Martín Ricardo Ciancio

Evolutionary Implications of Dental Eruption in Dasypus (Xenarthra)

Late eruption of the permanent dentition was recently proposed as a shared anatomical feature of endemic African mammals (Afrotheria), with anecdotal reports indicating that it is also present in dasypodids (armadillos). In order to clarify this question, and address the possiblity that late eruption is shared by afrotherians and dasypodids, we quantified the eruption of permanent teeth in Dasypus, focusing on growth series of D. hybridus and D. novemcinctus. This genus is the only known xenarthran that retains two functional generations of teeth. Its adult dentition typically consists of eight upper and eight lower ever-growing (or euhypsodont) molariforms, with no premaxillary teeth. All but the posterior-most tooth are replaced, consistent with the identification of a single molar locus in each series. Comparison of dental replacement and skull metrics reveals that most specimens reach adult size with none or few erupted permanent teeth. This pattern of growth occurring prior to the full eruption of the dentition is similar to that observed in most afrotherians. The condition observed in Dasypus and many afrotherians differs from that of most other mammals, in which the permanent dentition erupts during (not after) growth, and is complete at or near the attainment of sexual maturity and adult body size. The suture closure sequence of basicranial and postcranial epiphyses does not correlate well with dental eruption. The basal phylogenetic position of the taxon within dasypodids suggests that diphyodonty and late dental replacement represent the condition of early xenarthrans. Additionally, the inferred reduction in the number of molars to a single locus and the multiplication of premolars represent rare features for any living mammal, but may represent apomorphic characters for Dasypus.

The phylogenetic and biostratigraphic significance of new armadillos (Mammalia, Xenarthra, Dasypodidae, Euphractinae) from the Tinguirirican (Early Oligocene) of Chile

Synopsis Two new species of early Oligocene dasypodids are described from the Tinguiririca Fauna of Chile, the basis of the recently formalised Tinguirirican South American Land Mammal ‘Age’. Specimens recovered to date, all referable to the Euphractinae, include articulated portions of the movable bands and pelvic shield, an unassociated partial mandible and skull, and isolated osteoderms. Ornamentation of the osteoderms (i.e. the shape of the central figure and keel and the arrangement of the peripheral figures) indicates that these taxa represent early diverging members of the subfamily. Cranial remains from Chile somewhat resemble Sadypus Ameghino (?early Oligocene), particularly in their long, low rostra. One of the new species from Tinguiririca also occurs in Eo‐Oligocene faunas from Patagonia (Argentina) currently under study, providing a basis for long distance biochronological correlation. The material from Tinguiririca assumes special importance given that most Eocene and Oligocene dasypodids are known exclusively from isolated osteoderms. The unusally complete material from Tinguiririca thus provides important phylogenetic insights by clarifying the morphology of the cingulate exoskeleton during a key interval in the clades diversification.

New Palaeogene cingulates (Mammalia, Xenarthra) from Santa Rosa, Perú and their importance in the context of South American faunas

The record of Palaeogene cingulate xenarthrans in low latitudes is very poor. The cingulate fauna from the Yurúa River near Santa Rosa in eastern Perú is important because it is one of the oldest known from the Palaeogene of Perú and because of its tropical latitudinal position. Although remains are scarce, we recognize three new taxa: two species of Astegotheriini (Dasypodidae); Parastegosimpsonia peruana gen. et sp. nov., of small size, related to Eocene species from Patagonia; and another new species, ?Parastegosimpsonia sp. nov., which consists of an incomplete osteoderm representing the largest species of this tribe. A third species, Yuruatherium tropicalis gen. et sp. nov., of indeterminate suprageneric rank, shares features with Machlydotherium Ameghino (Casamayoran-Tinguirirican SALMA – middle Eocene-early Oligocene of Patagonia) and is similar to Eocoleophorus Oliveira et al. (Deseadan SALMA – late Oligocene of Brazil). We assign ?Machlydotherium intortum Ameghino (from the late Eocene of Patagonia) to Yuruatherium. Sediments bearing these cingulates also yielded rodents, marsupials and notoungulates, among the most frequent mammals. The absolute age of the sediments is unknown but an estimated age is inferred from studies of the mammalian assemblages. The age of the Santa Rosa local fauna is still controversial and given the groups taken into account, could be from Early Eocene to Late Oligocene. According to sequences of southern cingulate faunas (especially those of Dasypodidae), the cingulates from Santa Rosa also suggest an age between the Late Eocene and Early Oligocene. Nevertheless, the very low latitude of the Santa Rosa local fauna should be taken into account because in lower latitudes it is not uncommon to find taxa with a more generalized set of characters than those present in contemporary taxa from higher latitudes. http://zoobank.org/urn:lsid:zoobank.org:pub:37CAEF7C-3CCC-4C3C-9869-D584FD73323C

