Craniometric Variation in a Regional Sample from Antioquia, Medellín, Colombia

Population affinity estimation is frequently assessed from measurements of the cranium. Traditional models place individuals into discrete groups―such as Hispanic―that often encompass very diverse populations. Current research, including this study, challenges these assumptions using more refined population affinity estimation analyses. We examine craniometric data for a sample of individuals from different regions in Antioquia, Colombia. We first assessed the sample to understand intraregional variation in cranial shape as a function of birthplace or a culturally constructed social group label. Then, pooling the Colombian data, we compare cranial variation with global contemporary and prehistoric groups. Results did not indicate significant intraregional variation in Antioquia; classification models performed poorly (28.6% for birthplace and 36.6% for social group). When compared to other groups (American Black, American White, Asian, modern Hispanic, and prehistoric Native American), our model correctly classified 75.5% of the samples. We further refined the model by separating the pooled Hispanic sample into Mexican and Guatemalan samples, which produced a correct classification rate of 74.4%. These results indicate significant differences in cranial form among groups commonly united under the classification “Hispanic” and bolster the addition of a refined approach to population affinity estimation using craniometric data.

Desmodilliscus braueri crania compared to Pachyuromys duprasi (Desmodilliscini, Gerbillinae, Rodentia)

Molecular phylogenies support the monophyly of Desmodilliscus braueri and Pachyuromys duprasi as a clade basally split from all other gerbillines. While this monophyly supports their placement in a single tribe (Desmodilliscini), no morphological synapomorphies exist among desmodilliscines. This study compares the scale-independent cranial shapes of these two species using geometric morphometrics to determine how they differ and/or converge. Tribal synapomorphies, should they exist, may appear as interspecifically invariable cranial regions. No such invariable cranial regions were detected. The two species significantly differed in cranial size and shape. A small part of shape variation was allometric, with a weak unique allometric effect. No sexual size nor shape dimorphism was found. The sister taxa greatly differed in almost all cranial features, with Pachyuromys (when compared to Desmodilliscus) having a larger-sized cranium, with a larger bulla and suprameatal triangle, a more posteriorly placed palatine foramina, and more anteriorly shifted (and reduced) rostral cranial structures, due to being crowded by the hypertrophied bulla. Cranial variation patterns are consistent with the literature. The extreme morphological divergence among these species is explained by the distant divergence time and ecological differences. Absence of cranial shape synapomorphies does not preclude synapomorphies in other craniodental morphological features (e.g., detailed morphology of the dentition and cranial foramina) or in other morphological structures, such as the postcranial skeleton.

A Case of Multiple Stun Attempts in a Bovine Due to Chronic Disease Process Causing Cranial Abnormalities

The preslaughter stunning of bovine animals is a legal requirement in the European Union, unless the animal is being slaughtered according to religious rite. The legislation also requires the investigation and review of stunning methods in cases of failure to stun. This paper presents the results of one investigation into the possible reasons for multiple stun attempts on an animal that received five shot applications. The head was hard frozen to prevent the deformation of brain structures during splitting along the sagittal plane, and then underwent macroscopic examination to assess the likely causes of the repeated stun attempts. In this case, a pre-existing chronic disease process produced anatomical variations of the cranial cavity, increasing the thickness of the sinuses of the frontal bone to a depth of 9 cm and filling the sinuses with a fibrinous pus deposit. It was therefore concluded that the anatomical variation produced by the chronic disease process, in addition to the energy absorption provided by the thicker hide and fibrinous pus, led to the failure of the stunning equipment to achieve the desired stunned state in the animal. As the animal displayed cranial variation before slaughter, a review of the stunning systems should include a requirement that animals displaying any abnormalities should be stunned with the highest-powered cartridge available or a free bullet.

