Allometry and adaptation in the long bones of a digging group of rodents (Ctenomyinae) (original) (raw)
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Allometry and adaptation in the long bones of a digging group of rodents
Previous studies of rodent appendicular morphology suggest that digging activity induces changes in long bones, producing shorter and thicker structures. Subsequent hypotheses have been tested in Ctenomyinae, a group of octodontid rodents globally adapted to subterranean life. Slopes of the equations calrulated for extant animals and their corresponding confidence intervals agree with expectations in almost all cases. Results on fossil taxa are less clear, but suggest a morphocline from a plesiomorphic condition of the appendicular skeleton, present in the fossil genera, departing little from that of the current epigeous rodents, to a more derived long bone design in the species of the living genus Ctenomys, in accordance with their digging activity.
Biological Journal of the Linnean Society, 2008
To examine the evolution of burrowing specializations in the sister families Octodontidae and Ctenomyidae (Rodentia: Caviomorpha), we produced a synthetic phylogeny (supertree), combining both molecular and morphological phylogenies, and including both fossil and extant genera. We mapped morphological specializations of the digging apparatus onto our phylogenetic hypothesis and attempted to match morphological diversity with information on the ecology and behaviour of octodontoid taxa. Burrowing for sheltering and rearing is the rule among octodontids and ctenomyids, and adaptations for digging have been known from the Early Pliocene onward. However, only a few taxa have evolved fully subterranean habits. Scratch-digging is widespread among both semifossorial and fully subterranean lineages, and morphological changes associated with scratch-digging are not restricted to subterranean lineages. By contrast, various adaptations for chisel-tooth digging are restricted to some subterranean lineages and are combined differently in the octodontid Spalacopus, the fossil ctenomyid Eucelophorus, and some living Ctenomys. Some octodontid taxa are able to dig complex burrows in spite of having no substantial changes in musculoskeletal attributes. Hence, we suggest that, during the early evolution of those branches giving rise to fully subterranean ctenomyids and octodontids, a change in behaviour probably preceded the origin of structural adaptations.
Biological Journal of The Linnean Society, 2000
The Pliocenc caviomorph rodent Actenomys has long becn recognized as an early fossorial representative of the subfamily CtenomJ-inae (Octodontidae), which includes one living genus, C'tenomys (tuco-tucos), and several species widely distributed in South America. T o assess the degree of specialization for digging in Artenomys, we performed morphological comparisons with other octodontid genera (Octodon, Spa/acopus, and Ctenomts) of known mode of life and behaiiour. As a whole, our results indicate that, in terms of morphological specializations for digging, Bctenomys occupies an intermediate position between Octodon, a generalized semifossorial rodent which forages above ground, and Ctenomy.c-Spalucopu.c, two highly spccialized subterranean forms. The position of the deltoid process (humerus) and the length of the olecranon process (ulna)-two traits which affect the out-forces exerted by sc\-cral forelimb muscles-were in Actenomys intermediate between non-subterranean and subterranean taxa. The skull, particularly the rostrum, appears to be strong, and sagittal and nuchal crests are well marked. The zygomatic arches are as flared as those of the generalized Octodon. Notably, the upper and lower incisors of Actenomys were extremely procumbent, as in many highly specialized chisel-tooth digging species. Based upon thc stratigraphic and sedimentological analysis of the palaeosoils containing its fossil remains, we suggest that Actenomys lived in an environment of moderate to hig primary productivity. The texture of the palaeosoils indicate that theywere hard and highly cohesive. This situation, which contrasts with that observed in living Ctenomyinae, has relevant implications for burrowing cost. The integration of morphological and palaeoenvironmental data allowed testing of hypotheses about the palaeobiological attributes of this ancestral ctenomyine.
Biological Journal of The Linnean Society, 2000
The Pliocene caviomorph rodent Actenomys has long been recognized as an early fossorial representative of the subfamily Ctenomyinae (Octodontidae), which includes one living genus, Ctenomys (tuco-tucos), and several species widely distributed in South America. To assess the de gree of specialization for digging in Actenomys, we performed morphological comparisons with other octodontid genera (Octodon, Spalacopus, and Ctenomys) of known mode of life and behaviour. As a whole, our results indicate that, in terms of morphological specializations for digging, Actenomys occupies an intermediate position between Octodon, a generalized semi-fossorial rodent which forages above ground, and Ctenomys-Spalacopus, two highly specialized subterranean forms. The position of the deltoid process (humerus) and the length of the olecranon process (ulna)–two traits which affect the out-forces exerted by several forelimb muscles–were in Actenomys intermediate between non-subterranean and subterranean taxa. The skull, particularly the rostrum, appears to be strong, and sagittal and nuchal crests are well marked. The zygomatic arches arc as flared as those of the generalized Octodon. Notably, the upper and lower incisors of Actenomys were extremely procumbent, as in many highly-specialized chisel-tooth digging species. Based upon the stratigraphic and sedimentological analysis of the palaeosoils containing its fossil remains, we suggest that Actenomys lived in an environment of moderate to hig primary productivity. The texture of the palaeosoils indicate that theywere hard and highly cohesive. This situation, which contrasts with that observed in living Ctenomyinae, has relevant implications for burrowing cost. The integration of morphological and palaeoenvironmental data allowed testing of hypotheses about the palaeobiological attributes of this ancestral ctenomyine.
