The behaviour and activity budgets of two sympatric sloths; Bradypus variegatus and Choloepus hoffmanni.

It is usually beneficial for species to restrict activity to a particular phase of the 24-hour cycle as this enables the development of morphological and behavioural adaptations to enhance survival under specific biotic and abiotic conditions. Sloth activity patterns are thought to be strongly related to the environmental conditions due to the metabolic consequences of having a low and highly variable core body temperature. Understanding the drivers of sloth activity and their ability to withstand environmental fluctuations is of growing importance for the development of effective conservation measures, particularly when we consider the vulnerability of tropical ecosystems to climate change and the escalating impacts of anthropogenic activities in South and Central America. Unfortunately, the cryptic nature of sloths makes long term observational research difficult and so there is very little existing literature examining the behavioural ecology of wild sloths. Here, we used micro data loggers to continuously record, for the first time, the behaviour of both Bradypus and Choloepus sloths over periods of days to weeks. We investigate how fluctuations in the environmental conditions affect the activity of sloths inhabiting a lowland rainforest on the Caribbean coast of Costa Rica and examined how this might relate to their low power lifestyle. Both Bradypus and Choloepus sloths were found to be cathemeral in their activity, with high levels of between-individual and within-individual variation in the amounts of time spent active, and in the temporal distribution of activity over the 24-hour cycle. Daily temperature did not affect activity, although Bradypus sloths were found to show increased nocturnal activity on colder nights, and on nights following colder days. Our results demonstrate a distinct lack of synchronicity within the same population, and we suggest that this pattern provides sloths with the flexibility to exploit favourable environmental conditions whilst reducing the threat of predation.

Cranial osteology of a juvenile specimen of Acratocnus ye (Mammalia, Xenarthra, Folivora) and its ontogenetic and phylogenetic implications.

The present study comprises a description of the skull and jaw anatomy of a juvenile specimen of the Antillean sloth Acratocnus ye, from the Holocene of Haiti. Detailed descriptions and illustrations are provided of the skull bones and their sutural connections, which normally fuse in adults. Descriptions are also provided for the mandible and ear ossicles, as well as endocranial surfaces and sinuses exposed by breaks. The anatomy of our juvenile A. ye is compared to that of adult A. ye to assess ontogenetic changes in the skull. Several of these ontogenetic features are significant new observations that impact the relationships within Xenarthra as a whole, or between Xenarthrans and other placental mammals, most notably, the presence of a separate mesethmoid element, the presence of alveoli for a lower deciduous canine and anterior incisor, and the presence of separate rostral and caudal entotympanic elements. A full list of such changes are provided. In addition, the specimen provides information on phylogenetically relevant characters, including features unique to the genus Acratocnus, and features of the clade Choloepodini, including Acratocnus, the smaller extinct Antillean sloth Neocnus, and the extant two-toed sloth Choloepus. Contrary to previous studies, Acratocnus shares as many features with Choloepus as it does with its fellow Antillean form Neocnus in the present study, which is consistent with current morphology-based phylogenetic hypotheses regarding the relationships within Choloepodini. The current study highlights the need for further anatomical and phylogenetic investigations of Antillean sloths (Megalocnidae/Megalonychidae), and juvenile sloths in general.

Ossification pattern of the unusual pisiform in two-toed (Choloepus) and three-toed sloths (Bradypus).

Two-toed (Choloepus sp.) and three-toed (Bradypus sp.) sloths possess short, rounded pisiforms that are rare among mammals and differ from other members of Xenarthra like the giant anteater (Myrmecophaga tridactyla) which retain elongated, rod-like pisiforms in common with most mammals. Using photographs, radiographs, and µCT, we assessed ossification patterns in the pisiform and the paralogous tarsal, the calcaneus, for two-toed sloths, three-toed sloths, and giant anteaters to determine the process by which pisiform reduction occurs in sloths and compare it to other previously studied examples of pisiform reduction in humans and orangutans. Both extant sloth genera achieve pisiform reduction through the loss of a secondary ossification center and the likely disruption of the associated growth plate based on an unusually porous subchondral surface. This represents a third unique mechanism of pisiform reduction among mammals, along with primary ossification center loss in humans and retention of two ossification centers with likely reduced growth periods in orangutans. Given the remarkable similarities between two-toed and three-toed sloth pisiform ossification patterns and the presence of pisiform reduction in fossil sloths, extant sloth pisiform morphology does not appear to represent a recent convergent adaptation to suspensory locomotion, but instead is likely to be an ancestral trait of Folivora that emerged early in the radiation of extant and fossil sloths.

