Dissertations / Theses on the topic 'Mammals Locomotion'

Se déplacer dans l’eau ou sur terre implique de faire face à des contraintes mécaniques extrêmement différentes. L’eau est sensiblement plus dense et visqueuse que l’air et, par le fait, la locomotion aquatique est dominée par la traînée et la poussée d’Archimède alors que la locomotion terrestre est dominée par la gravité et l’inertie. Si les adaptations les plus extrêmes à la locomotion dans chacun de ces milieux sont bien documentées, les espèces semi-aquatiques qui se déplacent fréquemment dans ces deux milieux restent peu étudiées.Les mustélidés présentent une large diversité de spécialisations locomotrices tant du point de vue du type de milieu fréquenté que du point de vue du degré de spécialisation.Cela inclut trois événements indépendants d’apparition d’un mode de vie semi-aquatique avec pour représentants actuels : le vison d’Europe, le vison Américain et les loutres. En utilisant la morphométrie géométrique pour quantifier l’ensemble de la forme de l’humérus, du radius, de l’ulna, du fémur, du tibia et de la fibula, j’ai étudié les différences morphologiques de l’appareil locomoteur des mustélidés terrestres et semi-aquatiques. Étant donné que les visons et les loutres font face aux mêmes contraintes fonctionnelles liées à une locomotion à la fois terrestre et aquatique, j’ai testé si leur morphologie convergeait. Enfin, étant donné la différence de contraintes fonctionnelles induites par les deux milieux, j’ai testé si le milieu de locomotion avait un impact homogène sur l’appareil locomoteur ou si une spécialisation de certains os pouvait être observée.Si les visons diffèrent peu de leurs parents terrestres, les loutres montrent d’importantes différences en termes de taille, forme et proportions relatives des os. Les visons présentent une morphologie similaire à celle observée chez tous les Mustelinae.Néanmoins, la morphologie de l’humérus est convergente entre les deux visons, avec une courbure plus grande que chez leurs parents terrestres. La morphologie des visons résulte de spécialisations récentes de la morphologie versatile propre aux Mustelinae, leur mode de nage est similaire à celui des Mustelinae terrestres et ils ne montrent que de subtiles différenciations morphologiques.A l’opposé, les loutres présentent des os longs dont la forme diffère nettement de celle de leurs parents terrestres. De plus, elles montrent une grande diversité de formes, en opposition avec l’hypothèse qui voudrait que de fortes contraintes fonctionnelles, telles que celles induites par la locomotion aquatique, devraient conduire à un nombre limité de réponses évolutives possibles. Les loutres montrent un ensemble de caractéristiques morphologiques en lien avec la locomotion aquatique: des os robustes, avec de larges épiphyses, un stylopode court relativement au zeugopode et un grand bras de levier pour les extenseurs du coude. Seule la loutre de mer (Enhydra lutris) montre une spécialisation différente entre les pattes avant et arrière. Les pattes arrière sont dédiées à la locomotion aquatique avec un grand bras de levier pour les muscles de la hanche et un pied transformé en palette natatoire. La patte avant, en revanche, présente une ulna gracile, avec un processus olécrane court et un radius courbé cranialement, produisant un patronde co-variation unique. Ces particularités permettent de plus grands degrés de liberté dans les mouvements de l’avant-bras, et de fait, les capacités de manipulation uniques chez cette espèce.Ainsi les mustélidés semi-aquatiques présentent une diversité qui n’était pas attendue étant donné la différence de contraintes mécaniques imposées par la locomotion dans l’eau et sur terre. Les mustélidés semi-aquatiques semblent avoir évolué depuis une morphologie ancestrale versatile jusqu’à des formes très spécialisées,où la réduction progressive de la locomotion terrestre a permis une spécialisation différente entre les membres antérieurs et postérieurs
Moving in water and on land implies coping with drastically different mechanicalconstraints. Water is substantially more dense and viscous than air and thus aquaticlocomotion is dominated by drag and buoyancy when terrestrial locomotion is dominatedby gravity and inertia. If extreme adaptations to locomotion in each of thesetwo media are well described, semi-aquatic species that move extensively in bothmedia remain poorly studied.Mustelids presents a large diversity of locomotor specializations involving differentkinds of locomotor environments and different degrees of specialization. It encompassthree independent evolutions of a semi-aquatic lifestyle: the European mink,the American mink, and the otters. Using geometric morphometrics to quantify theshape of the entire humerus, radius, ulna, femur, tibia, and fibula I investigated morphologicaldifferences in the locomotor apparatus of terrestrial and semi-aquaticmustelids. As both minks and otters face functional pressures resulting from bothaquatic and terrestrial locomotion, I tested whether their morphology converged.Finally, considering the differences in the functional requirements of the two media,I explored whether the locomotor ecology has a homogeneous impact on thelocomotor apparatus or whether a functional specialization of certain parts can beobserved.Whereas minks show low morphological differentiation from their terrestrial relatives,otters diverged a lot in both shape, size, and the relative proportions of thelimb bones. Minks present a morphology that is similar to the one observed in otherMustelinae. Nevertheless, the shape of the humerus is convergent between thetwo minks, and shows a greater curvature than in their terrestrial relatives. Minksresult from recent specializations of the versatile morphology of Mustelinae witha swimming mode similar to the one of the terrestrial Mustelinae and only subtlemodifications of their long bone morphology.Conversely, otters present a long bone shape that is strongly divergent from theone of their terrestrial relatives. Additionally, they show very diverse long boneshapes in opposition to the hypothesis stating that strong functional requirements,as the ones induced by aquatic locomotion, should induce a limited number of potentialevolutionary responses. Otters show morphological features that are related to aquatic locomotion: robust bones with broad epiphyses, a short stylopodrelative to the zeugopod, and a long in-lever for elbow extensors. Only the sea otter(Enhydra lutris) presents a functional specialization that differs between hind andforelimb. The hind limb is dedicated to aquatic locomotion with a strong in-lever forthe hip muscles, and the feet that are modified into swimming paddles. Meanwhile,the forelimb presents a relatively gracile ulna with a short olecranon process and aradius that is curved more cranially, resulting in a drastic change in the pattern ofco-variation. These features are interpreted as providing greater degrees of freedomin the movements of the forearm, which allows the unique manipulative skillsof this species.Thus semi-aquatic mustelids present a diversity that was not expected given thestrong differences in the mechanical constraints imposed during locomotion in waterversus on land. Semi-aquatic mustelids appear to have evolved from the versatileancestral locomotor apparatus to highly specialized forms, where the progressivereduction of terrestrial locomotion allowed differential adaptation of the foreandhind limbs

