Visualizing shape transformation between chimpanzee and human braincases

The quantitative comparison of the form of the braincase is a central issue in paleoanthropology (i.e., the study of human evolution based on fossil evidence). The major difficulty is that there are only few locations defining biological correspondence between individual braincases. In this paper, we use mesh parameterization techniques to tackle this problem. We propose a method to conformally parameterize the genus-0 surface of the braincase on the sphere and to calibrate the parameterization to match biological constraints. The resulting consistent parameterization gives detailed information about shape differences between the braincase of human and chimp. This opens up new perspectives for the quantitative comparison of "featureless” biological structure

Hystricognathy vs Sciurognathy in the Rodent Jaw: A New Morphometric Assessment of Hystricognathy Applied to the Living Fossil Laonastes (Diatomyidae)

While exceptional for an intense diversification of lineages, the evolutionary history of the order Rodentia comprises only a limited number of morphological morphotypes for the mandible. This situation could partly explain the intense debates about the taxonomic position of the latest described member of this clade, the Laotian rock rat Laonastes aenigmamus (Diatomyidae). This discovery has re-launched the debate on the definition of the Hystricognathi suborder identified using the angle of the jaw relative to the plane of the incisors. Our study aims to end this ambiguity. For clarity, it became necessary to revisit the entire morphological diversity of the mandible in extant and extinct rodents. However, current and past rodent diversity brings out the limitations of the qualitative descriptive approach and highlights the need for a quantitative approach. Here, we present the first descriptive comparison of the masticatory apparatus within the Ctenohystrica clade, in combining classic comparative anatomy with morphometrical methods. First, we quantified the shape of the mandible in rodents using 3D landmarks. Then, the analysis of osteological features was compared to myological features in order to understand the biomechanical origin of this morphological diversity. Among the morphological variation observed, the mandible of Laonastes aenigmamus displays an intermediate association of features that could be considered neither as sciurognathous nor as hystricognathous

Exploring metameric variation in human molars: A morphological study using morphometric mapping

Human molars exhibit a type of metameric variation, which is the difference in serially repeated morphology within an organism. Various theories have been proposed to explain how this variation is brought about in the molars. Actualistic data that support the theories, however, are still relatively scarce because of methodological limitations. Here we propose new methods to analyse detailed tooth crown morphologies. We applied morphometric mapping to the enamel-dentine junction of human maxillary molars and examined whether odontogenetic models were adaptable to human maxillary molars. Our results showed that the upper first molar is phenotypically distinct among the maxillary molars. The average shape of the upper first molar is characterized by four well-defined cusps and precipitous surface relief of the occlusal table. On the other hand, upper third molar is characterized by smooth surface relief of the occlusal table and shows greater shape variation and distinct distribution patterns in morphospace. The upper second molar represents an intermediate state between first and third molar. Size-related shape variation was investigated by the allometric vector analysis, and it appeared that human maxillary molars tend to converge toward the shape of the upper first molar as the size increases. Differences between the upper first molar and the upper second and third molar can thus be largely explained as an effect of allometry. Collectively, these results indicate that the observed pattern of metameric variation in human molars is consistent with odontogenetic models of molar row structure (inhibitory cascade model) and molar crown morphology (patterning cascade model). This study shows that morphometric mapping is a useful tool to visualize and quantify the morphological features of teeth, which can provide the basis for a better understanding of tooth evolution linking morphology and development

Patterns of covariation in the masticatory apparatus of hystricognathous rodents: implications for evolution and diversification

International audienc

The bony labyrinth of late Permian Biarmosuchia: palaeobiology and diversity in non-mammalian Therapsida

