A New Species Of The Late Triassic Rhynchosaur Hyperodapedon From The Santa Maria Formation Of South Brazil

A new rhynchosaur, Hyperodapedon huenei sp. nov., is described from the Upper Triassic Santa Maria Formation of the Paraná Basin, Brazil. The holotype is an almost complete skull and mandible, collected at Inhamandá, in the state of Rio Grande do Sul, Brazil. The diagnosis of the genus Hyperodapedon Huxley is revised to include not only H. huxleyi Lydekker and H. gordoni Huxley (as generally accepted), but also the new species described here, various specimens usually assigned to ' Scaphonyx fischeri ' Woodward, and ' S '. sanjuanensis Sill. H. huenei sp. nov. exhibits a number of plesiomorphic features and appears to be the least derived species of Hyperodapedon , forming a sister taxon to the remaining members of the genus. A preliminary phylogenetic analysis for the more derived rhynchosaurs is presented. ' Scaphonyx ' sulcognathus Azevedo and Schultz represents the sister taxon of Hyperodapedon , while ' Rhynchosaurus ' spenceri Benton is considered to be a more derived Middle Triassic rhynchosaur. key words : Rhynchosauria, Hyperodapedon , Triassic, Brazil.     

Autopodial development in the sea turtles Chelonia mydas and Caretta caretta

The manus and pes were studied using whole-mount and histological preparations of ontogenetic series of Chelonia mydas and Caretta caretta. Patterns of connectivity and sequences of chondrification events are similar to those reported for other turtle species, with respect to both the primary axis and the digital arch. There is no evidence of anterior condensations in the region distal to the radius and the tibia, supporting the hypothesis that the radiale and tibiale are absent in turtles. The three middle metacarpals are the first elements to start ossification in the manus of C. mydas, while ossification has not started in the pes. In the hatchling of C. mydas, most carpals have started ossification, whereas tarsals are mostly still cartilaginous. In C. caretta, the first carpals to ossify are the ulnare and intermedium, followed by the pisiform. Among metatarsals, the fifth hooked metatarsal is the last one to start ossification. The fibulare and intermedium fuse early in chondrogenesis, later becoming the astragalocalcaneum. Ossification in the carpals of C. caretta starts while tarsals are still cartilaginous. The derived autopodial proportions in each autopodium of adults are laid out at the condensation stage, and features that were present in basal turtles are absent at all stages examined (developmental penetrance). In contrast to this, conservatism is expressed in the presence of similar patterns of connectivity during early chondrogenesis, and in the development of overall proportions of the manus versus pes. As in adult anatomy, the development of the autopodium of marine turtles is a mosaic of derived and plesiomorphic features.     

Heterochronic differences of Hoxa-11 expression in Xenopus fore- and hind limb development: Evidence for lower limb identity of the anuran ankle bones

 The wrist (carpus) and ankle (tarsus) of most tetrapods, as well as the wrist of anurans, contains relatively small nodular skeletal elements. The anuran tarsus, however, comprises a pair of long bones, the proximal tarsals tibiale and fibulare, which resemble the lower leg bones, tibia and fibula (zeugopodium). In this paper we investigate whether the proximal tarsals of Xenopus are of zeugopodial character identity, i.e. whether they develop under the influence of the same genes that pattern the lower limb. We compare Hoxa-11 expression in the forelimb bud with that in the hind limb bud by whole-mount in situ hybridization. Hoxa-11 has been implicated in the development of the lower limb. In Xenopus we note three differences between Hoxa-11 expression in fore- and hind limb buds: (1) Hoxa-11 expression is maintained until the hind limb bud reaches a larger size (2 mm) than that of the forelimb bud (1.5 mm); (2) Hoxa-11 expression is maintained over larger spatial domains than in the forelimb; and (3) Hoxa-11 expression has a pronounced posterior polarity in the hind limb, but not in the forelimb. Hind limb expression of Hoxa-11 can be understood as a heterochronic prolonging of the expression dynamic in the forelimb. Finally we found that the proximal tarsals start to develop within the expression domain of Hoxa-11, while in the forelimb the lower arm elements reach the distal expression limit of Hoxa-11. The gene expression data presented here support the notion of a zeugopodial identity of the proximal tarsal elements in Xenopus. Received: 20 January 1998 / Accepted: 27 March 1998     

Developmental basis of limb homology in Pleurodiran turtles,and the identity of the hooked element in the chelonian tarsus