The dermal armor of mylodontid sloths (Mammalia, Xenarthra) from Cueva del Milodón (Última Esperanza, Chile).

Dermal ossifications (osteoderms, dermal ossicles, osteoscutes) appear independently in various tetrapod lineages. In mammals, however, dermal ossifications are only present in some members of Xenarthra. This clade includes Cingulata (armadillos and their relatives), and Pilosa, including Vermilingua (anteaters) and Folivora (sloths). In extant xenarthrans, osteoderms are invariably present in cingulates whereas they are absent in pilosans. Among extinct sloths, however, a limited number of taxa possessed dermal ossifications. Records of mummified skins of ground sloths bearing osteoderms found in Cueva del Milodón (Southern Chile), with a late Pleistocene age, allowed us to analyze their micro- and macroscopic morphology. The main goal of this study is to closely examine a portion of a mylodontid skin portion using radiography. The arrangement, morphology and internal structure of the ossicles are analyzed and the results are discussed in the context of previous research. The results we obtained indicate that ossicles vary in shape and size, and the integument has four different patterns of arrangement of the ossicles: that is, areas without ossicles, disorganized ossicles, rows, and mosaic areas. The latter has two variants, with clusters of ossicles forming rosettes or stars. Thin sections of the ossicles allowed us to recognize and describe anatomical features of the bone and its mode of growth. Finally, paleobiological and functional considerations of the dermal armor are discussed along with its phylogenetic and chronological implications.

Evolution of bone cortical compactness in slow arboreal mammals.

Convergent evolution is a major topic in evolutionary biology. Low bone cortical compactness (CC, a measure of porosity of cortical bone) in the extant genera of "tree sloths," has been linked to their convergent slow arboreal ecology. This proposed relationship of low CC with a slow arboreal lifestyle suggests potential convergent evolution of this trait in other slow arboreal mammals. Femoral and humeral CC were analyzed in "tree sloths," lorisids, koala, and extinct palaeopropithecids and Megaladapis, in comparison to closely related but ecologically distinct taxa, in a phylogenetic framework. Low CC in "tree sloths" is unparalleled by any analyzed clade and the high CC in extinct sloths suggests the recent convergence of low CC in "tree sloths." A tendency for low CC was found in Palaeopropithecus and Megaladapis. However, lorisids and the koala yielded unexpected CC patterns, preventing the recognition of a straightforward convergence of low CC in slow arboreal mammals. This study uncovers a complex relationship between CC and convergent evolution of slow arboreality, highlighting the multifactorial specificity of bone microstructure.

A novel method for quantifying femoral neck anteversion: A case study in extinct and extant sloths.

Extinct sloths represent a wide range of morphological, locomotor, and body size variation. Researchers have examined femoral neck angle in two dimensions to hypothesize locomotor behaviors in this group; however, this measure does not account for femoral neck anteversion. Here, we present a new method for quantifying femoral neck anteversion angle, in addition to femoral neck angle, to capture the 3D position of the femoral head/neck. Femora of extant (n = 21; Bradypus and Choloepus) and extinct (n = 49; Acratocnus, Megalocnus, Neocnus, and Parocnus) sloths were surface scanned and their surface models used to calculate three angles of femoral neck anteversion and femoral neck angle. Femoral neck anteversion was calculated as the angle between the femoral neck axis and the geometric axis of the femoral condyles (GA), the 35% cross section axis, and a trochanter axis. Femoral neck angle was calculated as the angle between the femoral neck and shaft axes. Genera were compared using ANOVAs with post hoc multiple comparisons for each angle. Femoral neck angle and femoral neck anteversion relative to the cross section were also analyzed. Significant differences among genera exist for all angles, (p < .001) but not all angles separate all genera. Femoral neck and anteversion angles typically yield different results, demonstrating the utility of analyzing both angles. The GA and cross section angles are highly correlated in sloths, with the exception of comparisons among Megalocnus, Parocnus, and Neocnus, suggesting morphological variation in the distal femur. While this method was applied to sloths, it has broad applicability to mammalian groups.