Biarmosuchia, as the basalmost group of Therapsida (the stem group of mammals), are important for understanding mammalian origins and evolution. Unlike other therapsid groups, the bony labyrinth of biarmosuchians has not yet been studied, despite insightful clues that bony labyrinth morphology can provide to address palaeobiology and phylogeny of extinct animals. Here, using CT scanning, surface reconstruction and a 3D geometric-morphometric protocol of 60 semi-landmarks on the bony labyrinth of 30 therapsids (including three Mammaliaformes), it is demonstrated that bony labyrinth morphology of biarmosuchians is very distinctive compared to that of other therapsids. Despite the primitive nature of their cranial morphology, biarmosuchians display highly derived traits in the structure of the bony labyrinth. The most noticeable are the presence of a long and slender canal linking the vestibule to the fenestra vestibuli, an enlarged and dorsally expanded anterior canal, and the absence of a secondary common crus (except for one specimen), which sets them apart from other non-mammalian therapsids. These characters provide additional support for the monophyly of Biarmosuchia, the most recently recognized major therapsid subclade. Although implications of the derived morphology of the biarmosuchian bony labyrinth are discussed, definitive interpretations are dependent on the discovery of well-preserved postcranial material. It nevertheless sheds light on a previously overlooked diversity of bony labyrinth morphology in non-mammalian therapsids.The Palaeontological Scientific Trust (PAST) and its Scatterlings of Africa Programmes NRF South Africa DST-NRF Centre of Excellence in PalaeosciencesJN

Evolution and development of the strepsirrhine primate skull

Since Haeckel (1866), the evolutionary modification of ontogeny has been recognized as an important source of morphological innovation. Due to recent advances in developmental genetics and phenotypic analysis, evolutionary developmental (evo-devo) studies have regained considerable interest and led to fundamental changes in our understanding of how ontogeny and phylogeny are related. This thesis investigates the relationship between ontogeny and phylogeny in strepsirrhine primates. The suborder Strepsirrhini, which comprises galagos, lorises and Malagasy lemurs, is thought to have retained most of the ancestral primate condition (as opposed to the suborder Haplorrhini, which comprises tarsiers and anthropoids). Nevertheless, strepsirrhines are highly diverse in their morphology. Here, the focus is on cranial diversity, which is analyzed from a developmental perspective with a new set of geometric morphometric tools. First, patterns of cranio-mandibular variability in extant adult primates are analyzed. Taking into account the phylogenetic constraints applying to the skull morphology permits a quantification of how dietary specialization and activity patterns influence cranio-mandibular morphology in both primates suborders. Also, the skull morphology in strepsirrhines and haplorrhines is clearly distinct, and it is shown here that differences between and within infraorders can be traced back to differences in developmental modes. According to a hypothesis proposed by Beard (1988), “strepsirrhinism” represents the primitive condition of the primate skull. This thesis shows that the cranial morphology of the Omomyidae – a basal haplorrhine taxon comprising the genera Rooneyia, Necrolemur and Microchoerus – is closer to that of extant strepsirrhines than to that of haplorrhines, while the cranial morphology of Tarsius is closer to that of other extant haplorrhines, i.e., the anthropoids. Thus, it is probable that the shift towards a modern haplorrhine morphology occurred in one omomyid lineage, to the exclusion of the three genera mentioned above. New arguments are proposed to support the hypothesis that the cranio-mandibular morphologies of the cheirogaleids and galagids are the least derived from the ancestral condition of toothcombed strepsirrhines. This thesis presents a comparative geometric morphometric analysis of cranio-mandibular development in ten strepsirrhine and two haplorrhine species. Haplorrhines and strepsirrhines differ widely in ontogenetic trajectory direction, length and position. Within the strepsirrhines, divergence between taxon-specific ontogenetic trajectories and allometric grade shifts are more pronounced in lemurs than in lorises. This pattern of evolutionary modification of ontogenetic trajectories is interpreted in the context of the rapid adaptive radiation of lemurs. The last section uses insights obtained from the evolutionary developmental analysis of extant taxa for a comparative analysis of fossil strepsirrhine taxa. The morphologies of extant and extinct strepsirrhines are compared. In particular, the morphology of the skull is well known from two adapiform subfamilies, Adapinae and Notharctinae. Among the adapines, a size increase has occurred in the Leptadapis lineage via a shift in allometric grade, which suggests phyletic gigantism in this genus. Adapiforms exhibit longer ontogenetic trajectories than extant strepsirrhines. A trend toward a shortening of ontogenetic trajectories has occurred in the evolutionary history of strepsirrhines. This can be related to a context of general increase in encephalization within this lineage. Abstract 2: Due to recent advances in developmental genetics and phenotypic analysis, evolutionary developmental (evo-devo) studies regained considerable interest, and led to fundamental changes in our understanding of how ontogeny and phylogeny are related. This thesis investigates the relationship between ontogeny and phylogeny in strepsirrhine primates. Here, the focus is on cranial diversity, which is analyzed from a developmental perspective, and with a new set of geometric morphometric tools. A comparative geometric morphometric analysis of cranio-mandibular development is conducted in ten strepsirrhines and two haplorrhine species. Haplorrhines and strepsirrhines differ widely in ontogenetic trajectory direction, length and position. Within the strepsirrhines, divergence between taxon-specific ontogenetic trajectories and allometric grade shifts are more pronounced in lemurs than in lorises. The insights obtained from the evolutionary developmental analysis of extant taxa are used for a comparative analysis of Eocene fossil strepsirrhine taxa belonging to the infraorder Adapiformes. Among the adapine adapiforms, an increase in size via allometric grade shift has occurred in the Leptadapis lineage, which suggests phyletic gigantism in this genus. Adapiforms exhibit longer ontogenetic trajectories than extant strepsirrhines. A trend toward a shortening of ontogenetic trajectories has occurred in the evolutionary history of strepsirrhines. This trend can be related to the expression of developmental constraints in a context of selection for increase in encephalization. Zusammenfassung 2 Aufgrund jüngerer Fortschritte in der Entwicklungsgenetik sowie der phänotypischen Analyse ist das Interesse an der evolutionären Entwicklungsbiologie enorm gestiegen, und hat zu grundlegenden Veränderungen im Verständnis der Beziehung von Ontogenese und Phylogenese geführt. Diese Arbeit untersucht die Beziehung zwischen Ontogenese und Phylogenese am Beispiel der Feuchtnasenaffen (Strepsirrhini). Die kraniale Diversität dieser Primaten wird mit einer Palette neuer morphometrischer Werkzeuge analysiert. Resultate aus der evolutionären Entwicklungsbiologie existierender Taxa werden für eine vergleichende Analyse von fossilen Taxa der aus dem Eozän stammenden Unterordnung Adapiformes benutzt. Die evolutionäre Geschichte der Strepsirhini weist auf eine Tendenz in Richtung verkürzter ontogenetischer Trajektorien hin. Dies kann in einem Zusammenhang allgemeiner Enzephalisation in dieser Abstammungslinie gesehen werden

