Evolutionary morphology of the Tenrecoidea (Mammalia) carpal complex

The mammalian carpus can be difficult to interpret both phylogenetically and functionally. It is evolutionarily constrained in terms of functional morphology, yet there is considerable variation among many eutherian and metatherian lower and higher level taxa. The ecologically diverse Tenrecoidea (Mammalia) is a useful model for morphological interpretation of the interplay between function and phylogenetic constraint. Elements from the wrist and hand of 13 tenrecoid species, and one species each from Macroscelididae, Solenodontidae, and Erinaceidae, were compared to test form–function hypotheses of specific carpal, metacarpal, and phalangeal characters. Qualitative comparisons illustrate that several aspects of the tenrecoid carpus can be correlated with positional behaviour. Convergences within Tenrecoidea, and between tenrecoids and nontenrecoids with similar locomotor regimes, confirm a small number of carpal characters and a larger number of distal forearm, metacarpal, and phalangeal characters that reliably correspond with functional expectations. In addition, several features of the carpus appear to be phylogenetically constrained and indicate specific affinities within Tenrecoidea. Finally, there are a significant number of carpal features that vary among the studied taxa and remain ambiguous in terms of phylogenetic and/or functional significance.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 93 , 267–288.     

Functional morphology of the hindlimb of tupaiids (Mammalia,Scandentia) and its phylogenetic implications

In this study, the hindlimb of 12 species of tupaiids was analyzed functionally and compared to that of primates, dermopterans, and chiropterans. Many aspects of the tupaiid hindlimb vary in relation to differential substrate use. These differences include width of the ilium, shape of the acetabulum, size of the anterior inferior iliac spine, size of the greater and third trochanters, depth of the femoral condyles, shape of the patellar groove, and size of the tibial tuberosity. The hindlimb of the arboreal Ptilocercus lowii, the only ptilocercine, is better adapted for arboreal locomotion, whereas that of tupaiines is better adapted for rapid terrestrial (or scansorial) locomotion. The hindlimb of Ptilocercus seems to be habitually flexed and has more joint mobility, a condition necessary for movement on uneven, discontinuous arboreal supports. The tarsus of Ptilocercus facilitates inversion of the foot and its grasping hallux is capable of a great range of abduction. Tupaiines, on the other hand, are characterized by more extended hindlimbs and less mobility in their joints. These restricted joints limit movements more to the parasagittal plane, which increases the efficiency of locomotion on a more even and continuous surface like the ground. The hindlimb of tupaiines is adapted for powerful flexion and extension. Even the most arboreal tupaiines remain similar to terrestrial tupaiines in their hindlimb morphology, which probably reflects the terrestrial ancestry of Tupaiinae (but not Tupaiidae). Many attributes of the tupaiid hindlimb, especially those of the foot, reflect the arboreal ancestry of Tupaiidae and it is proposed that the ancestral tupaiid was arboreal like Ptilocercus. Also, compared to the hindlimb character states of tupaiines, those of Ptilocercus are more similar to those of other archontans, and it is proposed that the hindlimb features of Ptilocercus are primitive for the Tupaiidae. Hence, Ptilocercus should be considered in any phylogenetic analysis that includes Scandentia.     

Speciation and gene flow in two sympatric small mammals from Madagascar,Microgale fotsifotsy and M. soricoides (Mammalia: Tenrecidae)

Madagascar's shrew tenrecs (Mammalia: Tenrecidae; Microgale, Nesogale) represent an excellent system for studying speciation. Most species are endemic to the island's eastern humid forests, a region renowned for high levels of biodiversity and a high rate of in situ diversification. We set out to understand the speciation dynamics in a clade of recently described taxa: Microgale fotsifotsy and M. soricoides, which have nearly identical distributions in the moist evergreen forest, and M. nasoloi, which occurs in the western dry deciduous forest. A phylogenetic analysis using mitochondrial DNA data recovered two distinct clades of M. fotsifotsy: a south clade that is sister to, and broadly sympatric with, M. soricoides, and a north clade that is sister to the dry‐forest and distantly allopatric species M. nasoloi. To better understand this result, we analysed cranioskeletal measurements and performed demographic analyses using nuclear sequence data from ultraconserved elements. Nuclear data did not support a sister relationship between M. soricoides and the south clade of M. fotsifotsy but did demonstrate introgression between these clades, which probably explains the discordance between nuclear and mitochondrial phylogenies. Demographic analyses also revealed the absence of gene flow between the north and south clades of M. fotsifotsy. Morphometric data revealed several major differences between M. soricoides and M. fotsifotsy, as well as more subtle differences between the two clades of M. fotsifotsy. In light of these results, we treat the south clade of M. fotsifotsy as a new candidate species. Our findings demonstrate the utility of integrating multiple data types to understand complex speciation histories, and contribute to a growing body of evidence that species diversity on Madagascar is underestimated.     

