Guillermo H. Cassini

Historia natural del piche llorón Chaetophractus vellerosus (Mammalia: Xenarthra: Dasypodidae)

Fil: Abba, Agustin Manuel. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina

Systematics of hairy armadillos and the taxonomic status of the Andean hairy armadillo (Chaetophractus nationi)

Hairy armadillos constitute an ecologically homogeneous and morphologically similar group with currently 5 species classified in the subfamily Euphractinae. Among them, the Andean hairy armadillo Chaetophractus nationi (Xenarthra, Cingulata, Dasypodidae) is a small, endangered armadillo that has long been suspected to represent a high-altitude variant of Chaetophractus vellerosus. Here, we report the 1st phylogenetic systematics assessment of hairy armadillos using morphological and molecular analyses of all described species with focus on the status of the Andean hairy armadillo. Multivariate analyses of shape variation based on 3-dimensional landmark coordinates of skulls allowed a clear differentiation of each species with the exception of C. vellerosus and C. nationi, within which only a latitudinal and/or altitudinal gradient in size was apparent. Moreover, analyses of mitochondrial DNA control region (D-loop) revealed a single C. nationi haplotype that appeared to be identical with a C. vellerosus haplotype from Argentina. Identical sequences in C. vellerosus and C. nationi were also observed for 3 of the 5 non-coding nuclear markers investigated. Based on these data, we propose that C. nationi should be considered as a synonym of C. vellerosus. However, this taxonomic change should not preclude the protection of the high-altitude Bolivian populations that are steadily declining because of their overexploitation for traditional purposes. Finally, phylogenetic analyses of euphractine armadillos based on a combination of 6 non-coding nuclear markers and 2 nuclear exons suggest the paraphyly of the genus Chaetophractus, with C. vellerosus being more closely related to Zaedyus pichiy than to C. villosus.

Skull Geometric Morphometrics and Paleoecology of Santacrucian (Late Early Miocene; Patagonia) Native Ungulates (Astrapotheria, Litopterna, and Notoungulata)

Abstract. Three orders of South American extinct native ungulates are recorded from the Santa Cruz Formation along the Atlantic coast of Patagonia: Notoungulata (Adinotherium Ameghino, Nesodon Owen, Interatherium Ameghino, Protypotherium Ameghino, Hegetotherium Ameghino, and Pachyrukhos Ameghino), Litopterna (Theosodon Ameghino, Anisolophus Burmeister, Tetramerorhinus Ameghino, Diadiaphorus Ameghino, and Thoatheriurn Ameghino), and Astrapotheria (Astrapotherium Burmeister). An ecomorphological study based on geometric morphometries of the masticatory apparatus was performed. The reference sample included 618 extant specimens of the orders Artiodactyla, Perissodactyla, Hyracoidea, and Diprotodontia. Thirty six cranial and 27 mandibular three-dimensional landmarks were digitized. Allometric scaling, principal component analyses, and phylogenetic generalized estimating equations on the cranium and mandible were preformed. Analyses of cranial shape show strong phylogenetic constraints, whereas the mandibular analyses show a functional pattern related to habitat/ diet and hypsodonty. The extant brachydont ungulates from closed habitats show a more elongated and narrower mandibular symphysis with a lower mandibular corpus, than hypsodont, open habitat species. The latter have short symphyses with a high, curved mandibular corpus. This morphological pattern was also present among Santacrucian ungulates, allowing characterization of notoungulates mainly as open habitats dwellers, with some taxa foraging on grass (Protypotherium, Interatherium), and others on grass and leaves {Hegetotherium, Pachyrukhos, and Adinotheriurn), depending on the availability. Nesodon may have dwelled in mixed habitats and had a mixed feeding behavior, while small proterotheriids {Anisolophus and Thoatheriurn) may have fed predominantly on dicotyledonous plants. The remaining litopterns {Tetramerorhinus, Diadiaphorus, and Theosodon) and Astrapotherium may have foraged in closed habitats and fed on dicotyledonous plants.

Nuevos aportes a la historia natural de la mulita pampeana Dasypus hybridus (Mammalia, Dasypodidae)

This contribution presents new data about the natural history of the Dasypus hybridus (Desmarest, 1804) (Mammalia, Xenarthra, Dasypodidae). A seasonal monitoring using the capture and release method was performed over the course of three years in a 100 ha of four cattle farms in the Buenos Aires province, Argentina. Data were collected on food habits, space and time use, behavior, thermoregulation, population data, and morphology. A total of 71 captures were made. The main food items recorded were plant matter, ants and coleopterans, and did not occur seasonal differences in food habits. Dasypus hybridus concentred their activities during daytime, and were recorded a low frequency of activities during cold seasons (fall and winter). The long-nosed armadillo prefer humid soils and grasslands with high vegetation cover, and selected forest to refuge. The southern long-nosed armadillo were asocial. Rectal temperature was positively correlated with environmental temperature. The sex proportion was near to one, and no sexual dimorphism was observed. In general, the results of this study are in agreement with previous observations of other species of the same genera, but is necessary to highlight the trend observed in food habits and thermoregulatory strategy. This work provides new information about different aspects of a poor studied species that occur in a habitat subjected to high pressure to modification and use.