Description of brachial plexus of sloth (Bradypus variegatus) / Descrição do plexo braquial do bicho-preguiça (Bradypus variegatus)

The species Bradypus variegatus is known as the common sloth, an endemic mammal from neotropical regions, which has been suffering from devastating anthropogenic activities. Our study aimed to describe the brachial plexus of B. variegates, regarding the origin and distribution of nerves, through the sampling of 10 adult females. Analyses were carried out at the Anatomy Section, "Departamento de Morfologia e Fisiologia Animal", "Universidade Federal Rural de Pernambuco", under license no. 034/2015 of the Ethics Committee on the Use of Animals. The results determined that the brachial plexus of the common sloth starts from the fifth cervical spine segment until the second thoracic segment. This area contains the long and suprascapular thoracic nerves, which originate immediately from the medullary segment 5 and 6, respectively, and from the pectoral, subscapular, axillary, radial, musculocutaneous, medial, forearm and ulnar medial cutaneous nerves, arising from a trunk comprised of cervical spine nerves (C) 7, C8, C9, and thoracic (T) 1 and T2. Regarding other wild and domestic animals, different suggestions were observed about the origin of the plexus in B. variegatus, however, the constituent nerves and their innervation areas did not demonstrate any discrepancies.(AU)

A espécie Bradypus variegatus é conhecida como preguiça-comum. Trata-se de um mamífero endêmico de regiões neotropicais que vem sofrendo com a ação antrópica devastadora. Esses Bradipodídeos possuem três dedos nos membros torácicos e pélvicos, são arborícolas consagrados e descem ao solo apenas para excretar e trocar de árvore. O estudo teve como objetivo descrever o plexo braquial de B. variegatus em relação à origem e distribuição dos nervos. Para tal, utilizou-se 10 fêmeas adultas. As análises foram realizadas no Pavilhão de Anatomia do Departamento de Morfologia e Fisiologia Animal da Universidade Federal Rural de Pernambuco, sob a licença nº 034/2015 do Comitê de Ética no Uso de Animais. Os cadáveres foram obtidos após morte natural, fixados em formaldeído a 20%, conservados em solução salina a 30% em tanques e dissecados para a visualização dos nervos destinados a inervar os membros e músculos torácicos. Uma vez feito, constatou-se que o plexo braquial da preguiça-comum se origina do quinto segmento espinal cervical, se estendendo até o segundo segmento torácico. Sendo formado pelos nervos torácico longo e supraescapular, de origem imediatamente do segmento medular 5 e 6, respectivamente, e pelos nervos peitorais, subescapulares, axilar, radial, musculocutâneo, mediano, cutâneo medial do antebraço e ulnar, decorrentes de um tronco formado a partir de nervos espinais cervicais (C) 7, C8, C9, e torácicos (T) 1 e T2. Em comparação a outros animais silvestres e domésticos foram observadas diferentes disposições em relação à origem do plexo de B. variegatus, todavia, os nervos constituintes e suas áreas de inervação não apresentaram discrepâncias.(AU)

Macroscopic morphological aspects, ecometry and rebound tonometry of the eye bulb in sloth (Bradypus variegatus) / Aspectos morfológicos macroscópicos, ecometria e tonometria de rebote do bulbo ocular em bicho-preguiça (Bradypus variegatus)

The field related to the visual system of wild animals is deeply scarce. Settling anatomical and physiological parameters for these animals is still a descriptive vision for Bradypus variegatus (Schinz, 1825). Thus, our research aimed to determine patterns of normal eye for this species. For this purpose, eight eye bulbs were dissected from the carcasses obtained by natural death, and then performed an overview of ocular anatomical. Rebound tonometry (RBT) and ocular B-mode ultrasonography were also applied for eight eyes in four animals from "Parque Estadual Dois Irmãos", situated in the city of Recife, state of Pernambuco (PE), to estimate the intraocular pressure and ocular ecobiometry. The ocular morphology of sloth is similar as described for other species, however, with some peculiarities. They present a third eyelid emerging in the nasal region of the inferior conjunctival sac and retina and also contain little differentiated blood vessels. Medium the intraocular pressure (IOP) was 4.25mmHg with no difference for both eyes. Ultrasonography of ocular anatomy is also similar regarding other species. Ecobiometric patterns were evaluated to determine the anterior chamber depth, lens width, vitreous chamber depth, and axial length (AL) of ocular globe and the averaged as shown 0.63±1.11mm, 3.73±0.24mm, 6.15±0.41mm, 3.70±0.27mm, and 8.48±0.22mm, respectively. There was no difference between the right and left eyes. The RBT and ocular B-mode ultrasonography are fast exams and easy for animal testing. This study contributed to the characterization of ocular anatomy as well as settling medium values of IOP and intraocular measures; however, further research on physiology and histology is necessary to better understand the visual function of the species.(AU)