Evolutionary morphology of oblique ribs of bivalves

Fossil bivalves bearing oblique ribs first appeared in the Mid Ordovician but their diversity remained low during the Palaeozoic. The diversity soon increased after the Early Triassic, peaking in the Early Cretaceous. The Palaeozoic–Mesozoic record is dominated by burrowing bivalves (mainly pholadomyoids and trigonioids), which developed oblique ribs with symmetric profiles, probably adapted for shell reinforcement, although there are indications that the ribs of trigonioids also enhanced burrowing efficiency. After the Paleocene, the main groups of burrowing bivalves were veneroids (primarily tellinoideans and lucinoideans) and nuculoids, which generated oblique ribs of the shingled type, adapted to increase burrowing efficiency. The inferred change in function at the Mesozoic/Cenozoic boundary can be correlated with an increase in mean mobility of the bivalve faunas bearing oblique ribs through time. This implies a major ecological cause for the observed temporal patterns, which forced bivalve faunas to burrow more rapidly and efficiently. In particular, either the Phanerozoic increase in the diversity of durophagous predators or the accelerating rate of sediment reworking (both being a consequence of the Mesozoic Marine Revolution), or both, could have provided the necessary evolutionary force.     

Expression of hindlimb abnormalities under rearing temperature effects during the larval development of the salamander Pleurodeles waltl (urodele amphibian)

Anomalie m.p. is a spontaneous and heritable hindlimb abnormality described earlier. Twenty years later, Pleurodeles waltl larvae from the strain bearing anomalie m.p. and reared at room temperature or at 30°C, expressed abnormalities (ectrodactylia, hemimelia, ectromelia). A morphological study of all the hindlimbs and an analysis of the hindlimb skeleton of samples from the experimental animals confirmed that most of the skeletal malformations were identical to those previously reported and affected the disto-proximal and prepostaxial pattern of the hindlimb. Analysis of the effects of rearing temperature on the expression of anomalie m.p. showed that the effects varied according to the developmental period at which the heat treatment was applied; the sooner the heat treatment began, the more numerous and more various were the degrees of severity of the malformations. Moreover, heat treatment induced the expression of two additional malformations not yet described: the first one, named 'reversed knee joint', was characterized by a reversal of the knee joint, and the second one, named 'twisted foot', by a downward twisting of the foot. The epigenetic effects of rearing at 30°C on hindlimb development are discussed with regard to the differentiation or patterning.     

Functional morphology of the forelimb of tupaiids (Mammalia, Scandentia) and its phylogenetic implications

In this study, the forelimb of 12 species of tupaiids was analyzed functionally and compared to that of other archontan mammals. Several differences that relate to differential substrate use were found in the forelimb morphology of tupaiids. These differences included shape of the scapula, length and orientation of the coracoid process, size of the lesser tuberosity, shape of the capitulum, length of the olecranon process, and shape of the radial head and central fossa. The forelimb of the arboreal Ptilocercus lowii, the only ptilocercine, is better adapted for arboreal locomotion, while that of tupaiines is better adapted for terrestrial (or scansorial) locomotion. While the forelimb of the arboreal Ptilocercus appears to be habitually flexed and exhibits more mobility in its joints, a necessity for movement on uneven, discontinuous arboreal supports, all tupaiines are characterized by more extended forelimbs and less mobility in their joints. These restricted joints limit movements more to the parasagittal plane, which increases the efficiency of locomotion on a more even and continuous surface like the ground. Even the most arboreal tupaiines remain similar to their terrestrial relatives in their forelimb morphology, which probably reflects the terrestrial ancestry of Tupaiinae (but not Tupaiidae). The forelimb of Urogale everetti is unique among tupaiines in that it exhibits adaptations for scratch-digging. Several features of the tupaiid forelimb reflect the arboreal ancestry of Tupaiidae and it is proposed that the ancestral tupaiid was arboreal like Ptilocercus. Also, compared to the forelimb character states of tupaiines, those of Ptilocercus are more similar to those of other archontans and it is proposed that the attributes of the forelimb of Ptilocercus are primitive for the Tupaiidae. Hence, Ptilocercus should be considered in any phylogenetic analysis that includes Scandentia.     

