Embryonic development of the skeleton of Amphisbaena darwini heterozonata (Squamata: Amphisbaenidae).

An assemblage of amphisbaenian embryos has allowed us to characterize the external morphology of the developing embryos as well as the chondrification and ossification sequences of their skeletal elements. The external characterization of embryos serves as an incomplete developmental table. In contrast to the condition in other squamates, the premaxilla seems to arise azygously from the beginning or to represent very early fusion during embryogenesis. The tabulosphenoid forms from two cartilages to which are added extensive membranous ossifications. The two parietals engage in medial fusion at the midline, where the anterior process of the synotic tectum ossifies and forms the sagittal crest. The lateral element-X does not ossify until very late in embryogenesis and is interpreted as an epiphysial ossification. The compound mandibular bone arises from the ossification of the posterior part of Meckel's cartilage and the fusion of at least two dermal centers, interpreted as surangular and splenial. The vertebral column shows an antero-posterior gradient of vertebral differentiation. The number of vertebrae is fixed from the beginning of their differentiation. The remnants of pectoral and pelvic girdles are represented by cartilaginous rods. Some reproductive data obtained during the collection of data could be compared with those from the literature. J. Morphol. 239:1-25, 1999. © 1999 Wiley-Liss, Inc.

Unique locomotory mechanism of Mermis nigrescens, a large nematode that crawls over soil and climbs through vegetation.

Females of Mermis nigrescens, a nematode parasitic on grasshoppers, climb through terrestrial vegetation where they lay their eggs. The 100-mm-long body of these nematodes bridges gaps in this three-dimensional substratum, and crawls efficiently over planar surfaces. The nematodes do not use the classical undulant pattern of nematode locomotion as one coordinated unit; instead they propel themselves in several independent, locally controlled zones that propagate posteriorly. A repeated motion of their anterior end laces the body around fixed objects at which force may be applied. Propulsive force is applied to objects as the body glides past the contact site. Intermediate loops are elevated above the surface where they cannot contribute to propulsion. These loops rise and fall with time due to varying differences in propulsive forces between the contact sites. Forces are applied to the objects by internally generated bending couples that are propagated along the trunk, propelling the body in a cam-follower mechanism. Bending couples are generated by the contraction of ventral or dorsal longitudinal muscle bands that apply compressive force to the cuticle. The muscle bands, consisting of a single layer of obliquely striated muscle cells, are closely applied to the cuticle and are separated from it only by a fibrous basal lamina and a thin extension of a hypodermal cell. The myofilaments of each sarcomere are parallel to the body axis and attached perpendicularly via dense bodies (z-line equivalents) to the basal lamina, which in turn is fixed to the cuticle via filaments passing through the hypodermal cytoplasm, Consequently, forces are transmitted laterally to the cuticle over the entire length of the muscle, compressing it parallel to the surface without need for attachment to the terminal ends of the muscle cells. Thus the muscles are engineered for local control of bending and avoidance of buckling. There is evidence that the motor nervous system of Mermis may not be as simple as in classical nematode examples, which may explain why Mermis is capable of a much more localized control of locomotory motion. © 1994 Wiley-Liss, Inc.

Locomotor analysis of surface propulsion by three species of reduced-limbed fossorial lizards (Lerista: Scincidae) from western australia.

The relatively large, but superficially similar, Lerista macropisthopus, L. connivens, and L. lineopunctulata differ in bodily elongation and limb reduction, inhabit sandy areas, and move under sand. Visual analysis and computer-generated excursion and curvature graphs show that each species moves differently on smooth and rough surfaces, on surfaces with and without nails, and in channels. The reduced-limbed quadruped, Lerista macropisthopus walks frequently, using its four clawed limbs, whenever traction is available. Its undulating body curves uniformly but never generates slide-pushing curves. The biped L. connivens walks with its hindlimbs, although less frequently, and/or oscillates its tail in propelling its relatively stiff, short body. The biped L. lineopunctulata rarely uses its hindlimbs but always undulates body and. tail. It can use single nails in cam-follower progression. L. macropisthopus and L. connivens walk well in channels with rough bottoms, but only L lineopunctulata uses tunnel concertina to travel in channels with smooth bottoms. Friction of body surfaces dragged and of those transmitting propulsive forces is critical to these lizards and explains the division of movement into slow and rapid progression rates. Animals that have clawed limbs, no matter how reduced, use them. Body and tail generally are used differently. The tail may be flipped anteriorly to facilitate concertina. In nail arrays, travel is by simple, never by lateral, undulation. Apparently distinct motor coordination patterns are associated with differences in morphology, habit, and habitat. © 1994 Wiley-Liss, Inc.

Variations in the distribution of motor end-plates in the avian pectoralis.

