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.     

Cranial osteology of Picini (Aves: Piciformes: Picidae)

The Picini is composed of 26 species of woodpeckers from the old world that are grouped into seven genera. Given the absence of detailed studies on the cranial osteology of the Picini, the purpose of this study is to describe the cranial osteology of 14 species of Picini from six genera and to compare these species with each other, with other species of woodpeckers and with other bird groups. The results of the analysis of the bone structures of the skull of the Picini indicate that there are seven outstanding characteristic of bones involved in the functional mechanistics of the jaw apparatus. In the ossa cranii, these include the frontal overhang, the postorbital process, the extension of the parietal versus the frontal region and the temporal fossa. In the ossa faciei, these include the rostral expansion of the pterygoid, the ventral palatine fossa and the orbital process of the quadrate bone. For all of the structures associated with the cranial osteology of the investigated species, there is a clear distinction between the species of the genus Picus and the other species studied. Blythipicus rubiginosus, Chrysocolaptes lucidus, Reinwardtipicus validus, Gecinulus viridis and the species of the genus Dinopium exhibit additional particularities.     

Cranial ontogeny and sexual dimorphism in two new world monkeys: Alouatta caraya (Atelidae) and Cebus apella (Cebidae)

Pattern of skull development and sexual dimorphism was studied in Cebus apella and Alouatta caraya using univariate, bivariate, and multivariate statistics. In both species, sexual dimorphism develops because the common growth trajectory in males extends and because of differences in growth rates between sexes. The expectation that the ontogenetic bases of adult dimorphism vary interspecifically is well substantiated by this study. A. caraya exhibits transitional dimorphism in its subadult stage, although the condylobasal length, zygomatic breadth, and rostrum length are strongly dimorphic in the final adult stage, being greater in males. Most cranial measurements in C. apella exhibit significant dimorphism in the adult stage, being strongly influenced by a faster rate of growth in males. Sexual dimorphism is also evidenced through sex differences in growth rates in several cranial measurements. These results also indicate that different ontogenetic mechanisms are acting in C. apella and A. caraya and reveal differences in the way through which neotropical primates attain adult sexual dimorphism. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

Evidence for the reversibility of digit loss: a phylogenetic study of limb evolution in Bachia (Gymnophthalmidae: Squamata)

Reevolution of lost characters constitutes evidence that the capacity for producing specific phenotypes may remain latent after a trait is lost and be transmitted over many generations without visible effect. Although some evolutionary changes are easily reversible, it can be argued that the reappearance of complex characters would be nearly impossible. This idea is based on the assumption that, after a structure is lost, the genes related to its development will degenerate. In the present paper we test this idea with respect to digit loss in the gymnophthalmid genus Bachia. We present a molecular phylogeny of the genus Bachia and investigate the evolution of digit number in this taxon. Most members of this South American genus have undergone major reduction in hind limbs without ever losing all the digits in the forelimbs. We apply three statistical methods to test the hypothesis that trait loss is irreversible (Dollo's law). These are tree tests, parsimony-cost curves, and likelihood-ratio tests. Data is also analyzed under a simple probability model. All analyses provided strong evidence for reevolution of digit number in derived Bachia species. The evidence is stronger in toes (hind limb) than in fingers (forelimb). Other published examples of reevolution of complex traits are discussed in the light of the statistical approaches used in this paper. We conclude that there are a limited number of cases with strong evidence for the reevolution of lost morphological structures, raising questions about the mechanisms that retain the genetic information for a latent character.     

Phylogenetic relationships of a new genus and species of microteiid lizard from the Atlantic forest of north-eastern Brazil (Squamata, Gymnophthalmidae)

A new genus and species of a short limbed and slightly elongate gymnophthalmid lizard is described from the Atlantic rain forests of north-eastern Brazil. The new genus is also characterized by short and stout pentadactyl limbs, presence of prefrontals, absence of frontoparietals, distinctive ear opening and eyelid, two pairs of genials, a distinct collar, smooth, quadrangular, dorsal scales, quadrangular ventrals, fused postfrontal and postorbital bones, and two pairs of sternal ribs. The geographical distribution of the new taxon extends from the state of Rio Grande do Norte to the northern bank of the Rio São Francisco in the state of Alagoas. All specimens were obtained in leaf litter, an observation which agrees with the fossorial habits suggested by the body shape and massive aspect of the head of this species. A phylogenetic analysis based on external morphology, osteology, and molecular data recovered the new lizard as the sister genus to Anotosaura , and Colobosauroides as the sister group to these two.  © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society , 2005, 144 , 543−557.     

