The postcranial skeleton of Kingoria nowacki (von Huene) (Therapsida: Dicynodontia)

A new specimen of Kingoria nowacki (von Huene) with a complete pelvic girdle and hindlimb is reconstructed and the method of locomotion analysed. It is concluded that the hindlimb was modified from the normal dicynodont pattern in a direction comparable to that of advanced mammal-like reptiles which are presumed to have given rise to mammals. The pectoral girdle also had a modified form, but the humerus was probably conservative in its morphology. The hindlimb stride relied on protraction and retraction to effect movement while the forelimb relied on long axis rotation of the humerus. Possible reasons for the difference in morphology and function of the fore-and hindlimbs are discussed, and a functional sequence for the generation of the Kingoria pelvic girdle from that of other Permian dicynodonts is suggested.     

FUNCTIONAL AND EVOLUTIONARY ASPECTS OF THE POSTCRANIAL ANATOMY OF DICYNODONTS (SYNAPSIDA, THERAPSIDA)

Abstract:  Restoration of the major skeletal muscles and functional morphological analysis of the postcranium were carried out on two Triassic dicynodont genera, Wadiasaurus and Lystrosaurus . A phylogenetic analysis of 12 selected Permian and Triassic dicynodont taxa was conducted and the postcranial character states were then mapped onto the most parsimonious tree. The analysis revealed changes in pectoral girdle and forelimb morphology, which included reduction of the coracoid plate, increasing robustness of the deltopectoral crest, change in humeral orientation from lateral to caudolateral, increasing prominence of the humeral head, and increasing robustness of the radius. Such changes can be associated with a functional tendency to reduce the lateral component of the propulsive force while still in an abducted mode. On the other hand, changes associated with the pelvic girdle included expansion of the preacetabular iliac process, reduction of the postacetabular iliac process, craniocaudal expansion of the iliac blade, change in the shape of the pubis from flat and plate-like to small and rod-like with a cranial process, and change in acetabular orientation from lateral to caudolateral. The femoral head, starting from a cranioproximal position, progressively became dorsally pronounced and offset from the body. Other features/changes associated with the femur included increasing robustness of the trochanter major, and increasing flattening of the femoral midshaft. Changes in the axial skeleton included increasing stiffening of the trunk to reduce lateral undulations, increasing dorsoventral flexion, and increasing sacral vertebral count, which can be correlated with the preacetabular iliac expansion. These findings suggest that the dicynodont postcranial skeleton evolved towards more upright hindlimb morphology with the body held well off the ground.     

Proportions and function of the limbs of glyptodonts

Vizcaíno, S.F., Blanco, R.E., Bender, J.B. & Milne, N. 2010: Proportions and function of the limbs of glyptodonts. Lethaia, Vol. 44, pp. 93–101. This study examines the limb bone proportions and strength of glyptodonts (Xenarthra, Cingulata). Two methods are used to estimate the body mass and location of the centre of gravity of the articulated specimens. These estimates, together with measurements of the femur and humerus, are used to calculate strength indicators (SI). The other long bones of the limbs are used to calculate limb proportion indices that give an indication of digging ability, speed, and limb dominance in armadillos, the glyptodonts’ living closest relatives. The results show that regardless of how the body mass and centre of gravity are calculated, the majority of the glyptodont’s weight is borne by the hindlimbs. The SI calculations show that femora are sturdy enough to bear these loads. The fact that the femora have higher SI than the humerii indicates that sometimes the hindlimbs are required to bear an even greater proportion of the body weight, possibly when rising to a bipedal posture or pivoting on their hindlimbs to deliver a blow with their armoured tail. The analysis of limb proportions indicates that both the hindlimb and the forelimb have proportions that correlate strongly with body mass. This outcome supports the other results, but also shows that forelimbs must be also involved in manoeuvring the glyptodont body. □Glyptodonts, Mammalia, Xenarthra, limbs, strength indicators.     