Evolutionary stasis,ecophenotypy and environmental controls on ammonite morphology in the Late Cretaceous (Maastrichtian) Western Interior Seaway,USA

We test for the presence of evolutionary stasis in a species of Late Cretaceous ammonoid cephalopod, Hoploscaphites nicolletii, from the North American Western Interior Seaway. A comprehensive dataset of morphological traits was compiled across the entire spatial and temporal range of this species. These were analysed in conjunction with sedimentologically and geochemically derived palaeoenvironmental conditions hypothesized to apply selective pressures. All changes in shell shape were observed to be ephemeral and reversable, that is, no unidirectional trend could be observed in any of the morphological traits analysed. Correlations between palaeoenvironmental conditions and morphological traits suggests ecophenotypic processes were at play; however, either environmental changes were too minor and/or provided no isolating mechanism to drive speciation. These data support mechanisms of stasis such as homogenizing gene flow or stabilizing selection under a fluctuating optimum (probably reflecting spatiotemporally heterogeneous palaeoenvironmental conditions). Finally, changes in shell size were not significantly associated with changes in shell-specific δ¹⁸O, despite a correlation between shell size and δ¹⁸O averaged across horizons. This suggests a mismatch in scales of geochemical sampling that supports caution when making broad interpretations based on averaged geochemical data.     

A Morphological Basis for Assessing the Phylogeny of the "Tenrecoidea" (Mammalia, Lipotyphla)

A phylogenetic analysis of 35 mammalian taxa focusing on the lipotyphlan family Tenrecidae, based on 193 morphological character states across 71 characters, is undertaken to test several hypotheses of lipotyphlan relationships, including monophyly of the Lipotyphla, Tenrecidae, Malagasy Tenrecidae, and Caribbean Lipotyphla. Explicit tests of these hypotheses are central to understanding larger issues concerning Malagasy and Caribbean biogeography, in addition to mammalian phylogeny. Methodologically, several different parameters are created with which to determine the sensitivity of resulting clades to initial assumptions about a posteriori character weighting, missing data, and multistate character ordering. Clades produced by this data set that appear despite perturbations in these parameters and that are supported by other confidence-assessment techniques contradict Malagasy tenrecid monophyly and the association of soricids with the Caribbean taxon Solenodon. Results regarding tenrecid and lipotyphlan monophyly are more ambiguous and depend on certain assumptions regarding treatment of character ordering, weighting, and missing data. An alternative phylogeny supporting an African mammal clade receives no support from the data set discussed herein.     

Functional correlation between habitat use and leg morphology in birds (Aves)

Many of the morphological features of animals are considered to be adaptations to the habitat that the animals utilize. The habitats utilized by birds vary, perhaps more than for any other group of vertebrates. Here, we study possible adaptations in the morphology of the skeletal elements of the hind limbs to the habitat of birds. Measurements of the lengths of the femur, tibiotarsus and tarsometatarsus of 323 bird species from 74 families are used together with body mass data, taken from the literature. The species are separated into six habitat groups on the basis of literature data on leg use. A discriminant analysis of the groups based on leg morphology shows that swimming birds, wading birds and ground living species are more easily identified than other birds. Furthermore, functional predictions are made for each group based on ecological and mechanical considerations. The groups were tested for deviation from the norm for all birds for three indices of size- and leg-length-independent measures of the bones and for a size-independent-index of leg length. Several of the groups deviate significantly from the norm for one or more of the indices used, suggesting habitat-related adaptations in the leg morphology of birds. The results indicate that stability is an important factor affecting the leg morphology of primarily long-legged birds. The femur seems to be more important than previously thought because several of the groups have high femur indices, suggesting a positive selection pressure on this bone. On a general basis, the results suggest that the effect of leg length should be taken into consideration when discussing adaptations of mass-independent lengths of the long bones of the legs of birds.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 79, 461–484.     

The evolution of femoral osteology and soft tissues on the line to extant birds (Neornithes)

Femoral osteology and soft tissues evolved in a stepwise pattern in archosauromorph reptiles on the line to crown group birds. Crocodylia retains most ancestral archosaurian traits, whereas Dinosauromorpha (including birds) acquired many more derived traits. The complex sequence of changes included major shifts of several thigh muscle insertions. Medial rotation of the proximal femur (e.g. the femoral head) in archosaurs moved the greater trochanter laterally, bringing along the insertion of M. pubo-ischio-femoralis externus. Within Dinosauromorpha, the lesser trochanter moved proximally away from the trochanteric shelf. Presumably the lesser trochanter indicates the insertion of M. iliotrochantericus caudalis whereas the trochanteric shelf indicates the insertion of M. iliofemoralis externus. An accessory trochanter at the base of the lesser trochanter marks the insertion of M. pubo-ischio-femoralis internus 2 in tetanuran theropods. I propose hypotheses for the homologies of several intermuscular lines and other features on the femoral shaft. On the line to Neornithes, most changes of femoral morphology predated Aves and the origin of flight; few femoral features are unique to birds. Overall, the pattern of morphological evolution is consistent with stepwise functional evolution of the hindlimb within Dinosauromorpha on the line to Neornithes. The clade Ornithurae evolved the last few hindlimb apomorphies that characterize extant birds, in conjunction with more flexed hip and knee joints.     