Although Pleurodiran turtles represent an important component of extant turtle radiation, our knowledge of the development and homology of limb bones in turtles rests mostly upon observations made on derived members of the Cryptodiran clade. Herein, we describe limb development in three pleurodirans: Podocnemis unifilis Troschel, 1848, Podocnemis sextuberculata Cornalia, 1849 and Phrynops hilarii (Dumeril and Bibron, 1835), in an effort to contribute to filling this anatomical gap. For earlier stages of limb development, we described the Y‐shaped condensation that gave rise to the zeugopodial cartilages, and differentiation of the primary axis/digital arch that reveals the invariant pattern common to tetrapods. There are up to four central cartilaginous foci in the carpus, and the proximal tarsale is formed by the fusion of the fibulare, intermedium, and centrale 4. Digital development is similar for the five digits. Changes in toe V occur predominantly in the distal tarsale 5. Ontogenetic reduction of phalanges is observed in toe V of Podocnemis. Based on these results, we suggest that the hooked element present in the chelonian tarsus, and traditionally recognized as a modified fifth metatarsale, is actually the fifth distal tarsale. Additionally, our data on limb development of pleurodiran turtles supply more taxonomically comprehensive information to interpret limb configuration within the chelonian clade. © 2009 The Linnean Society of London, Zoological Journal of the Linnean Society, 2009, 155 , 845–866.     

Principal component analysis of the elongation of metacarpal and phalangeal bones

A hypothesis that the first principal component computed from the covariance matrix of logarithms reflected the specific growth rates of corresponding bones was taken to analyze the growth pattern of the tubular bones of the hand. The total length of 19 tubular bones of the right hand was measured on standardized radiographs of Japanese children (33 boys, 33 girls). Metacarpals in boys and bones of the fifth digit in girls showed higher growth coefficients. The second, third and fourth proximal, and the third and fourth middle phalanges showed lower coefficients for both sexes. These observations suggest the signs of proximal row dominance in boys and of fifth ray dominance in girls in the elongation of the hand bones. A marked sex difference was found in the fifth middle phalanx. In girls the growth coefficients of this bone was much larger than any other bones, but was moderate in boys.     

Limb development in the gekkonid lizard gonatodes albogularis: A reconsideration of homology in the lizard carpus and tarsus

Despite the attention squamate lizards have received in the study of digit and limb loss, little is known about limb morphogenesis in pentadactyl lizards. Recent developmental studies have provided a basis for understanding lizard autopodial element homology based on developmental and comparative anatomy. In addition, the composition and identity of some carpal and tarsal elements of lizard limbs, and reptiles in general, have been the theme of discussions about their homology compared to non‐squamate Lepidosauromorpha and basal Amniota. The study of additional embryonic material from different lizard families may improve our understanding of squamate limb evolution. Here, we analyze limb morphogenesis in the gekkonid lizard Gonatodes albogularis describing patterns of chondrogenesis and ossification from early stages of embryonic development to hatchlings. Our results are in general agreement with previous developmental studies, but we also show that limb development in squamates probably involves more chondrogenic elements for carpal and tarsal morphogenesis, as previously recognized on the grounds of comparative anatomy. We provide evidence for the transitory presence of distal carpale 1 and intermedium in the carpus and tibiale, intermedium, distal centralia, and distal tarsale 2 in the tarsus. Hence, we demonstrate that some elements that were believed to be lost in squamate evolution are conserved as transitory elements during limb development. However, these elements do not represent just phylogenetic burden but may be important for the morphogenesis of the lizard autopodium. J. Morphol., 2010. © 2010 Wiley‐Liss, Inc.     

Patterns of chondrogenesis and calcification in the developing limb of the lizard,Calotes versicolor

