Megalonyx Research Articles

A complete sabertooth cat cranium from the Midcontinent of North America and its evolutionary and ecological context

Outside of Rancho La Brea, southern California, United States, knowledge of the life history, ecology, and extinction of large, late Pleistocene carnivores in North America is frustrated by a scarcity of skeletal material and trustworthy radiocarbon dates. A complete Smilodon fatalis (sabertooth cat) cranium from southwestern Iowa, directly AMS radiocarbon dated to 11,685 ± 40 B.P. (13,605–13,455 cal B.P.), represents an important addition to the inventory of evidence for the taxon in the Midcontinent. Assessment of tooth eruption and wear combined with metric and nonmetric comparisons with coeval crania from Pit 61/67 at Rancho La Brea indicates the specimen belongs to a subadult male 2–3 years of age at death. Craniodental morphology falls within the range of variation in the Pit 61/67 males. Predicted live weight is 251 kg. One C1 has an antemortem bend fracture, and the absence of use-wear on the proximal remnant suggests death ensued within days of the injury. The radiocarbon date centers the animal in the Bølling-Allerød Chronozone (14,640–12,845 cal B.P.). Whereas regional conditions were generally warmer and wetter during this period, southwestern Iowa was a cool, dry non-analog boreal grassland/parkland that supported a diverse, large herbivore community, including Megalonyx jeffersonii (Jefferson's ground sloth), the taxon tentatively identified in this study as the focal prey. Bayesian modeling of 72 direct radiocarbon dates for the taxon suggests extinction of the late Quaternary Smilodon was a hemispheric and geologically synchronic phenomenon that occurred after 13,285 cal B.P.Subjects: vertebrate paleontology, paleoecology, paleozoology.

Paleobiology of Jefferson’s Ground Sloth (Megalonyx jeffersonii) derived from three contemporaneous, ontogenetically distinct individuals recovered from Southwestern Iowa, U.S.A.

ABSTRACT Although known from more than 180 sites in North America, sites with records of multiple Megalonyx elements and individuals are rare. The Tarkio site in southwestern Iowa is unique with three contemporaneous individuals at different stages of development. Among these is one of the largest (ca. 1286 kg) and most complete adult Megalonyx jeffersonii skeletons (ca. 50%, NISP, 123) known. An intermingled sub-adult (ca. 25%, NISP, 63) represents a comparatively complete skeleton for this ontogenetic stage. A third individual, an infant known only from both scapulae (NISP 2), is commingled with sub-adult remains. Scapula sizes indicate that the two juveniles were 50 and 30% of the adult’s size. Differential bone preservation and pattern of scatter shows that the adult decomposed lying on its left side and the remains were partially scavenged. Multiple taphonomic proxies demonstrate that the skeletons were subaerially exposed for a limited period, but fluvial transport was not a factor. These individuals, preserved in the same low-energy microstratigraphic unit, apparently died concurrently and probably represent a Megalonyx social unit. Using mammal body size to estimate life history, the estimated average lifespan for M. jeffersonii was around 19 years; gestation time was about 14 months; the interbirth interval was approximately 3 years; and sexual maturation occurred at around 6.5 years. OSL analysis indicates that the sloths were deposited about 106,000 years ago (MIS substage 5ec). Paleoenvironmental proxies suggest an interglacial environment of open woodland along a stream with marshes, like the environment in southwest Iowa today.

Inferring differential behavior between giant ground sloth adults and juveniles through scapula morphology

ABSTRACTAnimals with large differences in body size between adults and juveniles will often exhibit differences in behavior through ontogeny, and these behavioral differences can sometimes have direct effects on skeletal morphology. Scapula shape has been shown in several groups to be highly influenced by function and in some groups to be a good indicator of body size. Megalonyx and Paramylodon, two of the most common and widespread of the North American Plio-Pleistocene giant ground sloths, had overlapping temporal and geographic ranges. However, they have few co-occurrences in the fossil record. In this study, the scapulae of juvenile and adult Megalonyx jeffersonii and Paramylodon harlani were analyzed using geometric morphometrics and compared with those of the two genera of modern tree sloths, Bradypus and Choloepus. The ground sloths have significantly different scapula shapes from each other, as do the tree sloths. The scapula shapes between juveniles and adults of each genus are also significantly different from each other, with the scapulae of the juveniles of each species more circular in appearance than the more ovoid ones in adults. All four genera show significant allometry, but it is more apparent in adults than juveniles. However, there is no difference in nonallometric shape between adults and juveniles or between each pair of genera. The ground sloths exhibit similar changes in ontogeny to those observed in modern sloths, indicating that ground sloth juveniles may have engaged in similar behaviors to those of modern sloths, such as clinging to their mothers for transportation. Ground sloth juveniles also possess morphological traits that have been linked with semiarboreal behaviors.