Postcranial morphology of the extinct caviine rodent Microcavia criolloensis (late Pleistocene,South America)

A comparative study of the appendicular skeletal morphology, with a particular emphasis on the autopodial elements (manus and pes), of the extinct caviine rodent Microcavia criolloensis (Late Pleistocene, Uruguay), together with that of living species of Microcavia and some allied caviines is performed. Burrow‐digging and above‐ground behaviour by M. criolloensis could have evolved in the Late Pleistocene, as with its relative M. australis in the Recent. This is suggested based on the morphology of preserved articulated skeletons along with fossil burrow‐like structures. The most remarkable features are: in its forelimb, where the humerus has a structure that would have allowed it to perform similar activities to M. australis, based on humeral width across the epicondiles relative to total humerus length index and a good resistance as indicated by high values relating the diameter of the diaphysis to its total length. Qualitative comparison shows that M. criolloensis had a stout, wide manus with relatively short digits including short, wide phalanges, despite its large size. In its hind limb there is a stout hind‐foot with relatively short and wide metatarsals and phalanges, as compared with those of the recent species, that could arguably be considered a useful tool for shovelling out displaced soil. The generalized morphology suggests above‐ground behaviour together with digging ability. The environmental adaptations of M. criolloensis are also briefly discussed, which seem to differ from those of its extant relatives. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 154 , 795–806.     

Three-dimensional geometric morphometric analysis of the humerus: Comparative postweaning ontogeny between fossorial and semiaquatic water voles (Arvicola)

Different types of locomotion in phylogenetically close rodent species can lead to significantly different growth patterns of certain skeletal structures. In the present study, we compared the allometric and phenotypic trajectories of the humerus in semiaquatic (Arvicola sapidus) and fossorial (Arvicola scherman) water vole taxa, using three-dimensional geometric morphometrics, to investigate the relationships between functional and ontogenetic differences. Results revealed shared humerus traits between A. sapidus and A. scherman, specifically an expansion of the epicondylar and deltopectoral crests along postnatal ontogeny. In both species, the humerus of young specimens is more robust than in adults, possibly as a compensatory response for lower bone stiffness. However, significant interspecific differences were detected in all components of allometric and phenotypic trajectories. Noticeably divergent allometric trajectories were observed, probably as a result of different functional pressures exerted on this bone. Important differences in the form of the adult humerus between taxa were also found, particularly in features located in muscle insertion zones. Furthermore, the allometric regression revealed certain shape variation not associated with size in A. scherman, suggesting mechanical stress produced by the persistent digging activity during adulthood. A. scherman is a chisel-tooth digger that shares several traits in the humerus morphology with scratch-digger rodent species. Nevertheless, these shared characteristics are less pronounced in fossorial water voles, which is congruent with the different implications of the forelimb in the digging activity in these two types of diggers.     

A Tachyglossid-Like Humerus from the Early Cretaceous of South-Eastern Australia

A partial right humerus has been recovered from the Early Cretaceous (Albian) Eumeralla Formation at Dinosaur Cove in south-eastern Australia. General morphology, size and the presence of a single epicondylar foramen (the entepicondylar) suggest that the bone is from a mammal or an advanced therapsid reptile. The humerus is similar in size, shape and torsion to the equivalent bone of extant and late Neogene echidnas (Tachyglossidae) but, contrary to the situation in extant monotremes, in which the ulna and radius articulate with a single, largely bulbous condyle, it bears a shallow, pulley-shaped (i.e. trochlear-form) ulnar articulation that is confluent ventro-laterally with the bulbous radial condyle. This form of ulnar articulation distinguishes this bone from the humeri of most advanced therapsids and members of several major groups of Mesozoic mammals, which have a condylar ulnar articulation, but parallels the situation found in therian mammals and in some other lineages of Mesozoic mammals. As in extant monotremes the distal humerus is greatly expanded transversely and humeral torsion is strong. Transverse expansion of the distal humerus is evident in the humeri of the fossorial docodont Haldanodon, highly-fossorial talpids and some clearly fossorial dicynodont therapsids, but the fossil shows greatest overall similarity to extant monotremes and it is possible that the peculiar elbow joint of extant monotremes evolved from a condition approximating that of the fossil. On the basis of comparisons with Mesozoic and Cainozoic mammalian taxa in which humeral morphology is known, the Dinosaur Cove humerus is tentatively attributed to a monotreme. However, several apparently primitive features of the bone exclude the animal concerned from the extant families Tachyglossidae and Ornithorhynchidae and suggest that, if it is a monotreme, it is a stem-group monotreme. Whatever, the animal's true affinity, the gross morphology of its humerus indicates considerable capacity for rotation-thrust digging.     