Effects of size, phylogeny and locomotor habits on the pelvic and femoral morphology of South American spiny rats (Rodentia: Echimyidae)

The rodent family Echimyidae (spiny rats, hutias and coypu) is notable for its high phylogenetic and ecological diversity, encompassing ~100 living species with body mass ranging from 70 to 4500 g, including arboreal, epigean (non-arboreal or scansorial), fossorial and semi-aquatic taxa. In view of this diversity, it was hypothesized that echimyid morphological variation in the pelvis and femur should reflect: (1) allometric association with body mass; (2) morphofunctional specializations for the different locomotor habits; and (3) phylogenetic history. To test these propositions, we examined 30 echimyid species, in addition to eight species of two other octodontoid families, Abrocomidae and Octodontidae. Pelvic and femoral variation was assessed with linear morphometry, using bivariate and multivariate statistical methods, part of which was phylogenetically informed. Approximately 80% of the total variation among echimyids was explained by body mass, and some univariate measurements were found potentially to be effective as body mass estimators after simple allometric procedures, notably in the pelvis. Even considering the significant phylogenetic signal, variation in shape was largely structured by locomotor habits, mainly in the pelvis, suggesting that the echimyid hindlimb diversification was driven, in part, by selective pressures related to locomotor habits. Finally, echimyid femoral disparity was considerably greater than in other octodontoids, contrasting with their relatively modest cranial variation. Thus, this study suggests that hindlimb diversity constitutes a key factor for the exceptional echimyid ecological and phyletic diversification.

Cranial variation in Gryposaurus and biostratigraphy of hadrosaurines (Ornithischia: Hadrosauridae) from the Dinosaur Park Formation of Alberta, Canada

The Dinosaur Park Formation (Campanian) of Alberta documents one of the most diverse assemblages of hadrosaurine dinosaurs. Historically, two species of the genus Gryposaurus Lambe, 1914 have been recognized in the Dinosaur Park Formation, Gryposaurus notabilis Lambe, 1914 and Gryposaurus incurvimanus Parks, 1919, which are differentiated primarily on their nasal arch morphology. These two species have recently been suggested to represent either variable morphs within G. notabilis (e.g., ontogeny) or two distinct taxa within an evolving Gryposaurus lineage (e.g., anagenesis). These alternative hypotheses have never been adequately tested via detailed morphological comparisons, morphometrics, or biostratigraphy. A geometric morphometric analysis of hadrosaurine skulls from the Dinosaur Park Formation was performed to assess the influence of ontogeny on skull morphology. Gryposaurus incurvimanus skulls were found to be distinctly smaller, and morphologically divergent from those of G. notabilis, with larger G. notabilis skulls having higher nasal arches set farther back on the skull, a size-correlated pattern consistent with ontogenetic nasal retraction documented in other hadrosaurids. Stratigraphic data were used to map this morphology through time, to evaluate the anagenesis hypothesis. The stratigraphic distributions of the two species showed considerable overlap, rejecting anagensis and indicating that the sampled individuals lived over a short period of time (<0.5 Myr). Overall, our results suggest that the hypothesis that G. incurvimanus and G. notabilis represent different ontogenetic stages within a single species cannot be rejected. This study improves our understanding of the extent of potential individual variation within a single Gryposaurus species, which will be useful in assessing the validity of other hadrosaurines.

How flat can a horse be? Exploring 2D approximations of 3D crania in equids

ABSTRACTQuantitative analyses of morphological variation using geometric morphometrics are often performed on 2D photos of 3D structures. It is generally assumed that the error due to the flattening of the third dimension is negligible. However, despite hundreds of 2D studies, few have actually tested this assumption and none has done it on large animals, such as those typically classified as megafauna. We explore this issue in living equids, focusing on ventral cranial variation at both micro- and macro-evolutionary levels. By comparing 2D and 3D data, we found that size is well approximated, whereas shape is more strongly impacted by 2D inaccuracies, as it is especially evident in intra-specific analyses. The 2D approximation improves when shape differences are larger, as in macroevolution, but even at this level precise inter-individual similarity relationships are altered. Despite this, main patterns of sex, species and allometric variation in 2D were the same as in 3D, thus suggesting that 2D may be a source of ‘noise’ that does not mask the main signal in the data. However, the problem is complex and any generalization premature. Morphometricians should therefore test the appropriateness of 2D using preliminary investigations in relation to the specific study questions in their own samples. We discuss whether this might be feasible using a reduced landmark configuration and smaller samples, which would save time and money. In an exploratory analysis, we found that in equids results seem robust to sampling, but become less precise and, with fewer landmarks, may slightly overestimate 2D inaccuracies.