Sexual dimorphism in large-bodied primates: The case of the subfossil lemurs

Large body size has evolved repeatedly in the order Primates, not merely among anthropoids but also among prosimians. Whereas high degrees of sexual size dimorphism characterize many of the large-bodied anthropoids, this is not the case for extinct large-bodied lemurs. This paper uses finite mixture analysis and other techniques to ascertain just how much skull length dimorphism might be embedded in the generally unimodal distributions of skull lengths of giant extinct lemurs from single localities, and then compares these results with known skull length dimorphisms in extant lemurs and large-bodied catarrhines. We show that low levels of skull length sexual dimorphism (or none at all) characterize subfossil lemurs, and we explore several possible explanations for this phenomenon. Traditional explanations of sexual size dimorphism generally focus on body size or mating systems. These are not sufficient to explain the variation in sexual dimorphism that can be observed in the order Primates. © 1993 Wiley-Liss, Inc.     

Garden dormouse (Eliomys quercinus, Linnaeus 1766) without fenestration in angular process

One of the skull traits that separates the Leithiinae subfamily from other subfamilies of Gliridae family is a prominent fenestration in the angular process of the mandible. There is no reference in the literature of dormice from Leithiinae subfamily without this fenestration. However, some garden dormice (Eliomys quercinus) have been found without this fenestration in Spain. This lack of perforation may be due to an ossification of the angular process related to bone growth. Garden dormice skulls from different parts of Spain kept in two mammal collections were revised in order to detect animals without fenestration and to take measures that differ between young and adult dormice. The measures recorded did not differ between dormice with and without fenestration, and so, the entire angular process is not the result of an ossification process. Thus, the discovery of specimens without fenestration in the angular process should be taken into account in studies which need the identification of this species and other species from Leithiinae subfamily based on skull and mandibles traits.     

PROBLEMS OF THE ORIGIN OF REPTILES

The fossil records of the four living reptilian orders can be traced into the Triassic. The earlier ancestry of the turtles has not been established. Squamates and rhyncho-cephalians evolved from the Late Permian eosuchians; crocodiles from the thecodonts. The ancestry of the eosuchians and thecodonts is to be found in the central stock of Permo-Carboniferous reptiles, the captorhinomorphs. The earliest captorhino-morphs, from the Lower Pennsylvanian, are already fully developed reptiles. The limnoscelids and solenodonsaurids are more primitive forms, retaining features typical of anthracosaurian amphibians. Neither reptiles nor any appropriate ancestors are known prior to the Lower Pennsylvanian. Because of the absence of any true ancestors, the nature of the amphibian-reptilian transition must be studied on the basis of amphibians contemporary with the early reptiles. The Permian seymouriamorphs have long been accepted as relicts of the group which gave rise to reptiles, although Seymouria itself is specialized in many features of its anatomy. The Middle Pennsylvanian genus Gephyrostegus appears to resemble much more closely the anatomy expected in the ancestors of reptiles. This genus forms the basis for consideration of the anatomical, physiological and behavioural changes which culminated in the origin of reptiles. Study of the earliest known reptiles and their closest relatives among contemporary amphibians indicates that the initial adaptation leading to the emergence of the class was assumption of a terrestrial habit, with accompanying small body size. The small body size of the immediate ancestors of reptiles would have made it possible for them to produce sufficiently small eggs that they could develop in damp places on land without initially being supported and protected by extraembryonic membranes. The rapid increase in body size in all lineages of Pennsylvanian reptiles indicates the prior development of an amniotic egg. Fundamental to the emergence of reptiles was modification in the jaw mechanism from the kinetic inertial system of amphibians to a static pressure system. The latter was presumably developed in order for the developing reptiles to utilize more active terrestrial prey. This change in the jaw mechanism is reflected in the reorganization of the palate which serves as a morphological basis for denning the establishment of reptilian status. At approximately the same stage as the change in palatal structure, the definitive reptilian vertebral pattern was developed. The apparent closure of the otic notch and the probable reorientation of the stapes in the amphibian-reptilian transition presumably resulted from the decrease in relative skull size and do not appear to be related to any change in hearing ability. The tympanum probably maintained the same relative relationship with the squamosal and supratemporal throughout this transition. On the basis of the present fossil record, all adequately known Palaeozoic reptiles appear to have had a common ancestry among the predecessors of the known gephyro-stegids. The family Diadectidae is the only important group whose specific relationships cannot be established. On the basis of this study, the following taxonomic changes are suggested: the family Limnoscelidae should not be included among the captorhinomorphs. The seymouria-morph concept should be restricted to forms having the specializations of Seymouria, the discosauriscids and kotlassids. Gephyrostegids should be specifically excluded from the Seymouriamorpha and should be included in a separate taxon among the anthra-cosaurs of equal rank with embolomeres and seymouriamorphs.     