Ontogenetic allometry constrains cranial shape of the head‐first burrowing worm lizard Cynisca leucura (Squamata: Amphisbaenidae)

Amphisbaenians are fossorial, predominantly limbless squamate reptiles with distinct cranial shapes corresponding to specific burrowing behaviors. Due to their cryptic lifestyles and the scarcity of museum specimens, little is known of their intraspecific variation, particularly regarding cranial osteology. This represents a critical lack of information, because the majority of morphological investigations of squamate relationships are based on cranial characters. We investigated cranial variation in the West African Coast Worm Lizard Cynisca leucura, a round‐headed member of the Amphisbaenidae. Using geometric morphometric analyses of three‐dimensional computed tomographic scans, we found that cranial osteology of C. leucura is highly conserved, with the majority of shape changes occurring during growth as the cranium becomes more slender and elongate, accompanied by increasing interdigitation among the dermal roofing bones. Elements of the ventral portion of the cranium remain loosely connected in adults, possibly as a protective mechanism against repeated compression and torsion during burrow excavation. Intraspecific variation was strongly correlated with size change from juveniles to adults, indicating a dominant role of ontogenetic allometry in determining cranial shape. We found no evidence of sexual dimorphism, either during growth or among adults. Given the fossorial habits of C. leucura, we hypothesize that cranial allometry is under strong stabilizing selection to maintain adequate proportions for head‐first digging, thereby constraining the ability of individuals to respond to differing selection pressures, including sexual selection and variation in diet or microhabitat. For species in which digging imposes less mechanical stress (e.g., in softer sand), allometric associations during growth may be weakened, allowing changes to the ontogenetic trajectory and subsequent morphological traits. Such developmental dissociation between size and shape, known as heterochrony, may also be implicit in the evolution of the other amphisbaenian cranial shapes (shovel, spade, and keel), which may themselves be functionally adapted for their respective burrowing techniques. J. Morphol. 277:1159–1167, 2016. © 2016 Wiley Periodicals, Inc.     

Variation in the growth and development of the hind limbs in frogs of the genus Telmatobius (Anura: Telmatobiidae)

There are remarkable interspecific differences in the sizes of the larvae of Andean frogs of the genus Telmatobius. This size variation seems to be associated with the duration of the larval stage and may affect the hind-limb morphology in Telmatobius. Larval, juvenile, and adult Telmatobius rubigo and T. oxycephalus were examined to determine the variation in relative sizes of hind-limb elements, their growth patterns during postmetamorphic life, and skeletal ontogeny. The results showed that the proportionately shorter hind limbs of T. rubigo relative to those of T. oxycephalus are associated with the protracted development and ossification of hind limbs during the prolonged larval life of T. rubigo. Postmetamorphically, the hind limbs grew faster than the body in juveniles of both species in contrast to the relative growth rates of the hind limbs and bodies of the adults. The growth phase of juvenile T. rubigo seems shorter than that of juvenile T. oxycephalus; possibly, this heightens the difference in the relative lengths of hind limbs after metamorphosis. Temperature affects the effects of thyroid hormone on growth and development, and T. rubigo lives at much higher, colder elevations than does T. oxycephalus. It is not clear whether the developmental differences described here are plastic (i.e., environmentally induced) or genetically fixed in each species.     