First record of the extinct ground sloth, Megalonyx jeffersonii, (Xenarthra, Megalonychidae) from New York and contributions to its paleoecology

The first record of the Jefferson ground sloth, Megalonyx jeffersonii, in New York is reported. The specimen consists of a partial synsacrum recovered from a peat deposit near Newburgh, Orange County. Compared to other synsacra of Megalonyx, the number of vertebrae is anomalous with one less caudal vertebra than expected. Stable isotope analysis of the bone shows a δ13C value of 20.5‰ and implies a diet of only C3 plants. The specimen has a radiocarbon date of 11,450 ± 55 BP indicating the presence of this taxon in the region immediately prior to the extinction of the North American Pleistocene megafauna.

Vertebrate paleontology, stratigraphy, and paleohydrology of Tule Springs Fossil Beds National Monument, Nevada (USA)

Tule Springs Fossil Beds National Monument (TUSK) preserves 22,650 acres of the upper Las Vegas Wash in the northern Las Vegas Valley (Nevada, USA). TUSK is home to extensive and stratigraphically complex groundwater discharge (GWD) deposits, called the Las Vegas Formation, which represent springs and desert wetlands that covered much of the valley during the late Quaternary. The GWD deposits record hydrologic changes that occurred here in a dynamic and temporally congruent response to abrupt climatic oscillations over the last ~300 ka (thousands of years). The deposits also entomb the Tule Springs Local Fauna (TSLF), one of the most significant late Pleistocene (Rancholabrean) vertebrate assemblages in the American Southwest. The TSLF is both prolific and diverse, and includes a large mammal assemblage dominated by Mammuthus columbi and Camelops hesternus. Two (and possibly three) distinct species of Equus, two species of Bison, Panthera atrox, Smilodon fatalis, Canis dirus, Megalonyx jeffersonii, and Nothrotheriops shastensis are also present, and newly recognized faunal components include micromammals, amphibians, snakes, and birds. Invertebrates, plant macrofossils, and pollen also occur in the deposits and provide important and complementary paleoenvironmental information. This field compendium highlights the faunal assemblage in the classic stratigraphic sequences of the Las Vegas Formation within TUSK, emphasizes the significant hydrologic changes that occurred in the area during the recent geologic past, and examines the subsequent and repeated effect of rapid climate change on the local desert wetland ecosystem.

Vertebrate paleontology, stratigraphy, and paleohydrology of Tule Springs Fossil Beds National Monument, Nevada (USA)

Tule Springs Fossil Beds National Monument (TUSK) preserves 22,650 acres of the upper Las Vegas Wash in the northern Las Vegas Valley (Nevada, USA). TUSK is home to extensive and stratigraphically complex groundwater discharge (GWD) deposits, called the Las Vegas Formation, which represent springs and desert wetlands that covered much of the valley during the late Quaternary. The GWD deposits record hydrologic changes that occurred here in a dynamic and temporally congruent response to abrupt climatic oscillations over the last ~300 ka (thousands of years). The deposits also entomb the Tule Springs Local Fauna (TSLF), one of the most significant late Pleistocene (Rancholabrean) vertebrate assemblages in the American Southwest. The TSLF is both prolific and diverse, and includes a large mammal assemblage dominated by Mammuthus columbi and Camelops hesternus. Two (and possibly three) distinct species of Equus, two species of Bison, Panthera atrox, Smilodon fatalis, Canis dirus, Megalonyx jeffersonii, and Nothrotheriops shastensis are also present, and newly recognized faunal components include micromammals, amphibians, snakes, and birds. Invertebrates, plant macrofossils, and pollen also occur in the deposits and provide important and complementary paleoenvironmental information. This field compendium highlights the faunal assemblage in the classic stratigraphic sequences of the Las Vegas Formation within TUSK, emphasizes the significant hydrologic changes that occurred in the area during the recent geologic past, and examines the subsequent and repeated effect of rapid climate change on the local desert wetland ecosystem.