Creating morphological diversity in reptilian temporal skull region: A review of potential developmental mechanisms

Reptilian skull morphology is highly diverse and broadly categorized into three categories based on the number and position of the temporal fenestrations: anapsid, synapsid, and diapsid. According to recent phylogenetic analysis, temporal fenestrations evolved twice independently in amniotes, once in Synapsida and once in Diapsida. Although functional aspects underlying the evolution of tetrapod temporal fenestrations have been well investigated, few studies have investigated the developmental mechanisms responsible for differences in the pattern of temporal skull region. To determine what these mechanisms might be, we first examined how the five temporal bones develop by comparing embryonic cranial osteogenesis between representative extant reptilian species. The pattern of temporal skull region may depend on differences in temporal bone growth rate and growth direction during ontogeny. Next, we compared the histogenesis patterns and the expression of two key osteogenic genes, Runx2 and Msx2, in the temporal region of the representative reptilian embryos. Our comparative analyses suggest that the embryonic histological condition of the domain where temporal fenestrations would form predicts temporal skull morphology in adults and regulatory modifications of Runx2 and Msx2 expression in osteogenic mesenchymal precursor cells are likely involved in generating morphological diversity in the temporal skull region of reptiles.     

Lerista bougainvillii,a case study for the evolution of viviparity in reptiles

Many factors, both environmental and biotic, have been suggested to facilitate or hinder the evolution of viviparity (live-bearing) in reptiles. Viviparity has evolved recently within the Australian scincid lizard Lerista bougainvillii and the species includes oviparous, viviparous, and reproductively intermediate (with prolonged egg retention) populations; thus, it offers an exceptional opportunity to evaluate the validity of these hypotheses. We carried out such tests by (i) comparing environmental conditions over the geographic ranges occupied by oviparous, viviparous, and intermediate populations (to identify possible selective forces for the evolution of viviparity), and (ii) comparing morphological, reproductive and ecological traits of L. bougainvillii with those of other sympatric scincid species (to identify traits that may have predisposed this taxon to the evolution of viviparity). The areas occupied by viviparous L. bougainvillii are significantly colder than those occupied by both their intermediate and oviparous conspecifics, in accord with the “cold-climate” hypothesis for reptilian viviparity. Rainfall is similar over the ranges of the three forms. Climatic unpredictability (as assessed by the magnitude of year-to-year thermal variation) is lower for viviparous animals, in contradiction to published speculations. Comparison with 31 sympatric scincid species showed that L. bougainvillii is not atypical for most of the traits we measured (e.g., body size, clutch size, thermal preferenda and tolerances). However, oviparous L. bougainvillii do display several traits that have been suggested to facilitate the evolution of viviparity. For example, pregnancy does not reduce locomotor ability of females; the lizards are semi-fossorial; even the oviparous females produce only a single clutch of eggs per year; and they ovulate relatively late in summer, so that the time available for incubation is limited.     

Theory of negative capacitance in membrane impedance measurements

Summary Three possible explanations of the negative capacitance seen in theChara corallina membrane impedance are critically examined. These explanations are based on: (1) voltage-dependent channel kinetics; (2) electro-osmosis; and (3) extracellular negative capacitance. It is shown that the first two can produce negative capacitance only with parameters which differ by several orders of magnitude from measured values. The last mechanism can produce a very large magnitude negative capacitance, in the appropriate frequency range. Possible experimental tests are discussed.     

Parthenogenetic reproduction in lizards: Histological evidence

Hermaphroditism and sex reversal have not previously been ruled out adequately as possible explanations for the existence of unisexual species of reptiles. Therefore, we examined serial histological sections of the complete urogenital systems of nine F₂ specimens belonging to two ontogenetic series of Cnemidophorus exsanguis raised in captivity in isolation from males, as well as the urogenital system of the F₁ mother of one of these series. No evidence of spermatozoa or testicular tissue was found in any specimen. Comparative material reveals that the histology of the urogenital tract, including the mesonephric kidney in adults, is similar to that of females of bisexual species of Cnemidophorus. We conclude that C. exsanguis is a unisexual, parthenogenetic species whose normal reproduction does not involve sex reversal, self-fertilization, gynogenesis, hybridogenesis, or spermatozoa in any way whatsoever.     

中国晚二叠世原始恐头兽类化石一新属种——甘肃玉门晚二叠世脊椎动物群系列报道之二

记述了甘肃玉门上二叠统西大沟组上部恐头兽类Anteosauridae科一新属新种——玉门中华猎兽(Sinophoneus yumenensis gen.et sp.nov.),该化石与俄罗斯伊舍夫地区Ⅱ带的Titanophoneus处于同一进化水平,其时代应为晚二叠世早期.这是我国首次发现的原始肉食anteosaurid恐头兽类头骨化石,甘肃西部成为继俄罗斯、南非之后该类原始似哺乳爬行动物化石的又一重要产地.     