In this thesis, the shape of the distal humerus trochlea is analysed using landmark-based morphometrics and multivariate methods, with the aim of exploring locomotor evolution in carnivorans. Elbow joint morphology is used together with body size and craniodental morphology to characterize past and present carnivorans. Evolutionary implications are studied at the ordinal, familial, and species levels, testing specific hypotheses about scaling, morphological constraints, evolutionary trajectories, and potential for social pack-hunting behaviour. The circumference of the distal humerus trochlea is found to be highly correlated with body mass, and appears to scale similarly throughout the order Carnivora. A general predictive model for carnivoran bodymass is presented (a=0.601; b= 2.552; r2=0.952, SEE=0.136, p<0001, n=92), which removes the need for the investigator to actively choose between the diverging estimates that different predictors and their equations often produce. At the elbow joint, manual manipulation and locomotion appear to be conflicting functions, thus suggesting mutually exclusive lifestyles involving either forelimb grappling or pursuit. At large body sizes, carnivorans are distributed over a strongly dichotomised pattern (grappling or locomotion), a pattern coinciding with the postulated threshold in predator-prey size ratio at 21.5-25 kg. This pattern is compared to that of two carnivoran faunas from the Tertiary. In the Oligocene (33.7-23.8 Myr BP), the overall pattern is remarkably similar to that observed for extant Carnivora. In the Miocene (23.8-11.2 Myr BP) carnivores show a similarly dichotomised pattern as the Oligocene and Recent, although the whole pattern is shifted towards larger body sizes. This difference is suggested to be a reflection of the extraordinary species richness of browsing ungulates in the early Miocene of North America. Such an increase in prey spectrum would create a unique situation, in which large carnivores need not commit to a cursorial habitus in order to fill their nutritional requirements. Finally, the elbow joints and craniodental morphology (14 measurements) of fossil canids were examined with the aim of assessing the potential for pack-hunting in fossil canids. It is clear that small and large members of the Recent Caninae share similar craniodental morphologies. However, this pattern is not present in Borophaginae and Hesperocyoninae. In the latter, large representatives are characterized by being short-faced, with reduced anterior premolars and enlarged posterior premolars, thus approaching a “pantherine-like” craniodental configuration. These traits are interpreted as an adaptation for killing prey with canine bites. It is similarly determined that, unlike recent Caninae, all analyzed species of borophagines and hesperocyonines have retained the ability to supinate their forearms. It is therefore likely that manual manipulation was part of their hunting behaviour, thus removing an essential part of the argument for social pack-hunting in these forms, as the benefits of such a strategy become less obvious.