New mammal faunal data from Cerdas, Bolivia, a middle-latitude Neotropical site that chronicles the end of the Middle Miocene Climatic Optimum in South America

ABSTRACT We provide new and revised identifications of mammals from the early middle Miocene (Langhian age, Colloncuran South American Land Mammal Age [SALMA]) of Cerdas, Bolivia. We also formally name a new typothere notoungulate, Hegetotherium cerdasensis, sp. nov., that can be distinguished by the absence of an external talonid sulcus on m3 and its small size (15–25% smaller than Hegetotherium mirabile). We refer several typothere specimens from Nazareno, Bolivia, to H. cerdasensis, which suggests that the two sites are of similar age. We report the first sparassodont and astrapothere remains from Cerdas. Sparassodont remains include an associated basicranium and mostly complete mandible; the species appears to represent a new, small-bodied borhyaenoid. Astrapothere remains consist of many tooth fragments from a new species of the subfamily Uruguaytheriinae. A partial sloth dentary from Cerdas likely pertains to the subfamily Megatheriinae and is the first report of the family Megatheriidae from the site. A newly discovered peltephilid armadillo specimen includes a partial articulated carapace that supports recognition of the Cerdas taxon as a new species. The two dasypodids of Cerdas (one Euphractini, one Eutatini) represent two new species closely related to undescribed species from the late middle Miocene (Serravallian age, Laventan SALMA) of Quebrada Honda, Bolivia. The mammals of Cerdas indicate that (1) the middle latitudes (southern tropics) contributed significantly to the diversity of Miocene mammal communities in South America; and (2) the Middle Miocene Climatic Optimum was a key factor in the differentiation of South American mammal assemblages.

Reassessment of the hairy long-nosed armadillo "Dasypus" pilosus (Xenarthra, Dasypodidae) and revalidation of the genus Cryptophractus Fitzinger, 1856.

The hairy long-nosed armadillo, currently referred as Dasypus (Cryptophractus) pilosus, is an enigmatic species endemic to montane cloud forests and subparamo of Peruvian Andes. Its strikingly different external features, which include the carapace concealed by abundant hair, the presence of more movable bands, and a slender skull, have raised questions regarding its taxonomic status as subgenus or as genus. This paper assesses this issue based on a cladistic study and provides a detailed comparative description of the species, including the first account on the distinctive ornamentation of its osteoderms. Based on several unique characters in the carapace, skull, mandible, and teeth, as well as on the external phylogenetic position relative to other Dasypus, we favor the assignment of the hairy long-nosed armadillo to other genus. As result, we revalidate the original generic epithet, so that the valid name of the species is Cryptophractus pilosus Fitzinger, 1856.

When xenarthrans had enamel: insights on the evolution of their hypsodonty and paleontological support for independent evolution in armadillos

All xenarthrans known to date are characterized by having permanent teeth that are both high crowned and open rooted, i.e., euhypsodont, and with a type of hypsodonty different from that of the rest of Placentalia: dentine hypsodonty. Also, most xenarthrans lack enamel; however, its presence has been reported in the fossil armadillo Utaetus buccatus and in living Dasypus. Considering the divergence of Xenarthra from other eutherians that possessed enameled teeth, the absence of enamel is a derived character. Diverse specializations are known in the dentition of xenarthrans, but the primitive pattern of their teeth and dentitions is still unknown. Here, we describe the mandible and teeth of a fossil armadillo, Astegotherium dichotomus (Astegotheriini, Dasypodidae), from the early Middle Eocene of Argentine Patagonia, with teeth showing both true enamel and closed roots. It is the oldest xenarthran with mandibular remains exhibiting protohypsodonty and is therefore likely representative of ancestral cingulates and xenarthrans generally. Astegotherium supports a recent hypothesis based on molecular data that enamel loss occurred independently not only within xenarthrans but also within dasypodid armadillos.