Youngest radiocarbon age for Jefferson's ground sloth, Megalonyx jeffersonii (Xenarthra, Megalonychidae)

A partial skeleton of the extinct ground sloth, Megalonyx jeffersonii, recovered from a farm near Millersburg, Ohio in 1890, was radiocarbon dated for the first time. The ungual dated is part of a skeleton mounted for exhibit at the Orton Geological Museum at Ohio State University and was the first mounted skeleton of this animal. From its initial discovery the bones were treated with multiple organic compounds that had the potential to compromise the radiocarbon age and the specimen required special treatments in order to obtain a valid radiocarbon age. The 14C measurement on the ungual from this skeleton (11,235±4014Cyr BP=13,180–13,034calyr BP) is the youngest 14C age presently determined for M. jeffersonii.

Description of the stylohyal bone of a giant sloth (Lestodon armatus)

The hyoid apparatus in fossil Xenarthrans is rarely preserved. Its largest bone, the stylohyal, is the most frequently found as an isolated element. It is known for some species of Pleistocene ground sloths (Megalonyx jeffersonii, Megatherium americanum, Paramylodon harlani, Nothrotheriops shastensis, Glossotherium robustum and Scelidotherium leptocephalum) but not for the largest mylodontid Lestodon armatus. Here we describe a right stylohyal found in the late Pleistocene megafaunal bonebed of the Arroyo del Vizcaino site, Uruguay, as two perfectly matched pieces that were within a few centimeters of each other. A small notch, possibly a conchoidal flaked perimortem fracture, is observed in the lateral face. The specimen, whose general form is a sinusoid cylinder with the proximal end expanded and compressed, must have belonged to a juvenile individual, since it lacks both the distal and proximal surfaces that articulate with the skull and the epihyal, respectively. Instead, both ends show an irregular surface as those seen in the contact with the growth cartilage. Additionally, its maximum length is 105 mm, larger than the equivalent part of the stylohyal of adult Glossotherium. At the expanded proximal end that articulates with the skull the large fossa found in Glossotherium and Scelidotherium cannot be observed, which could be due to a taxonomic difference, to the stage of growth or both of them. The bone shows marks, several interpreted as caused by trampling and at least one with features as those left by human tools. P. Sebastian Tambusso. Seccion Paleontologia, Facultad de Ciencias, Universidad de la Republica, Igua 4225, 11400 Montevideo, Uruguay pasebita@gmail.com H. Gregory McDonald. Museum Management Program, National Park Service, 1201 Oakridge Drive, Fort Collins, Colorado 80521 USA greg_mcdonald@nps.gov Richard A. Farina. Seccion Paleontologia, Facultad de Ciencias, Universidad de la Republica, Igua 4225, 11400 Montevideo, Uruguay dogor@netgate.com.uy

New evidence for Late Pleistocene human exploitation of Jefferson's Ground Sloth (Megalonyx jeffersonii) from northern Ohio, USA

The nature and extent of early human exploitation of late Pleistocene mega-mammals of North America have been vigorously debated; however, direct evidence of predation has been established for a small number of taxa. Until now, evidence of butchering and human utilization of ground sloths has been limited to South America. Osteological and taphonomic analyses of one curated collection of Jefferson's Ground Sloth (Megalonyx jeffersonii) from northern Ohio, USA, have identified possible butchering marks on one femur. Historical research determined that the skeletal remains were originally recovered from a bog prior to 1915. Metric assessment of the ten skeletal elements identified this sloth as one of the largest individuals on record. SEM analysis of the left femur documented forty-one stone-tool marks, and their pattern and location indicate the filleting of leg muscles. XAD-purified bone collagen from the femur returned an AMS 14C radiocarbon age of 11,740±35 bp (13,738 to 13,435 cal. bp), which is as much as 700 years older than the calculated maximum age for Clovis. Although diminished somewhat by the lack of primary provenience data, these results offer significant evidence for late Pleistocene human exploitation of this North American taxon.

A report on late Quaternary vertebrate fossil assemblages from the eastern San Francisco Bay region, California

