Functional signals and covariation in triquetrum and hamate shape of extant primates using 3D Geometric Morphometrics

AbstractObjectivesExtinct hominins can provide key insights into the development of tool use, with the morphological characteristics of the thumb of particular interest due to its fundamental role in enhanced manipulation. This study quantifies the shape of the first metacarpal’s body in the extant Homininae and some fossil hominins to provide insights about the possible anatomical correlates of manipulative capabilities.Materials and methodsThe extant sample includes MC1s of modern humans (n=42), gorillas (n=27) and chimpanzees (n=30), whilst the fossil sample included Homo neanderthalensis, Homo naledi and Australopithecus sediba. 3D geometric morphometrics were used to characterize the overall shape of MC1’s body.ResultsHumans differ significantly from extant great apes when comparing overall shape. H. neanderthalensis mostly falls within the modern human range of variation although also showing a more robust morphology. H. naledi varies from modern human slightly, whereas A. sediba varies from humans to an even greater extent. When classified using a linear discriminant analysis, the three fossils are categorized within the Homo group.DiscussionThe results are in general agreement with previous studies on the morphology of the MC1. This study found that the modern human MC1 is characterized by a distinct suite of traits, not present to the same extent in the great apes, that are consistent with an ability to use forceful precision grip. This morphology was also found to align very closely with that of H. neanderthalensis. H. naledi shows a number of human-like adaptations consistent with an ability to employ enhanced manipulation, whilst A. sediba apparently presents a mix of both derived and more primitive traits.

Download Full-text

Tooth Shape Adaptations in Aglyphous Colubrid Snakes Inferred from 3D Geometric Morphometrics and Finite Element Analysis

10.1101/765719 ◽

2019 ◽

Author(s):

Mahdi Rajabizadeh ◽

Sam Van Wassenbergh ◽

Christophe Mallet ◽

Martin Rücklin ◽

Anthony Herrel

Keyword(s):

Finite Element Analysis ◽

Finite Element ◽

Geometric Morphometrics ◽

Yield Criterion ◽

Sister Group ◽

Element Analysis ◽

Tooth Shape ◽

3D Geometric Morphometrics ◽

Von Mises Yield Criterion ◽

Von Mises

AbstractTo date there are few detailed and quantitative studies investigating the evolution of the tooth shape and function in Aglyphous snakes in relation to diet. To study dental adaptations to diet, a lineage that is of particular interest due to its large range of adult body sizes, is the one including dwarfed snakes of the genus Eirenis and their immediate sister group, whip snakes of the genus Dolichophis. A considerable evolutionary decrease in the size is observed from a Dolichophis-like ancestor to the miniature Eirenis, coupled with a considerable shift in their diet from a regime consisting mainly of endotherms with endoskeleton to ectotherms bearing a hard exoskeleton. Maxilla, palatine, pterygoid and dentary teeth were examined in an adult and a juvenile of Dolichophis schmidti, one Eirenis punctolineatus and one Eirenis persicus. 3D Geometric Morphometrics comparison revealed maxilla and palatine teeth of the E. persicus are blunt and conical shape while those teeth are sharp and elongated in E. punctatolineatus as well as the adult and juvenile D. schmidti. A similar difference could be noted for the pterygoid teeth. In contrast, the dentary teeth are not as different among the examined snakes. Blunt and conically shaped teeth, as observed in E. persicus, seem to be more adapted for biting hard bodied, arthropod prey, while sharp and elongated teeth in Dolichophis and E. punctatolineatus, are specialized for puncturing endotherm prey. The results of a finite element analysis confirms that during biting a hard bodied prey, the generated stresses in E. persicus tooth is mostly confined to the tip of the tooth and mostly well below the von Mises yield criterion the tooth. In contrary, D. schmidti tooth appears less well suited for biting a hard prey since the generated stresses widely distribute across the tooth with values roughly 2 to 3 times higher than the von Mises yield criterion of the tooth. A lower degree of specialization that was observed among the dentary teeth in the examined snakes suggest a similar functional constraint in pushing the prey against the upper tooth rows.

Download Full-text