The Paleocene and early to middle Eocene Family Phenacodontidae includes three species--Tetraclaenodon puercensis, Phenacodus vortmani, and P. primaevus--with available postcranial material for an investigation of postural and locomotor capabilities. The details of bone and joint morphology are compared within the phenacodontids and with several extant analogues whose postural and locomotor capabilities and morphological correlates are known better. Several aspects of the postcranial morphology of the phenacodontids, especially P. vortmani and P. primaevus, suggest cursorial capabilities. The anterior thoracic vertebral column has limited flexibility dorsoventrally and mediolaterally, but the articular surfaces in the lumbar section, especially in the larger P. primaevus, tend to allow dorsoventral movement while restricting mediolateral movement, thus potentially adding to total stride length. The digitigrade limb posture, again especially developed in P. vortmani and P. primaevus, adds to limb length and stride length. Several features of the joints in the forelimb and hindlimb restrict motion to the parasagittal plane or enhance thrust against the ground in the parasagittal pIane, thus contributing to forward motion. The curvatures of the glenoid fossa and the humeral head enhance flexion and extension and restrict abduction. The mediolateral width and shapes of the articular surfaces in the elbow joint prevent supination. The flexor hinge in the wrist allows a powerful thrust against the ground during push-off. The keels in the distal metapodials maintain that thrust in the parasagittal plane. In the hindlimb, the high greater trochanter and the third trochanter increase the mechanical advantage of some extensors of the femur. The deep patellar groove suggests strong extension at the knee. Similarly, the deep grooves and distinct condyles of the distal tibia and dorsal surface of the astragalus, along with the relatively long calcaneal tuberosity, suggest powerful flexion at the ankle joint and confine motion at the upper ankle joint to flexion and extension. The phenacodontids and especially Phenacodus vortmani and P. primaevus were good runners, particularly compared with their Paleocene and Eocene contemporaries. Within the genus Phenacodus, the more slender P. vortmani, with its more elongate distal elements of the hindlimb, probably was the more efficient runner.

