No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
Fossils explained 51: Sloths
Abstract
Sloths.
... The overall size of the cave, especially the original heights of 2.0 m of the North Tunnel and of the beginning of the South Tunnel, permits us to attribute the cave to ground sloths, possibly to one of the genera Scelidotherium, Mylodon, Glossotherium or possibly Lestodon. Sloths had the necessary morphological adaptations for digging tunnels (BARGO et al., 2000, NAISH, 2005. Tunnels of similar sizes, morphologies and surface structures on the walls have been found on several other places in Southern Brazil (e.g., FRANK et al., 2010). ...
The cave known as "Toca do Tatu" ("armadillo shelter") (28º46'21.2''S, 49º53'45.9''W) is located in the
municipality of Timbé do Sul, in the state of Santa Catarina (Brazil) and is 48.5 m long, with two almost
parallel tunnels that converge to a larger space within the cave. The general morphology of the cave and
locally abundant claw scratches on the walls show that the cave was created as a shelter probably dug by
ground sloths during the Cenozoic. In the euphotic and disphotic zones of both tunnels more than 35 m2 of
the walls are covered by rock art with over 5 different geometries, showing that the cave was reoccupied
later by pre-Columbian populations. Witnesses report that treasure hunters opened the cave entrance by
removing the predominantly sandy sediments accumulated in the front of the cave, which almost completely
blocked its entrances. These treasure hunters left tool traces on the cave walls and widened another access to
the deeper spaces of the cave. Finally, tourists who visited the site over the past decades have left signs such
as names, dates and symbols on the walls, ending the cycle of agents that created this cave and left their
traces in it.
... There are possible explanations for this result, but they only can be tested in future studies. First of all, the giant sloth metabolism could have affected the isotopic content in their body tissues, but all the giant sloths are extinct and their unusual form makes comparisons with recent large mammals very complicated (Naish, 2005). Second , the oscillations in climatic conditions could affect the d ...
The skull is a unique and complex structure of vertebrates and a main focus of morphological and systematic studies. Although Crocodilians represent an important component of Archosauria group, our knowledge of the development and homology are few. Herein, we describe the detailed development sequence of skull of the Caiman yacare (Daudin, 1802) in an effort to contribute to filling this anatomical gap. Embryos were sampled randomly at a regular intervals during full incubation period and morphological descriptions are based on cleared and stained and embryos. The ossification pattern of C. yacare follow general aspects for reptiles and others tetrapods. The first ossification centers occur in dermal bones involved in primary functions such as feeding and breathing, like maxillae, dentary, splenial, angular, pterygoid, ectopterygoid and jugal, including the teeth. Bones of dorsal portion of the neurocraniun ossify later, showing a cranial fontanelle that remains at the hatching. The parietal, frontal and opisthotic have more than one ossification center that fuse during ontogeny. The ossification center for parasphenoid was absent and only one ossification center is present for basisphenoid bone. The posterior portion of the skull is formed for ossification centers of chondrocranium substitution that ossify in later stages.
Significance
It has long been proposed that rules stemming from the mechanisms used during development can constrain the range of evolvable variations in a given form, but few empirical examples are known. We have focused on developmental processes determining proportions of phalanx size along individual digits (fingers/toes) of vertebrates. We find that phalangeal variation seen in nature is indeed constrained by an ancestral developmental program, limiting morphologies to a continuum from nearly equal-sized phalanges to a large-to-small gradient of relative sizes. Nonetheless, later innovations in distal regulation expanded variational possibilities for groups that needed greater grasping ability. These data provide a better understanding of how properties of developmental systems work in combination with natural selection to guide evolution of skeletal proportions.
In this unique book, Peter S. Ungar tells the story of mammalian teeth from their origin through their evolution to their current diversity. Mammal Teeth traces the evolutionary history of teeth, beginning with the very first mineralized vertebrate structures half a billion years ago. Ungar describes how the simple conical tooth of early vertebrates became the molars, incisors, and other forms we see in mammals today. Evolutionary adaptations changed pointy teeth into flatter ones, with specialized shapes designed to complement the corresponding jaw. Ungar explains tooth structure and function in the context of nutritional needs. The myriad tooth shapes produced by evolution offer different solutions to the fundamental problem of how to squeeze as many nutrients as possible out of foods. The book also highlights Ungar's own path-breaking studies that show how microwear analysis can help us understand ancient diets. The final part of the book provides an in-depth examination of mammalian teeth today, surveying all orders in the class, family by family. Ungar describes some of the more bizarre teeth, such as tusks, and the mammal diversity that accompanies these morphological wonders. Mammal Teeth captures the evolution of mammals, including humans, through the prism of dental change. Synthesizing decades of research, Ungar reveals the interconnections among mammal diet, dentition, and evolution. His book is a must-read for paleontologists, mammalogists, and anthropologists. © 2010 The Johns Hopkins University Press. All rights reserved.
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.
Remains of Eremotherium, representing a large-sized megatheriid ground sloth, are known from localities in North, Central, and South America. Usually these remains are currently assigned to the following three species, based largely on geographic provenance: E. laurillardi (Lund), E. mirabile (Leidy), and E. rusconii (Schaub). However, two large, recently recovered collections of Eremotherium remains from Jacobina, Bahia, Brazil, and Daytona Beach, Florida, USA, do not support the separation of these species. Instead, these collections demonstrate the existence of a single Panamerican species. The range of variation is larger than was suspected and the morphological characteristics used in species distinction are not diagnostically valid.The valid name for this species is E. laurillardi (Lund, 1842). The type is a juvenile molariform (ZMUC 1130) from the Pleistocene of Lagoa Santa, Minas Gerais, Brazil. E. mirabile (Leidy, 1855) and E. rusconii (Schaub, 1935) fall as junior synonyms.
