NDLI: Digital arcade in the autopodia of Synapsida: standard position of the digits and dorsoventral excursion angle of digital joints in the rays II

Content Provider	Springer Nature Link
Author	Kümmell, Susanna B. Frey, Eberhard
Copyright Year	2012
Abstract	In most extant Mammalia, the digits II–V are flexed to a digital arcade in the middle joint during most of the propulsion phase. An extension occurs only at the end of the propulsion phase, but the digits never extend dorsally in the middle joint. In most extant Reptilia, however, the digits do not show any arcade in the middle joint and are extended dorsally during the propulsion phase. The mechanical effect of a digital arcade is a reduction of the lever arm of the ground reaction force and an increase of that of the profound flexor tendon. This saves muscular force and increases the pressure application force of terminal sole pads or claws. In autopodia with a digital arcade, a Z-configuration is formed by the middle and basal phalanges as well as the metapodialia, forming a spring that economises the rolling movement. Fossil Synapsida between Early Permian and Late Cretaceous were analysed to reconstruct the posture of their digits. The middle joints of the digits II–V in most Therapsida including Mesozoic Mammaliamorpha formed a digital arcade and possessed terminal and basal sole pads similar to extant Mammalia. The claws did not necessarily add to friction during the rolling mode. This is reconstructed from the possible excursion angles of the digital joints and their mechanical constraints, from ichnofossils and from autopodia preserved in situ. The digital arcade must have evolved within the non-therapsid Synapsida or perhaps earlier. The digital arcade, however, was reduced or absent in Gobiconodon, Cistecephalus and the graviportal Kannemeyeriiformes.
Starting Page	171
Ending Page	196
Page Count	26
File Format	PDF
ISSN	18671594
Journal	Palaeobiodiversity and Palaeoenvironments
Volume Number	92
Issue Number	2
e-ISSN	18671608
Language	English
Publisher	Springer-Verlag
Publisher Date	2012-04-03
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Synapsida Autopodia Digital arcade Standard position Excursion angle Z-configuration Animal Systematics/Taxonomy/Biogeography Biodiversity Freshwater & Marine Ecology Plant Systematics/Taxonomy/Biogeography Paleontology
Content Type	Text
Resource Type	Article
Subject	Ecology Geology Ecology, Evolution, Behavior and Systematics Global and Planetary Change Paleontology

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