The first skeletal condensation appears deep at the base of the limb bud near the somites, when the apical ectodermal ridge (AER) is maximally developed. Thereafter the skeletal elements generally appear in a proximodistal sequence but most of the mesopodial cartilages appear well after the metapodial ones and one of them, tarsalia-1, even after the phalangeal ones. The skeletal elements that fuse or “disappear” during the development are the cartilaginous condensation of fibulare, and the precartilaginous condensation of the distal centrale in the tarsus, and possibly the mesenchymatous condensation of the intermedium in the carpus. The calcification of all the long cartilages is perichondral and osseous while that of all the mesopodial and other cartilages, like epiphyses and sesamoids, is endochondral and nonosseous except the partly osseous astragalus and fibulare. The limbs of the mature adult have many sesamoids and metaplastic calcifications. The AER starts regressing after the appearance of the first skeletal condensation but is retained on the digital tips, though in a moderately regressed condition, almost till the time of the appearance of all the phalangeal condensations. These studies on the mesopodium differ with most studies on reptilian and avian mesopodia in favoring the view that very few skeletal condensations fuse or disappear during the development. They thus raise important issues concerning the ontogeny and phylogeny of the pentadactyl limb. While the AER has a substantial role in the limb morphogenesis, it most probably is not responsible for the information to mesoderm regarding the number, size, shape and relative position of the skeletal elements in the limb.     

History of Ichnology: The Misconceived Footprints of Rhynchosaurs

In 1842 Richard Owen described a Triassic reptile from Grinshill, Shropshire, which he named Rhynchosaurus articeps. He suggested that footprints found in the same beds were those of this fossil. However, the footprints were characterised by a backward-pointing toe and so were of the type now known as Rotodactylus. Huxley (1877), Woodward (1907), and Benton (1990) have subsequently shown that the five digits of Rhynchosaurus point forward and so could not have left these footprints. In 1896 Beasley classified the Triassic footprints found in Cheshire, his type D prints being those earlier assigned to rhynchosaurs. His D1 prints were named Rhynchosauroides articeps by Maidwell (1911). However, these D1 prints, which come from a lower horizon in the Anisian, are consistently too small to match Owen's fossil. Beasley's D3 form, now named Synaptichnium pseudosuchoides Nopcsa, is more likely to represent the footprints of Rhynchosaurus articeps, although further research and study of more complete trackways will be necessary to clarify whether these are the footprints of Archosauromorphs, such as rhynchosaurs or possibly those of Archosauriformes, for example, erythrosuchids or proterosuchids. Maidwell's Rhynchosauroides rectipes and Rhynchosauroides membranipes, originally believed to be distinct ichnospecies, are more likely to be synonyms, their apparent differences reflecting variations in the substrate traversed.     

Increased SCE levels in Mediterranean Italian buffaloes affected by limb malformation (transversal hemimelia)

In recent years some buffalo farms in Campania have reported the birth of calves with limb malformation, especially with transversal hemimelia. We investigated 20 Mediterranean Italian buffaloes (8 males and 12 females) from one day to six months of age, of which 10 were affected by transversal hemimelia (group 1) and 10 were healthy controls (group 2). The following clinical and radiological patterns were observed in the malformed animals: hind limbs amputated, the right amputated off the second tarsus bones and the left amputated off the proximal epiphysis metatarsus, and the right thoracic limb hypoplasic (1 female); left hind limb amputated off the proximal epiphysis metatarsus (2 females and 1 male); left hind limb amputated off the third tarsus bones (1 female); left hind limb amputated off the tibia (1 female and 1 male); left hind limb amputated off the distal epiphysis metatarsus (1 female); left hind limb amputated off the first phalanx (1 male); right hind limb amputated off the proximal epiphysis metatarsus (1 male). In their malformed limbs all the animals presented more or less developed outlines of claws. The mean rate of SCE/cell in animals with transversal hemimelia was 8.80 +/- 3.19, that of the controls 6.61 +/- 2.73. The difference was statistically significant (P < 0.001).     

The problem of the number of tarsomeres in the regenerated cockroach leg.

There are 5 tarsomeres in the normal cockroach leg, but this number is often reduced in regenerated legs. In order to examine this complicated situation, fore-, mid-, and hindlegs of German cockroaches were amputated at 11 different tarsal levels and at 18 different times during the last instar. When tarsi were amputated at or proximal to the 3rd tarsomere, 4-segmented tarsi regenerated. When legs were amputated distal to the 3rd tarsomere, the regenerated tarsi had 5 segments. Three-segmented tarsi rarely regenerated when legs were amputated proximal to 3rd tarsomere and in the latter half of the instar period. The lengths of all tarsomeres of regenerated tarsi were measured together with those of unoperated contralateral tarsomeres, and the ratios of the former to the latter were calculated. The ratios ranged from 28 to 138% for the various tarsomeres and levels of amputation. From a comparison of the ratios and morphological observations, it was suggested that the 3rd tarsomere of the normal 5-segmented tarsus has disappeared in the regenerated 4-segmented tarsus. Pads and disto-lateral spines of tarsomeres were observed on unoperated and regenerated tarsi. It was of interest that double spines were often found on the 4-segmented tarsi, mostly on the 2nd tarsomere, just proximal to the position of the missing 3rd tarsomere. This observation supported the idea that the 3rd tarsomere has not simply disappeared, but has probably fused with the 2nd tarsomere.     