The functional morphology and internal structure of the forelimb of the Early Triassic non-mammaliaform cynodont Thrinaxodon liorhinus

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 2015.Thrinaxodon liorhinus, a cynodont that has been of captivating importance in the evolution of therapsids, is one of the best known transitional fossil taxa from non-mammaliaform cynodonts to mammals. The species is abundant in the South African Karoo Basin and is one of the best represented taxa immediately after the Permian-Triassic mass extinction. One of the key adaptive characteristics that may have aided in their survival was fossorialism. Numerous fossils of Thrinaxodon have been found in burrows or in a curled-up position, which has provided important circumstantial evidence for the formalization of the hypothesis of Thrinaxodon as a burrower. However, finding a fossil inside a burrow or even in a curled-up position only provides firm evidence for burrow use, not for burrow creation. Direct evidence for burrowing capability can come from the understanding of the functional morphology of Thrinaxodon limbs. The present study investigates internal and external structure of the Thrinaxodon forelimb, a variety of reptiles characterized by different behavioural patterns, and other cynodonts in order to advance present knowledge about the functional morphology of the transitional phase cynodont. The study uses Geometric Morphometric analyses, forelimb metric indices, torsion and cortical thickness of humeri in order to determine the extent to which, the Thrinaxodon forelimb functionally and structurally resembles that of a fossorial mammal versus a digging reptile. Results of the study tease apart the extent to which the Thrinaxodon forelimb illustrates modifications due to gait (e.g., sprawling versus semi-sprawling) versus a fossorial lifestyle. This would indicate that Thrinaxodon retained the reptilian skeletal configuration and adapted a posture that had begun to resemble parasagittal more than sprawling or semi-sprawling gait. Nonetheless, Thrinaxodon exhibits forelimb structural similarities to digging species, whether mammals or reptiles