Gabriel M. Martin

INTRASPECIFIC VARIATION IN LESTODELPHYS HALLI (MARSUPIALIA: DIDELPHIMORPHIA)

Abstract The Patagonian opossum, Lestodelphys halli, is known from a few skeletons of captured animals and several isolated fragments recovered from owl pellets in Argentina. Recently, more than 300 remains (mandibles, maxillae, crania, and other bones) were found in owl pellets and associated bones, comprising the largest known collection of L. halli. A detailed morphological analysis of craniomandibular and dental variation is reported and comparisons with other small didelphids also are made. Intraspecific variation is discussed and differential diagnosis of the species is presented.

A Brief History of South American Metatherians

With more than 100 species, living South American marsupials (Mammalia, Metatheria) give only a glimpse of the much higher taxonomic and ecological diversity acquired by metatherians throughout the Cenozoic Era. The term Metatheria designs a taxon within Mammalia that includes not only Marsupialia but also all therian mammals more related to Marsupialia than to Eutheria. Several features (e.g., epipubic ones) formerly considered as diagnostic of Metatheria are now regarded either a primitive condition or not present in all members of this group. Other derived features, such as the presence of a shelf-like, inflected angular process in the lower jaw, are consistently present in all metatherians. A brief characterization of all major South American, Cenozoic metatherian lineages is given: “basal ameridelphians,” Sparassodonta, Didelphimorphia, Paucituberculata, Microbiotheria, and Polydolopimorphia (the latter including Polydolopiformes and Bonapartheriiformes). Three periods can be distinguished in the history of our knowledge of Cenezoic South American Metatheria: the first one (1878–1930) is intimately linked to Florentino Ameghino, Argentina’s most notable paleontologist; much of our knowledge on extinct metatherians from South America was elaborated by him. The second period (1930–1977) occurred under the influence of George Gaylord Simpson’s ideas. Bryan Patterson and Rosendo Pascual also had an important imprint in South America’s Mammalian Paleontology. The third period (1977-present) is currently evolving under new phylogenetic, taxonomic, and paleobiogeographic paradigms; influences are multiple and major reviews of specific lineages are currently in the making. A final note on the incompleteness of Cenozoic South America’s fossil record is made: only the mid to high latitudes, basically in the Southern Cone, are moderately well-sampled in their terrestrial fossil record.

Erratum to: Post-Weaning Cranial Growth in Shrew Opossums (Caenolestidae): A Comparison with Bandicoots (Peramelidae) and Carnivorous Marsupials

The patterns of development and skull ontogeny in caenolestids have been poorly studied, resulting in a limited knowledge. In this work, we report and compare the allometric growth trends of 15 variables in the three living groups of the Family Caenolestidae, represented by Caenolestes fuliginosus, Lestoros inca, and Rhyncholestes raphanurus. We analyzed the bivariate and multivariate allometry in comparison with morphologically convergent Australasian peramelids, as well as with other marsupials and placentals previously studied. We also report the phylogenetic signal and optimization of the confidence intervals of the variables analyzed in two alternative hypotheses, where Ameridelphia is considered as monophyletic and paraphyletic. Rhyncholestes raphanurus and C. fuliginosus shared more allometric trends than any other between-taxa comparisons. Notwithstanding, several statistics were higher in R. raphanurus, except for those variables related to temporal muscles and bite. The close relationship between R. raphanurus and L. inca is also supported by the longitudinal growth of the rostrum, although with a clear growth extension in R. raphanurus. The allometric trends reported for L. inca reflect a more predaceous condition compared to other caenolestids. Bandicoots and caenolestids did not show a particularly shared growth pattern, with the latter being morphologically more conservative. Ameridelphia was paraphyletic in the shortest tree regarding the optimization of the confidence intervals. However, the growth of several variables supported monophyletic groups in both hypotheses. Skull ontogeny in marsupials is informative in several aspects of the mandible and neurocranium reflecting the high phylogenetic signal displayed by variables related to these cranial regions.

Distribution of Lyncodon patagonicus (Carnivora, Mustelidae): changes from the Last Glacial Maximum to the present

Abstract The Patagonian weasel (Lyncodon patagonicus) is one of the least known carnivores from South America, and excluding some contributions, knowledge of it seems anecdotal. It is supposed to inhabit herbaceous and arid environments of Argentina and Chile. Here we assess the potential distribution of the Patagonian weasel both during the present and the Last Glacial Maximum (LGM). We also integrate some of this information, providing a historical and geographic analysis (both through ecological niche modeling and biogeographic schemes) of the distribution of L. patagonicus. We found 2 major core areas of distribution, 1 in northwestern Argentina and another in southern Argentina (i.e., Patagonia). Patagonian weasel distribution seems to be primarily related to cold areas with marked temperature seasonality and elevations below 2,000 m above sea level. From LGM to the present, we observed a major retraction in potential distribution areas that might indicate the existence of a vicariance process affecting Patagonian weasel distribution. Resumen El Huroncito Patagónico (Lyncodon patagonicus) es uno de los carnívoros menos conocidos de Sudamérica, y excluyendo algunas contribuciones, su conocimiento parece anecdótico. Se supone que habita ambientes áridos con vegetación herbácea de Argentina y Chile. En el presente estudio evaluamos la distribución potencial del Huroncito Patagónico durante el presente y el Último Máximo Glacial (UMG). Para ello integramos información proveniente de análisis históricos y geográficos (Modelado de Nicho Ecológico y esquemas biogeográficos) de la distribución de L. patagonicus. De esta manera obtuvimos dos grandes áreas núcleo de distribución para la especie, una en el noroeste de Argentina y otra hacia el sur de Argentina (i.e., Patagonia). La distribución del Huroncito Patagónico parece estar relacionada en primer lugar con áreas frías de marcada estacionalidad térmica y altitudes por debajo de los 2000 m.s.n.m. El modelo generado indica que desde el UMG hasta el presente, hubo una mayor retracción en las áreas de distribución potencial, lo cual podría indicar la existencia de un proceso de vicarianza que afectó la distribución del Huroncito Patagónico.