Formation and specification of distal leg segments in Drosophila by dual Bar homeobox genes, BarH1 and BarH2

Here, we show that BarH1 and BarH2, a pair of Bar homeobox genes, play essential roles in the formation and specification of the distal leg segments of Drosophila. In early third instar, juxtaposition of Bar-positive and Bar-negative tissues causes central folding that may separate future tarsal segments 2 from 3, while juxtaposition of tissues differentially expressing Bar homeobox genes at later stages gives rise to segmental boundaries of distal tarsi including the tarsus/pretarsus boundary. Tarsus/pretarsus boundary formation requires at least two different Bar functions, early antagonistic interactions with a pretarsus-specific homeobox gene, aristaless, and the subsequent induction of Fas II expression in pretarsus cells abutting tarsal segment 5. Bar homeobox genes are also required for specification of distal tarsi. Bar expression requires Distal-less but not dachshund, while early circular dachshund expression is delimited interiorly by BarH1 and BarH2.     

The ossification centers in the lower end of tibiotarsus in domestic fowl.

The morphogenesis of lower end of tibia in chick is studied commonly but the process of ossification of the same has received very little attention so far. The present study is directed to throw some light on the appearance of ossification centers in the lower end of tibiotarsus of chick. The histology of lower end of tibiotarsus was studied by procuring developing tibiotarsi from chick embryos (20) of 6th day incubation till hatching and 3 post hatched chicks. The transparancies of chick embryos at different incubation periods and post hatched chicks were prepared by Dawson's Alizarin staining method. Three cartilage center (tibial, fibulare and intermedium) appeared in 6...9 days of incubation period in the tarsal region. These gradually fused with the lower end of tibia. Three ossification centres developed in the lower end of tibiotarsus. One for intermedium appeared on 16th day and two fotibial and fibulare on 20th day. All these three centres could be located in the transparancies of the chick embryos in tarsal region. The present study proves that the three cartilages centres maintain their individuality during the ossification process even though those fuse completely with the lower end of tibia in chick. The centers for tibial and fibulare are similar to epiphyseal centres of mammals in histological details.     

Anatomical features associated with preaxial duplication (pd): a recessive mutation in the rat

Preaxial polydactyly of the fore- and hindlimbs was found in Wistar-derived rats in 1978. Genetic analysis indicated that the polydactyly was due to the effects of an autosomal recessive gene (gene symbol; pd). Polydactylous homozygous rats had two or three pollices (six or seven digits) in the forelimbs and one to three preaxial extra digits (six to eight digits) in the hindlimbs. Skeletal examination revealed the presence of the extra carpal, metacarpal, and phalangeal bones that seemed to be complete or incomplete duplication of the navicular, greater multangular, first metacarpal, and phalanges of digit I in the forelimbs. In the hindlimbs, extra tarsal, metatarsal, and phalangeal bones were also observed preaxially. These extra elements seemed to be mirror-image duplications of the talus, navicular, second cuneiform, third cuneiform, cuboid, and metatarsals and phalanges of digits II-V with the absence of the first cuneiform, tibiale, first metatarsal, and phalanges of digit I. In addition, morphological changes were observed in the humerus, radius, and ulna in the forelimbs and femur, tibia, and fibula in the hindlimbs. Especially in the radius and tibia, thickening and bifurcation were found, indicating incomplete duplication of these bones. Based on these findings, the limb anomaly was classified as preaxial carpometacarpal/tarsometatarsal-type polydactyly with incomplete duplication of the radius and tibia. The mutant rats had other associated anomalies such as accessory spleens and cryptorchism. The males are sterile, whereas the females breed normally.     