The diversification of eutherian mammals following the end-Cretaceous mass extinction was a critical period in evolutionary history. The Palaeocene is marked by the proliferation of archaic mammals which exhibit a mosaic of primitive and derived anatomies and whose phylogenetic affinities with extant mammals remain contentious. Consequently, macroevolutionary studies assessing the timing and recovery of eutherian mammals following the end-Cretaceous mass extinction are inhibited by our relatively poor knowledge of the mammals which thrived during the Palaeocene. One group of Palaeocene mammals in particular, the ‘Condylarthra’ have proven especially enigmatic and, as historically conceived, includes families of ungulate-grade mammals some of which are considered the ancestral stock from which modern perissodactyls and artiodactyls arose. The Periptychidae are a distinctive ‘condylarth’ family and were among the first mammals to appear after the extinction. As such they constitute an excellent empirical case study towards resolving the evolutionary relationships and understanding the palaeobiology of Palaeocene mammals. The overarching aim of this thesis has been to generate a comprehensive higher-level phylogenetic hypothesis of Periptychidae and shed light on the species-level interrelationships of taxa historically identified as periptychids and other ‘condylarth’ exemplars. This aim has been achieved by the undertaking a comprehensive anatomical re-description of the archetypal periptychid, Periptychus carinidens, based on a wealth of new fossils recovered from the San Juan Basin in New Mexico, USA. The anatomical information described in this thesis has also facilitated a greater understanding of ecology and functional morphology of Periptychus and its kin. Periptychus carinidens was a medium-sized, robust, stout-limbed animal that was mediportal and adopted a plantigrade mode of locomotion. The cranial and dental anatomy of Periptychus is broadly concurrent with the inferred plesiomorphic eutherian condition albeit more robust in its overall construction. The broad facial region, tall sagittal and nuchal crests and distinctive dentition with strong enamel crenulations and compressive wear are likely indicative of durophagous diet made up of dense, fibrous, plant-based food stuffs. The postcranial skeleton of Periptychus is a miscellany of morphologies with often paradoxical functional implications. Despite its robustness, Periptychus retained a moderately high degree of multiaxial movement and dexterity in its limbs with prominent muscle attachment sites indicative of powerful, non-rapid limb movements. Well-developed manual and digital flexors and extensors are further indicative of some scansorial and fossorial capability. Periptychus and other Palaeocene mammals are characterised by their robust anatomy and tend to lack any obvious extant analogues impeding our understanding of eutherian ecological diversity during the Palaeocene and the roles of many so-called ‘archaic’ mammals. Multivariate analyses on a dataset of functionally significant limb measurements show that Palaeocene mammals exhibit a distinct and more constrained range of locomotor ability defined by their prevalent robust morphology. However, there are subtle distinctions between archaic taxa indicating ecomorphical diversity possibly due to niche partitioning, that are not easily comparable to extant mammals. This suggests that, far from being generalized ancestral stock, Palaeocene taxa were experimenting with their own unique locomotor styles. The extinction of many archaic groups at the end of the Palaeogene is associated with a trend towards increasingly open habitats, which was less conducive to the survivorship of robust, ambulatory mammals. The anatomy of Periptychus combines a basic early placental body plan with numerous unique specialisations in its dental, cranial and postcranial anatomy that not only exemplify the ability of mammals to adapt and evolve following catastrophic environmental upheaval but provide a prime exemplar by which to tackle the taxonomic and systematic conundrum that is ‘Condylarthra’. A cladistic analysis was conducted to determine the phylogenetic affinities of Periptychidae within Placentalia. 141 taxa were scored for 503 characters including 40 periptychid species and 63 novel characters. The dataset was analysed under parsimony optimality criteria and the resulting phylogeny shows a well resolved strict consensus topology with numerous well-supported relationships which help elucidate periptychid phylogeny. The analysis presented here finds Periptychidae as a monophyletic group to the exclusion of several purported periptychid taxa which are recovered with the ‘arctocyonid’, Baioconodon nordicum. The in-group relationships of Periptychidae are resolved to broadly support the subfamilial arrangement proposed by previous workers. Alticonus is recovered the most basal, unambiguous periptychid taxon. Ampliconus forms a paraphyletic stem from Alticonus to all other unequivocal periptychid taxa. Conacodontinae forms a clade which includes Auraria as the most basal taxon relative to Oxyacodon, which forms a paraphyletic stem to Conacodon. The hypsodont periptychids, Haploconus + Goleroconus form a clade, separate from both ‘Anisonchinae’ and Conacodontinae, both of which they have previously been affiliated to. ‘Anisonchinae’ forms a paraphyletic stem relative to Periptychinae. Mithrandir oligustus is the most basal ‘anisonchine’. Gillisonchus is generically distinct from both Mithrandir and ‘Anisonchus’ due to morphological similarities with Hemithlaeus and the Periptychinae. Periptychinae forms a well-supported clade with Hemithlaeus and Tinuviel resolved to be more closely related to Ectoconus than Periptychus + Carsioptychus. Periptychus is a member of Periptychinae and most closely related to Carsioptychus within Periptychini. The phylogeny reported here indicates that Periptychidae were an incredibly successful family during much of their early history and were particularly prolific during the middle Puercan. Most species were small to medium sized animals; however, members of Periptychinae attained large body sizes within less than half a million years of the end-Cretaceous mass extinction. Periptychids were prolific during early Puercan, but spent the majority of their evolutionary history exhibiting high turnover, with many short-lived species, with the notable exception of three genera: Anisonchus, Haploconus and Periptychus, which prevailed through the Torrejonian. These periptychids are among the most enduring Palaeocene taxa known and reiterate the importance of the Periptychidae in understanding the recovering and radiation of Placentalia following the end-Cretaceous mass extinction.