Postnatal ontogeny of limb proportions and functional indices in the subterranean rodent Ctenomys talarum (Rodentia: Ctenomyidae)

Burrow construction in the subterranean Ctenomys talarum (Rodentia: Ctenomyidae) primarily occurs by scratch‐digging. In this study, we compared the limbs of an ontogenetic series of C. talarum to identify variation in bony elements related to fossorial habits using a morphometrical and biomechanical approach. Diameters and functional lengths of long bones were measured and 10 functional indices were constructed. We found that limb proportions of C. talarum undergo significant changes throughout postnatal ontogeny, and no significant differences between sexes were observed. Five of six forelimb indices and two of four hindlimb indices showed differences between ages. According to discriminant analysis, the indices that contributed most to discrimination among age groups were robustness of the humerus and ulna, relative epicondylar width, crural and brachial indices, and index of fossorial ability (IFA). Particularly, pups could be differentiated from juveniles and adults by more robust humeri and ulnae, wider epicondyles, longer middle limb elements, and a proportionally shorter olecranon. Greater robustness indicated a possible compensation for lower bone stiffness while wider epicondyles may be associated to improved effective forces in those muscles that originate onto them, compensating the lower muscular development. The gradual increase in the IFA suggested a gradual enhancement in the scratch‐digging performance due to an improvement in the mechanical advantage of forearm extensors. Middle limb indices were higher in pups than in juveniles–adults, reflecting relatively more gracile limbs in their middle segments, which is in accordance with their incipient fossorial ability. In sum, our results show that in C. talarum some scratch‐digging adaptations are already present during early postnatal ontogeny, which suggests that they are prenatally shaped, and other traits develop progressively. The role of early digging behavior as a factor influencing on morphology development is discussed. J. Morphol. 275:902–913, 2014. © 2014 Wiley Periodicals, Inc.     

Appendicular skeleton in Bachia bicolor (Squamata: Gymnophthalmidae): osteology,limb reduction and postnatal skeletal ontogeny

The osteology of the appendicular skeleton and its postnatal development are described in Bachia bicolor, a serpentiform lizard with reduced limbs. The pectoral girdle is well developed and the forelimb consists of a humerus, ulna, radius, five carpal elements (ulnare, radiale, distal carpals 4–3, centrale), four metacarpals (II, III, IV, V) and phalanges (phalangeal formula X‐2‐2‐2‐2). In the hindlimb, the femur is small and slender, and articulates distally with a series of ossified amorphous and extremely reduced elements that correspond to a fibula, tibia and proximal and distal tarsals 4 and 3. The pelvic girdle consists of ischium, pubis and ilium, but its two halves are widely separated; the ilium is the least reduced element. We describe the ossification and development during postnatal skeletal ontogeny, especially of epiphyseal secondary centres, ossifications of carpal elements, apophyseal ossifications and sesamoids. Compared to other squamates, B. bicolor shows an overall reduction in limb size, an absence of skeletal elements, a fusion of carpal elements, an early differentiation of apophyseal centres, and a low number of sesamoids and apophyseal centres. These observations suggest that the reductions are produced by heterochronic changes during postnatal development and probably during embryonic development; therefore the appendicular skeleton exhibits a pattern of paedomorphic features.     

Taenidium and Associated Ichnofossils in Fluvial Deposits,Cretaceous Tuscaloosa Formation,Eastern Alabama,Southeastern U.S.A

Casts of the foraging tunnels of eastern American moles ( Scalopus aquaticus ) show impressions from the moles' mani along the lateral walls. The number of discernable impressions ranges from one to five, each showing two or three long, flat, blunt-ended claws. The size and shape of the impressions matches the claws on the paddle-like manus of S. aquaticus . The impressions are spaced at regular intervals of about two cm, and probably represent points at which the mole pushed off from the tunnel wall with alternating laterad digging strokes. Tunnel width generally exceeds height by about 15%, reflecting the laterally compressed body of the mole. These tunnel casts help show that clear, recognizable traces can be preserved in loose, humic soils, and demonstrate the type of traces left by a “lateral-thrust” digger with fully sprawled stance, such as S. aquaticus . Identification of traces on the tunnels of living moles may be applied to the fossil record, in which fossilized burrows with similar marks could be attributed to extinct burrowing moles or mole-like locomotion.     