Two new specimens of the aquatic sloth Thalassocnus from the Pliocene of Peru are described, one of T. carolomartini McDonald and Muizon, 2002 and the other T. yaucensis, sp. nov. Comparisons with the type species of Thalassocnus, T. natans, demonstrates that T. carolomartini and T. yaucensis are more similar morphologically to each other than to other species of the genus and are more derived. For example, both have a more elongated rostrum (premaxillae and mandibular spout) and more robust, quadrate to circular molariform teeth. The aquatic sloth Thalassocnus is sufficiently distinct morphologically that it is placed in a new subfamily, the Thalassocninae, and the Nothrotheriinae is raised to family rank. The morphological features shared by T. carolomartini and T. yaucensis indicate these species were better adapted to grazing on marine vegetation than earlier species of Thalassocnus.
This study is undertaken in order to evaluate specific hypotheses of relationship among extant and extinct sloths (Mammalia, Xenarthra, Tardigrada). Questions of particular interest include the relationship among the three traditional family groupings of extinct ground sloths and the monophyletic or diphyletic origin of the two genera of extant tree sloths. A computer-based cladistic investigation of the phylogenetic relationships among 33 sloth genera is performed based upon 286 osteological characteristics of the skull, lower jaw, dentition and hyoid arch. Characters are polarized via comparisons with the following successive outgroups, all members of the supraordinal grouping Edentata: the Vermilingua, or anteaters; the Cingulata, or armadillos and glyptodonts; the Palaeanodonta; and the Pholidota, or pangolins. The results of the analysis strongly corroborate the diphyly of living tree sloths, with the three-toed sloth Bradypus positioned as the sister-taxon to all other sloths, and the two-toed sloth Choloepus allied with extinct members of the family Megalonychidae. These results imply that the split between the two extant sloth genera is ancient, dating back perhaps as much as 40 Myr, and that the similarities between the two taxa, including their suspensory locomotor habits, present one of the most dramatic examples of convergent evolution known among mammals. The monophyly of the three traditional ground sloth families Megatheriidae, Megalonychidae and Mylodontidae is confirmed in the present study, and the late Miocene–Pleistocene nothrotheres are shown to form a clade. It is suggested that this latter clade merits recognition as a distinct family-level grouping, the family Nothrotheriidae. The monophyly of the Megatherioidea, a clade including members of the families Megatheriidae, Megalonychidae and Nothrotheriidae, is also supported. Within Megatherioidea, the families Nothrotheriidae and Megatheriidae form a monophyletic group called the Megatheria. The relationships within the families Megatheriidae and Mylodontidae are fully and consistently resolved, although the hypothesized scheme of relationships among the late Miocene to Pleistocene members of the mylodontid subfamily Mylodontinae differ strongly from any proposed by previous authors. Within the family Megalonychidae, Choloepus is allied to a monophyletic grouping of West Indian sloths, although the relationships within this clade are not fully resolved. © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society, 2004, 140, 255–305.
The traditional point of view that fossil ground sloths (Xenarthra) were a relatively uniform, ecologically little diverse group has been recently challenged. Marine habits have been ascribed to Thalassocnus natans of the Pliocene of Peru. Also, a more diverse diet has been proposed by one of us (R.A.F.) for some Lujanian (late Pleistocene-early Holocene of South America genera of ground sloths. In this paper, an aspect of this latter hypothesis is tested, i.e. that Megatherium americanum had morphological features that are better explained by its having had carnivorous habits rather than by solely herbivorous ones. Specifically, the question of its forearms having been designed for optimizing speed rather than strength of extension is addressed. Such a trait might have been associated with a potentially aggressive use of the animal large claws, whereas a strong extension would be more proper for tearing branches out. On the other hand the high mechanical advantage of the biceps might have made it possible for the animal to have lifted and carried heavy weights. This in turn, suggests the possibility that the animal could have manipulated large prey (for instance, turning dorsally armoured preys or carcasses upside down to expose softer parts and cached large food pieces in a safer place. By this view, Megatherium americanum would be the largest land mammal hunter to have existed.
Advancements in ancient DNA analyses now permit comparative molecular and morphological studies of extinct animal dung commonly preserved in caves of semiarid regions. These new techniques are showcased using a unique dung deposit preserved in a late glacial vizcacha (Lagidium sp.) midden from a limestone cave in southwestern Argentina (38.5° S). Phylogenetic analyses of the mitochondrial DNA show that the dung originated from a small ground sloth species not yet represented by skeletal material in the region, and not closely related to any of the four previously sequenced extinct and extant sloth species. Analyses of pollen and plant cuticles, as well as analyses of the chloroplast DNA, show that the Cuchillo Curá ground sloth browsed on many of the same herb, grass, and shrub genera common at the site today, and that its habitat was treeless Patagonian scrub-steppe. We envision a day when molecular analyses are used routinely to supplement morphological identifications and possibly to provide a time-lapse view of molecular diversification.