A Paleogeographic Overview of Tropical Fossil Sloths: Towards an Understanding of the Origin of Extant Suspensory Sloths?

Modern sloths are among the more characteristic mammals of South and Central American faunas. Recent discovery in four Paleogene, 22 Neogene, and dozens of Pleistocene fossiliferous localities in the tropics has revealed an unexpected paleobioversity constituted by some 81 fossil sloth species. Probably originating in southern South America near the Eocene/Oligocene transition, sloths were represented in the tropics during the late Oligocene by Pseudoglyptodon, Mylodontidae, and Megalonychidae. The latter occupied the West Indies between at least the late early Miocene and late Pleistocene, and two mylodontid clades, Octodontobradyinae and Urumacotheriinae, were characteristic of Amazonian localities from the Colhuehuapian and the Laventan periods, respectively, until the end of the Miocene. Megatheriinae and Nothrotheriidae appeared during the middle Miocene, colonizing the tropics and then North America, where Mylodontidae and Megalonychidae had already been present since the early late Miocene. Nothrotheriids are more abundant and diversified during the late Miocene in the tropics than in southern South America. Remains closely related to either of the modern sloths are absent from the fossil record, including those in the tropics. The characteristic suspensory posture of Bradypus and Choloepus appeared independently and likely after the Miocene epoch, and thus well after the hypothesized split suggested by molecular studies of the respective clades of these genera. Given their current widespread distribution in and reliance on the tropics, prospecting efforts for the direct fossil kin of suspensory sloths should concentrate on deposits in the Amazonian region, as this area has shown promise in producing fossil sloths.     

Phylogenetic relationships among sloths (Mammalia, Xenarthra, Tardigrada): the craniodental evidence

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.     

Neogene sloth assemblages (Mammalia,Pilosa) of the Cocinetas Basin (La Guajira,Colombia): implications for the Great American Biotic Interchange

We describe sloth assemblages from the Cocinetas Basin (La Guajira peninsula, Colombia), found in the Neogene Castilletes and Ware formations, located in northernmost South America, documenting otherwise poorly known biotas. The tentative referral of a specimen to a small megatherioid sloth, Hyperleptus?, from the early–middle Miocene Castilletes Formation, suggests affinities of this fauna with the distant Santa Cruz Formation and documents a large latitudinal distribution for this taxon. The late Pliocene Ware Formation is much more diverse, with five distinct taxa representing every family of ‘ground sloths’. This diversity is also remarkable at the ecological level, with sloths spanning over two orders of magnitude of body mass and probably having different feeding strategies. Being only a few hundred kilometres away from the Isthmus of Panama, and a few hundred thousand years older than the classically recognized first main pulse of the Great American Biotic interchange (GABI 1), the Ware Formation furthermore documents an important fauna for the understanding of this major event in Neogene palaeobiogeography. The sloths for which unambiguous affinities were recovered are not closely related to the early immigrants found in North America before GABI 1.     

A new nothrotheriid xenarthran from the early Pliocene of Pomata‐Ayte (Bolivia): new insights into the caniniform–molariform transition in sloths

Tardigrade xenarthrans are today represented only by the two tree sloth genera Bradypus and Choloepus, which inhabit the Neotropical rainforests and are characterized by their slowness and suspensory locomotion. Sloths have been recognized in South America since the early Oligocene. This monophyletic group is represented by five clades traditionally recognized as families: Bradypodidae, Megalonychidae, Mylodontidae (?), Megatheriidae (?) and Nothrotheriidae (?). A new nothrotheriid ground sloth represented by a dentary and several postcranial elements, Aymaratherium jeani gen. nov. , sp. nov. , from the early Pliocene locality of Pomata‐Ayte (Bolivia) is reported. This small‐ to medium‐sized species is characterized especially by its dentition and several postcranial features. It exhibits several convergences with the ‘aquatic’ nothrotheriid sloth Thalassocnus and the giant megatheriid ground sloth Megatherium (M.) americanum, and is interpreted as a selective feeder, with good pronation and supination movements. The tricuspid caniniform teeth of Aymaratherium may represent a transitional stage between the caniniform anterior teeth of basal megatherioids and basal nothrotheriids (1/1C‐4/3M as in Hapalops or Mionothropus) and the molariform anterior teeth of megatheriids (5/4M, e.g. Megatherium). To highlight the phylogenetic position of this new taxon among nothrotheriid sloths, we performed a cladistic assessment of the available dental and postcranial evidence. Our results, derived from a TNT treatment of a data matrix largely based on a published phylogenetic data set, indicate that Aymaratherium is either sister taxon to Mionothropus or sister to the clade Nothrotheriini within Nothrotheriinae. They further support the monophyly of both the Nothrotheriinae and the Nothrotheriini, as suggested previously by several authors.     

