A new genus of Devonian tetrapod from North‐East Greenland,with new information on the lower jaw of Ichthyostega

Abstract: A new genus and species of Devonian tetrapod has been identified from material collected in 1947 from the southern slope of Mt. Celsius, Ymer Ø, North‐East Greenland. The specimen preserves both lower jaws, partial palate, premaxillae and maxillae, with a natural mould of parts of the shoulder girdle. The new taxon, Ymeria denticulata, shows differences in dentition, skull ornament and lateral line expression from both Acanthostega and Ichthyostega, but it shows a closer resemblance to the latter. A cladistic analysis not only suggests that Ymeria lies adjacent to Ichthyostega on the tetrapod stem, but also reveals substantial topological instability. As the third genus and the fifth species of tetrapod identified from North‐East Greenland, it demonstrates the high diversity of Devonian tetrapods in that region.     

Allometry and adaptation in the catarrhine postcranial skeleton

Seven measurements were taken on the postcranial skeleton of 249 specimens representing ten species of catarrhine primates and tested to determine their relationship with size. Size was measured as skeletal weight on each individual. It was found that the interspecific line based on the entire sample was in some cases determined not only by morphological adjustments for size variation but also by changes in locomotor adaptations of differently sized species within the sample. It is suggested that it is consequently preferable to study allometric relationships within a species or within a group of species that differ in size but are similar in their mode of locomotion. The allometric analysis reveals some interesting patterns within the data. Limb lengths scaled with either negative allometry or isometry over the entire sample. Within the species groups isometry was the rule except for pongid femurs, which showed negative scaling. Humerus length scaled at the same rate in pongids as in cercopithecoids but had a slightly higher intercept value. While colobines and cercopithecines scaled at similar rates for all seven dimensions, the colobine line was shifted to a position above that for cercopithecines in every case. It is suggested that this is a result of adaptation for leaping in the former group. Other implications of the allometric results are discussed.     

Postcranial stem tetrapod remains from the Devonian of Scat Craig, Morayshire, Scotland

The postcranial stem tetrapod remains from Scat Craig include a neural arch, humerus, tibia, femur, and incomplete pectoral girdles and ilia. These elements are all large or very large compared with the corresponding bones of other stem tetrapods. They correlate well in size with the proportions of Elginerpeton , the known stem tetrapod from Scat Craig, and probably belong to this genus. The neural arch has weak zygapophyses, and the ilia and shoulder girdles resemble those of Ichthyostega . The femur is strongly twisted, with the intercondylar fossa facing anteroventrally, so the hind limb probably functioned as a paddle. The tibia is broad, as in Acanthostega and Ichthyostega . The humerus is approximately intermediate in shape between those of osteolepiforms and later stem tetrapods, but seems to have a ventral radial facet like Ichthyostega . Overall, the postcranial bones combine apparent synapomorphies with Ichthyostega and characters which are uniquely primitive among stemgroup tetrapods. This character combination is incongruent. A recently discovered postorbital bone from the site is, strictly speaking, indeterminable but may belong to Elginerpeton ; it broadly resembles the postorbitals of Ichthyostega and Acanthostega , and demonstrates that the typical stem tetrapod facial morphology had evolved before the end of the Frasnian.     

Comparable disparity in the appendicular skeleton across the fish–tetrapod transition,and the morphological gap between fish and tetrapod postcrania

Appendicular skeletal traits are used to quantify changes in morphological disparity and morphospace occupation across the fish–tetrapod transition and to explore the informativeness of different data partitions in phylogeny reconstruction. Anterior appendicular data yield trees that differ little from those built from the full character set, whilst posterior appendicular data result in considerable loss of phylogenetic resolution and tree branch rearrangements. Overall, there is a significant incongruence in the signals associated with pectoral and pelvic data. The appendicular skeletons of fish and tetrapods attain similar levels of morphological disparity (at least when data are rarefied at the maximum sample size for fish in our study) and occupy similarly sized regions of morphospace. However, fish appear more dispersed in morphospace than tetrapods do. All taxa show a heterogeneous distribution in morphospace, and there is a clear separation between fish and tetrapods despite the presence of several evolutionarily intermediate taxa.     

Subspecific genetic differences in the saddle-back tamarin (Saguinus fuscicollis) postcranial skeleton

Saddle-back tamarins (Saguinus fuscicollis) have been differentiated into subspecies based on coat color and facial morphology. Morphology of first-generation genetic hybrids can provide an understanding of population differences and evolution that may otherwise be difficult to obtain. This study compares postcranial morphology in two hybrids of saddle-back tamarins (S. f. illigeri x S. f. lagonotus and S. f. illigeri x S. f. leucogenys) to the purebred subspecies. We examine whether postcranial morphology differs between the purebred subspecies and their hybrids, and whether hybrids exhibit heterosis indicative of genetic differences between the parental subspecies. Fifty postcranial dimensions, or traits, were measured on 287 S. fuscicollis skeletons. Measurements were corrected for sex differences and environmental differences (wild-derived or laboratory-born). Females were larger than males for most postcranial dimensions, especially in the pelvis. Significant environmental differences were found throughout the postcranial skeleton, with wild-derived animals generally larger than animals born in the laboratory. Significant heterosis was found for six postcranial traits in the S. f. illigeri x S. f. leucogenys cross, and heterosis was found for 15 postcranial traits in the S. f. illigeri x S. f. lagonotus cross. These results suggest that subspecies differences in skeletal morphology are generally due to genetic rather than environmental differences. The subspecies appear to represent geographic isolates that differ in gene frequencies and directional dominance for skeletal traits.     