Intraspecific variability in Lestoros inca (Paucituberculata, Caenolestidae), with reports on dental anomalies and eruption pattern

Abstract Caenolestids are a group of poorly known South American marsupials with a restricted distribution in páramo and subpáramo environments of the Andes from Colombia and western Venezuela to Bolivia (represented by the genera Caenolestes and Lestoros), and in Valdivian rain forest in southern Chile and Argentina where a single species (Rhyncholestes raphanurus) lives. The Incan shrew opossum, Lestoros inca, lives in mountains of southern Peru and extreme northwestern Bolivia. Despite being common in trapping surveys, little is known of its cranial and dental intraspecific variability, tooth eruption pattern, and dental anomalies. The objective of this work was to analyze the intraspecific variability of L. inca, which includes an anatomical description of the skull and dentition and analysis of clinal variation, tooth eruption patterns, and dental anomalies. The eruption pattern found in L. inca confirms the sequence P3 → m4 → p3 → M4 as the general pattern for living paucituberculatans. Missing teeth between the procumbent incisor and the 2nd lower premolar are the most common anomaly found (n = 14, 20% of the analyzed specimens). Comparisons with other living caenolestids, lack of clinal variation and significant differences between populations support L. inca as a separate, clearly distinct species. The information presented herein can be used in anatomical and paleontological studies dealing with caenolestids in particular and marsupials in general and also provides a sound basis for anatomical inferences made from fossils. Resumen Los cenoléstidos comprenden un grupo poco conocido de marsupiales sudamericanos, cuya distribución se encuentra restringida a los ambientes de páramo y subpáramo en la Cordillera de los Andes desde Colombia y el oeste de Venezuela hasta Bolivia (representados por los géneros Caenolestes y Lestoros), y el bosque valdiviano del sur de Chile–Argentina donde habita Rhyncholestes raphanurus. Una de estas especies, el ratón runcho andino Lestoros inca, habita el páramo y subpáramo desde el sur del Perú al extremo norte de Bolivia. A pesar de ser común en trampeos, es poco lo que se conoce de esta especie en cuanto a variabilidad intraespecífica, patrón de erupción y anomalías dentarias, y otros rasgos anatómicos. El objetivo de este trabajo es analizar la variabilidad intraespecífica de L. inca, incluyendo una descripción anatómica del cráneo y dentición, analizar la variación clinal, patrones de erupción y anomalías dentarias. La falta de variación clinal o diferencias poblacionales significativas, brindó soporte al tratamiento de L. inca como una única especie. El patrón de erupción dentario encontrado en la especie (P3 → m4 → p3 → M4) confirma esta secuencia como el patrón generalizado para los paucituberculata vivientes. La falta de dientes, entre los incisivos procumbentes y el segundo premolar inferior, fueron la anomalía dentaria más comúnmente encontrada (20% de los ejemplares analizados). Comparaciones con cenoléstidos vivientes permiten considerar a L. inca como especie válida y claramente diferente del resto. La información aquí presentada podrá ser usada en estudios anatómicos y paleontológicos sobre cenoléstidos en particular y marsupiales en general, aportando, además, información anatómica que permitirá realizar inferencias en fósiles.

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

Observations on the behavior of Caenolestes fuliginosus (Tomes, 1863) (Marsupialia, Paucituberculata, Caenolestidae) in captivity

We describe the behavior in captivity of the dusky shrew-opossum Caenolestes fuliginosus from 17 specimens captured at Finca La Martinica (Colombia), which were kept alive in plastic terraria for different periods of time (between 1 and 12 consecutive days). We found that C. fuliginosus can climb and jump well and uses its nonprehensile tail as a support when climbing. Feeding observations showed a preference towards an animalivorous diet, which included moths/butterflies (Insecta, Lepidoptera), stick-insects (Insecta, Phasmatoidea), flatworms (Platyhelminthes, Turbellaria), earthworms (Annelida, Oligochaeta), frogs (Amphibia, e.g., Pristimantis sp.), and dead rodents (Rodentia, Sigmodontinae, e.g., Microryzomys sp., Thomasomys sp.). Individuals were active throughout the day and night, with no indication of daily torpor. Our observations showed C. fuliginosus is not aggressive towards congeners and often aggregates during rest, especially when several individuals are placed together. Unlike other New World marsupials, C. fuliginosus showed nonagonistic group feeding behavior when consuming carcasses. Stereotyped behavior patterns (e.g., grooming) were not frequently observed. Our work provides comparative information for further studies on caenolestids and other New World marsupials.