Premaxillae of the Extinct Megalonychid Sloths <Emphasis Type="Italic">Acratocnus</Emphasis>, <Emphasis Type="Italic">Neocnus</Emphasis>, and <Emphasis Type="Italic">Megalonyx</Emphasis>, and their Phylogenetic Implications (Mammalia,Xenarthra)

In most folivorans, the premaxilla is loosely attached to the maxilla, so that it is often missing in otherwise very well-preserved fossil skulls. Despite its infrequent preservation in sloths, the premaxilla has been shown to have phylogenetically significant variation among the taxa that do preserve the element. In the family Megalonychidae, the premaxilla is known only in the early taxon Eucholoeops (Santacrucian South American Land Mammal Age [SALMA]), the extant two-toed sloth Choloepus, and the North American Neogene taxon Megalonyx, the last described only in an unpublished Master’s thesis. We report here the discovery of the premaxilla in two genera of extinct megalonychids, Neocnus and Acratocnus. These small bodied, semiarboreal megalonychid sloths are endemic to the islands of the Greater Antilles. Though the presence of sloths in the Caribbean dates at least to the late Oligocene, the best known taxa derive from Pleistocene to Holocene cave deposits in Puerto Rico, Hispaniola, and Cuba. We also describe the premaxilla in two species of Megalonyx from North America, the Blancan North American Land Mammal Age (NALMA) M. leptostomus and Rancholabrean NALMA M. jeffersonii. These species show a progressive reorientation of the premaxilla within Megalonyx from a primitive horizontal element to a nearly vertical element, and some significant changes in the anatomy of the incisive foramen. Morphological evidence suggests that a broadened, plate-like premaxilla constitutes a synapomorphy for the entire clade Megalonychidae. Furthermore, although Eucholoeops retains a short anterior process of the premaxilla like that of megatherioid sloths, this process is lacking in the other megalonychids, suggesting that the loss of this process may unite late Miocene to Recent megalonychids.     

Dental anomalies within extant members of the mammalian Order Pilosa

Recent discovery of a supernumerary dental anomaly in two‐toed sloths led to an extensive review of extant sloth specimens to look for additional anomalies. In total, 881 museum specimens were examined. These revealed two primary types of anomalies, hyperdontia (extra teeth) and anodontia (loss of teeth), occurring at a rate of 2.4% (n = 21). Two‐toed sloths, Choloepus, were more likely to have hyperdontia in the anterior dentition, whereas three‐toed sloths, Bradypus, experienced anodontia more frequently with the upper caniniforms. Both genera experienced both anomalies. The majority affected the upper dentition, with only three specimens exhibiting mandibular anomalies. Beyond the patterns of tooth positioning, all anomalies were random with respect to age, sex and geography. A few specimens not counted in the initial assessment expressed incomplete anodontia, indicating that the loss occurred postnatally and was not an embryological anomaly. For Bradypus, the findings provide new support for the hypothesis that the taxon represents a neotenic lineage and opens new possibilities about its relationship to the extinct ground sloths with a suggested rooting above that of the basal position it typically occupies for Folivora.     

A goose-sized anseriform bird from the late Oligocene of France: the youngest record and largest species of Romainvilliinae

We describe a new anseriform bird from the late Oligocene of Saint-André, Marseille, in southern France. Saintandrea chenoides, gen. et sp. nov. is the first avian species reported from the locality, which is well known for its mammalian fossils. The new species belongs to the extinct Romainvilliinae and represents the latest occurrence of the taxon, which was before only known from the late Eocene and early Oligocene of Europe. S. chenoides is also the largest species of Romainvilliinae and increases the known morphological diversity of the taxon. The identification of a goose-sized representative of the Romainvilliinae in the late Oligocene of Europe raises the possibility that some of the large late Paleogene or early Neogene Anseriformes with uncertain phylogenetic affinities also belong to this taxon.     

<Emphasis Type="Italic">Xibalbaonyx oviceps</Emphasis>, a new megalonychid ground sloth (Folivora,Xenarthra) from the Late Pleistocene of the Yucatán Peninsula,Mexico, and its paleobiogeographic significance

Here we describe a new genus and species of giant ground sloth, Xibalbaonyx oviceps (Megalonychidae, Xenarthra), from the drowned cave system of the northeastern Yucatán Peninsula. The specimen is Late Pleistocene in age and was discovered in the Zapote sinkhole (cenote) near Puerto Morelos in the Mexican state of Quintana Roo. Xibalbaonyx oviceps differs significantly from all hitherto known Megalonychidae including those from the Greater Antilles and South America. The new taxon suggests a local Caribbean radiation of ground sloths during the Late Pleistocene, which is consistent with the dispersal of the group along a Mexican corridor.     

