Rico Schellhorn

Habitat adaptations in the felid forearm

Extant cats inhabit different kinds of habitat, for example open landscapes, forests, and rocky mountainous areas. In this study, the radius and ulna of extant felids were investigated to identify ecomorphological adaptations to different habitats. Simple scatter plots and multivariate analyses (factor analysis, discriminant function analysis) revealed two distinct clusters of cats preferring open habitats to cats preferring closed habitats (i.e., forests). We also applied our approach to an existing, large database of extant cats to determine the effect of intraspecific variation on the forearm bones. According to our dataset, cat species adapted to closed habitats have relatively shorter but thicker forearm bones whereas those with longer and slimmer forearms are adapted to open habitats. Cats that inhabit mountainous habitats show no distinct differences in adaptation and plot in one of the other two habitat categories. Overall, the radius measurements are sufficient to distinguish open and forest habitats, but with inclusion of the ulna measurements, the results are more confident. The presented method of using just four measurements of the forearm bones has much potential for application to fossil taxa. We tested the approach for fossil taxa from the Miocene to Pleistocene with the result that most fossil felids were adapted to closed habitats but with some species being adapted to more open intermediate habitats.KurzfassungRezente Katzen kommen in verschiedenen Habitaten wie offenen Landschaften, Wäldern und Gebirgen vor. In der vorliegenden Studie wurden die Unterarmknochen (Radius und Ulna) von rezenten Katzen untersucht, um Anpassungen an die verschiedenen Habitate zu unterscheiden. Streudiagramme mit den Messwerten und den Ergebnissen durchgeführter multivariater Analysen (Faktorenanalyse, Diskriminanzfunktionsanalyse) zeigen eine Trennung zwischen Katzen, die an offene oder geschlossene Habitate angepasst sind. Diese Methoden wurden auf eine publizierte Datenmatrix mit mehreren Arten und Individuen pro Spezies angewandt. An geschlossene Habitate angepasste Katzen haben generell kürzere und dickere Unterarmknochen, im Gegensatz zu schlankeren und längeren bei Katzen offener Habitate. Die begrenzte Anzahl an Katzen gebirgiger Habitate zeigt keine Anpassungen verschieden von den beiden anderen Gruppen. Allgemein reichen die Messwerte des Radius aus, um Katzen offener Habitate von denen geschlossener zu unterscheiden. Mit den Messwerten der Ulna kombiniert sind die Ergebnisse deutlicher. Infolge der Unterscheidung verschiedener Habitate mit insgesamt nur vier Messwerten an den beiden Unterarmknochen, birgt die Methode hohes Potential zur Anwendung auf fossile Taxa. Die Anwendung auf miozäne und pleistozäne Katzen zeigte eine Anpassung an geschlossene Habitate mit einigen Trends hin zu offeneren Habitaten.

Biometric study of ruminant carpal bones and implications for phylogenetic relationships

The mammalian Carpus is a complex of several small bones with multiple interactions during walking. Therefore, it is highly probable that different mammalian families developed distinctive constellations in their Carpi, which could be useful for biometric identification of phylogenetic groupings. The carpal bones of nineteen extant ruminant species (nine bovid, nine cervid, and one moschid) have been investigated to search for biometric traits which are diagnostic for the three families. Additionally, we searched for diverging functional adaptations in the carpal constellations. Therefore, measurements have been taken from the five main carpals, which are carrying the body weight. As a sesamoid bone, Os carpi accessorium was excluded. After transformation of the data into their natural logarithms, multivariate methods of factor analyses and discriminant analyses were performed for each bone. Bivariate plots of the factor scores allowed a clear separation of bovids and cervids. The only one species of the Moschidae (Moschusmoschiferus) lies closer to the cervids than to the bovids. The grouping is due to phylogenetic relationships and not due to functional differences in the groups or differing habitat preferences. Generally, the carpals of cervids are more slender and higher in contrast to the bulky and flat carpals in bovids. This approach could be used to assign isolated carpal bones found in fossil sites to their ruminant family.

