative, qualitative morphofunctional analysis was performed, allowing proposing hypotheses about biological role of the limb in substrate preferences, and locomotor strategies. The anatomy of the forelimb of Santacrucian sloths resembles more closely extant anteaters such as Tamandua and Myrmecophaga, due to the robustness of the elements, development of features related to attachment of ligaments and muscles, and conservative, pentadactylous, and strong‐clawed manus. The reconstructed forelimb musculature was very well developed and resembles that of extant Pilosa (especially anteaters), although retaining the basic muscular configuration of generalized mammals. This musculature allowed application of powerful forces, especially in adduction of the forelimb, flexion and extension of the antebrachium, and manual prehension. These functional properties are congruent with both climbing and digging activities, and provide support for proposed Santacrucian sloths as good climbing mammals, possibly arboreal or semiarboreal, being also capable diggers. Their climbing strategies were limited, thus these forms relied mainly on great muscular strength and curved claws of the manus to move cautiously on branches. Anat Rec, 2013.

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.

First Record and a New Species of Seriema (Aves: Ralliformes: Cariamidae) from Santacrucian (Early-Middle Miocene) Beds of Patagonia

Living seriemas (Ralliformes, Cariamidae) are long-legged cursorial birds that comprise only two very closely related, and perhaps congeneric, species (Gonzaga, 1996): Cariama cristata and Chunga burmeisteri. They are endemic to South America and may represent surviving Neotropical relicts of an early ralli form radiation within the suborder Cariamae. Phorusrhacids, idiornithids, and bathornithids are also extinct components of ralliforms, a large terrestrial stock of predator or scavenger birds, which were abundant during the Tertiary of South and North America, and Europe (Mourer Chauvire, 1981, 1983; Alvarenga and H?fling, 2003). The phylogenetic relation ships and paleobiogeographic history of phorusrhacids, idior nithids, and bathornithids are still far from being resolved. Tertiary fossils of the cariamid subtaxon Cariaminae are scarce and restricted to the questionable record of Riacama caliginea Ameghino 1899 from the late Oligocene (Deseadan age) of Santa Cruz Province (see Brodkorb, 1967; Tonni, 1980; Tambussi and Noriega, 1996; Agnolin, 2004), and the early-middle Pliocene (Montehermosan age) record of Chunga incerta Tonni (1974) from Buenos Aires Province, both in Argentina. In this contribution we present new remains of seriemas re covered in 2005 by a joint expedition of the Museo de La Plata, Argentina, and Duke University, USA. They come from the middle levels of the Santa Cruz Formation (Upper-middle Mio cene) along the Atlantic coast of southernmost continental Pata gonia, Argentina, between the Coyle and Gallegos rivers. These localities are situated at about 52 degrees South latitude, about 100 km north to the Magallanes Strait (Fig. 1). In the mentioned area, the Santa Cruz Formation bears a terrestrial vertebrate fauna exceptional in its richness with over 70 species recorded in about 30 fossiliferous levels (Tauber, 1997a, Tauber 1997b; Tauber et al., 2004) that represents the richest assemblage of pre-Pleistocene mammalian skulls and ar ticulated skeletons known in the continent (Hatcher, 1903). A description of the localities and horizons that produced the fossils reported here is provided in the following section. Although still far fewer than mammals, these localities have provided quite a number of bird remains. Many of them were described and beautifully figured in the extensive Reports of the Princeton University Expeditions to Patagonia (Sinclair and Farr, 1932). They include Phorusrhacos longissimus Ameghino 1887, Brontornis burmeisteri Moreno and Mercerat 1891, Patagornis marshi Moreno and Mercerat 1891, Psilopterus bachmanni (Moreno and Mercerat 1891), and Psilopterus lemoinei (Moreno and Mercerat 1891), among the Phorusrhacids. Other bird taxa recorded at the Santa Cruz Formation include Tinamidae (Chiappe, 1991), Rheidae (Opisthodactylus patagonicus Ame ghino 1891), Pelecanidae (Liptornis hesternus Ameghino 1895), Plataleidae (Protibis cnemialis Ameghino 1891), Anatidae (Eone ornis australis Ameghino 1895; Eutelornis patagonicus Ameghino 1895), Aramidae (Anisolornis excavatus Ameghino 1891), and Falconiformes (Badiostes patagonicus Ameghino 1895; Thegornis debilis Ameghino 1895 and T. musculosus Ameghino 1899). Most of these taxa were erected on the basis of very fragmentary and eroded specimens, together with brief and poorly illustrated descriptions, that make difficult to assess their validity (Olson, 1981, 1985; Tonni, 1980; Tambussi and Noriega, 1996). Some of them have been recently revised (Alvarenga and H?fling, 2003; Agnolin, 2004, 2006, 2007).

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.

Phylogeny and Taxonomy of the Patagonian Miocene Falcon Thegornis musculosus Ameghino, 1895 (Aves: Falconidae)

Abstract The fossil record of the family Falconidae is poor and fragmentary. Extinct representatives from South America include the late early Miocene (Santacrucian) Thegornis musculosus and Thegornis debilis. Both species were originally described as Falconidae and afterwards moved to Accipitridae Circinae or Buteoninae. The analysis of a very well preserved and complete specimen of T. musculosus with similar stratigraphic and geographic provenances of the type material (lower levels of Santa Cruz Formation, coast of Patagonia, Argentina) corroborates the validity of the genus and its falconid affinities. The skull and postcranial morphology exhibit strong resemblances with the open-savannah inhabiting Herpetotheres and the forest-dwelling Micrastur (Herpetotherinae) but differ substantially from Falconinae (Falconini plus Caracarini). Detailed comparisons with a broad arrange of falconiform taxa in a cladistic framework, confirm its phylogenetic placement within the Herpetotherinae and sister to H. cachinnans. The ecotonal margins produced by the vanishing of humid forests that developed during changes in Patagonian plant communities throughout early Neogene times are hypothesized as a plausible scenario to understand the evolution of this basal clade of falcons.

Tooth Root Size, Chewing Muscle Leverage, and the Biology of Homunculus patagonicus (Primates) from the late early Miocene of Patagonia

Abstract. Inferences about the diet of Miocene platyrrhine monkeys have relied upon the morphology of the molar teeth, specifically the crests on the molars. Using a library of Micro-CT images of a broad comparative sample of living platyrrhines (callitrichines, cebines, pitheciids and atelids), late early Miocene Homunculus, and the early Miocene Tremacebus and Dolichocebus, we extend these inferences by examining the surface areas of the tooth roots, anchor points for the periodontal ligaments. From muscle scars on the skull, we estimate the mechanical leverage of the chewing muscles at bite points from the canine to the last molar. Extant platyrrhines that gouge bark to obtain exudates do not have especially large canine roots or anterior premolar roots compared with their less specialized close relatives. Extant platyrrhines that have more folivorous diets have much larger molar roots than do similar-sized more frugivorous species. Homunculus patagonicus has large postcanine roots relative to body size and poor masticatory leverage compared to the extant platyrrhines in our sample. The large postcanine roots, heavy tooth wear, and moderately-long shearing crests suggests a diet of abrasive, resistant foods. However, relatively poor jaw adductor leverage would have put the masticatory apparatus of Homunculus at a mechanical disadvantage for producing high bite forces compared to the condition in extant platyrrhines. Tremacebus and Dolichocebus, like Homunculus, have larger tooth root surfaces than comparable-sized living platyrrhines. They also resemble Homunculus in being more prognathic and having posteriorly-located temporalis origins - all features of a relatively poor leverage system.