<Emphasis Type="Italic">Baraguatherium takumara</Emphasis>, <Emphasis Type="Bold">Gen. et Sp. Nov., the Earliest Mylodontoid Sloth (Early Miocene) from Northern South America</Emphasis>

We report a new genus and species of sloth, based on a partial mandible and associated femur, from the early Miocene of Venezuela. Baraguatherium takumara, gen. et sp. nov., represents the earliest member of the Mylodontoidea recognized from northern South America. Phylogenetically and morphologically, Baraguatherium possesses some plesiomorphic characters: a vasodentine layer in the core of the tooth similar to Octodontotherium, Paroctodontotherium, and Orophodon; molariforms parallel to the long axis of the toothrow; teeth with a very thin layer of cementum; mf1-mf3 series of similar size and bilobate; mf3 conspicuously piriform; and occlusal surface of tooth beveled, which places it at the base of the Mylodontidae clade. Baraguatherium was found in continental deposits that also preserve abundant wood and leaves associated with a near shore marine complex, indicating that Baraguatherium lived in a coastal tropical forest in the early Miocene in northern South America. The presence of a vasodentine layer in the core of the tooth is quite similar to Octodontotherium, Paroctodontotherium, and Orophodon and allows assignment of this new taxon to the Mylodontoidea.     

Molecular evidence for a diverse green algal community growing in the hair of sloths and a specific association with <Emphasis Type="Italic">Trichophilus welckeri</Emphasis>(Chlorophyta,Ulvophyceae)

Background  

Sloths are slow-moving arboreal mammals inhabiting tropical rainforests in Central and South America. The six living species of sloths are occasionally reported to display a greenish discoloration of their pelage. Trichophilus welckeri, a green algal species first described more than a century ago, is widely believed to discolor the animals fur and provide the sloth with effective camouflage. However, this phenomenon has not been explored in any detail and there is little evidence to substantiate this widely held opinion.     

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.     

First observation on mating and reproductive seasonality in maned sloths <Emphasis Type="Italic">Bradypus torquatus</Emphasis> (Pilosa: Bradypodidae)

Information on mating season is of paramount importance for our understanding of reproductive behavior, yet little is currently known about the breeding season of Xenarhtra as a whole and sloths in particular. A pair of maned sloths was observed copulating in September 2005 in the Atlantic Forest region of south-eastern Brazil. Our studies on mating of the manned sloth as well of other hitherto unpublished records of newborn sloths seen in the wild, together with a review of previous information, indicate that B. torquatus is a seasonal breeder. Infants are born predominantly at the end of the wet season and beginning of the dry season (February–April), and copulation concentrates in the late dry and early wet seasons (August–October). This strategy allows for the energy-demanding gestation and lactation to take place during the less stressful period of the year.     

Spatial ecology and conservation of two sloth species in a cacao landscape in limón,Costa Rica

The spatial ecology of sloths was studied in an agricultural landscape in Limón Province, Costa Rica. Two sloth species, the three-toed sloth (Bradypus variegatus) and the two-toed sloth (Choloepus hoffmanni), actively used and traveled through a cacao agroforest and its contiguous living fence rows and riparian forests. This agroecosystem was embedded in an agricultural landscape dominated by banana and pineapple plantations and pastures with dispersed trees. The two-toed sloth (C. hoffmanni) was found in 101 tree species and used 34 for food; the three-toed sloth (B. variegatus) was found in 71 tree species and used 15 for food. Choice of preferred species differed between the two sloth species. Trees commonly used by sloths for food and/or refuge in the cacao agroforest included Erythrina poeppigiana, Cecropia obtusifolia, Leucaena leucocephala; in the living fence rows, Cordia alliodora, Erythrina poeppigiana, Ocotea sinuata and Trophis racemosa; in the riparian forests, Coussapoa villosa, Cecropia obtusifolia, Hura crepitans, Pterocarpus officinalis and Spondias mombin; and in the pastures with dispersed trees, Cordia alliodora, Coussapoa villosa, Erythrina poeppigiana, Ocotea sinuata and Hura crepitans. This study demonstrates the importance of the cacao agroforest as well as arboreal elements in other land uses in providing resources for sloth conservation in a larger agricultural landscape.     