Here we report on vertebrate fossil assemblages from two late Quaternary localities in the eastern San Francisco Bay region, Pacheco 1 and Pacheco 2. At least six species of extinct mammalian megaherbivores are known from Pacheco 1. The probable occurrence of Megalonyx jeffersonii suggests a late Pleistocene age for the assemblage. Pacheco 2 has yielded a minimum of 20 species of mammals, and provides the first unambiguous Quaternary fossil record of Urocyon, Procyon, Antrozous, Eptesicus, Lasiurus, Sorex ornatus, Tamias, and Microtus longicaudus from the San Francisco Bay region. While a radiocarbon date of 405 ± 45 RCYBP has been obtained for a single bone sample from Pacheco 2, the possibility that much of the assemblage is considerably older than this date is suggested by (1) the substantial loss of collagen in all other samples for which radiocarbon dating was unsuccessfully attempted and (2) the occurrence of Microtus longicaudus approximately 160 km to the west of, and 600 m lower in elevation than, its present range limit. The taphonomic data and limited stratigraphic information for the two localities suggest deposition of bones within a riparian system. Multiple lines of evidence including the taxonomic composition and the relative abundance of skeletal elements point to the original accumulation of most, if not all, of the small vertebrate remains at Pacheco 2 by owls. Based on taxonomic composition, Pacheco 1 appears to have been located in a mosaic of grassland and woodland habitats, and Pacheco 2 in moist woodland with dense underbrush and a body of freshwater.

First Report of Jefferson's Ground Sloth (Megalonyx jeffersonii) in North Dakota: Paleobiogeographical and Paleoecological Significance

A well-preserved ungual of a pes documents the presence of Jefferson’s ground sloth (Megalonyx jeffersonii )a t the end of the Wisconsinan in North Dakota. This is the 1st report of M. jeffersonii in North Dakota, and one of few records from the upper Great Plains. An accelerator mass spectrometer radiocarbon age of 11,915 6 40 years ago was obtained from the specimen, suggesting that the sloth resided in North Dakota during the Rancholabrean Land Mammal Age, just before extinction of the species. Palynological records from sites near the sloth occurrence and of the same age indicate that it resided in a cool, moist, spruce-dominated forest habitat in a riparian setting along the Missouri River. Its presence in that setting corroborates the notion that Jefferson’s ground sloth was a browsing inhabitant of gallery forests associated with rivers. It is likely that M. jeffersonii used river valleys, such as the Missouri River valley, as migration routes.

Latest Pleistocene paleoecology of Jefferson's ground sloth ( Megalonyx jeffersonii) and elk-moose ( Cervalces scotti) in northern Illinois

New records of Jefferson's ground sloth ( Megalonyx jeffersonii) and elk-moose ( Cervalces scotti) from Lang Farm provide the first precise temporal correlation of these taxa with the specific environments inhabited by them near the time of their extinction. Six AMS 14C measurements establish an age of 11,405 ± 50 14C yr B.P. for Lang Farm Cervalces and an age of 11,430 ± 60 or 11,485 ± 40 14C yr B.P. for the Megalonyx. These measurements represent the youngest 14C dates for these two genera based on direct dating. Comparison of the dates with pollen data from northern Illinois indicates that these species inhabited a nonanalog environment that was transitional from mid-latitude tundra to mixed conifer and deciduous woodland. Although spruce ( Picea sp.) was dominant, it was less abundant than prior to 12,500 14C yr B.P. The presence of black ash ( Fraxinus nigra) and fir ( Abies sp.) indicates a wet climate and heavy winter precipitation. This may have been the preferred habitat for Cervalces because of its narrow geographic range. However, this habitat type was only one of many occupied by Megalonyx as indicated by its broad geographic distribution.

The Ground Sloth, <i>Megalonyx</i>, from Pleistocene Deposits of the Old Crow Basin, Yukon, Canada

The bear-sized ground sloth Megalonyx, endemic to North America, was widespread during the Pleistocene, reaching as far north as Alaska, Yukon, and Northwest Territories. Twenty-two specimens collected from 10 localities in the Old Crow Basin, northern Yukon, include several bones that can be referred to Jefferson's ground sloth (Megalonyx jeffersonii) on the basis of the distinctive morphology of the upper and lower caniniform teeth. All of the Yukon specimens are relatively small, suggesting a geological age earlier than Wisconsinan - probably Sangamonian. The Alaskan, Yukon, and Northwest Territories records imply that the species occupied a broad east-west range in northwestern North America during a warm phase of the late Pleistocene.

A Mandible of Megalonyx from the Pleistocene of Oklahoma

A Mandible of Megalonyx from the Pleistocene of Oklahoma

On the Occurrence of Megalonyx Jeffersonii (Harlan) in Central Ohio

On the Occurrence of Megalonyx Jeffersonii (Harlan) in Central Ohio

On Myomorphus cubensis, a new subgenus of Megalonyx

<i>On</i> Myomorphus cubensis, <i>a new subgenus of</i> Megalonyx

Remarks on the Structure of the Feet of Megalonyx

Remarks on the Structure of the Feet of Megalonyx