An Old World hummingbird from the Oligocene: a new fossil from Polish Carpathians

A near-complete, partially articulated skeleton of a hummingbird was recently found in the menilite shales of the Polish Flysh Carpathians. The specimen is dated to the Early Oligocene (Rupelian, approx. 31 Myr). It shares derived characters with extant hummingbirds and plesiomorphic characters with swifts. Its long, thin beak and short and stout humerus and ulna are typical for hummingbirds, but the coracoid resembles that observed in swifts. The osteology of the specimen is generally similar to that of the hummingbird described from the Early Tertiary of Germany but because it clearly differs in some characters from the German hummingbird Eurotrochilus inexpectatus, it is described as a new species of the same genus.     

Skeletal allometry and interlimb scaling patterns in mustelid carnivorans

To address the effects of an evolutionary increase in body size on long bone skeletal allometry, scaling patterns relating body mass, bone length, limb length, midshaft diameters, and cross-sectional properties of the humerus and femur were analyzed for four species of scansorial mustelids. Humeral and, to a lesser extent, femoral allometry is consistent with expectations of elastic similarity: bone and limb length scale with negative allometry on body mass while bone robusticity (cross-sectional parameters against bone length) scales with strong positive allometry. Differences between fore- and hindlimb scaling patterns, however, are observed, with size-dependent increases in forelimb length and humeral strength and robusticity exceeding those of the hindlimb and femur. It is hypothesized that this greater fore- than hindlimb lengthening results in postural modifications that serve to straighten the hindlimb of larger bodied scansorial mustelids relative to smaller mustelids. Straightening of hindlimb joints would more precisely align the long axis of the femur with peak (vertical) ground reaction forces, thereby accounting for the reduction in relative bending stresses acting on the femur compared to the humerus. J. Morphol. 235:121–134, 1998. © 1998 Wiley-Liss, Inc.     

Digging adaptation in insectivorous subterranean eutherians. The enigma of Mesoscalops montanensis unveiled by geometric morphometrics and finite element analysis

The enigmatic Early Miocene fossorial mammal Mesoscalops montanensis shows one of the most modified humeri among terrestrial mammals. It has been suggested, on qualitative considerations, that this species has no extant homologues for humerus kinematics and that, functionally, the closest extant group is represented by Chrysochloridae. We combine here three dimensional geometric morphometrics, finite element analysis and phylogenetic comparative methods to explore the shape and mechanical stress states of Mesoscalops montanensis as well as of extant and extinct Talpidae and Chrysochloridae under realistic digging simulations. Evolutionary convergence analyses reveal that the shape of Mesoscalops montanensis represents a unique morphology in the context of fossorial mammals and that its functional performance, albeit superficially similar to that of extant Chrysochloridae, still represents a nonconvergent optimum for adaptation to digging. J. Morphol. 276:1157–1171, 2015. © 2015 Wiley Periodicals, Inc.     

Claw morphometrics in monitor lizards: Variable substrate and habitat use correlate to shape diversity within a predator guild

Numerous studies investigate morphology in the context of habitat, and lizards have received particular attention. Substrate usage is often reflected in the morphology of characters associated with locomotion, and, as a result, claws have become well‐studied ecomorphological traits linking the two. The Kimberley predator guild of Western Australia consists of 10 sympatric varanid species. The purpose of this study was to quantify claw size and shape in the guild using geometric morphometrics, and determine whether these features correlated with substrate use and habitat. Each species was assigned a Habitat/substrate group based on the substrate their claws interact with in their respective habitat. Claw morphometrics were derived for both wild caught and preserved specimens from museum collections, using a 2D semilandmark analysis. Claw shape significantly separated based on Habitat/substrate group. Varanus gouldii and Varanus panoptes claws were associated with sprinting and extensive digging. Varanus mertensi claws were for shallow excavation. The remaining species’ claws reflected specialization for some form of climbing, and differed based on substrate compliance. Varanus glauerti was best adapted for climbing rough sandstone, whereas Varanus scalaris and Varanus tristis had claws ideal for puncturing wood. Phylogenetic signal also significantly influenced claw shape, with Habitat/substrate group limited to certain clades. Positive size allometry allowed for claws to cope with mass increases, and shape allometry reflected a potential size limit on climbing. Claw morphology may facilitate niche separation within this trophic guild, especially when considered with body size. As these varanids are generalist predators, morphological traits associated with locomotion may be more reliable candidates for detecting niche partitioning than those associated directly with diet.     

