Marcos D. Ercoli

Muscular Anatomy of the Forelimbs of the Lesser Grison (Galictis cuja), and a Functional and Phylogenetic Overview of Mustelidae and Other Caniformia

The extrinsic and intrinsic forelimb musculature of the lesser grison (Galictis cuja), a short-legged mustelid of southern South America, is studied for the first time. We present descriptions, muscular maps, and weight data. Muscular anatomy description of the lesser grison provides the framework for discussing the myological diversity of mustelids and other caniforms, for addressing nomenclatural problems (such as synonymy and homonymy), and for highlighting some functional and phylogenetically informative traits. We recognize in the lesser grison features shared by all mustelid species, and some other caniforms, especially mephitids, such as the presence of rhomboideus profundus, an angular head of triceps brachii, and, apparently, the absence of a flexor digitorum brevis manus. An unexpected record of articularis humeri, a proximal origin of the brachioradialis, and the absence of the tensor fascia antebrachii are recorded for this species. As other ictonychines and mustelines, Galictis cuja possesses stronger and subdivided protractors and sagittal rotators of the forelimbs, as well as shoulder and elbow extensors. These features allow for resistance in landing during bounds and increase the stride length during epigean and subterranean crouched locomotion. Powerful neck musculature assists during hunting and carrying of prey. Weakness of some retractors and intrinsic flexors is related to a relatively minor importance of the forelimbs as propellers during bounding and the lack of other specializations. The configuration of the rhomboideus and the absence of coracobrachialis seem to be informative at the subfamiliar level within Mustelidae. The comprehensive and comparative review of available information leads us to propose possible solutions to old nomenclatural problems and of identification. This allows us to reassess of some myological features as diagnostic of caniform clades.

The More, the Better: The Use of Multiple Landmark Configurations to Solve the Phylogenetic Relationships in Musteloids

Although the use of landmark data to study shape changes along a phylogenetic tree has become a common practice in evolutionary studies, the role of this sort of data for the inference of phylogenetic relationships remains under debate. Theoretical issues aside, the very existence of historical information in landmark data has been challenged, since phylogenetic analyses have often shown little congruence with alternative sources of evidence. However, most analyses conducted in the past were based upon a single landmark configuration, leaving it unsettled whether the incorporation of multiple configurations may improve the rather poor performance of this data source in most previous phylogenetic analyses. In the present study, we present a phylogenetic analysis of landmark data that combines information derived from several skeletal structures to derive a phylogenetic tree for musteloids. The analysis includes nine configurations representing different skeletal structures for 24 species. The resulting tree presents several notable concordances with phylogenetic hypotheses derived from molecular data. In particular, Mephitidae, Procyonidae, and Lutrinae plus the genera Martes, Mustela, Galictis, and Procyon were retrieved as monophyletic. In addition, other groupings were in agreement with molecular phylogenies or presented only minor discordances. Complementary analyses have also indicated that the results improve substantially when an increasing number of landmark configurations are included in the analysis. The results presented here thus highlight the importance of combining information from multiple structures to derive phylogenetic hypotheses from landmark data.

The Functional and Phylogenetic Implications of the Myology of the Lumbar Region, Tail, and Hind Limbs of the Lesser Grison (Galictis cuja)

Mustelids are a morphofunctionally diversified group. However, there are no descriptions of the postcranial musculature of South American mustelid species except for some comments from the 19th century. Here, we present the first description of the myology of the hind limbs, and lumbar, sacral, and caudal regions of the lesser grison (Galictis cuja), a short-legged South American mustelid, including muscle maps and weight data. We interpret the function and the evolution of several muscular features within a comparative framework and through the optimization of these traits onto a phylogeny. The configuration of the axial musculature (e.g., m. quadratus lumborum with short bundles, heavy iliocostalis, and forward originated sacrocaudalis dorsalis) and the presence of strong ankle musculature are features shared with mustelines and, to a lesser degree, with other musteloids. These could be related to a high mobility of the axial skeleton and strong control of the movement of the ankle joint, in relation to the acquisition of epigean bounding gaits, a crouched locomotion, and enhanced maneuverability inside burrows. We recorded many phylogenetically significant traits, shared with other arctoids (e.g., subdivision of m. gluteus profundus and semimembranosus, presence of a single belly for m. sartorius, and absence of articularis coxae) or exclusively musteloids (e.g., frequent fusion between m. piriformis and gluteus medius). Some features (e.g., restricted origin of the caudal belly of the m. semitendinosus, absence of gluteofemoralis, and unusually complex fibularis brevis) seem to be derived conditions acquired in some mustelid clades. Our results sustain the value of myological data for functional and phylogenetic studies.