Variability and variation in Dromiciops Thomas, 1894 (Marsupialia, Microbiotheria, Microbiotheriidae)

The genus Dromiciops Thomas is the only living representative of the order Microbiotheria. Throughout the history of the taxon, it was considered to comprise a continental and an insular form (D. australis and D. gliroides), a single species (D. gliroides), or, as recently described, 3 different species (D. bozinovici, D. mondaca, and D. gliroides). I analyzed the morphometric and morphologic variability (differences in morphological characters within a sample or species) and variation (differences in morphological characters among samples or species) in Dromiciops. Comparisons to test for secondary sexual dimorphism were made within and between continental and insular samples for localities with the largest samples available. Due to the lack of sexual dimorphism, males and females were analyzed together to test for: 1) differences between continental and insular samples; 2) differences between the arrangement of recently described species using a larger series of available specimens; and 3) clinal variation. Results support Dromiciops as composed of 1 valid species (D. gliroides), without clinal variation. Based on the samples I examined, several characters previously used as diagnostic for the 3 species previously recognized (e.g., incisive and palatal fenestrae, mandibular height) vary intraspecifically and are not valid as diagnostic.

Chronological implications of the nothrotheriid ‘ Xyophorus ’ (Mammalia, Xenarthra) from the Collón Curá Formation (Miocene of Patagonia, Argentina)

Abstract The specimen described herein and assigned to ‘Xyophorus’ sp. (Mammalia, Xenarthra, Tardigrada) was collected in the locality Cerro Zeballos, northwestern Chubut Province, Argentina. The fossiliferous sediments bearing the specimen are correlated with Collón Curá Formation. The specimen has the features described for other members of ‘Xyophorus’ (e.g. shape and size of the molariforms, relationship between diastema length, m1 and m2 length) and has a Diastema Length/Tooth Row Length index (DL/TRL index) of ca. 14, between that of ‘X.’ villarroeli (12.07) from the Mauri Formation, Bolivia (ca. 10.3 Ma) and that of ‘X.’ bondesioi (16.45) from Arroyo Chasicó Formation, Argentina (ca. 10–8.7 Ma). The relationship between DL/TRL index and age of the bearing sediments, would suggest a Tortonian age (late Miocene) for the deposits of Collón Curá Formation at Cerro Zeballos, which results in a ‘younger age’ compared to the middle Miocene age traditionally accepted for the Collón Curá Formation bearing the Colloncuran fauna sensu stricto. Although no absolute ages for Cerro Zeballos are available yet, the geographic proximity of Cerro Zeballos to Cushamen River (with levels dated at ca. 11.2 Ma) supports the tentative Tortonian age indicated by the presence of ‘Xyophorus’ sp.

Dispersal of Vertebrates from Between the Americas, Antarctica, and Australia in the Late Cretaceous and Early Cenozoic

The early Paleocene diversity of metatherians in Tiupampan faunas of South America and the pre-Tiupampan Paleocene polydolopimorphian Cocatherium speak in favor of an earliest Paleocene or Late Cretaceous dispersal of metatherians from North America. No Late Cretaceous metatherian or eutherian mammals have been recovered to date in South America, but the late Campanian to Maastrichtian hadrosaurine dinosaurs in Argentina, as well as the late Maastrichtian of the Antarctic Peninsula, is evidence of a biotic connection to North America. Placental ‘condylarths’ in the Tiupampan may have been related to, and dispersed southward relative to, Puercan taxa in North America and perhaps reflect a somewhat later event in comparison to metatherians. Other than hadrosaurine dinosaurs, Late Cretaceous vertebrates of South America are basically Gondwanan in affinities and reflect (and survived) the pre-106 Ma connection between South America, Africa, and Antarctica. The potential for a Late Cretaceous dispersal of metatherians would be compatible with a continued dispersal to Australia at that time, also supported by plate tectonic relationships, notwithstanding the basically endemic coeval Australian dinosaur fauna, and recognizing the essential absence of a Late Maastrichtian land vertebrate record there. An early Paleocene connection between at least Antarctica and South America is documented by the presence of a monotreme in the Peligran fauna of Patagonia. This, coupled with the fact that post-Peligran mammal faunas in South America and the Antarctic Peninsula (from at least 52 Ma in that location) are composed of derived metatherian as well as placental mammals, suggests that dispersal of metatherians to Australia had been achieved prior to the Eocene. Such timing is compatible with the still plesiomorphic level of Australian metatherians from the early Eocene Tingamarra fauna of Australia, the marine sundering of the Tasman Gate at about 50 Ma and the development of a continuously marine southern coastline of Australia from about 45 Ma effectively foreclosed overland mammal and other vertebrate dispersal to Australia thereafter.