Mass estimation of Santacrucian sloths from the Early Miocene Santa Cruz Formation of Patagonia, Argentina

Miocene deposits of the Santa Cruz Formation, Patagonia, comprise a diverse and excellently preserved vertebrate fauna, allowing detailed paleobiological and paleoecological studies based on three ecological parameters: body mass, diet, and substrate preference. In contrast to the small and arboreal extant sloths, Bradypus and Choloepus, Santacrucian sloths were much more diverse and larger, and comprised 11 genera previously characterized as arboreal or climbing forms. Here, we focus on body mass estimation based on measurements of postcranial elements. We present a morphometric database comprising 64 linear, base-ten logged variables applied to Santacrucian sloths and a wide sample of extant mammals, as well as the body mass of the extant taxa as reported in the literature. To detect any potential phylogenetical bias, we performed a variance decomposition test on our sample of extant mammals. Based on four orthogram statistics, logged body mass was found not to be dependent on phylogenetic tree topology. Predictive equations for the body mass of extant mammals were generated through multiple regression analysis, using weighting procedures to avoid taxonomic biases and stepwise analysis to discard redundant variables. Using this procedure, we derived separate equations for the scapula, humerus, radius, ulna, pelvis, femur, tibia plus fibula, astragalus, and calcaneum. These equations were then applied to estimate the body mass of our sample of Santacrucian sloths. We obtained an average body mass of about 70 kg for the megalonychid Eucholoeops. Among stem megatherioids, Hapalops ranged between 30 and 80 kg, Analcimorphus was estimated at 67 kg, and Schismotherium at 44 kg. Larger genera included the megatheriid Prepotherium (∼123 kg), and the mylodontids Analcitherium (∼88 kg) and Nematherium (∼89 kg). The medium to large body size of Santacrucian sloths imposed constraints on their climbing abilities. Megalonychids and stem megatherioids were likely unable to access the finest branches, while megatheriids and mylodonts were more terrestrial forms.

Ulnar articular surface 3-D landmarks and ecomorphology of small mammals: a case study of two early Miocene typotheres (Notoungulata) from Patagonia

Articular surfaces reflect the relative movements between adjacent bones, and the ones involved in the elbow joint provide information about forelimb movements and may be useful for making inferences about the substrate use. The proximal articular surface of the ulna was examined through 3-D geometric morphometrics, in order to assess its usefulness as a proxy for paleoecological interpretations; particularly for two small mammals from the early Miocene of Patagonia. The sample was composed of 22 extant small mammals (rodents, carnivorans and primates) and two extinct typotheres: Hegetotherium mirabile (Hegetotheriidae) and Interatherium robustum (Interatheriidae). Forty-five landmarks were taken and principal component analysis (PCA) was used to explore the morphospace structure. The results of PCA for the whole surface were inconclusive; therefore, successive analyses were made, subdividing the surface into sub-units. The PCA for the proximal part of the trochlear notch was the most informative, allowing the recognition of morphospaces with functional value: one for digging rodents and another for most climbers. Neither typothere would have had a specialisation for climbing or digging in the features analysed. This study allows morphological patterns on different parts of a joint to be detected; interpreted, at least partially, as differential responses to different kinds of mechanical stress.

Postnatal ontogenetic scaling of pampas deer (Ozotoceros bezoarticus celer: Cervidae) cranial morphology

Abstract The pampas deer Ozotoceros bezoarticus is a medium-sized, elegant, and lightly built cervid that was once a characteristic inhabitant of open grasslands across a wide geographical distribution in South America. In Argentina, the subspecies Ozotoceros bezoarticus celer is the most southern and abundant populations and relatively well represented in osteological collections permitting a morphometric study of cranial ontogeny. We measured 17 cranial variables on an ontogenetic series in order to evaluate the multivariate allometry of neurocranial and splanchnocranial components through developmental stages. The cranial ontogenetic pattern in O. b. celer exhibits a conservative plan in which both sexes share most of the allometric trends except in three variables related to the rostrum. Isometry was detected in 9 out of 17 variables, whereas four grows with negative allometry, and only nasal length showed positive allometry. As for most mammals, those variables related to the neurocranial components and sensorial capsules exhibit negative allometry. The growth of the rostrum indicates that both sexes have longer face than younger. However, the lack of allometry in most of the variables seems to be supporting the idea of a younger with the general appearance of an adult but smaller size.