Intraspecific variation in the domestic cat bony labyrinth revealed by different measurement techniques

The knowledge of intraspecific variation is important to make assumptions on an interspecific level. To study intraspecific variation in the bony labyrinth morphology of the domestic cat, eleven specimens of Felis silvestris catus and two additional subspecies (F. s. lybica, F. s. ornata) were investigated. The sample comprises skulls of adult males and females, as well as juvenile cats. Each bony labyrinth endocast was virtually reconstructed based on µCT scans. To estimate the radius of curvature of each inner ear semicircular canal, three different approaches were tested. The comparison of the different methods resulted in different absolute values for the measured radii. The assumed best structure to precisely characterize the size of a semicircular canal is the inner perimeter. Within the tested sample, the anterior semicircular canal is always the largest, while the posterior semicircular canal is the second largest and the lateral semicircular canal the smallest in most cases. The coefficient of variation lies below 10% for all bony labyrinth measurements within the sample. The inner perimeter values of each semicircular canal are similar within all investigated specimens, even though the skull length of adult cats is twice as long as that of juvenile cats. Thus, inner ear biometry of the domestic cat seems stable throughout growth series and can therefore be used for systematic and ecological studies and the inclusion of juvenile individuals is reasonable. It is noteworthy that the inner perimeter values of the semicircular canals do not vary as much as the values of the angles spanned between the three canals within the sample. The inner ear within the cat skull is oriented about 25° to 31° to the palate (angle between the plane anchored to the lateral semicircular canals (SC) and the plane anchored to the palate). The cochlea coils between 3.00 and 3.25 turns in the investigated sample.

A potential link between lateral semicircular canal orientation, head posture, and dietary habits in extant rhinos (Perissodactyla, Rhinocerotidae)

Extant rhinoceroses share the characteristic nasal horn, although the number and size of horns varies among the five species. Although all species are herbivores, their dietary preferences, occipital shapes, and common head postures vary. Traditionally, to predict the “usual” head posture (the most used head posture of animals during normal unstressed activities, i.e., standing) of rhinos, the occipital shape was used. While a backward inclined occiput implies a downward hanging head (often found in grazers), a forward inclined occiput is related to the horizontal head posture in browsing rhinos. In this study, the lateral semicircular canal (LSC) of the bony labyrinth was virtually reconstructed from µCT‐images in order to investigate a possible link between LSC orientation and head posture in extant rhinoceroses. The usual head posture was formerly reconstructed for several non‐rhinoceros taxa with the assumption that the LSC of the inner ear is held horizontal (parallel to the ground) during normal activity of the living animal. The current analysis of the LSC orientation resulted in a downward inclined usual head posture for the grazing white rhinoceros and a nearly horizontal head posture in the browsing Javan rhinoceros. The other three browsing or mixed feeding species show subhorizontal (closer to horizontal than a downgrade inclination) head postures. The results show that anatomical and behavioral aspects, like occipital shape, presence and size of horns/tusk‐like lower incisors, as well as feeding and feeding height preferences influence the usual head posture. Because quantitative behavioral data are lacking for the usual head postures of the extant rhinos, the here described relationship between the LSC orientation and the resulting head posture linked to feeding preferences gives new insights. The results show, that the inner ear provides additional information to interpret usual head postures linked to feeding preferences that can easily be adapted to fossil rhinoceroses.

The vertebrate middle and inner ear: A short overview

The evolution of the various hearing adaptations is connected to major structural changes in nearly all groups of vertebrates. Besides hearing, the detection of acceleration and orientation in space are key functions of this mechanosensory system.

Analyzing ungulate long bones as a tool for habitat reconstruction

The long bones (humerus, radius, metacarpus, femur, tibia, metatarsus) of 51 extant bovid and 7 equid specimens were measured in order to test the hypothesis that they show adaptations to different habitats. We performed factor analyses (FAs) with principal component extraction method and plotted the extracted factors (Fs) in simple scatterplots. The preferred habitats (grassland, forest, mountainous regions) were labeled in the plots, and our results show three clearly separated clusters for F2 vs. F3. According to our interpretation, F1 reflects the body size of the specimens while F2 is most probably reflecting cursorial adaptations. F3 is largely affected by dimensional bone characteristics adapted to maneuver in the environment, and therefore, F3 is somehow linked to habitat. The investigated equids are plotting within the cluster of bovids preferring grassland habitats, which is surprising because of different constructions of the metapodials in perissodactyls and ruminants. Performed linear discriminant analyses (LDAs) are supporting our FA results. This approach combines biometrics with statistics and presents a tool, which easily can be applied helping to identify the paleo-habitat or the paleo-ecology of extinct bovids with implications on fossil localities.