The postcranial skeleton of the Lower Jurassic eosuchian Gephyrosaurus bridensis

The postcranial skeleton of the reptile Gephyrosaurus bridensis is described. The material was extracted from the Lower Jurassic fissure infillings of South Wales and comprises the broken and dissociated bones of many different individuals. The skeleton, like the skull, retains many primitive features which justify the inclusion of Gephyrosaurus within the Eosuchia. A comparison of the skeleton with that of other genera supports the conclusion that Gephyrosaurus represents a separate eosuchian lineage. The skeleton is that of a small, unspecialized terrestrial reptile which could move quickly in pursuit of prey.     

Walking in skates (Chondrichthyes, Rajidae): anatomy, behaviour and analogies to tetrapod locomotion

Pelvic fin walking in skates is common. However, the structure and function of pelvic fins have not been analysed. Pelvic fins of skates of the genus Psammobatis and Rioraja agassizi are externally divided into an anterior leg-like lobe and a posterior fin-like lobe. Internally, the anterior lobes are supported by a compound radial, a proximal radial and distal radials that resemble a thigh, a calf and a foot, respectively, and three associated radials arising from the pelvic girdle. A highly developed radial condyle on the pelvic girdle enables broad 'limb' movements. The muscular arrangement of the anterior lobes is formed by protractor, retractor, flexor and extensor muscles, clearly departing from the generalized fin muscle arrangement of elasmobranchs. Walking is composed of propulsion and recovery phases. A backward movement of the compound radial in the horizontal plane characterizes the propulsive phase. The proximal radial connects vertically the compoundradial with the foot-like distal radials, which are anchored on the bottom. During the recovery phase, the foot-like structure is lifted off the bottom and the entire limb-like anterior lobe is moved forwards for starting a new cycle. Walking in skates resembles the ancestral tetrapod sprawling locomotion seen in many salamanders and lizards. Pelvic fin anatomy and walking behaviour in skates and hemiscylliid sharksare compared. Ecological and evolutionary implications of walking locomotion in skates are also discussed.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77 , 35–41.     

The postcranial anatomy of Suminia getmanovi (Synapsida: Anomodontia), the earliest known arboreal tetrapod

The basal anomodont Suminia getmanovi Ivakhnenko, 1994 from the late Palaeozoic of Russia is highly specialized in its masticatory apparatus, and has been suggested to represent the earliest arboreal tetrapod in the fossil record. Its postcranial anatomy is described in detail for the first time, revealing a large number of autapomorphies for this small herbivore. These include a reduced number of presacral and therein dorsal vertebrae, an elongate neck, a long and possibly prehensile tail, a procoracoid with a notch at its ventromedial margin rather than a foramen, an iliac blade with a robust ridge at its anteromedial edge, a pubis with a puboischiadic fenestra and separate pubic foramen, and elongate limbs. Additional autapomorphic characters are displayed in the autopodium, which comprises about 40% of the entire limb length. These features include an enlarged, phalangiform distal carpal 1 and tarsal 1, a short and robust first metacarpal, a crescent‐shaped distal tarsal 4, and elongate penultimate phalangeal elements. The phylogenetic relationships of basal anomodonts are revisited using an expanded data set, with the addition of key taxa and several postcranial characters. Unlike dicynodonts, Suminia retained the plesiomorphic phalangeal formula for amniotes of 2‐3‐4‐5‐3 (manus) and 2‐3‐4‐5‐4 (pes). This pattern is achieved by the retention of disc‐like phalangeal elements between the proximal and penultimate phalanges in digits III, IV (manus and pes), and V (pes only). In light of the new material, Suminia can be recognized as the most complete basal anomodont, offering new insights into the early evolution of the group. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 162 , 661–698.     

Sexual dimorphism in the postcranial skeleton of New World primates

This study examines sexual dimorphism in 24 dimensions of the postcranial skeleton of four platyrrhine species: Callithrix jacchus, Saguinus nigricollis, Saimiri sciureus, and Cebus albifrons. The two callitrichid species show a relatively small amount of variation in the degree of sexual dimorphism among the different dimensions. Variation is considerably higher in the two cebid species as reflected by a mosaic pattern of sexual dimorphisms with males being significantly larger than females in some dimensions, and females significantly larger than males in others. In dimensions of the pectoral girdle and limb bones, males and females in each of the two cebid species are essentially scaled versions of each other, with males being peramorphic compared to females. This pattern is primarily the result of time hypermorphosis, i.e. an extension of the growth period in time in males. Rate hypermorphosis, i.e. an increase in the rate of growth in time in males, appears to play an additional role, however, in S. sciureus. By contrast, in dimensions of the true pelvis, sex differences in shape are dissociated from those in size. They are interpreted as the result of acceleration, i.e. increase in rate of shape change in females, as an adaptation to obstetrical functions. Interspecific analyses indicate positive allometry of mean degree of postcranial dimorphism with respect to body size. This coincides with previous findings by Leutenegger and Cheverud [1982, 1985] on the scaling of sexual dimorphism in body weight and canine size, and thus supports their model which posits selection on body size as the prime mover for the evolution of sexual dimorphism.     