Evolution of the axial skeleton in armadillos (Mammalia,Dasypodidae)

Intraspecific and interspecific variation in cervical, thoracic, and lumbar region of the vertebral column of Dasypodidae were examined in a phylogenetic framework. The number of vertebrae for each region were recorded for 86 specimens and metric data for each vertebra (centrum length, high, and width) were recorded for 72 specimens, including eight of the nine living genera. The number of vertebrae and degree of fusion between them were used to define four characters which were plotted on two alternative phylogenies of Dasypodidae. The ratio between centrum height and width is similar across all taxa analyzed except for Chlamyphorus, which exhibits a deviation in the last two lumbars. Tolypeutes matacus is unique among the taxa examined in having a second co-osified bone called postcervical bone, which is a fusion of the seventh cervical and first thoracic vertebrae. The thoraco-lumbar numbers of dasypodids are reduced when compared with other xenarthrans and are more diverse than those of some other mammalian clades of similar geological age and higher ecomorphological diversity. Changes in size are somewhat coupled with changes in the number of body segments. Independent of the phylogenetic framework taken, changes in size are accompanied with small changes in numbers of thoracolumbar vertebrae within each genus. There are functional and phylogenetic correlates for changes in number of thoraco-lumbar vertebrae in dasypodids.     

Skull morphology and functionality of extant Felidae (Mammalia: Carnivora): a phylogenetic and evolutionary perspective

Felids morphology and ecological role as hypercarnivores are quite constant, despite considerable body size variation among species. Skull morphological and functional features of 34 extant cat species were evaluated under a phylogenetic framework of the Felidae. Twenty skull measurements were analysed through Principal Component Analysis to assess the species morphofunctional spaces. Force indexes were obtained from static equilibrium equations to infer jaw mechanics. Correlations between morphological, functional, and ecological traits were tested by phylogenetically independent contrasts. In spite of the general cat‐like pattern, specific features on the skulls allowed differentiation among groups. Acinonyx jubatus, for instance, showed a shorter and shallower temporal fossa than other big cats, and their bite functionality is marked by an increased contribution of the masseteric system. A morphofunctional dichotomy between Neotropical and Eurasian/African small cats was detected, and is associated with the major transversal axes of the skulls. According to the contrast analyses, the skull size is correlated with the bite force and prey size, but it is uncorrelated with the variations on jaw mechanics (from temporalis or masseter muscle optimizations). Also, there was no correlation between functional differences on jaw muscles and the ratio of prey weight to cat weight. The efficiency of the jaw apparatus among cats is quite consistent; therefore, the different evolutionary trends of jaw mechanics seem to be caused by the casuistic fixation of phenotypical variations, rather than by specific adaptative selections. © 2010 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161 , 414–462.     

Phylogeny of the Procyonidae (Mammalia: Carnivora): molecules, morphology and the Great American Interchange