Geometry and evolutionary parallelism in the long bones of cavioid rodents and small artiodactyls
Journal of Biosciences, 2011
Morphological parallelism between South American cavioid rodents and small artiodactyls from the Old World has been postulated for a long time. Our study deals with this question from the point of view of biomechanical characteristics of the long bones. For this, cross-sectional area, second moment of the area, polar moment, athletic ability indicators and strength were calculated for the long bones (i.e. humerus, radius, femur and tibia) of five species of cavioids and two species of artiodactyls. Regressions of all these variables to body mass were established. Regarding the cross-sectional area, the confidence intervals show that the exponents calculated are not significantly different from the geometrical predicted value. The exponents obtained for the second moment of area and the polar moment are not significantly different from the geometrical prediction, except for the humerus. The two indicators of athletic ability scaled as expected, but the bending indicator of athletic ability of the femur was not correlated to body mass. The exponent calculated for femur strength is not different from zero, while the strength of the humerus decreases slightly with the body mass. Additional statistical tests (ANCOVAs) showed no difference between the values of these variables calculated for the samples studied of artiodactyls and rodents. The present results are consistent with the hypothesis that there is significant evolutionary parallelism between cavioid rodents and small artiodactyls.
Biological Journal of the …, 2003
Morphological analysis of the skull of the subterranean rodent Ctenomys , a highly speciose genus which uses both claws and teeth when digging, shows that for a broad range of species size, scaling was associated with both variation and maintenance of shape. Our results show that the angle of incisor procumbency (AIP), a character largely viewed as an adaptation to digging with teeth, is highly variable. We found a non-significant relationship between AIP and basicranial axis (basioccipital + basisphenoid) length, a measure of overall skull size. Accordingly, both small and large Ctenomys species possess either high or low AIP. A significant relationship between AIP and diastema length, given the rostral allometry seen in Ctenomys , suggests that hypermorphosis to a certain extent influences AIP. However, the roots of the incisor are lateral to those of the cheek teeth and their position may thus shift freely. This observation supports the notion that skull structural design, and to a certain extent rostral allometry, underlies variation in AIP. On the other hand, the positive allometry of incisor width and thickness indicates that, in larger species, proportionately powerful incisors are able to resist greater bending forces. We found that the out-lever arm of the jaw adductor muscles scales with positive allometry against basicranial axis length. However, we found an isometric relationship between in-and out-lever arms. In this case, conservation of skull proportions, regardless of variation in size, is a feature possibly related to the maintenance of an effective tooth digging capability. Functional and ecological data are discussed when assessing the implications of size and shape variation in the skull of Ctenomys .
Functional morphology of the forelimb of Early Miocene caviomorph rodents from Patagonia
Lethaia, 2018
Caviomorph rodents (New World Hystricognathi) are represented in the Santa Cruz Formation of Patagonia (Early Miocene, Santacrucian) by four superfamilies. From this unit, excellent cranial and associated postcranial remains of Neoreomys, Eocardia, Schistomys (Cavioidea), Perimys (Chinchilloidea) and Steiromys (Erethizontoidea) are known. To interpret their use of substrate, a comparative description of limb bones (scapula, humerus, radius and ulna) of the five genera was performed within a taxonomic and ecologically diverse sample of extant rodents. Using palaeobiological inferences based on the habits and functional morphology of members of the extant sample, hypotheses were generated for the use of substrate by the Santacrucian taxa. Neoreomys would have had a marked flexo-extension capacity of the humerus and a moderate flexion of the manus. This genus and Eocardia would have had a complete and stabilized forearm extension, with wide stride and moderate extension of the forearm for the latter. Schistomys presents features similar to Eocardia. Perimys would have had strong external rotation of the humerus, moderate flexion of the manus and moderate, complete and stabilized extension of the forearm. Steiromys would have had good pronation/supination capacity, strong internal rotation of the humerus and flexion of the forearm and manus. Neoreomys would have been ambulatory and an occasional runner. Eocardia and Schistomys would have been good runners. Perimys would have been a digger and Steiromys a climber. This morphological disparity reflects a high ecological diversity, compatible with differential use of space during the
PeerJ, 2016
Studies linking postcranial morphology with locomotion in mammals are common. However, such studies are mostly restricted to caviomorphs in rodents. We present here data from various families, belonging to the three main groups of rodents (Sciuroidea, Myodonta, and Ctenohystrica). The aim of this study is to define morphological indicators for the astragalus and calcaneus, which allow for inferences to be made about the locomotor behaviours in rodents. Several specimens were dissected and described to bridge the myology of the leg with the morphology of the bones of interest. Osteological characters were described, compared, mechanically interpreted, and correlated with a "functional sequence" comprising six categories linked to the lifestyle and locomotion (jumping, cursorial, generalist, fossorial, climber and semi-aquatic). Some character states are typical of some of these categories, especially arboreal climbers, fossorial and "cursorial-jumping" taxa. Such ...
Mammalian Biology, 2017
We explored the distribution of tooth-and scratch-digging specializations in species of the subterranean rodent Ctenomys (tuco-tucos) from diverse environments and representing different clades. Principal component analysis of craniodental and postcranial indexes with functional relevance showed that specializations for tooth-digging on one hand, and scratch-digging on the other, formed two uncorrelated groups of variables; functionally significant enamel traits varied concurrently with the tooth-digging specialization axis. Species occupied all sectors of the morphospace showing that craniodental and forelimb specializations have not been mutually exclusive in the evolution of the genus.