O campo de estudo relacionado ao sistema visual de animais silvestres é muito escasso. Estabelecer parâmetros anatômicos e fisiológicos para estes animais ainda está restrito a uma visão descritiva, assim ocorre em Bradypus variegatus (Schinz, 1825). Diante deste fato, objetivou-se com este estudo determinar padrões de normalidade oftálmica nesta espécie. Para isto foram dissecados oito bulbos oculares de cadáveres obtidos por morte natural e realizada a descrição anatômica ocular. Além disso, foram realizadas tonometria de rebote (TonoVet®) e ultrassonografia em modo B em oito olhos de quatro animais provenientes do Parque Estadual Dois Irmãos, Recife/PE, para avaliação da pressão intraocular e realização da ecobiometria ocular. A anatomia ocular do bicho-preguiça é semelhante à descrita para outras espécies com algumas particularidades. Apresentam uma terceira pálpebra emergindo na região nasal do saco conjuntival inferior e retina com vasos sanguíneos pouco diferenciados. A pressão intraocular média foi de 4,25mmHg não havendo diferença entre os olhos direito e esquerdo. A anatomia ocular ultrassonográfica é semelhante à encontrada para outras espécies. Os padrões ecobiométricos obtidos foram: profundidade da câmara anterior, espessura do cristalino, diâmetro do cristalino, profundidade da câmara vítrea e comprimento axial do bubo ocular com tamanhos médios de 0,63±1,11mm, 3,73±0,24mm, 6,15±0,41mm, 3,70±0,27mm e 8,48±0,22mm, respectivamente. Não houve diferença entre os olhos direito e esquerdo. A tonometria de rebote e a ultrassonografia ocular em modo B são exames de rápida e fácil execução, sendo bem tolerados pelos animais. Este estudo contribuiu para a caracterização anatômica ocular e para o estabelecimento de valores médios da pressão intraocular e das medidas intraoculares, no entanto são necessárias outras pesquisas na área da fisiologia e histologia para melhor compreensão da função visual da espécie.(AU)

Descrição anatômica da artéria carótida externa e seus ramos na preguiça-comum / Anatomical description of external carotid artery and its branches in sloth

Bradypus variegatus, espécie pertencente à família Bradypodidae e à superordem Xenarthra, pode ser considerada modelo biológico de caráter multidisciplinar. Assim, realizou-se um trabalho de descrição anatômica da artéria carótida externa (ACE) e dos seus ramos no bicho-preguiça B. variegatus. Utilizaram-se 10 animais adultos, sendo todos fêmeas, que foram submetidos à dissecação, constatando-se que a artéria (a.) carótida comum se bifurca, em externa e interna, no nível do primeiro anel traqueal. A ACE, então, segue estendendo-se até a maxila, onde emite ramos para a região temporal e para o polo posterior do olho. Em todos os animais estudados, foram observados sete ramos principais da ACE, que, segundo a sua origem e localização, foram denominados como a. auricular, a. lingual, a. facial, a. alveolar, a. inferior, a. temporal, a. maxilar e a. oftálmica. Os ramos maxilar e oftálmico correspondem aos terminais e os demais são ramos colaterais. Em 50% dos animais analisados, foi verificada a presença de anastomoses arteriais e 40% deles apresentaram o acréscimo de um ramo aos principais. Desses, 30% demonstraram a presença de um ramo traqueal e 10% de um ramo sublingual, sendo esses ramos colaterais.(AU)

Bradypus variegatus is a species belonging to the family Bradypodidae and superorder Xenarthra, which should be considered as a multidisciplinary biological model. Thus, an anatomical description of the external carotid artery (ACE) and its branches in sloth B. variegatus was studied. Ten adult animals, all of them female, were submitted to dissection, and it was observed that the common carotid artery (a.) bifurcates in external and internal at the level of the first tracheal ring. Then, ACE extends through the maxilla where it launches branches to the temporal region and posterior eye side. For all sampled animals, seven principal branches of ACE were observed, and according to their origin and location were denominated as auricular, lingual, facial, bottom alveolar, temporal, maxillary and ophthalmic arteries. The maxillary and ophthalmic branches correspond to the terminals and the other branches are collateral. Presence of arterial anastomoses was observed in 50% of the sampled animals and 40% of them had increase of a branch on the principal. In these, 30% had presence of one tracheal branch and 10% of a sublingual branch, considering these branches as collateral.(AU)

Brain anatomy of two-toed sloth (Choloepus didactylus, Linnaeus, 1758): A comparative gross anatomical study of extant xenarthrans.