The First Record of the Pterosaur Ichnogenus Purbeckopus in the Late Berriasian (Early Cretaceous) of Northwest Germany

A hypichnium of a manus imprint (preserved as plaster cast) indicates for the first time the presence of the large pterosaur ichnotaxon Purbeckopus cf. pentadactylus Delair, 1963 in the late Berriasian of northwest Germany. It is only the second record of Purbeckopus globally and the first pterosaur track from Germany. It provides evidence of a very large pterosaur (wingspan c. 6 m) in this area and from this time period not yet represented by skeletal remains. When compared with the English type material, the specimen exhibits some differences that are related mostly to different properties of the substrate on which both were left. These include, in the German track, an impression of the metacarpo-phalangeal joint of the wing finger, normally not present in pterosaur tracks. Also interesting is the rather blunt termination of the deeply impressed digits I–III, indicating rather short and blunt claws, which seem more suitable for walking than for grasping or climbing. The specimens of Purbeckopus in England and Germany occur in different environments: the English locality was situated close to a brackish lagoon, while the German site belongs to a limnic-deltaic system at the margin of a large, freshwater lake.     

Evolutionary implications of the unusual walking mechanics of the common marmoset (C. jacchus)

Several features that appear to differentiate the walking gaits of most primates from those of most other mammals (the prevalence of diagonal-sequence footfalls, high degrees of humeral protraction, and low forelimb vs. hindlimb peak vertical forces) are believed to have evolved in response to requirements of locomotion on thin arboreal supports by early primates that had developed clawless grasping hands and feet. This putative relationship between anatomy, behavior, and ecology is tested here by examining gait mechanics in the common marmoset (Callithrix jacchus), a primate that has sharp claws and reduced pedal grasping, and that spends much of its time clinging on large trunks. Kinematic and kinetic data were collected on three male Callithrix jacchus as they walked across a force platform attached to the ground or to raised horizontal poles. The vast majority of all walking gaits were lateral-sequence. For all steps, the humerus was retracted (<90 degrees relative to a horizontal axis) or held in a neutral (90 degrees ) position at forelimb touchdown. Peak vertical forces on the forelimb were always higher than those on the hindlimb. These three features of the walking gaits of C. jacchus separate it from any other primate studied (including other callitrichids). The walking gaits of C. jacchus are mechanically more similar to those of small, nonprimate mammals. The results of this study support previous models that suggest that the unusual suite of features that typify the walking gaits of most primates are adaptations to the requirements of locomotion on thin arboreal supports. These data, along with data from other primates and marsupials, suggest that primate postcranial and locomotor characteristics are part of a basal adaptation for walking on thin branches.     

The anatomy of the forelimb in the anteater (Tamandua) and its functional implications

The forelimbs of anteaters play a major role in obtainment of food, defense, and locomotion. The greatly enlarged claws on the manus are used for ripping open insect nests and insect-infested wood; the claws also serve as the animals' only defensive weapons, since they lack teeth. Specialization of the claws for these functions has also had a substantial effect on the ways in which the forelimb is used for posture and locomotion. Modifications of the forelimb in the anteater Tamandua include the following. Attachments of the medial head of triceps are rearranged so as to greatly increase capability for powerful flexion of the claws. Ability to flex the elbow and to retract the humerus is also augmented; these movements would assist digital flexion in applying traction with the claws to material being torn away during food procurement. This traction can be supplemented by a variety of powerful side-to-side and/or twisting movements of the hand, brought about primarily by axial rotation of the upper arm and forearm. The digital joints are reinforced to resist the deviational and torsional loading to which the digits would be subjected during such movements. The morphological modifications of the forelimb in Tamandua are discussed in terms of how they affect the mechanical capabilities of the limb, what functions the limb is best designed to perform, how they may relate to what little is known about the specialized behavior of this animal, and what behavioral predictions may be made based on mechanical design.     