Gape size,its morphological basis,and the validity of gape indices in western diamond‐backed rattlesnakes (crotalus atrox)

Maximum gape is important to the ecology and evolution of many vertebrates, particularly gape‐limited predators, because it can restrict the sizes and shapes of prey that can be eaten. Although many cranial elements probably contribute to gape, it is typically estimated from jaw length or jaw width, or occasionally from a combination of these two measures. We measured maximum gape directly for 18 individuals of the western diamond‐backed rattlesnake, Crotalus atrox. We measured each individual's body length, several external cranial dimensions, several cranial osteological dimensions from cleaned skeletons, and we calculated gape index values from two published gape indices (GI). Cranial bone lengths and gape circumference showed negative allometry with snout–vent length (SVL), indicating that small individuals have relatively larger heads and gapes than their larger conspecifics. We then used Akaike's Information Criterion to determine which external and osteological measurements were the best predictors of gape. Body size (SVL) was the best predictor of maximum gape overall; however, when SVL was excluded from the analysis, quadrate (QL) and mandible lengths (MdLs) were the best predictors of maximum gape using both external and osteological measurements. Quadrate length probably contributes directly to gape; however, the importance of MdL to gape is less clear and may be due largely to its allometric relationships with head length and SVL. The two published GI did not prove to be better indicators of actual gape than the jaw and QLs in this study, and the gape values they produced differed significantly from our empirically determined gapes. For these reasons, we urge caution with the use and interpretation of computed GI in future studies. The extensive variation in quadrate and mandible morphology among lineages suggest that these bones are more important to variation in gape among species and lineages than within a single species. J. Morphol., 2013. © 2012 Wiley Periodicals, Inc.     

Cranial morphology and development: new light on the evolution of language

A hypothesis is presented which may explain within a single framework both the large behavioural differences and the large differences in head morphology between the great apes and humans. All these differences can be parsimoniously explained by a shift of few regulatory genes controlling the onset of the division of late migrating neurons in the human cortex. This simple shift resulted in the following effects: 1) the neurocranium responded to brain enlargement by increasing mineral deposition on its external surface, increasing its overall size and mass. 2) This increase in the braincase was largely achieved by developmental reabsoption of the face bones. 3) The relative shift in growth between these two skull components also induced a rearrangement at the basicranium level. This brought about the facial orthognatism of modernHomo and, as a mechanical by-product, the descent of the larynx into the throat. Brain enlargement led to a large increase in cognitive capacity, and as a developmental byproduct, produced a mechanical organ preadapted for speech, as well as bringing about the reduction of canines and the origin of the chin. In this study, the phylogenetic basis, the selective pressures, and the behavioural consequences of this process during hominization are examined. Cognitiveversus communicative aspects of human language are distinguished and discussed. Cognitive capacities were the first to be selected due to the survival advantage of mapping huge territories during the expansion of the Plio-Pleistocene savanna ecotone. The present hypothesis is then compared with current theories leading to the conclusion that it is a more parsimonious explanation. It integrates data from a wide array of fields of human biology, pathology and clinical medicine, all assessed from evolutionary and ecological perspectives.     

The development of cephalic armor in the tokay gecko (Squamata: Gekkonidae: Gekko gecko)

Armored skin resulting from the presence of bony dermal structures, osteoderms, is an exceptional phenotype in gekkotans (geckos and flap-footed lizards) only known to occur in three genera: Geckolepis, Gekko, and Tarentola. The Tokay gecko (Gekko gecko LINNAEUS 1758) is among the best-studied geckos due to its large size and wide range of occurrence, and although cranial dermal bone development has previously been investigated, details of osteoderm development along a size gradient remain less well-known. Likewise, a comparative survey of additional species within the broader Gekko clade to determine the uniqueness of this trait has not yet been completed. Here, we studied a large sample of gekkotans (38 spp.), including 18 specimens of G. gecko, using X-rays and high-resolution computed tomography for visualizing and quantifying the dermal armor in situ. Results from this survey confirm the presence of osteoderms in a second species within this genus, Gekko reevesii GRAY 1831, which exhibits discordance in timing and pattern of osteoderm development when compared with its sister taxon, G. gecko. We discuss the developmental sequence of osteoderms in these two species and explore in detail the formation and functionality of these enigmatic dermal ossifications. Finally, we conducted a comparative analysis of endolymphatic sacs in a wide array of gekkotans to explore previous ideas regarding the role of osteoderms as calcium reservoirs. We found that G. gecko and other gecko species with osteoderms have highly enlarged endolymphatic sacs relative to their body size, when compared to species without osteoderms, which implies that these membranous structures might fulfill a major role of calcium storage even in species with osteoderms.     