The neural system plays an important role in understanding some features of animals. Anatomical complexity correlates with the increase of functional capacity. Xenarthrans include anteaters (Vermilingua), armadillos (Cingulata) and sloths (Folivora). This group is the base of eutherian mammals, and understanding the anatomy of its neural system could provide data for functional and evolutionary interpretations. The gross anatomy of the xenarthran brain is recorded. Four extant families of Pilosa and two families of Cingulata were sampled. Usual dissection procedures were used, and the brains were analysed macroscopically. The brain of two-toed sloth, three-toed sloth, six-banded armadillo, giant anteater and collared anteater are gyrencephalic. Pygmy anteater, nine-banded armadillo, great long-nosed armadillo, southern naked-tailed armadillo and giant armadillo are lissencephalic. In most species, the rhinal fissure presents two segments, rostral and caudal (except in Vermilingua and three-toed sloth). The diencephalon and brainstem present similar anatomy. The cerebellum is wide and presents four lobes (rostral, central, caudal and floccular). Its average volume is 12.16% (Folivora), 14.26% (Vermilingua) and 18.61% (Cingulata). Among these groups, there is a statistical difference between Folivora/Cingulata concerning the cerebellum average. The general pattern of the brain of the xenarthrans is similar to that of other mammals.

Phylogeny, Macroevolutionary Trends and Historical Biogeography of Sloths: Insights From a Bayesian Morphological Clock Analysis.

Sloths, like other xenarthrans, are an extremely interesting group of mammals that, after a long history of evolution and diversification in South America, became established on islands in the Caribbean and later reached North America during the Great American Biotic Interchange. In all three regions, they were part of the impressive Pleistocene megafauna. Most taxa became extinct and only two small, distantly related tree-dwelling genera survived. Here, we incorporate several recently described genera of sloths into an assembled morphological data supermatrix and apply Bayesian inference, using phylogenetic and morphological clock methods, to 64 sloth genera. Thus, we investigate the evolution of the group in terms of the timing of divergence of different lineages and their diversity, morphological disparity and biogeographical history. The phylogeny obtained supports the existence of the commonly recognized clades for the group. Our results provide divergence time estimates for the major clades within Folivora that could not be dated with molecular methods. Lineage diversity shows an early increase, reaching a peak in the Early Miocene followed by a major drop at the end of the Santacrucian (Early Miocene). A second peak in the Late Miocene was also followed by a major drop at the end of the Huayquerian (Late Miocene). Both events show differential impact at the family level. After that, a slight Plio-Pleistocene decline was observed before the marked drop with the extinction at the end of the Pleistocene. Phenotypic evolutionary rates were high during the early history of the clade, mainly associated with Mylodontidae, but rapidly decreased to lower values around 25 Ma, whereas Megalonychidae had lower rates at the beginning followed by a steady increase, peaking during the Late Miocene and the Pliocene. Morphological disparity showed a similar trend, with an early increase, followed by a slowly increasing phase through the Late Oligocene and Early Miocene, and ending with another increase beginning at the middle of the Miocene. Biogeographic analysis showed southern South America as the most probable area of origin of the clade and the main region in which the early diversification events took place. Both Megatheriinae and Nothrotheriinae basal nodes were strongly correlated with Andean uplift events, whereas the early history of Mylodontidae is closely associated with southern South America and also shows an early occupation of the northern regions. Within Megalonychidae, our results show Choloepus as a descendant of an island dispersing ancestor and a probable re-ingression to South America by a clade that originated in Central or North America.

Bone cortical compactness in 'tree sloths' reflects convergent evolution.

Bone remodeling, one of the main processes that regulate bone microstructure, consists of bone resorption followed by the deposition of secondary bone at the same location. Remodeling intensity varies among taxa, but a characteristically compact cortex is ubiquitous in the long bones of mature terrestrial mammals. A previous analysis found that cortical bone in a few 'tree sloth' (Bradypus and Choloepus) specimens is heavily remodeled and characterized by numerous immature secondary osteons, suggesting that these animals were remodeling their bones at high rate until late in their ontogeny. This study aims at testing if this remodeling is generally present in 'tree sloths', using a quantitative analysis of the humeral cortical compactness (CC) among xenarthrans. The results of the investigation of humeral diaphyseal cross-sections of 26 specimens belonging to 10 xenarthran species including specimens from both extinct and extant species indicate that in 'tree sloths' the CC is significantly lower than in the other sampled xenarthrans. No significant difference was found between the CC of the two genera of 'tree sloths'. Our results are consistent with the hypothesis that the cortical bone of 'tree sloths' in general undergoes intense and balanced remodeling that is maintained until late (possibly throughout) in their ontogeny. In the light of xenarthran phylogeny, low CC represents another convergence between the long-separated 'tree sloth' lineages. Although the exact structural and/or functional demands that are associated with this trait are hitherto unknown, several hypotheses are suggested here, including a relationship to their relatively low metabolism and to the mechanical demands imposed upon the bones by the suspensory posture and locomotion, which was independently acquired by the two genera of 'tree sloths'.