Most avian muscles consist of serially arranged, overlapping fibers that do not extend the length of the muscle. This condition appears to be plesiomorphic with respect to diapsid reptiles. The presence of this serialfibered architecture is evidenced by bands of stained motor end-plates (meps) perpendicular to the columns of fibers and dividing each column into a series of "segments." The avian pectoralis was chosen for a study of variation in the distribution of meps within a single muscle. We report the interspecific variation for 158 specimens in 63 species. We also use additional specimens to examine intraspecific variation. Setting aside hummingbirds, which have an unique and clearly derived condition, the number of mep bands along a column of fibers near the shoulder falls within a remarkably small range. The number of segments is not obviously related to phylogenetic relatedness or to any characteristic of flight or ecology and is only slightly related to size. The largest specimens do average more segments per column, but there are no trends among small to medium-sized species, suggesting that there is an upper limit to fiber length. However, the shape of the sternum and pattern of connective tissue in the pectoralis alleviate the need for additional fibers in many large birds. These findings suggest that the architecture of the avian pectoralis is subject to some as yet unexplained selection that stabilizes the number of myofibers and/or motor neurons. The findings provide few clues as to whether the significant factors are phylogenetic, functional, ontogenetic, or some combination of these. © 1993 Wiley-Liss, Inc.

Phylogenetic relationships and molecular evolution in uropeltid snakes (Serpentes: Uropeltidae): allozymes and albumin immunology.

Multilocus electrophoretic methods and microcomplement fixation comparisons of serum albumin are used to assess phylogenetic relationships among species of uropeltid snakes, to infer aspects of their population biology and biogeography, and to evaluate their relationships to other primitive snakes (Henophidia). There is very good agreement between phylogenetic inferences derived from the electrophoretic data and those derived from the albumin immunological data. Protein variation detected by electrophoresis is relatively high among 17 operational taxonomic units (OTUs) examined. The mean number of alleles per locus (5.1 across all OTUs), levels of polymorphism (25% of loci), and heterozygosity (4-6%), are typical of, or greater than, values reported for other snakes. Species of uropeltids are genetically highly differentiated, as measured by genetic distances (lowest interspecific Nei's unbiased genetic distances, 0.22-0.27 among several Sri Lankan species; 2.3 between Teretrurus of India and other uropeltines). The phylogenetic tree most consistent with both the immunological and electrophoretic data shows uropeltines from Sri Lanka to be monophyletic, but the Indian species are paraphyletic with respect to those from Sri Lanka. Rhinophis travancoricus of India is inferred to be the sister taxon to the Sri Lankan radiation. As the genera are presently understood, neither Rhinophis nor Uropeltis appears to be monophyletic. A biogeographic scenario derived from the phylogenetic hypothesis suggests an early diversification of uropeltids in India, followed by a single invasion into the lowlands of Sri Lanka. Subsequent evolution on Sri Lanka resulted in occupation of montane biotopes. Cylindrophis is the sister group to uropeltines and is considered a member of the Uropeltidae. The immunological data indicate no phylogenetic association between uropeltids and other 'anilioid' taxa, specifically Anilius, Loxocemus or Xenopeltis, although we cannot rule out a very remote relationship. We specifically reject the hypothesis that uropeltines and scolecophidians form a clade relative to henophidians. High levels of genetic variation and a trend toward negative FIS values for polymorphic loci in three populations suggest generally large effective population sizes and outbreeding in these species. The niche-width variation hypothesis for allozyme loci is not supported by the uropeltid data. In comparison to other vertebrates, the relationship between Nei's genetic distance and albumin immunological distance in uropeltids suggests either conservative albumin evolution or strong differentiation at electrophoretic loci.

Mastication in the tuatara, Sphenodon punctatus (reptilia: Rhynchocephalia): Structure and activity of the motor system.

The masticatory pattern of Sphenodon punctatus, the sole remaining rhynchocephalian, now restricted to islands off the coast of New Zealand, has been analyzed by detailed anatomy, cinematography, cinefluoroscopy, and electromyography. Food reduction consists of a closing, crushing bite followed by a propalineal sliding of the dentary row between the maxillary and palatine ones. The large, fleshy tongue can be protruded to pick up small prey, and also plays a major role in prey manipulation. The rotational closing movement of the jaw, supporting the basic crushing movement, is induced by the main adductor musculature. It is followed by a propalineal anterior displacement relying heavily on the action of the M. pterygoideus. The fiber lengths of the several muscles reflect the extent of shortening. The most obvious modification appears in the M. pterygoideus, which contains a central slip of pinnately arranged short fibers that act a period different from that of the rest of the muscle; their action increases the power during the terminal portion of the propalineal phase. This also allows the animal to use its short teeth in an effective shearing bite that cuts fragments off large prey. The action of single cusped dentary teeth acting between the maxillary and palatine tooth rows provides a translational crushing-cutting action that may be an analog of the mammalian molar pattern. However, this strictly fore-aft slide does not incorporate capacity for later development of lateral movement.