The Structure of the Mammalian Predator Guild in the Santa Cruz Formation (Late Early Miocene)

The Santa Cruz Formation (late early Miocene, Santacrucian age) registers 11 species of mammalian predators (Metatheria, Sparassodonta). Together with large carnivorous flightless birds, they comprised the terrestrial predator guild. The Santacrucian sparassodonts were diverse in body size, had different locomotory habits, and were primarily hypercarnivores. The objective of this work is to analyze the guild structure of the sparassodonts of the Santa Cruz Formation, using the variables of body mass, diet, and locomotion as proxies. Furthermore, we analyze the interaction with other predators and potential prey. The univariated test V of Poole and Rathcke and the multivariated test of Clark-Evans were used to construct the models. In the multivariate test, we made a Principal Component Analysis to resume and standardize the variables. With body mass and locomotion we obtained an evenly spaced pattern of segregation for the sparassodont species, being non-significant and significant, respectively. The pattern was aggregated and significant only with diet. The analysis of all variables together resulted in an evenly spaced and significant pattern, which is consistent with character displacements (segregation of species throughout the morphospace) that would help to diminish interspecific competition during the Santacrucian age and would allow selection of prey species of different sizes and substrate specializations. When the body size pattern of predator birds and sparassodonts were plotted together, the pattern is evenly spaced and non-significant. Other factors, including locomotion, would differentiate these species and their ecological niches.

Tracing the origin of the panda’s thumb

We investigate the relative development of the carnivoran radial sesamoids to untangle the evolution of this iconic structure. In the pandas (both giant and red), this ‘false thumb’ is known to perform a grasping role during bamboo feeding in both the red and giant pandas. An original locomotor role has been inferred for ailurids, but this remains to be ascertained for ursids. A large sample of radial sesamoids of Indarctos arctoides from the Miocene of Batallones-3 (Spain) indicates that this early ailuropodine bear displayed a relatively hypertrophied radial sesamoid, with a configuration more similar to that of the red panda and other carnivorans than to that of giant pandas. This false thumb is the first evidence of this feature in the Ursidae, which can be linked to a more herbivorous diet. Moreover, in the two extant pandas, the false thumb should not be interpreted as an anatomical convergence, but as an exaptive convergence regarding its use during the bamboo feeding, which changes the evolutionary view of this singular structure.

Myology of the Head, Neck, and Thoracic Region of the Lesser Grison ( Galictis cuja ) in Comparison with the Red Panda ( Ailurus fulgens ) and Other Carnivorans: Phylogenetic and Functional Implications

The lesser grison (Galictis cuja) and the red panda (Ailurus fulgens) represent two opposed morpho-functional musteloid extremes. The mid-sized lesser grison is primarily terrestrial, a frequent burrow-dweller, and carnivorous, while the larger, scansorial red panda eats bamboo. This study documents the axial myology of these species, including muscle descriptions, weights, and optimizations. Muscle maps are also provided for the lesser grison, representing the first axial maps for a wild-caught carnivoran. The functional analyses revealed that G. cuja, contrary to A. fulgens, possesses longer, stronger, and subdivided neck muscles. It also possesses a thoraco-lumbar iliocostalis system that is more developed than the longissimus complex, and numerous, robust, and laterally inserted deep bellies of the cervical and thoracic transversospinalis systems. These specializations allow powerful neck movement during hunting and transport of heavy prey as well as axial flexibility, facilitating bounding gaits and lateral movements while navigating subterranean galleries. Some myological traits of the red panda differ from those expected in a highly herbivorous taxon (e.g., m. sternocephalicus, m. masseter), and may reflect its depredatory ancestry. The optimization analysis revealed phylogenetically informative traits across Carnivora, including the absence of m. longissimus capitis in Mephitidae, the absence of spinous thoracic origins for m. biventer cervicis in Musteloidea, and the presence of a relatively lateral insertion of m. rectus dorsalis capitis intermedius in the clade Ictonychinae+Lutrinae+Mustelinae. This study reveals key associations between axial myological and osteological features that will prove useful for future studies of carnivorans.