Homeotic transformations reflect departure from the mammalian 'rule of seven' cervical vertebrae in sloths: inferences on the Hox code and morphological modularity of the mammalian neck.

BACKGROUND: Sloths are one of only two exceptions to the mammalian 'rule of seven' vertebrae in the neck. As a striking case of breaking the evolutionary constraint, the explanation for the exceptional number of cervical vertebrae in sloths is still under debate. Two diverging hypotheses, both ultimately linked to the low metabolic rate of sloths, have been proposed: hypothesis 1 involves morphological transformation of vertebrae due to changes in the Hox gene expression pattern and hypothesis 2 assumes that the Hox gene expression pattern is not altered and the identity of the vertebrae is not changed. Direct evidence supporting either hypothesis would involve knowledge of the vertebral Hox code in sloths, but the realization of such studies is extremely limited. Here, on the basis of the previously established correlation between anterior Hox gene expression and the quantifiable vertebral shape, we present the morphological regionalization of the neck in three different species of sloths with aberrant cervical count providing indirect insight into the vertebral Hox code. RESULTS: Shape differences within the cervical vertebral column suggest a mouse-like Hox code in the neck of sloths. We infer an anterior shift of HoxC-6 expression in association with the first thoracic vertebra in short-necked sloths with decreased cervical count, and a posterior shift of HoxC-5 and HoxC-6 expression in long-necked sloths with increased cervical count. CONCLUSION: Although only future developmental analyses in non-model organisms, such as sloths, will yield direct evidence for the evolutionary mechanism responsible for the aberrant number of cervical vertebrae, our observations lend support to hypothesis 1 indicating that the number of modules is retained but their boundaries are displaced. Our approach based on quantified morphological differences also provides a reliable basis for further research including fossil taxa such as extinct 'ground sloths' in order to trace the pattern and the underlying genetic mechanisms in the evolution of the vertebral column in mammals.

Ramos do arco aórtico e da aorta torácica em bicho-preguiça (Bradypus variegatus) / Branches of the aortic arch and thoracic aorta of the sloth (Bradypus variegatus)

As preguiças são mamíferos arborícolas, bem específicos quanto aos hábitos e à morfofisiologia. Essa condição faz delas ainda mais vulneráveis aos impactos ambientais. Com o objetivo de fornecer informações que auxiliem na clínica médico-cirúrgica desses Xenarthras, realizou-se um estudo do arco aórtico e da artéria aorta torácica, a fim de se identificarem seus principais ramos. Foram utilizados 10 animais da espécie Bradypus variegatus, sendo uma fêmea e três machos submetidos a dissecação, por meio da qual foram obtidas medidas de diâmetro e comprimento dos vasos, enquanto três fêmeas e três machos destinaram-se à técnica de radiografia digital com contraste. Constatou-se uma sintopia uniforme do arco, bem como da porção descendente da artéria aorta no tórax. No entanto, a topografia difere consideravelmente. Com base nos ramos, percebeu-se, independentemente do sexo, uma maior variação naqueles originados do arco e dos que emergem da artéria aorta torácica e irrigam estruturas medianas e do antímero direito do tórax. Foram obtidos valores maiores para o diâmetro das artérias na fêmea do que nos machos e, para o comprimento da artéria aorta torácica, foram encontrados valores correspondentes em ambos. Toda essa variação dos bradipodídeos apresenta diferenças em relação a outros mamíferos.(AU)

Sloths are arboreal mammals, very specific, regarding their habits and morphology. This condition makes them even more vulnerable to environmental impacts. In order to provide information to assist in the medical and surgical assistance to these Xenarthras, a study of the aortic arch and thoracic portion of the descending aorta was carried out with the purpose of identify its main branches. Ten animals of the Bradypus variegatus species were used. One female and three males were submitted to dissection, where measurements of vessel diameter and length were obtained, while three females and three males were submitted to the digital contrast x-ray technique. There was a uniform syntopy of the arch, as well as of the descending portion of the aorta in the thorax. However, the topography differs considerably. Based on the branches, regardless of gender, a greater variation was observed in those originating from the arch, and those that emerge from the thoracic aorta and irrigate medial structures and the right antimere of the thorax. Greater values were obtained for the diameter of the arteries in the female than in the males and corresponding values for the length of the thoracic aorta in both. All this variation is possibly related to the adaptive processes of Bradipodidae over time.(AU)

Sloths of the Atlantic Forest in the sixteenth and seventeenth centuries.

