Limb proportions and adaptations in caviomorph rodents (Rodentia: Caviomorpha)

Abstract

Caviomorph rodents (Rodentia: Caviomorpha) are an anatomically variable group with diverse ecological and morphological types, including cursorial, digging, fossorial and swimming forms. Their appendicular skeleton is rather generalized and extreme modifications or reductions in the long bones of limbs are not present. It is of special interest to evaluate functional adaptive variations of the appendicular skeleton within this group. Although much work has been devoted to study structure, function, and kinematics of legs in mammals, most studies do not consider particular functions and behaviour within different mammalian lineages. Morphometric and biomechanical studies were performed to test the relationship between adaptation and morphology of the bones of the proximal and middle limb segments in terrestrial caviomorph rodents. Fifty-four specimens belonging to 10 species with different limb adaptations and representing a wide range of body sizes were measured. Diameters and functional lengths of long bones were taken and nine functional indices were built. Humerus (HRI) and ulna (URI) robustness, humerus deltoid (SMI) and epicondyle (EI) development, olecranon proportion (IFA), femur (FRI) and tibia (TRI) robustness, and gluteal muscle insertion at femur (GI), were calculated. Only TRI and, to a lesser degree, SMI and EI, were significantly related to body mass. A functional sequence (cursorial-generalized-occasional diggingdiggers) which seems to reflect an increase in force and muscular development in middle segments of the fore limb is recognized. The hind limb shows a decrease in the speed efficiency of the femur and an increase in limb robustness in the transition from cursorial to digging forms. Although overlapping of speed and force functions in the limbs is evident, functional differentiation for speed in the proximal, and force in the middle segments can be inferred.

Ulnar articular surface 3-D landmarks and ecomorphology of small mammals: a case study of two early Miocene typotheres (Notoungulata) from Patagonia

“…In addition, the mediolateral convexity of the proximal trochlear (including the anconeal process) would improve the stability and minimise possible dislocations (increasing the congruence between humerus and ulna) at the elbow joint. If we had classified M. coypus as a swimmer (Samuels & Van Valkenburgh 2008), our results would be consistent with previous studies that indicate convergent features between diggers and swimmers associated with large forces produced by the forelimbs (Elissamburu & Vizcaíno 2004).…”

“…Two typotheres from the early Miocene of Patagonia well represented in the collections are Hegetotherium mirabile (Hegetotheriidae) and Interatherium robustum (Interatheriidae), which were traditionally considered saltatorial and cursorial, respectively (Sinclair 1909). Using ratios with functional importance, of both forelimb and hindlimb, applied in living caviomorph rodents (Elissamburu & Vizcaíno 2004), the larger H. mirabile (body mass around 5 kg; Cassini et al 2012b) has been characterised as a digger (Elissamburu 2004) or an occasional digger (Cassini et al 2012a), and the smaller I. robustum (body mass around 2 kg; Cassini et al 2012b) as a digger (Elissamburu 2004) or an occasional digger with putative swimming or climbing capabilities (Cassini et al 2012a).…”

Going underground: postcranial morphology of the early Miocene marsupial mole Naraboryctes philcreaseri and the evolution of fossoriality in notoryctemorphians

“…philcreaseri, we compared its Index of Fossorial Ability (IFA; sometimes referred to as Olecranon Length Index) -a commonly used metric that is strongly correlated with the degree of fossoriality in various groups of mammals (Vassallo, 1998;Vizcaino et al, 1999;Elissamburu and Vizcaíno, 2004;Lagaria and Youlatos, 2006;Warburton et al, 2013;Woodman and Gaffney, 2014) -with that of Notoryctes and other fossorial and subterranean mammals (table 1). We calculated IFA as (olecranon length/(total ulnar length-olecranon length))*100, following Vizcaino and Milne (2002).…”

“…philcreaseri are all very robust for their length, and the articular surfaces of these bones are relatively large in surface area. Short, robust limb bones are characteristic of semi-fossorial and fossorial mammals (Casinos et al, 1993;Farina and Vizcaino, 1997;Vizcaino et al, 1999;Campione and Evans, 2012), being better able to withstand the high muscular and reaction forces acting through the bones during digging (Hildebrand and Goslow, 2001;Elissamburu and Vizcaíno, 2004). The relatively large surface area of humeral head, capitulum and radial fovea of Na.…”

Goniometria dos membros pélvicos de pacas (Cuniculus paca) criadas em cativeiro

“…Provavelmente, isso esteja relacionado com as diferenças de postura em estação entre as espécies. A paca como roedor caviomorfo é classificada como escavador ocasional, e a conformação dos membros está num aspecto transitório entre os hábitos cursores e escavadores, possuindo membros pélvicos robustos para compensar uma perda de velocidade (Elissamburu & Vizcaíno 2004, Hildebrand & Goslow Jr 2006. Adicionalmente, as pacas estão associadas mais a ações furtivas ou de natação do que as de velocidade, com membros pélvicos gerando maior impulso propulsor em relação aos torácicos (Biknevicius 1993).…”