L'urotensine II (UII) est un neuropeptide cyclique isolé initialement à partir de l'urophyse des poissons. Sa caractérisation, douze ans plus tard, dans un extrait de cerveau de grenouille a démontré pour la première fois sa présence chez les tétrapodes. Cette découverte étendue récemment chez les lamproies, des vertébrés primitifs, ainsi que la présence de récepteurs de l''UII chez le rat, nous ont conduits à rechercher l'existence de l'UII chez les mammifères. Le premier volet de cette étude a consisté à caractériser l'ADNc codant la prépro-UII de grenouille et à étudier la distribution tissulaire des ARNm. Sur la base des résultats acquis chez cette espèce, les ADNc codant les précurseurs de l'UII ont été caractérisés chez l'homme, le rat et la souris. Toutes les isoformes d'UII connues a ce jour renferment l'hexapeptide CFWKYC. L'alignement des séquences d'ADNc a montré que l'organisation des prépro-UII de mammifères, de grenouille et de carpe, est similaire. La distribution tissulaire des ARNm de la prépro-UII révèle que le gène est principalement exprimé dans les motoneurones spinaux et crâniens alors que, de façon paradoxale, l'effet pharmacologique prédominant de l'UII semble s'exercer au niveau du système cardiovasculaire. Dans le but de rechercher les fonctions biologiques du peptide, nous avons étudié l'expression du gène de l'UII au cours de l'ontogénèse, chez le rat. Nous avons montre que du 14 ème au 21ème jour de vie foetale, le gène de l'UII est fortement exprimé dans les motoneurones sacrés de la moelle épinière, son expression s'étendant aux niveaux cervicaux, thoraciques et lombaires, après la naissance. En conclusion, nos résultats suggèrent que l'UII pourrait exercer, en plus des effets cardio-vasculaires bien démontrés, une activité régulatrice sur la locomotion.

For primates, and other arboreal mammals, adopting suspensory locomotion represents one of the strategies an animal can use to prevent toppling off a thin support during arboreal movement and foraging. While numerous studies have reported the incidence of suspensory locomotion in a broad phylogenetic sample of mammals, little research has explored what mechanical transitions must occur in order for an animal to successfully adopt suspensory locomotion. Additionally, many primate species are capable of adopting a highly specialized form of suspensory locomotion referred to as arm-swinging, but few scenarios have been posited to explain how arm-swinging initially evolved. This study takes a comparative experimental approach to explore the mechanics of below branch quadrupedal locomotion in primates and other mammals to determine whether above and below branch quadrupedal locomotion represent neuromuscular mirrors of each other, and whether the patterns below branch quadrupedal locomotion are similar across taxa. Also, this study explores whether the nature of the flexible coupling between the forelimb and hindlimb observed in primates is a uniquely primate feature, and investigates the possibility that this mechanism could be responsible for the evolution of arm-swinging.

To address these research goals, kinetic, kinematic, and spatiotemporal gait variables were collected from five species of primate (Cebus capucinus, Daubentonia madagascariensis, Lemur catta, Propithecus coquereli, and Varecia variegata) walking quadrupedally above and below branches. Data from these primate species were compared to data collected from three species of non-primate mammals (Choloepus didactylus, Pteropus vampyrus, and Desmodus rotundus) and to three species of arm-swinging primate (Hylobates moloch, Ateles fusciceps, and Pygathrix nemaeus) to determine how varying forms of suspensory locomotion relate to each other and across taxa.