The Procyonidae (Mammalia: Carnivora) have played a central role in resolving the controversial systematics of the giant and red pandas, but phylogenetic relationships of species within the family itself have received much less attention. Cladistic analyses of morphological characters conducted during the last two decades have resulted in topologies that group ecologically and morphologically similar taxa together. Specifically, the highly arboreal and frugivorous kinkajou (Potos flavus) and olingos (Bassaricyon) define one clade, whereas the more terrestrial and omnivorous coatis (Nasua), raccoons (Procyon), and ringtails (Bassariscus) define another clade, with the similar-sized Nasua and Procyon joined as sister taxa in this latter group. These relationships, however, have not been tested with molecular sequence data. We examined procyonid phylogenetics based on combined data from nine nuclear and two mitochondrial gene segments totaling 6534bp. We were able to fully resolve relationships within the family with strongly supported and congruent results from maximum parsimony, maximum likelihood, minimum evolution, and Bayesian analyses. We identified three distinct lineages within the family: a (Nasua, Bassaricyon) clade, a (Bassariscus, Procyon) clade, and a Potos lineage, the last of which is sister to the other two clades. These findings, which are in strong disagreement with prior fossil and morphology-based assessments of procyonid relationships, reemphasize the morphological and ecological flexibility of these taxa. In particular, morphological similarities between unrelated genera possibly reflect convergence associated with similar lifestyles and diets rather than ancestry. Furthermore, incongruence between the molecular supermatrix and a morphological character matrix comprised mostly of dental characters [Baskin, J.A., 2004. Bassariscus and Probassariscus (Mammalia, Carnivora, Procyonidae) from the early Barstovian (Middle Miocene). J. Vert. Paleo. 24, 709-720] may be due to non-independence among atomized dental characters that does not take into account the high developmental genetic correlation of these characters. Finally, molecular divergence dating analyses using a relaxed molecular clock approach suggest that intergeneric and intrageneric splits in the Procyonidae mostly occurred in the Miocene. The inferred divergence times for intrageneric splits for several genera whose ranges are bisected by the Panamanian Isthmus is significant because they suggest diversification well precedes the Great American Interchange, which has long been considered a primary underlying mechanism for procyonid evolution.     

The postcranial dimensions of the La Chapelle-aux-saints 1 Neandertal

The La Chapelle-aux-Saints 1 Neandertal has figured prominently in considerations of Neandertal body size and proportions. In this context, a reassessment of its major long bones and a reassembly of its principal pelvic elements (sacrum and right ilium) was undertaken. There are secure measurements for its humeral and radial lengths and its femoral head diameter, but the femoral and tibial lengths were almost certainly greater than previous values. The resultant humeral, femoral and tibial lengths are similar to those of other male Neandertals, its femoral head diameter is among the largest known for Middle and Late Pleistocene humans, but its radial length is relatively short. The pelvic assembly provides modest bi-iliac and inlet transverse diameters compared with the few sufficiently complete and undistorted Middle and Late Pleistocene archaic human pelves, but its dimensions are similar to those of large male early modern humans.     

Evolutionary significance of oral morphology in the carnivorous tadpoles of tiger frogs, genus Hoplobatrachus (Ranidae)

We describe the larval stages of three species of the Asian-African tiger frogs Hoplobatrachus chinensis, H. occipitalis and H. tigerinus . The tadpoles of all three species are very similar, with peculiar oral features: (1) double rows of needle-like labial teeth, (2) strong emarginations on the large jaw sheaths and (3) keratinized spurs on the buccal floor. Characters 1 and 2 (and perhaps 3) are probably related to the carnivorous habits of these tadpoles. A molecular phylogeny based on 2430 base pairs of two nuclear and four mitochondrial genes corroborated monophyly of Asian and African Hoplobatrachus, and identified Euphlyctis as their sister group. Tadpoles of the latter genus lack buccal spurs and double labial tooth rows but share large jaw sheaths, the upper with a medial projection. Therefore, the common ancestor of Euphlyctis and Hoplobatrachus probably was also characterized by this state, and may have been facultatively carnivorous. Further carnivorous specializations in Hoplobatrachus could explain why tiger frogs have been so successful in populating arid environments where ponds are at high risk of desiccation. Larval morphology may prove to be the key innovation which enabled them to disperse, in the Late Cenozoic, into their current very wide distribution area in Asia and Africa.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 81 , 171–181.     

The mole's thumb -- evolution of the hand skeleton in talpids (Mammalia)

Osteological specimens representing 15 out of the 16 currently recognized talpid genera were examined and scored for seven discrete morphological characters of the hand. The phylogenetic distribution of these characters was studied in the context of alternative hypotheses of talpid relationships, using three species of shrews and a hedgehog as outgroups. All talpids show a similar number and arrangement of carpal bones. The most obvious differences concern the presence of additional sesamoid bones, the relative size of the os falciforme when present, and the degree of fusion of the scaphoid and lunate in the proximal carpal row. Marked differences in the relative length and proportions of the metacarpals also exist. The development of the carpals in Talpa europaea was studied through examination of histological sections of the hand of an embryo and a neonate. Whereas carpal anatomy in the neonate mirrors the arrangement and proportions of the adult, in the embryo the scaphoid and lunate are still separate, there are no signs of the os falciforme, and the size proportions of metacarpals to carpals are obviously different to those of the adult. A prehallux or tibial sesamoid, serial homologue to the os falciforme or prepollex (a radial sesamoid), does not have an obvious functional role, and its presence might be the result of a common epigenetic control in the hand and the foot resulting in a non-adaptive structure in the latter.