Sloths were a curiosity item for Europeans in the 16th and 17th centuries, and several descriptions of them exist in bestiaries and texts of that time. Here, we assemble the descriptions and drawings of sloths from the travellers and naturalists of those centuries in the Brazilian Atlantic Forest. The sloth was a novelty to the European audience, and it was described in many strange and inaccurate ways: as a monster, a beast, or an odd child. It served as a source of admiration, amusement, and confusion among naturalists and travellers of the 16th and 17th centuries. We also raised the question about the identity of Carolus Clusius' sloth, a drawing published in Exoticorum libri decem (1605). We compared his drawing with earlier depictions and descriptions, from André Thevet (1516-1590) to George Marcgrave (1610-1644). We present evidence to validate the first drawing of the maned sloth, completed 206 years before the official taxonomic description.

The hidden teeth of sloths: evolutionary vestiges and the development of a simplified dentition.

Xenarthrans are unique among mammals in retaining simplified teeth that are rootless and homodont, which makes it difficult to determine dental homologies. We apply computerized tomography to prenatal developmental series of extant sloths, Bradypus and Choloepus, to further elucidate the patterns of morphological variation in their dentition. We also propose new criteria based on sequences of dental mineralization, and the presence of vestigial teeth, to distinguish between caniniforms and postcaniniforms. We report for the first time the presence of vestigial incisors in Bradypus. We also show the presence of a vestigial tooth in front of the lower caniniform in both extant sloth genera and the existence of two generations for the upper caniniform in Choloepus. The study of their sequence of mineralization indicates that the lower and upper caniniform teeth are not homologous in sloths, and suggests that upper caniniforms are not homologous between the two extant sloth genera. Our results show that assessing the developmental processes and functional constraints remains crucial to understand the dental variations observed in sloths, and more generally, tooth class homology issues in mammals. Applied to the tooth row of all extinct sloths, these developmental data illuminate a potentially ancestral dental formula for sloths.

The locomotion of Babakotia radofilai inferred from epiphyseal and diaphyseal morphology of the humerus and femur.

Palaeopropithecids, or "sloth lemurs," are a diverse clade of large-bodied Malagasy subfossil primates characterized by their inferred suspensory positional behavior. The most recently discovered genus of the palaeopropithecids is Babakotia, and it has been described as more arboreal than Mesopropithecus, but less than Palaeopropithecus. In this article, the within-bone and between-bones articular and cross-sectional diaphyseal proportions of the humerus and femur of Babakotia were compared to extant lemurs, Mesopropithecus and Palaeopropithecus in order to further understand its arboreal adaptations. Additionally, a sample of apes and sloths (Choloepus and Bradypus) are included as functional outgroups composed of suspensory adapted primates and non-primates. Results show that Babakotia and Mesopropithecus both have high humeral/femoral shaft strength proportions, similar to extant great apes and sloths and indicative of forelimb suspensory behavior, with Babakotia more extreme in this regard. All three subfossil taxa have relatively large femoral heads, also associated with suspension in modern taxa. However, Babakotia and Mesopropithecus (but not Palaeopropithecus) have relatively small femoral head surface area to shaft strength proportions suggesting that hind-limb positioning in these taxa during climbing and other behaviors was different than in extant great apes, involving less mobility. Knee and humeral articular dimensions relative to shaft strengths are small in Babakotia and Mesopropithecus, similar to those found in modern sloths and divergent from those in extant great apes and lemurs, suggesting more sloth-like use of these joints during locomotion. Mesopropithecus and Babakotia are more similar to Choloepus in humerofemoral head and length proportions while Palaeopropithecus is more similar to Bradypus. These results provide further evidence of the suspensory adaptations of Babakotia and further highlight similarities to both extant suspensory primates and non-primate slow arboreal climbers and hangers. J. Morphol. 277:1199-1218, 2016. © 2016 Wiley Periodicals, Inc.