Comparative histology and ontogenetic change in the carapace of armadillos (Mammalia: Dasypodidae)

Abstract Among extant mammals, the presence of osteoderms is limited to armadillos (Xenarthra, Dasypodidae), being one of its distinctive features. The osteoderms are articulated to form a carapace that covers their body dorsally. In this paper we study the integumentary structures of the armadillos Chaetophractus vellerosus, Chaetophractus villosus, Euphractus sexcinctus, and Zaedyus pichiy (Euphractinae), Dasypus hybridus, and Dasypus novemcinctus (Dasypodinae) within a comparative framework, aiming to identify patterns common to the family and to the subfamilies Dasypodinae and Euphractinae, as well as peculiarities of each species. Differences between the two subfamilies were observed in the dorsal integument, related to the production of blood cells and the mobility of the carapace. The Euphractinae present more numerous and larger cavities filled with adipose tissue in the osteoderms, as well as more marginal follicles than the Dasypodinae. These provide thermal insulation that could be related to their distribution in cooler climates. The sebaceous glands associated with surface follicles are also more developed in the Euphractinae and could be related to preventing the desiccation of the cornified scales in arid climates.

A new acaremyid rodent (Caviomorpha, Octodontoidea) from Scarritt Pocket, Deseadan (late Oligocene) of Patagonia (Argentina)

ABSTRACT Octodontoidea is the most diverse caviomorph clade presently represented in South America by Octodontidae, Echimyidae, and Abrocomidae. Some evidence suggests that in the past they were taxonomically even more diverse, including several independent lineages with no modern representatives, sometimes considered as families. One of them is Acaremyidae, known until now from the Colhuehuapian—Colloncuran (early to early—middle Miocene) of Patagonia. Here we describe a new octodontoid rodent from the Deseadan (late Oligocene) of Scarritt Pocket (Patagonia): Changquin woodi, gen. et sp. nov. Cladistic analysis indicates that the new species is an acaremyid related to the Santacrucian (early Miocene) Sciamys. Acaremyidae was recovered as a monophyletic group. C. woodi, gen. et sp. nov., the oldest representative of Acaremyidae, extends the family biochron back to the late Oligocene, and indicates that acaremyids differentiated before the Deseadan. C. woodi represents the first Deseadan octodontoid displaying protohypsodont cheek teeth, showing that the Deseadan was a period of important diversification for octodontoids, as it was for the cavioids. C. woodi adds a new element to the faunal differences observed between Patagonian and Bolivian Deseadan faunas. A new U-Pb laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) date (27.17 ± 0.54 Ma) for Scarritt Pocket is provided.

First record of supernumerary teeth in Glyptodontidae (Mammalia, Xenarthra, Cingulata)

Fil: Gonzalez Ruiz, Laureano Raul. Universidad Nacional de la Patagonia; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina

Internal Morphology of Osteoderms of Extinct Armadillos and Its Relationship with Environmental Conditions

The most complete and continuous fossil record of armadillos is composed mostly by isolated osteoderms, frequently found in paleontological and archaeological sites that bear continental South American mammals. Their external morphology has been used to define several species. In the last decade, many authors have focused on the internal structure of vertebrate osteoderms using histological and paleohistological studies. These studies allowed identification of useful features in systematic and phylogenetic contexts. In armadillos, osteoderms are constituted by compact bone tissue (primary and secondary osteons, and concentric layers or lamellae) that delimits cavities, which could contain different soft tissues (adipose tissue, hair follicles, bone marrow, and sweat and sebaceous glands). Traditional paleohistological techniques have allowed the recognition of homologous cavities to those found in osteoderms of current species and from comparison deduce which kind of tissue could had occupied them. We have recently utilized 3D reconstructions in osteoderms of extant species of armadillos to analyze the micromorphology, disposition, and the relationship of different cavities and understand them in depth. Here, we present the results of the application of paleohistology and microtomography in osteoderms of representatives of diferent taxa of extinct Dasypodidae (Astegotheriini, Stegotheriini, “Utaetini,” Euphractini, Eutatini), which allowed us to compare homologous structures based on their three-dimensional reconstruction. The results, added to the previous external morphology studies, have allowed us to define morphological patterns (consistent within each linage). The variation of the volume and extension of cavities associated with different tissues could be strongly associated with changes in the climate and environmental conditions of the species distribution areas.