From the data collected in this study it is evident the specialized gait characteristics present during above branch quadrupedal locomotion in primates are not observed when walking below branches. Instead, gait mechanics closely replicate the characteristic walking patterns of non-primate mammals, with the exception that primates demonstrate an altered limb loading pattern during below branch quadrupedal locomotion, in which the forelimb becomes the primary propulsive and weight-bearing limb; a pattern similar to what is observed during arm-swinging. It is likely that below branch quadrupedal locomotion represents a “mechanical release” from the challenges of moving on top of thin arboreal supports. Additionally, it is possible, that arm-swinging could have evolved from an anatomically-generalized arboreal primate that began to forage and locomote below branches. During these suspensory bouts, weight would have been shifted away from the hindlimbs towards forelimbs, and as the frequency of these boats increased the reliance of the forelimb as the sole form of weight support would have also increased. This form of functional decoupling may have released the hindlimbs from their weight-bearing role during suspensory locomotion, and eventually arm-swinging would have replaced below branch quadrupedal locomotion as the primary mode of suspensory locomotion observed in some primate species. This study provides the first experimental evidence supporting the hypothetical link between below branch quadrupedal locomotion and arm-swinging in primates.

Dissertation

Long projections from the brainstem to the lumbar cord activate locomotion. Using in vitro neonatal rats our laboratory showed that relay (propriospinal - PS) neurons also contribute to transmission of the locomotor signal. This thesis examines whether locomotor-related PS neurons exist in adult mammals, which has important clinical implications. The brainstem of adult decerebrate rats was stimulated to elicit stepping. The following manipulations were performed: 1) suppression of synaptic transmission to PS neurons, 2) lesioning of direct bulbospinal projections to lumbar segments, and 3) neurochemical excitation of PS neurons. In addition, in the absence of brainstem stimulation, the ability of neurochemically excited PS neurons to induce stepping was examined. Brainstem-evoked locomotion was suppressed by synaptic blockade, enhanced by PS neuron excitation, persists after lesioning of long-direct projections, and hindlimb stepping was elicited by PS neuron excitation alone. The findings support the existence of a locomotor-related PS system in adult mammals.
October 2016

L’inhibition est nécessaire à la génération d’outputs coordonnés entre muscles antagonistes lors de la locomotion. Une baisse de la concentration neuronale en ions chlorure au cours du développement des mammifères conduit à l’émergence de l’inhibition. Cette baisse repose sur l’équilibre entre deux cotransporteurs cation-chlorure, KCC2 et NKCC1. KCC2 expulse Cl- de la cellule alors que NKCC1 pompe Cl- dans la cellule. L’opossum Monodelphis domestica naît dans un état très immature. Le seul comportement locomoteur qu’il présente à la naissance consiste en des mouvements rythmiques et alternés des membres antérieurs pour grimper le long du ventre de la mère vers une tétine. Les membres postérieurs sont des bourgeons immobiles dont le développement est en grande partie postnatal. Pour cette raison, cette espèce constitue un modèle idéal pour l’étude du développement locomoteur. Afin d’étudier les mécanismes conduisant à l’émergence de l’inhibition durant le développement moteur, nous avons décrit l’expression développementale de KCC2 et NKCC1 chez l’opossum postnatal par immunohistochimie au niveau des renflements spinaux. Les motoneurones et afférences primaires ont été identifiés en utilisant un marquage rétrograde au TRDA. Le marquage pour KCC2 et NKCC1 est détecté dans la moelle épinière ventrale dans la matière grise et blanche présomptive dès la naissance, ce qui suggère que l’inhibition serait déjà mise en place avant la naissance, permettant subséquemment l’alternance des membres antérieurs observée chez les nouveau-nés. L’expression développementale de KCC2 et NKCC1 suit des gradients ventrodorsal et médiolatéral, tels qu’observés chez les rongeurs (rats et souris). Le patron mature d’expression de ces cotransporteurs est observé aux alentours de la 5ème semaine postnatale lorsque la locomotion de l’opossum est mature. Enfin, entre la naissance et P5, les dendrites exprimant KCC2 au niveau de la corne dorsale sont retrouvées en apposition aux afférences primaires ce qui suggère un rôle de KCC2 dans la formation des circuits sensori-moteurs.
Inhibition is necessary to generate coordinated outputs between antagonistic muscles during locomotion. Inhibition is set by a lowering in neuronal chloride concentration during mammalian development. This lowering relies on the proper balance between two cation-chloride cotransporters, KCC2 and NKCC1. KCC2 extrudes Cl- out of the cell while NKCC1 pumps Cl- into the cell. The opossum Monodelphis domestica is born at a very rudimentary stage of development. Newborn opossums show rhythmic and alternate movements of the forelimbs as they crawl on the mother's belly to a nipple. The hindlimbs are immobile paddle-shaped buds and their development is mostly postnatal. Thus, this species is an ideal model to study motor development. In order to investigate the mechanisms involved in the appearance of inhibition during motor development, we described the developmental expression of KCC2 and NKCC1 on postnatal opossums using immunohistochemistry in the spinal cord enlargements. Motoneurons and primary sensory afferents were identified using retrograde labeling with TRDA. Immunolabeling for both KCC2 and NKCC1 is detected in the ventral spinal cord in the presumptive grey and white matter from birth on, suggesting that the development of inhibition begins before birth, enabling the alternate movements exhibited by the newborns. The developmental expression of KCC2 and NKCC1 follows ventrodorsal and mediolateral gradients, similar to those demonstrated in rodents (rats and mice). The mature pattern for both cotransporters is observed around the 5th week at a time when opossums demonstrate mature patterns of locomotion. Between birth and P5, dendrites expressing KCC2 in the dorsal horn superimpose on the primary afferents, suggesting a role for KCC2 in the establishment of sensorimotor circuits.