Reproductive System of Brown-throated Sloth (Bradypus variegatus, Schinz 1825, Pilosa, Xenarthra): Anatomy and Histology.

In recent years, habitat degradation led to the decline of some populations of brown-throated sloth. The aim of this study was to describe morphological features of the female reproductive system of the species. The oval ovaries were partially surrounded by ovarian bursa. An external cortex and an inner medulla were present. Corpora lutea and corpora albicans together with follicles at various stages of development each with a single oocyte were found in the cortex. Uterine tubes were tortuous, tubular, travelled around the perimeter of the ovary and possessed a folded mucosa with ciliated pseudostratified epithelium. Uterus was simplex, with no horns and divided into three parts: a pear-shaped cranial segment and a long caudal uterine segment (both forming the body of the uterus) and two cervices. Uterus presented three layers: mucosa, lined by pseudostratified epithelium, muscular and serosa. The cervices connected the uterus to the urogenital sinus, a distensible cavity with longitudinal mucosal folds lined by transitional epithelium that extended from the external urethral orifice and the external uterine ostia to the vulva, which was lined by a keratinized stratified squamous epithelium. Brown-throated sloth presented a bipartite clitoris with paired crura, bodies and glandes. The presence of a double cervix and a bipartite clitoris was unique features of the species.

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.

Morfologia e morfometria da traqueia da preguiça (bradypus variegatus): conhecimentos para procedimentos de emergência / Morphological and morphometric trachea sloth (bradypus variegatus): knowledge for emergency procedures

Por ser uma espécie pouco estudada, principalmente do ponto de vista morfológico, objetivou-se conhecer a anatomia da traqueia da preguiça (Bradypus variegatus) a fim de fornecer informações para facilitar a eleição de tubo endotraqueal adequado, máscara laríngea ou cânula de traqueostomia para anestesia e procedimentos de emergência, uma vez que a mesma revelou-se possuidora de uma morfologia especial. Foram investigados 11animais jovens de idades diferentes, sendo quatro machos e sete fêmeas, provenientes do Museu Emilio Goeldi e doados a UFRA. Os exemplares foram perfundidos via intramuscular com solução aquosa de formol a 10% para fins de conservação e posteriormente foram dissecados em nível cervico-torácico, por meio de mesoscopia, expondo-se desde a laringe até os brônquios principais direito e esquerdo ao nível do hilo pulmonar. As traqueias foram divididas em cinco regiões (região cervical, região da primeira flexura, região da segunda flexura, região da terceira flexura e região da carina) as quais foram mensuradas altura e largura, assim como o comprimento traqueal total e parte do material foi submetido à técnicas de rotina histológica. Macroscopicamente, destacou-se a presença de sinuosidades acentuadas em porção médio caudal, contemplando a carina. O comprimento médio traqueal foi de 14,6cm. Microscopicamente, a traqueia era constituída por placas separadas de cartilagem hialina constituindo cada anel, sendo revestido por epitélio estratificado ciliado. Apesar da traqueia da preguiça comum apresentar revestimento padrão encontrado na traqueia de outros animais, na literatura não há registros de outras espécies que tenham morfologia macroscópica nas condições descritas, o que nos leva a sugerir, quando necessário acesso para ventilação de emergência, a prática da IOT e não a de traqueostomia.

As the sloth (Bradypus variegatus) is a little studied species, especially from a morphological point of view, this research aimed to define the anatomy of its trachea. The information would facilitate the selection of a proper endotracheal tube, laryngeal mask or tracheostomy tube for anesthesia and emergency procedures, since it appeared to have a special morphology. Eleven young animals of different ages were investigated, four males and seven females, obtained from the Emilio Goeldi Museum and donated to UFRA. The specimens were infused intramuscularly with 10% aqueous formaldehyde for preservation and were later dissected at the cervico-thoracic level, by mesoscopia, exposing the area from the larynx to the right and left primary bronchi at the hilum. The tracheae were divided into five regions (cervical, first flexure, second flexure, third flexure, and carina) for which length and width were measured, as well as the total tracheal length. Sharp windings were seen in the middle caudal portion, including the carina. The average tracheal length was 14.6 cm. Microscopically, the trachea was made up of separate plates of hyaline cartilage forming each ring, lined with ciliated epithelium. Despite the trachea of the common sloth displaying the same lining pattern found in other animals, there are no reports in the literature of other species having a macroscopic morphology as described here, which leads us to suggest, where appropriate access to emergency ventilation, the practice of IOT and not tracheostomy.