A syndrome of mutualism reinforces the lifestyle of a sloth

Arboreal herbivory is rare among mammals. The few species with this lifestyle possess unique adaptions to overcome size-related constraints on nutritional energetics. Sloths are folivores that spend most of their time resting or eating in the forest canopy. A three-toed sloth will, however, descend its tree weekly to defecate, which is risky, energetically costly and, until now, inexplicable. We hypothesized that this behaviour sustains an ecosystem in the fur of sloths, which confers cryptic nutritional benefits to sloths. We found that the more specialized three-toed sloths harboured more phoretic moths, greater concentrations of inorganic nitrogen and higher algal biomass than the generalist two-toed sloths. Moth density was positively related to inorganic nitrogen concentration and algal biomass in the fur. We discovered that sloths consumed algae from their fur, which was highly digestible and lipid-rich. By descending a tree to defecate, sloths transport moths to their oviposition sites in sloth dung, which facilitates moth colonization of sloth fur. Moths are portals for nutrients, increasing nitrogen levels in sloth fur, which fuels algal growth. Sloths consume these algae-gardens, presumably to augment their limited diet. These linked mutualisms between moths, sloths and algae appear to aid the sloth in overcoming a highly constrained lifestyle.     

Sloth Hair as a Novel Source of Fungi with Potent Anti-Parasitic,Anti-Cancer and Anti-Bacterial Bioactivity

The extraordinary biological diversity of tropical forests harbors a rich chemical diversity with enormous potential as a source of novel bioactive compounds. Of particular interest are new environments for microbial discovery. Sloths – arboreal mammals commonly found in the lowland forests of Panama – carry a wide variety of micro- and macro-organisms on their coarse outer hair. Here we report for the first time the isolation of diverse and bioactive strains of fungi from sloth hair, and their taxonomic placement. Eighty-four isolates of fungi were obtained in culture from the surface of hair that was collected from living three-toed sloths (Bradypus variegatus, Bradypodidae) in Soberanía National Park, Republic of Panama. Phylogenetic analyses revealed a diverse group of Ascomycota belonging to 28 distinct operational taxonomic units (OTUs), several of which are divergent from previously known taxa. Seventy-four isolates were cultivated in liquid broth and crude extracts were tested for bioactivity in vitro. We found a broad range of activities against strains of the parasites that cause malaria (Plasmodium falciparum) and Chagas disease (Trypanosoma cruzi), and against the human breast cancer cell line MCF-7. Fifty fungal extracts were tested for antibacterial activity in a new antibiotic profile screen called BioMAP; of these, 20 were active against at least one bacterial strain, and one had an unusual pattern of bioactivity against Gram-negative bacteria that suggests a potentially new mode of action. Together our results reveal the importance of exploring novel environments for bioactive fungi, and demonstrate for the first time the taxonomic composition and bioactivity of fungi from sloth hair.     

The Convergent Evolution of Suspensory Posture and Locomotion in Tree Sloths

Recent phylogenetic analyses imply a distant relationship and long separated evolution of two-toed sloths (Choloepus) and three-toed sloths (Bradypus). No known fossil sloth is interpreted to have been suspensory. As a consequence, the suspensory posture and locomotion of the extant genera likely evolved convergently in both lineages, forming a new framework for the analysis of functional aspects of the locomotor apparatus of extant tree sloths. The suspensory posture and locomotion has altered functional demands from the phylogenetically plesiomorphic non-suspensory pronograde situation. Here, anatomical traits that have been argued to be of adaptive significance for quadrupedal suspensory locomotion are reviewed and the evolution of these traits is discussed in light of the new framework. Experimental data are largely limited to Choloepus, but help to deduce functional aspects of the anatomy in Bradypus as well. The most important adaptive traits are hands and feet modified into relatively rigid hook-like appendages, great mobility of all joints proximal to the midcarpal and transverse tarsal joints, relatively long arms with a relatively short scapula, a rounded thorax with a small diameter, a highly mobile sterno-clavicular articulation, and emphasis on powerful flexion in the proximal limb joints via advantageous lever arms. Despite these changes, patterns of limb kinematics remained conservative during the course of evolution in the lineages leading to extant tree sloths, and it is suggested here that this also applies to the pattern of neuromuscular control of limb movements during locomotion. Morphological ‘solutions’ to altered functional demands posed by inversed orientation of the body differ in the two genera of extant tree sloths, thereby corroborating the proposed diphyly. Convergent evolution in tree sloths may be attributed to functional constraints posed by fossorial adaptations in early Xenarthra that canalized sloths to adopt a suspensory posture and locomotion in the arboreal habitat.     