Contained in this thesis are seven chapters, five each with a specific scientific focus relating to the study of basal carnivoramorphans or the evolution of locomotion. Presented here is the first detailed description of the only known postcranial skeletal elements of "Miacis" uintensis, found to differ markedly from previously described "miacids" (a paraphyletic assemblage of early fossil Carnivoramorphans), invalidating the notion that all "miacids" were very similar in their postcranial morphology and locomotor styles. The majority of the differences indicate an animal less well adapted to an arboreal lifestyle than has been inferred for other early "miacid" carnivoramorphans. A new genus and species of basal non-Viverravidae Carnivoramorpha, Dawsonicyon isami, is named and described. This new taxon is dentally compared to all known genera of nonviverravid basal carnivoramorphans, as well as with all known species of the problematic genus Miacis. Both "Miacis" uintensis and Dawsonicyon isami are incorporated into a phylogenetic analysis and preliminary functional interpretations of a scansorial locomotor mode are offered for both of these taxa. Following these two descriptive chapters, over 100 postcranial characters are added to the existing data set, which is dominated by cranio-dental characters. The addition of these new characters permits the inclusion of a large number of basal carnivoraforms known solely or predominantly from postcranial characters, that previously would have been `unplaceable' in a phylogenetic analysis. The resultant phylogeny recovers most of the same clades identified in previous studies, but resolves some relationships differently within the basal carnivoraforms. A novel (unnamed) monophyletic subclade of the Carnivoraformes is recovered, supported in part by characters from both the prior and new data sets. The inclusion of a substantial suite of postcranial characters expands the ability to assess the relationships of basal carnivoramorphan taxa, and permits the inclusion of many taxa represented only by incomplete material. Subsequent to the additional of post-cranial characters the matrix is enlarged again, creating the largest anatomical matrix to date for Carnivoramorpha, with 60 extant and fossil taxa and 243 morphological characters. Taxon sampling emphasizes basal carnivoramorphans, and this matrix includes almost every early species for which significant postcranial or non-dental cranial material is known. Resulting trees support the monophly of Carnivoramorpha, Carnivoraformes, and Carnivora as successively diverging clades, as has been found in previous studies, with excellent resolution of interrelationships of taxa within basal Carnivoraformes. Pangolins are found to be the sister clade of Carnivoramorpha to the exclusion of Creodonta. Basal carnivoramorphan taxa previously used to represent a putative basal condition for the group (e.g., species of Vulpavus) are instead found to be highly nested within a monophyletic subclade that is sister-group to most other carnivoramorphans. Nimravidae is strongly supported as a noncrown Carnivora lineage, in contrast to most prior studies. Finally, the evolution of prehensile tails is examined via the identification of phylogenetically independent osteological correlates of prehensility. These features are examined in all living taxa therian known to have independently evolved a prehensile tail, and a close relative that lacks a prehensile capability. This examination reveals that the distal caudal vertebrae are more reliable for the identification of prehensility in a taxon than the more anterior, though there are general trends observed in more proximal caudals. When these indicator features are examined in a complete fossil Cimolestidae from the Green River Formation they allow for the confident identification of prehensility in this specimen. This specimen represents the first known postcranial morphology for the clade Cimolestidae and is the oldest known Eutherian with a prehensile tail.