Redescription and palaeobiology of Palaeoscorpius devonicus Lehmann, 1944 from the Lower Devonian Hunsrück Slate of Germany

Abstract: Palaeoscorpius devonicus Lehmann, 1944 is known from only a single specimen, found in the Eschenbach Pit near Bundenbach in the Lower Devonian Hunsrück Slate of Germany. It is a key fossil, having been interpreted both as the most basal member of the Scorpiones and as one of the order’s most likely candidates for an aquatic mode of life. Prepared both ventrally and dorsally, some aspects of its morphology remain problematic. Here, with the aid of new techniques, including computed tomography, we present a re‐investigation of this scorpion’s anatomy and a new reconstruction, with a particular focus on the species’ original habitat. On the basis of the environmental interpretation of the Hunsrück Slate and the completeness of the specimen, previous authors concluded that P. devonicus was marine, but none offered convincing morphological evidence. Recent studies of the deposit’s environment suggest that the Hunsrück Sea was part of an intrashelf basin, relatively close to the coastline, and fossils of land plants show that terrestrial wash‐in occasionally occurred. Our revised interpretation of the fossil’s morphology demonstrates that the scorpion was most probably terrestrial. Internal mesosomal organs are interpreted as book lungs, but other terrestrial adaptations are lacking. The absence of both coxapophyses and gnathobases makes determining the scorpion’s feeding mechanism difficult. Interpreting the scorpion’s character states within a phylogenetic framework, especially the possible presence of book lungs, implies either that the plesiomorphic position of P. devonicus is no longer supported or that the development of book lungs had already taken place early in the scorpion lineage.     

New information on the structure and relationships of Buchanosteus (Placodermi: Euarthrodira) from the Early Devonian of New South Wales

New material of the Early Devonian placoderm Buchanosteus confertitubercutatus (Chapman) is described, and a revised diagnosis is presented. The new material permits a detailed account of endocranial morphology; a canal for the orbital artery is identified for the first time, the courses of the efferent pseudobranchial and ophthalmica magna arteries are reinterpreted, and new information is presented on the structure of the palatoquadrate and parasphenoid. The presence of an eyestalk is established. Interrelationships of euarthrodiran taxa are briefly discussed; Buchanosteus is referred to the suborder Brachythoraci, which is redefined on the structure of the cheek and elongation of the submarginal plate. Other phylogenetically significant characters for brachythoracid taxa are considered to be the reduction of the trunk-shield and the shape of central and preorbital plates in the skull-roof. Revised diagnoses are presented for the order Euarthrodira, suborder Brachythoraci, infraorder Phlyctaenioidei and family Buchanosteidae. Parabuchanosteus murrumbidgeensis (White) is considered synonymous with Buchanosteus con/eftituberculatus.     

Phylogenetic interrelationships of the eel families Derichthyidae and Colocongridae (Elopomorpha: Anguilliformes) based on the pectoral skeleton

A cladistic analysis of the eel families Derichthyidae and Colocongridae is herein proposed for the first time on the basis of morphological data. We discovered dozens of new phylogenetic characters derived from a detailed analysis of the pectoral skeleton, an anatomical system neglected by most previous studies. Our maximum parsimony analysis indicates that Colocongridae sensu lato is paraphyletic, with its two constituent genera Coloconger and Congriscus appearing as successive sister groups of derichthyids. Monophyly of the family Derichthyidae, which has been questioned by some studies, is herein strongly supported by 10 unambiguous synapomorphies. We also stress the importance of the appendicular skeleton as a useful source of phylogenetic information for the resolution of systematic problems within Anguilliformes.     

Terrestrial adaptations in the postcranial skeletons of guenons

Arboreal and semiterrestrial guenons show similar osteological features of the limbs across a wide range of species, environments, and geography, while the more terrestrially committed guenons exhibit greater morphological divergence. An ecomorphological comparison of two sympatric guenons living in Kibale Forest, Uganda, reveals an array of anatomical adaptations for terrestriality in the limbs of Cercopithecus lhoesti similar to those found in Erythrocebus patas. In contrast, Cercopithecus aethiops, although also frequent users of the terrestrial environment, generally exhibit fewer morphological adaptations characteristic of a terrestrial lifestyle. It appears that significant morphological modification for terrestriality has occurred twice within the diverse radiation of living guenons with C. aethiops perhaps representing a third group in the making. © 1994 Wiley-Liss, Inc.