Molecular development of fibular reduction in birds and its evolution from dinosaurs

Birds have a distally reduced, splinter‐like fibula that is shorter than the tibia. In embryonic development, both skeletal elements start out with similar lengths. We examined molecular markers of cartilage differentiation in chicken embryos. We found that the distal end of the fibula expresses Indian hedgehog (IHH), undergoing terminal cartilage differentiation, and almost no Parathyroid‐related protein (PTHrP), which is required to develop a proliferative growth plate (epiphysis). Reduction of the distal fibula may be influenced earlier by its close contact with the nearby fibulare, which strongly expresses PTHrP. The epiphysis‐like fibulare however then separates from the fibula, which fails to maintain a distal growth plate, and fibular reduction ensues. Experimental downregulation of IHH signaling at a postmorphogenetic stage led to a tibia and fibula of equal length: The fibula is longer than in controls and fused to the fibulare, whereas the tibia is shorter and bent. We propose that the presence of a distal fibular epiphysis may constrain greater growth in the tibia. Accordingly, many Mesozoic birds show a fibula that has lost its distal epiphysis, but remains almost as long as the tibia, suggesting that loss of the fibulare preceded and allowed subsequent evolution of great fibulo–tibial disparity.     

Insect walking techniques on thin stems

The attachment ability of insects on surfaces are associated not only with the micro- and nanostructure of the adhering part of an attachment device, but also with the global scale kinematics responsible for contact formation and release. In the present study, the locomotory techniques of several representatives of insects from four different orders (Orthoptera, Heteroptera, Coleoptera, and Hymenoptera), possessing different types of attachment structures, are described. The study is based on video recordings of insects walking on a flat surface and on cylindrical rods of various thickness, imitating plant stems. Attachment devices of tarsi and pretarsi were visualized using Scanning Electron Microscopy. The results show a different manner in the use of adhesive structures on substrates with various curvatures. Insects bearing attachment pads on proximal tarsomeres usually touch flat and curved substrates using all tarsomeres, whereas insects with their attachment devices on the distal tarsomeres usually walk on flat surfaces using the distal tarsomeres of the overextended tarsus. On substrates, with diameters comparable to or larger than the tarsus length, insects walk above the stem by clasping the stem with the bent tarsi. On thin stems, insects clasp the stem between their tarsi and hang under the stem. Thus, on thin and thick rods, forces applied to attachment organs act in opposite directions. There are two methods of leg positioning for walking on a rough flat substrate. In the first case, the tarsus is straightened and the rough substrate is gripped between the claws and the proximal complex of attachment devices (tarsal euplantulae, fossulae spongiosa, and terminal spurs of tibiae). In the second case the tibia does not touch the substrate; the insect is supported only by distal tarsomeres. The tarsus is in an overextended condition. On rods, with diameters comparable to or larger than the tarsus length, insects walk by clasping the stem with the bent tarsi. This posture is characteristic for the majority of insects independent of the tarsal position they normally use while walking on a plane. If the rod’s diameter is smaller than the tarsus length, walking insects usually clutch it between contralateral tarsi. Using such a posture they are supported by interlocking or by strong friction, generated by attachment devices of the proximal tarsomeres, and do not use attachment devices of the pretarsus. Contact with the substrate is reinforced due to the coordinated contralateral clutch using all supporting legs. It is concluded that the use of different types of attachment structures correlates with locomotory techniques. Handling Editor: Heikki Hokkanen     

Tubular hand bone growth during the latter half of the prenatal period: an allometric analysis

The growth of the 19 tubular hand bones from fetal months 5 to 9 was studied by the allometric method. The hand bones were carefully dissected under a low power stereoscopic microscope. The length and breadth of all bones was found to be monophasic in relation to crown-rump length. In general, maximum bone and ossified shaft lengths in the same row group demonstrate similar allometric coefficients. The specific growth rate of ossified shaft length for all fetal hand bones is greater than the growth rate of maximum length. The highest allometric coefficients for both maximum length and ossified shaft length were obtained from the middle phalanges. The shape of the metacarpals and distal phalanges becomes thinner, while the other bones become thicker or maintain their length-breadth ratio. The relative growth pattern of the first proximal phalanx differed from the middle phalangeal group of the other digits. This suggests that current nomenclatures for the three bones of the pollex is appropriate.     

Skeletal evidence for kneeling in prehistoric Ecuador.

Bony changes on the superior distal surface of the metatarsals and the superior proximal surface of the first proximal foot phalanx are described in a prehistoric skeletal sample from Coastal Ecuador. The location and morphology of the alterations, as well as their association with femoral "squatting facets" strongly suggests they were produced by prolonged hyperdorsiflexion of the toes, probably resulting from habitual kneeling posture. Comparative data are presented from five other New World skeletal samples.