Comparative myology of the ankle of Leopardus wiedii and L. geoffroyi (Carnivora: Felidae): functional consistency with osteology, locomotor habits and hunting in captivity

Leopardus wiedii (margay) is the only arboreal Neotropical felid able to climb head-first down trees, due to its ability to rotate its tarsal joint 180°. A closely related, similar-sized species, L. geoffroyi (Geoffroys cat) exhibits more typical terrestrial habits and lacks the arboreal capabilities of L. wiedii. There is osteological evidence that supports a mechanical specialization of L. wiediis tarsal joint for inversion, but there have been no studies on the myology of this specialization. Based on comparative gross-anatomy dissections of zeugo- and autopodial muscles related to the ankle joint of one margay specimen and two Geoffroýs cats, we identified myological specializations of L. wiedii that support its arboreal abilities. In addition, we documented both species hunting the same prey (domestic pigeon Columba livia, Aves: Columbidae) in captivity, to complement. We report differences in the origin, insertion and belly in 8 of the 10 dissected muscles. At least 3 of these interspecific variations can be associated with strengthening of the main muscles that command inversion/eversion movements of the tarsal joint and support the body weight in the head-down climbing position typical of L. wiedii. Frame-by-frame video reconstructions depict the sequence of movements in these species while hunting and highlight the advantages of the arboreal abilities of L. wiedii.

Morpho-functional analysis of the mastoid region of the extinct South American mustelid †Stipanicicia pettorutii

Fil: Ercoli, Marcos Dario. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales ; Argentina. Universidad Nacional de Jujuy. Instituto de Ecorregiones Andinas. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Salta. Instituto de Ecorregiones Andinas; Argentina. Universidad Nacional de Jujuy. Instituto de Geologia Minera; Argentina

A novel series of forepaw muscles for mammals observed in the Patagonian weasel Lyncodon patagonicus

The intrinsic autopodial musculature of mammals is composed of a relatively stable number of muscular groups. Here, we present the first myological studies of Lyncodon patagonicus, a South American mustelid that is morphologically and ecologically poorly known. The typical intrinsic muscles of the manus of Lyncodon are similar to those of its sister taxon Galictis, although there exist few variations, including additional subdivisions and relatively more distal insertions in some muscles. A striking feature is the presence of a novel series of forepaw muscles never before described for mammals. These muscles, named here mm. flexores digitorum proprii manus, are represented by a medial and a lateral belly for each digit and are located immediately distal to the mm. flexores breves profundi. They are located distally alongside the tendons of the latter, along the palmar aspect of the phalangeal series, and they insert onto the flexor tubercle of the distal phalanx of each digit. We propose that the incorporation of these muscles in the forepaw musculature of Lyncodon, in addition to some other osteo-myological features, imply a distinctive morpho-functional adaptation to increase the force of flexion and independence of digital movements likely used to grasp prey during hunting. This hypothesis should be confirmed by future ecological and behavioral studies on this species.

Systematic and morphogeometric analyses of Pachyrukhinae (Mammalia, Hegetotheriidae) from the HuayquerÍas, Mendoza (Argentina): biostratigraphic and evolutionary implications

ABSTRACT We present new remains of Pachyrukhinae (Hegetotheriidae) from the Huayquerías del Este (Mendoza, Argentina). We identify Tremacyllus impressus, proposing T. subdiminutus as a synonym and providing new data on postcranial bones for this taxon. Tremacyllus specimens from Mendoza reveal a wide and continuous morphological variation that encompasses the morphological differences of species previously considered valid, emphasizing the need for a systematic study focused on all representatives of the genus. We also recognize Paedotherium typicum, which shows a combination of features differing from other species of the genus. The large sample allows us to improve the diagnosis for both the genus Tremacyllus and the species T. impressus and P. typicum. Both species coexist in the Huayquerías Formation; T. impressus is also present in the Tunuyán Formation, whereas the specimens recognized as Paedotherium in this unit were not identifiable at species level. Applying geometric morphometric methods on the dentition, we partially support the taxonomic decisions. We present the first phylogenetic analysis including all the species of Tremacyllus and Paedotherium, using morphological characters of skull and postcranium. According to our results, Tremacyllus is a monophyletic group supported by two synapomorphies, whereas Paedotherium is paraphyletic, in agreement with the prior hypothesis. The record of Paedotherium typicum presented here extends the biochron of this taxon into the late Miocene, which is relevant for establishing biostratigraphic and paleobiogeographic affinities with other Miocene localities.