Osteology and cranial musculature of Caiman latirostris (crocodylia: Alligatoridae)

Caiman latirostris Daudin is one of the extant species of Caimaninae alligatorids characterized taxonomically only by external morphological features. In the present contribution, we describe the cranial osteology and myology of this species and its morphological variation. Several skull dissections and comparisons with other caimans were made. Although jaw muscles of living crocodiles show the same general “Bauplan” and alligatorids seem to have a similar cranial musculature pattern, we describe some morphological variations (e.g., in C. latirostris the superficial portion of the M. adductor mandibulae externus did not reach the postorbital; the M. adductor mandibulae internus pars pterygoideus dorsalis did not reach the pterygoid and lacrimal and contrary to the case of C. crocodilus the M. adductor mandibulae internus pars pterygoideus ventralis attaches to the posterodorsal surface of the pterygoid and the pterygoid aponeurosis, without contacting the dorsal and ventral surface of the pterygoid margin; the M. intermandibularis is attached to the anterior half of the splenial and posteriorly inserts medially by a medial raphe that serves as attachment zone for M. constrictor colli, and the M. constrictor colli profundus presents a medial notch in its anterior margin). In addition, the skull of C. latirostris differs from that of other caimans and possesses several characters that are potential diagnostic features of this species (e.g., outline of glenoid cavity in dorsal view, extension of the rostral ridges, and occlusion of the first dentary tooth). Nevertheless, these characters should be analyzed within the phylogenetic context of the Caimaninae to evaluate its evolutionary implications for the history of the group. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

Comparative growth in the postnatal skull of the extant North American turtle Pseudemys texana (Testudinoidea: Emydidae)

Bever, G.S. 2007. Comparative growth in the postnatal skull of the extant North American turtle Pseudemys texana (Testudinoidea: Emydidae). —Acta Zoologica (Stockholm) 88 : 000–000 Postnatal growth is one of the many aspects of developmental morphology that remains distinctly understudied in reptiles. Variation and ontogenetic scaling within the skull of the extant emydid turtle, Pseudemys texana is described based on 25 continuous characters. Results indicate that skull shape in this species changes little during postnatal growth relative to the only cryptodire taxa for which comparable datasets are available (Apalone ferox and Sternotherus odoratus). This relative lack of change results in the paedomorphic retention of a largely juvenile appearance in the adult form of P. texana. The skulls of males and females, despite the presence of distinct sexual dimorphism in size, grow with similar scaling patterns, and the few observed differences appear to reflect alteration of the male growth trajectory. Comparisons with A. ferox and S. odoratus reveal a number of similarities and differences that are here interpreted within a phylogenetic context. These preliminary hypotheses constitute predictive statements that phylogenetically bracket the majority of extant cryptodire species and provide baseline comparative data that are necessary for the future recognition of apomorphic transformations. Plasticity of ontogenetic scaling as a response to the homeostatic needs and behaviour of individuals commonly is evoked as a limitation of ontogenetic scaling as a means to inform phylogenetic studies. These evocations are largely unfounded considering that variability itself can evolve and thus be phylogenetically informative.     

New species of Schulzia (Nematoda: Molineidae) in Ptychoglossus festae (Squamata: Gymnophthalmidae) from Panama

Schulzia ptychoglossi n. sp. (Strongylida: Molineidae) from the intestines of Ptychoglossus festae (Squamata: Gymnophthalmidae) is described and illustrated. Schulzia ptychoglossi n. sp. represents the fourth species assigned to the genus and is most similar to the Venezuelan species S. usu by possessing a cervical inflation that begins a short distance from the anterior end of the body. Schulzia ptychoglossi differs from S. usu in that ray 8 separates midway between the root and tip of the dorsal ray in S. ptychoglossi, but separates close to the root of the dorsal ray in S. usu.