Teeth complexity, hypsodonty and body mass in Santacrucian (Early Miocene) notoungulates (Mammalia)

Notoungulates, native South American fossil mammals, have been recently objective of several palaeoecological studies. Ecomorphology and biomechanics of the masticatory apparatus, together with micro and mesowear analyses on tooth enamel, were applied in order to understand their palaeobiology. In particular, the relationship between some dental traits (hypsodonty, occlusal surface area and complexity) and body mass is still poorly understood. These features were measured by means of the hypsodonty index (HI), occlusal surface area (OSA) and tooth area (OTA), enamel crest complexity (ECC) and length (OEL). The relationships between these indices were evaluated in five pan-contemporaneous Santacrucian Notoungulata genera from Patagonia: Adinotherium and Nesodon (Toxodontia), Interatherium, Protypotherium and Hegetotherium (Typotheria). While OSA, OTA and OEL were size dependent and strongly correlated, HI and ECC were size independent. All notoungulates analysed have very hypsodont teeth, indicating high rates of tooth wear in response to an increase of abrasives consumed with the food; their tooth occlusal area and complexity could be related to chewing efforts associated with the toughness of the plants consumed. HI, OSA and ECC were considered useful for palaeoecological reconstructions, but the results presented here show that these three features are integrated as a complex, so should not be evaluated separately.

Prevalence and intensity of fleas parasitizing an isolated population of screaming hairy armadillo in Buenos Aires province, Argentina: host-related factors and temporal dynamics

Fleas (Siphonaptera) of an isolated population of Chaetophractus vellerosus (Mammalia: Xenarthra) from Magdalena (Buenos Aires province) were studied, and their presence was associated with host-related factors (age, sex, weight, size, and physical condition) and temporal dynamics (seasonality and year). Three species of fleas were identified: Polygenis (Polygenis) platensis (Rhopalopsyllidae), Tunga penetrans (Tungidae), and Pulex irritans (Pulicidae). Prevalences were significant for year, season, and physical condition. Intensities were significantly different for year, physical condition, and weight. The intensities of fleas were higher in 2009 than in other years, probably because of lower rainfall than the annual average leading to extremely dry climatic conditions in 2008. Intensities decreased in individuals with major body weight and increased in individuals with poor physical condition. In this study, the dynamics of the flea community associated with an armadillo population is analyzed for the first time taking into account host-related factors and temporal dynamics, and also how these factors influence the community.

Modeling the Mammalian Jaw Mechanism: a Comprehensive Synthesis

At a time when continuum mechanics proposes a unified model for rigid bodies, deformable solids, and fluids using sophisticated mathematical descriptions, it is a courageous intellectual challenge to advance a classic Newtonian approach to explain the mechanics of the mammalian jaw. The Greek mathematician Archimedes (c.287 BC−c.212 BC) proposed the principle of the lever, a mechanism of force transfer with a stiff beam acting across a rotation point, or fulcrum, that may enhance either force or speed at the end of the beam. The study of the masticatory mechanics and morphology of the temporomandibular joint allow assessment of the overall capacity of the masticatory apparatus as a lever system. Jaws work as a third class lever system, with the input force acting between the pivot and output force. The temporomandibular joint acts as a pivot, the masticatory muscles provide the input force, and the output force is produced by the teeth acting on food. In a series of articles written over forty years, Walter Stalker Greaves further refined this basic model in the context of the diverse designs of mammalian jaws. However, a chronological reading of these papers would require, as Greaves himself notes, the integration of a great amount of unordered information. Fortunately, Greaves has done this work for us in his excellent book The Mammalian Jaw: a Mechanical Analysis, published recently by Cambridge University Press, which integrates and organizes the information provided and concepts developed in his articles. In this neat bit of work, Greaves presents in four chapters his understanding of the mammalian jaw mechanism in a logical linear sequence, beginning with a basic geometrical mechanical model that increases in complexity as the chapters progress. The first chapter deals with the basic two-dimensional lever system and “the one third rule,” one of Greave’s more interesting proposals. Through analysis of the bite forces on teeth, the reaction forces on the joint, and the sum of bite forces along the jaw, the model estimates the location of the line of action of the resultant force from the three masticatory muscles acting together. It also explains why biting is restricted to locations where the joint forces are compressive and, consequently, why teeth must always be positioned anterior to the muscle resultant. In the second chapter the jaw is viewed as a threedimensional lever. In this model the resultant force is located within a triangular region defined by the two joints and the biting point. Althoughmore abstract, this model’s explanatory potential is promising. Three regions are described: Region I, extending from the incisors to the premolars; Region II, the location of the molars; and Region III, edentulous and extending from the joint to the last molar. The application of this more complex model provides explanations for the contour of the dental arcade, the location of the carnassial teeth, the mediolateral position of the tooth row, and the length-towidth ratio of the jaw. The third chapter reviews the mechanical consequences of vector resultant inclination (anterior to posterior), and the mechanical and functional consequences of different heights G. H. Cassini División Mastozoología, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Av. Angel Gallardo 470, C1405DJR Ciudad Autónoma de Buenos Aires, Argentina