El origen de los félidos macairodontinos: aspectos funcionales de la anatomía cráneo-cervical de Paramachairodus ogygia (Kaup, 1832) (Felidae, machairodontinae) de Batallones-1 (Vallesiense, MN 10)

Los llamados “félidos dientes de sable” aparecen en el registro fósil a partir del Mioceno superior, desapareciendo hace tan solo unos 10.000 años. Los últimos representantes de este grupo fueron los cazadores dominantes en las comunidades de mamíferos de las que formaron parte. Su anatomía, altamente especializada, es bastante bien conocida gracias a yacimientos como Rancho La Brea (EEUU), del cual se conocen restos de miles de individuos de Smilodon fatalis. Sin embargo, muy poco se sabía sobre la anatomía de los primeros macairodontinos y sobre el origen de este modelo de depredador. El descubrimiento del complejo de yacimientos del Cerro de los Batallones (Torrejón de Velasco, Madrid) ha proporcionado gran cantidad de restos de uno de los macairodontinos más primitivos, Paramachairodus ogygia, lo que ha permitido estudiar en profundidad su anatomía funcional, en concreto en este trabajo el complejo cráneo-cervical, y proponer una hipótesis que explique el origen para este grupo tan especializado de carnívoros.

Late Pleistocene records of felids from Medicine Hat, Alberta, including the first Canadian record of the sabre-toothed cat Smilodon fatalis

In the late 1960s, a team led by C.S. Churcher and A. MacS. Stalker collected over 1000 vertebrate fossils, mostly representing large herbivorous mammals, from bluffs along the South Saskatchewan River near Medicine Hat, Alberta, Canada. The records from this area also include the only documented case of the sabre-toothed cat Smilodon fatalis, but these specimens have not been described or illustrated, and therefore, their identification has never been verified. Here, all felid fossils recovered from the Medicine Hat bluffs are described and identified. We confirm the presence of the machairodontine S. fatalis and three additional taxa: the feline Lynx and the pantherines Panthera cf. P. atrox (American lion) and Panthera cf. P. spelaea (cave lion). Notably, this record of S. fatalis is its first confirmed occurrence in Canada and is a significant northerly range expansion, bringing the global distribution of this species in line with what is typical for a large felid. Should the tentative record of Panthera cf. P. spelaea be correct, this would represent its first occurrence in Alberta and a southeastern range extension, bringing it into the range of P. atrox. The possible presence of both P. atrox and P. spelaea suggests that Late Pleistocene pantherine biogeography in North America may be more complex than previously believed, particularly during relatively warm interglacial periods.

Static Scaling and the Evolution of Extreme Canine Size in a Saber-Toothed Cat (Smilodon fatalis)

The canines of saber-toothed cats are a classic example of an extreme morphology, yet important questions pertaining to their evolution remain unanswered. Recent analyses suggest these structures functioned as tools of intrasexual combat where trait size acts as both a weapon of battle and signal of competitive ability. However, classic skeletal reconstructions suggest saber-tooth canines evolved as specialized hunting tools. Either scenario could have led to the evolution of extreme canine size and distinguishing between these hypotheses is therefore difficult. This is made more challenging by the fact that natural observation of saber-toothed cats is impossible, and biologists must rely on measures of static morphology to study the patterns of selection that favored extreme canine size. Here I analyze the static intraspecific scaling relationship between canine size and body size in the saber-toothed cat, Smilodon fatalis, to determine whether or not extreme canine size functioned as a sexually selected signal. I review the literature surrounding the evolution of sexually selected signals and the methods recently established by O’Brien et al. (2018), show how static scaling relationships can be useful, reliable tools for inferring patterns of selection, especially in fossil organisms, and provide evidence that extreme canine size in saber-toothed cats was not the product of selection for effective sexual signals, but instead evolved as either a pure intrasexually selected weapon or a hunting tool.

A new specimen-dependent method of estimating felid body mass

Background. The estimation of body mass of long extinct species of the family Felidae has been a focus of paleontology. However, most utilized methods impose expected proportions on the fossil specimens being estimated, resulting in a high chance of underestimation or overestimation. This study proposes a new method of estimating felid body mass by accounting for osteological proportionality differences between the extinct taxa being estimated and the living species being used as comparisons. Method. Using a manipulation of the cube law, 36 equations were formulated that estimate body mass based on certain humeral and femoral dimensions. The formulated equations were used to examine whether the mass of living comparison species, namely the tiger (Panthera tigris), the lion (Panthera leo), and the jaguar (Panthera onca), depends equally on a select set of long bone dimensions. The body mass of five extinct felids, namely Panthera atrox, Panthera spelaea, Panthera tigris soloensis, Smilodon populator, and Smilodon fatalis, was also estimated. Results. Living comparisons species were found to somewhat incorrectly estimate other living comparison species. All five extinct taxa were found to weigh well over 300 kg, with the largest of the species weighing nearly 500 kg. Discussion. The inability of one living comparison species to predict the mass of another with strong accuracy suggests that bone dimensions do not solely influence body mass. Discrepancies between the masses of Smilodon populator and Smilodon fatalis were likely the product of the difference in available niches in late Pleistocene North and South America. The masses of Panthera spelaea and Panthera atrox indicate a discrepancy in sociality between the two closely related species. Lastly, the extreme body mass of Panthera tigris soloensis points to great plasticity within the tiger lineage in terms of size, indicating that such variations among tiger populations may not warrant subspeciation.