Multi‐scale effects of habitat structure and landscape context on a vertebrate with limited dispersal ability (the brown‐throated sloth,Bradypus variegatus)

As human population, food consumption, and demand for forest products continue to rise over the next century, the pressures of land‐use change on biodiversity are projected to intensify. In tropical regions, countryside habitats that retain abundant tree cover and structurally complex canopies may complement protected areas by providing suitable habitats and landscape connectivity for a significant portion of the native biota. Species with low dispersal capabilities are among the most at risk of extinction as a consequence of land‐use change. We assessed how the spatial distribution of the brown‐throated sloth (Bradypus variegatus), a model species for a vertebrate with limited dispersal ability, is shaped by differences in habitat structure and landscape patterns of countryside habitats in north‐central Costa Rica using a multi‐scale framework. We quantified the influence of local habitat characteristics and landscape context on sloth occurrence using mixed‐effects logistic regression models. We recorded 27 sloths within countryside habitats and found that both local and landscape factors significantly influenced their spatial distribution. Locally, sloths favored structurally complex habitats, with greater canopy cover and variation in tree height and basal area. At the landscape scale, sloths demonstrated a preference for habitats with high proportions of forest and nearby large tracts of forest. Although mixed‐use areas and tree plantations are not substitutes for protected forests, our results suggest they provide important supplemental habitats for sloths. To promote the conservation and long‐term viability of sloth populations in the tropical countryside, we recommend that land managers retain structurally complex vegetation and large patches of native habitat.     

A reappraisal of the phylogeny of Mylodontidae (Mammalia,Xenarthra) and the divergence of mylodontine and lestodontine sloths

The phylogeny of mylodontid sloths has recently been the subject of multiple studies. Contrasting hypotheses have been proposed, especially for the relationships among late Miocene–Pleistocene mylodontines and lestodontines. In this paper, a new and detailed phylogenetic analysis is conducted, after adding new characters and taxa previously unexplored from a phylogenetic point of view. New features derived from postcranial skeletal anatomy are added to previous studies based on craniodental evidence. In this way, the current reappraisal represents the first exhaustive phylogenetic study on the Mylodontidae that incorporates features coded for the entire skeleton. When available, multiple specimens of each bony element are observed for each operational taxonomic unit, in order to take into account intraspecific variation. The taxonomic sample of this study considers Mylodontinae at the specific level. However, many other Mylodontidae are considered, and their phylogenetic relationships tested. The taxonomic sample of this study is enriched with new taxa from central and northern South America, with the aim of compensating for the knowledge bias in favour of austral mylodontids, which have historically been more extensively studied than those from tropical latitudes. Special emphasis is given to the phylogenetic relationships of Mylodontinae, and particularly to the mylodontine and lestodontine sloths, that are recovered in the present study as monophyletic clades, and together form a larger monophyletic group. According to the present results, the Mylodontini–Lestodontini split occurred at the middle–late Miocene transition, giving rise to independent adaptive radiations across South and North America.     

Estimation of hearing capabilities of Early Miocene sloths (Mammalia,Xenarthra, Folivora) and palaeobiological implications

The Miocene Santacrucian sloths are a very important assemblage because they represent the first major radiation among sloths and, therefore, they could provide many insights about sloth evolution and diversity. Based on other studies, the hearing capabilities of Pleistocene sloths were identified. For a deeper understanding of these capabilities from an evolutionary point of view, in this article we study the hearing capabilities of Santacrucian sloths. We estimate the frequency range and the best frequency of hearing of six species of stem-megatherines and one species of mylodont. In most cases, the best frequency of hearing is much lower than the expected value for the estimated body mass of the species. This general shift towards low values of frequency is different than the pattern observed in mammals where sound localisation is improved by an increased sensitivity to high frequencies. In this article, we also propose some palaeobiological inferences of the low-frequency shift of hearing range in Miocene Santacrucian sloths.     

On the move: sloths and their epibionts as model mobile ecosystems

Sloths are unusual mobile ecosystems, containing a high diversity of epibionts living and growing in their fur as they climb slowly through the canopies of tropical forests. These epibionts include poorly studied algae, arthropods, fungi, and bacteria, making sloths likely reservoirs of unexplored biodiversity. This review aims to identify gaps and eliminate misconceptions in our knowledge of sloths and their epibionts, and to identify key questions to stimulate future research into the functions and roles of sloths within a broader ecological and evolutionary context. This review also seeks to position the sloth fur ecosystem as a model for addressing fundamental questions in metacommunity and movement ecology. The conceptual and evidence-based foundation of this review aims to serve as a guide for future hypothesis-driven research into sloths, their microbiota, sloth health and conservation, and the coevolution of symbioses in general.