The Late Permian herbivore Suminia and the early evolution of arboreality in terrestrial vertebrate ecosystems

Abstract

Vertebrates have repeatedly filled and partitioned the terrestrial ecosystem, and have been able to occupy new, previously unexplored habitats throughout their history on land. The arboreal ecospace is particularly important in vertebrate evolution because it provides new food resources and protection from large ground-dwelling predators. We investigated the skeletal anatomy of the Late Permian (approx. 260 Ma) herbivorous synapsid Suminia getmanovi and performed a morphometric analysis of the phalangeal proportions of a great variety of extant and extinct terrestrial and arboreal tetrapods to discern locomotor function and habitat preference in fossil taxa, with special reference to Suminia. The postcranial anatomy of Suminia provides the earliest skeletal evidence for prehensile abilities and arboreality in vertebrates, as indicated by its elongate limbs, intrinsic phalangeal proportions, a divergent first digit and potentially prehensile tail. The morphometric analysis further suggests a differentiation between grasping and clinging morphotypes among arboreal vertebrates, the former displaying elongated proximal phalanges and the latter showing an elongation of the penultimate phalanges. The fossil assemblage that includes Suminia demonstrates that arboreality and resource partitioning occurred shortly after the initial establishment of the modern type of terrestrial vertebrate ecosystems, with a large number of primary consumers and few top predators.

Decoupling of morphological disparity and taxic diversity during the adaptive radiation of anomodont therapsids

“…Anomodonts showed a wide range of body sizes and ecological adaptations, including terrestrial, semi-aquatic, fossorial and arboreal forms [20–22]. Members of the most speciose anomodont subclade, the Dicynodontia, exhibited caniniform tusks in the upper jaw, a turtle-like beak and stocky bodies with short limbs and tails.…”

On the Validity and Phylogenetic Position of Eubrachiosaurus browni, a Kannemeyeriiform Dicynodont (Anomodontia) from Triassic North America

“…Only the Kannemeyeriiformes underwent a significant diversification during the Triassic, with roughly 40 known species [4], [8]. Unlike Permian anomodonts, however, which are known from ∼90 species spanning mouse-to-rhinoceros sizes and occupying an array of niches (including fossorial and arboreal forms) [9], [10], all kannemeyeriiforms were medium- to large-bodied [11], graviportal herbivores with relatively erect posture and gait [12], [13].…”

Endocranial Casts of Pre-Mammalian Therapsids Reveal an Unexpected Neurological Diversity at the Deep Evolutionary Root of Mammals

“…The NMT were among the first terrestrial tetrapods to have a wide variety of body sizes and to adapt to various types of locomotion, from a sprawling to parasagittal posture [Kemp, 2005;Fröbisch, 2006], and exploit a variety of ecological niches, from arboreal to subterranean [Smith, 1987;Fröbisch and Reisz, 2009;Nasterlack et al, 2012]. Their fossils are found today on every continent, including Antarctica [Kitching et al, 1972;Colbert and Kitching, 1981].…”