Locomotion in any environment requires the use of energy to overcome the physical

forces inherent in the environment. Most large marine vertebrates have evolved

streamlined fusiform body shapes to minimize the resistive force of drag when in

a neutral position, but nearly all behaviors result in some increase in that force.

Too much energy devoted to locomotion may reduce the available surplus necessary

for population-level factors such as reproduction. The population of North Atlantic

right whales has not recovered following legal protection due to decreased fecundity,

including an increase in the intercalf interval, an increase in the years to first calf and

an increase in the number of nulliparous females in the population. This reproductive

impairment appears to be related to deficiencies in storing enough energy to meet the

costs of reproduction. The goal of this study was to determine whether increases in

moving between prey patches at the cost of decreased foraging opportunities could

shift these whales into a situation of negative energy gain. The first step is to

understand the locomotor costs for this species for the key behaviors of traveling and

foraging.

This study investigated the cost of locomotion in right whales by recording the

submerged diving behaviors of free-ranging individuals in both their foraging habitat

in the Bay of Fundy and their calving grounds in the South Atlantic Bight with a

suction-cupped archival tag. The data from the tags were used to quantify the oc-

currence of different behaviors and their associated swimming behaviors and explore

three behavioral strategies that reduce locomotor costs. First, the influence that

changes in blubber thickness has on the buoyancy of these whales was investigated

by comparing the descent and ascent glide durations of individual whales with differ-

ent blubber thicknesses. Next, the depth of surface dives made by animals of different

sizes was related to the depth where additional wave drag is generated. Finally, the

use of intermittent locomotion during foraging was investigated to understand how

much energy is saved by using this gait. The final piece in this study was to deter-

mine the drag related to traveling and foraging behaviors from glides recorded by

the tags and from two different numerical simulations of flow around whales. One, a

custom developed algorithm for multiphase flow, was used to determine the relative

drag, while a second commercial package was used to determine the absolute mag-

nitude of the drag force on the simplest model, the traveling animal. The resulting

drag estimates were then used in a series of theoretical models that estimated the

energetic profit remaining after shifts in the occurrence of traveling and searching

behaviors.

The diving behavior of right whales can be classified into three stereotyped be-

haviors that are characterized by differences in the time spent in different parts of the

water column. The time budgets and swimming movements during these behaviors

matched those in other species, enabling the dive shapes to be classified as foraging,

searching and traveling behaviors. Right whales with thicker blubber layers were

found to perform longer ascent glides and shorter descent glides than those with

thinner blubber layers, consistent with the hypothesis that positive buoyancy does

influence their vertical diving behavior. During horizontal traveling, whales made

shallow dives to depths that were slightly deeper than those that would cause ad-

ditional costs due to wave drag. These dives appear to allow whales to both avoid

the costs of diving as well as the costs of swimming near the surface. Next, whales

were found to glide for 12% of the bottom phases of their foraging dives, and the

use of `stroke-glide' swimming did not prolong foraging duration from that used by

continuous swimmers. Drag coefficients estimated from these glides had an average

of 0.014 during foraging dives and 0.0052 during traveling, values which fall in the

range of those reported for other marine mammals. One numerical simulation deter-

mined drag forces to be comparable, while the other drastically underestimated the

drag of all behaviors. Finally, alterations to the behavioral budgets of these animals

demonstrated their cost of locomotion constitutes a small portion (8-12%) of the

total energy consumed and only extreme increases in traveling time could result in a

negative energy balance. In summary, these results show that locomotor costs are no

more expensive in this species than those of other cetaceans and that when removed

from all the other stressors on this population, these whales are not on an energetic

`knife edge'.

Dissertation