Autopodial skeletal diversity in hystricognath rodents: Functional and phylogenetic aspects

Abstract

Metapodials and phalanges of the second to fourth digital ray were measured for the hands and feet of 214 specimens belonging to 45 extant species of hystricognath rodents, encompassing members of all major clades of the radiation. Principal components analysis (PCA), the phalangeal index of the third digital ray in the hands and feet, and the relationship between second and fourth digital ray were used to investigate intrinsic autopodial proportions as well as to provide a base for comparisons between hands and feet. PCA separated cursorial Hystricognathi from arboreal ones, but lead to little distinction in other locomotory modes. Cursors have longer metapodials and shorter phalanges, particularly in their hind limb, while arboreal species have relatively longer manual and pedal phalanges. Terrestrial, scansorial, fossorial, and semi-aquatic species were not clearly distinguished, but there is a tendency towards elongated manual digits and relatively short feet in most fossorial species. Closely related species with similar locomotory habits tend to group together in PCA morphospace, and also have similar phalangeal indices. The results are in agreement with current hypotheses on locomotory adaptations of the hand and foot, and concur with many previous findings on autopodial proportions in arboreal, cursorial, and fossorial species. They also highlight the limited use of autopodial proportions for inferring systematic affinities. The lack of distinction in the majority of species is likely related to the lack of highly specialized locomotory types in Hystricognathi.

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

“…Such a pattern is well known in extant primates and other placental mammals, as well as marsupials, chameleons, certain tree frogs and perching birds (Cartmill 1985;Hildebrand & Goslow 2001). Moreover, arboreal vertebrates with grasping hands and feet display distinct phalangeal proportions when compared with non-arboreal relatives (Hopson 2001;Bloch & Boyer 2002;Weisbecker & Warton 2006;Weisbecker & Schmid 2007). Arboreal vertebrates are frequently known from the fossil record and include taxa from the reptilian as well as synapsid lineages of amniotes.…”

“…Measurements of extant tetrapods were taken from chamaeleonids, agamids and iguanids among reptiles, and several groups of mammals, including Primates, Dermoptera, Chiroptera and didelphimorphian Marsupialia. In addition, data for diprotodontian marsupials, rodents and selected primates and lacertids were obtained from the literature (Arnold 1998;Hamrick 2001;Weisbecker & Warton 2006;Weisbecker & Schmid 2007). All measurements were plotted on ternary diagrams using the software package PAST v. 1.78 (Hammer et al 2001).…”

Diversity and evolution of femoral variation in Ctenohystrica

“…Information about body mass was obtained from Nowak (1999) and panTHERIA database by Jones et al (2009). Information about locomotor types was obtained from Nowak (1999), Elissamburu and Vizcaíno (2004), Weisbecker and Schmid (2007), Samuels and Valkenburgh (2008) (2007), Samuels and Valkenburgh (2008) and the IUCN Red List (2011). The locomotor type of the fossil NMB SA-259 was defined as 'unknown', and its body mass was calculated as the mean of values resulting from body mass estimation calculations performed by Geiger et al (2013) using three different methods.…”

“…Similarly, hindlimb specializations evidenced in cursorial caviomorphs were compared to those displayed among members of Carnivora that adopt a cursorial mode of locomotion (Elissamburu and Vizcaíno, 2004). The high variability in some features of the femur may reflect the overall lack of highly specialized forms among Ctenohystrica (Weisbecker and Schmid, 2007), but should also be considered more broadly in the context of other postcranial elements. The anatomy of the femur is a fundamental factor that determines the way and the range a limb can be moved and hence an important subject for functional study, nevertheless limb elements are serially repeated homologous structures that do not function in isolation.…”

“…Seckel and Janis, 2008;Morgan, 2009;Steiner-Souza et al, 2010;Elissamburu and De Santis, 2011), long bones (Biknevicius, 1993;Elissamburu and Vizcaino, 2004;Samuels and Van Valkenburgh, 2008;Morgan and Á lvarez, 2013) and the autopodial skeleton (e.g. Weisbecker and Schmid, 2007;Morgan and Verzi, 2011). These studies have used morphological traits, described as ratios or quantified using biomechanical indices or geometric morphometric descriptors of shape, to identify functional specializations and instances of adaptive convergence underpinned by shared function and/or ecology.…”