Postcranial morphology,functional adaptations and palaeobiology of Callistoe vincei,a predaceous metatherian from the Eocene of Salta,north‐western Argentina

Abstract: Callistoe vincei Babot et al., 2002 is a Paleogene borhyaenoid known from exceptionally complete postcranial elements, which provides rare information about the anatomy and evolutionary history of metatherian predators during the South American Cenozoic. The axial skeleton of Callistoe is characterized by the peculiar transverse processes of the cervical vertebrae emphasizing lateral instead of sagittal traction. There is no clavicle and eighteen thoracolumbar vertebrae, of which only five are lumbars. The shoulder and elbow joints suggest movements restricted to parasagittal flexion/extension that are consistent with primarily terrestrial locomotion, as is also emphasized in Borhyaena tuberata and Lycopsis longirostrus. On the manus, the pollex is not reduced and the ungual phalanges indicate very long claws, similar to those observed in some extant digging taxa. This feature is unique to C. vincei among borhyaenoids. The knee joint is characterized by the presence of ossified patellae but shallow femoral trochleae. This joint suggests that the leg was nearly parasagittal, a position also inferred for Borhyaena. The astragalus shape is consistent with parasagittal flexion/extension, as in all Miocene–Pliocene borhyaenoids. The hind foot is characterized by reduced claws in comparison with the manus as well as the slenderness of the first and fifth digits, another peculiarity of C. vincei. The habitat of Callistoe was a temperate humid forest and according to the known fossil record, Callistoe was the largest mammalian predator of its time, sharing the predator ecological niche with crocodiles.     

The aquatic Lystrosaurus: An alternative lifestyle

Certain distinctive features of the skull and postcranial skeleton of Lystrosaurus are discussed. The mechanics of the skull are re‐evaluated and it is concluded that the skull was modified relative to Permian forms to produce a bigger bite force and more vertical component of the adductor muscles, while preserving a wide gape. A zone of weakness, acting as a shock absorption system, was present in the premaxillary‐nasal region of the skull. Antero‐posterior movement of the lower jaw had been reduced. It is concluded that the skull was used to crush resistant plant matter.

The external nasal opening presents no evidence for a valvular structure, but may have housed a nasal gland.

The flared scapula produced a slightly greater mechanical advantage in the limb protractors and retractors.

The manus was short and broad, suitable for digging, but the claws were flat and rounded.

The wide knee‐joint indicated powerful foot‐moving muscles.

The palaeoenvironment of the Lystrosaurus‐Thrinaxodon Assemblage Zone is examined. It was probably drier than usually described. The fauna contained many terrestrial elements.

Lystrosaurus was probably a fully terrestrial animal which may have excavated burrows for itself, but was not a committed burrower like Cistecephalus.     

Growth patterns as deduced from bone microstructure of some selected neotherapsids with special emphasis on dicynodonts: Phylogenetic implications

Osteohistological analysis of the dicynodonts Endothiodon, Diictodon, Lystrosaurus and Wadiasaurus reveals distinctly different growth patterns within a framework of an overall fast growth. The late Permian endemic taxon from India, Endothiodon mahalanobisi and the South African Diictodon feliceps had periodic fast growth. The early Triassic Lystrosaurus murrayi and the middle Triassic Wadiasaurus indicus had an initial fast growth followed by a relatively slow growth later in ontogeny as is observed from the presence of peripheral parallel fibred bone. Although all examined dicynodont genera had an indeterminate growth strategy, the bone microstructure of Wadiasaurus suggests that its growth was much slower than that of other dicynodonts examined. Mapping of osetohistological character states on a cladogram depicting the inter-relationship between available neotherapsid genera shows that fibrolamellar bone tissue, overall fast growth and indeterminate growth strategy were plesiomorphic for the neotherapsids. A considerable reduction in developmental plasticity and evolution of apparently independent growth trajectories from environmental conditions are evident within the non-mammalian cynodonts, with the advanced tritylodontids achieving almost a mammalian growth trajectory.