Microvertebrates preserved in mammal burrows from the Holocene of the Argentine Pampas: a taphonomic and paleoecological approach

Microvertebrates are a major component of many assemblages recovered from the Quaternary of the Argentine Pampas. The main goal of this paper is to analyse the taphonomic history of a Holocene microfossil bonebed, recovered from the infilling of a burrow. Evidences suggest the plains vizcacha Lagostomus maximus as the putative producer of the burrow. The assemblage includes individuals belonging to different taxa of mammals (marsupials and rodents) and reptiles (snakes). Taphonomic features suggest that the accumulation inside the burrow was related to flooding processes in the plain. The burrow was a natural trap that favoured the accumulation and preservation of remains corresponding to individuals from different sources. According to the taphonomic evidence, some individuals (Lagostomus maximus, Lestodelphys halli and Serpentes indet.) died inside the burrow, whereas others (Microcavia australis, Reithrodon auritus and Ctenomys sp.) died outside the burrow, and after a time of being exposed on the surface their remains were transported by surface run-offs into the burrow. The record of Lestodelphys halli and Serpentes indet. in the burrow produced by Lagostomus maximus could be related to a circumstantial use. Mammal burrows are a significant taphonomic mode for the late Cenozoic of the Argentine Pampas

Body Shape and Life Style of the Extinct Balearic Dormouse Hypnomys (Rodentia, Gliridae): New Evidence from the Study of Associated Skeletons

Hypnomys is a genus of Gliridae (Rodentia) that occurred in the Balearic Islands until Late Holocene. Recent finding of a complete skeleton of the chronospecies H. morpheus (Late Pleistocene-Early Holocene) and two articulated skeletons of H. cf. onicensis (Late Pliocene) allowed the inference of body size and the calculation of several postcranial indexes. We also performed a Factorial Discriminant Analysis (FDA) in order to evaluate locomotory behaviour and body shape of the taxa. Using allometric models based on skull and tooth measurements, we calculated a body weight between 173 and 284 g for H. morpheus, and direct measurements of articulated skeletons yielded a Head and Body Length (HBL) of 179 mm and a Total Body Length of 295 mm for this species. In addition to the generally higher robustness of postcranial bones already recorded by previous authors, H. morpheus, similar to Canariomys tamarani, another extinct island species, displayed elongated zygopodium bones of the limbs and a wider distal humerus and femur than in an extant related taxon, Eliomys quercinus. Indexes indicated that Hypnomys was more terrestrial and had greater fossorial abilities than E. quercinus. This was also corroborated by a Discriminant Analysis, although no clear additional inference of locomotory abilities could be calculated

Estimación de la masa corporal en géneros del Orden Notoungulata

The Notoungulata are a highly diverse group of fossil mammals with no living relatives. Virtually no body mass estimations are available for most of the genera in this order, and there is no objective method to select body mass estimators. The goal of this work is to estimate the body mass of Notoungulata taxa and detect the best predictive equations for this purpose, for each genera and family and for the order as a whole. A total of 535 fossil specimens from 50 genera are included. For each genus, body mass is estimated through 24 allometric equations calculated using 19 appendicular skeleton measurements and three dental measurements of extant mammals, taken with digital caliper. According to estimated values, the body mass interval for the order ranges from 0.57 kg in <i>Archaeophylus</i> (Interatheriidae) to 3797 Kg in <i>Mixotoxodon</i> (Toxodontidae), reflecting the great body size diversity characteristic of the group. The smallest sizes occur in the families Notostylopidae, Oldfieldthomasiidae, Archaeopithecidae, Interatheriidae, Archaeohyracidae and Hegetotheriidae; intermediate sizes among the Notohippidae, Isotemnidae and Mesotheriidae, and large sizes among the Homalodotheriidae. In the Leontiniidae and Toxodontidae, sizes range from intermediate to large; the latter display the greatest variation in body mass and the largest taxa. Compared to Holarctic ungulates, the smaller forms of notoungulates display a wider and more variable range of body mass and greater functional variation of the limbs.<br><br>Los Notoungulata son un grupo de mamíferos fósiles ampliamente diversos y sin representantes vivientes. Prácticamente no se disponen de estimaciones de la masa corporal para la mayoría de los géneros incluidos en este Orden, ni de un método objetivo para seleccionar los estimadores de masa. El objetivo del trabajo es estimar la masa corporal de los representantes del Orden Notoungulata y reconocer cuales son las mejores ecuaciones predictivas para tal fin, respecto a cada taxón en particular, a cada familia y al Orden en general. Se incluyen 535 ejemplares fósiles correspondientes a 50 géneros del orden. La masa corporal de cada género se estima sobre la base de 24 ecuaciones alométricas construidas en mamíferos vivientes, basadas en 19 medidas del esqueleto apendicular y tres medidas dentarias tomadas con calibre digital. El intervalo de masa corporal dado por los valores estimados para el orden se encuentra entre 0,57 kg en <i>Archaeophylus</i> (Interatheriidae) y 3797 Kg en <i>Mixotoxodon</i> (Toxodontidae), lo que refleja la gran diversidad de tamaños corporales que caracteriza al grupo. Los menores tamaños se dan en las familias Notostylopidae, Oldfieldthomasiidae, Archaeopithecidae, Interatheriidae, Archaeohyracidae y Hegetotheriidae; tamaños intermedios en los Notohippidae, Isotemnidae y Mesotheriidae y tamaños grandes en Homalodotheriidae. En los Leontiniidae y Toxodontidae los tamaños van de intermedios a grandes, siendo esta última la de mayor variación de masa y con los taxones de mayor tamaño. En comparación con los ungulados holárticos, los notoungulados presentan un intervalo más amplio y variable de masa corporal hacia las formas de menor tamaño y con mayor variedad funcional en las extremidades

Testing a developmental model in the fossil record: molar proportions in South American ungulates

A developmental model, based upon murine rodents, has been proposed by Kavanagh et al. (2007) to explain lower molar proportions in mammals. We produce a clade-wide macroevolutionary test of the model using the dental evolutionary trends in a unique radiation of extinct mammals endemic to South America (“Meridiungulata”) that comprise a diverse array of molar morphologies. All of the South American ungulate groups examined follow the inhibitory cascade model with the exception of two groups: Interatheriidae (Notoungulata) and Astrapotheria. For most taxa studied, ratios between lower molar areas are greater than 1.0, indicating a weak inhibition by m1 on the subsequent molars in the tooth row, and a trend to greater absolute size of the posterior molars. Comparisons of mean ratios between clades indicate that a significant phylogenetic signal can be detected, particularly between the two groups within Notoungulata— Typotheria and Toxodontia. Body mass estimates were found to be significantly correlated with both m3/m1 and m2/m1 ratios, suggesting that the larger body size achieved the weaker inhibition between the lower molars. Molar ratio patterns are examined and discussed in relation to the independent and numerous acquisitions of hypsodonty that are characteristic of dental evolution in “Meridiungulata.