The atlas-axis complex of the mammal-like reptiles

The atlas-axis complexes of four of the major groups of the mammal-like reptiles are discussed. These represent the four principal types of occipital condyle found in the Synapsida: hemispherical in the pelycosaurs, kidney-shaped in the gorgonopsids, trefoil-shaped in the dicynodonts and double in the cynodonts. In each case the possible movements of the skull are analysed in detail. It is shown that the central theme of the wide variation of this structure found within the synapsid reptiles is the manner in which the problem of achieving rotation of the head about a longitudinal axis was solved.
An attempt is made to elucidate the functional evolution of the atlas-axis complex within these reptiles and the significance of the differences between the reptilian and the mammalian complexes is noted.     

Cranial morphology of the Early Permian mesosaurid Mesosaurus tenuidens and the evolution of the lower temporal fenestration reassessed

The Early Permian mesosaurids are the oldest known aquatic amniotes with an exclusively Gondwanan distribution. Although several hundred of complete skeletons have been discovered and intensively studied, the anatomy and taxonomic composition of the group, as well as its phylogenetic relationships remain controversial. Several well-preserved mesosaurid specimens found in Uruguay justify a new anatomical reconstruction of the skull of Mesosaurus tenuidens, differing from earlier ones especially in the presence of a lower temporal fenestra. The significance of this structure for the evolution of temporal fenestration in amniotes is evaluated according to the two most recent phylogenetic hypotheses, in which mesosaurids are basalmost sauropsids or basalmost parareptiles. A synapsid-like fenestration may be the primitive condition for Amniota, and it may be also a basal condition for parareptiles, because recent phylogenies suggest a basal position for mesosaurids and lanthanosuchoids within that group, and both possess a lower temporal fenestra. Our results also give a moderately strengthened support for diapsid affinities of turtles.     

Morphology of the temporal skull region in tetrapods: research history,functional explanations,and a new comprehensive classification scheme

The morphology of the temporal region in the tetrapod skull traditionally has been a widely discussed feature of vertebrate anatomy. The evolution of different temporal openings in Amniota (mammals, birds, and reptiles), Lissamphibia (frogs, salamanders, and caecilians), and several extinct tetrapod groups has sparked debates on the phylogenetic, developmental, and functional background of this region in the tetrapod skull. This led most famously to the erection of different amniote taxa based on the number and position of temporal fenestrae in their skulls. However, most of these taxa are no longer recognised to represent natural groupings and the morphology of the temporal region is not necessarily an adequate trait for use in the reconstruction of amniote phylogenies. Yet, new fossil finds, most notably of parareptiles and stem-turtles, as well as modern embryological and biomechanical studies continue to provide new insights into the morphological diversity of the temporal region. Here, we introduce a novel comprehensive classification scheme for the various temporal morphotypes in all Tetrapoda that is independent of phylogeny and previous terminology and may facilitate morphological comparisons in future studies. We then review the history of research on the temporal region in the tetrapod skull. We document how, from the early 19th century with the first recognition of differences in the temporal region to the first proposals of phylogenetic relationships and their assessment over the centuries, the phylogenetic perspective on the temporal region has developed, and we highlight the controversies that still remain. We also compare the different functional and developmental drivers proposed for the observed morphological diversity and how the effects of internal and external factors on the structure of the tetrapod skull have been interpreted.     

Water-filled bromeliad as roost site of a tropical lizard,Urostrophus vautieri (Sauria: Leiosauridae)

Bromeliads are a conspicuous component of tropical forests. Whereas several amphibian species are closely associated with bromeliads, reptiles are much less frequently observed in bromeliads and only a few species use bromeliads for egg deposition or as roost site. We report on an adult Urostrophus vautieri that was sleeping in a water-filled bromeliad. The individual was submerged except for head and shoulder. To our knowledge, it is the first time that such behavior has been observed in an arboreal Neotropical lizard.     

Comprehensive DNA barcoding of the herpetofauna of Germany

We present the first comprehensive DNA barcoding study of German reptiles and amphibians representing likewise the first on the European herpetofauna. A total of 248 barcodes for all native species and subspecies in the country and a few additional taxa were obtained in the framework of the projects ‘Barcoding Fauna Bavarica’ (BFB) and ‘German Barcode of Life’ (GBOL). In contrast to many invertebrate groups, the success rate of the identification of mitochondrial lineages representing species via DNA barcode was almost 100% because no cases of Barcode Index Number (BIN) sharing were detected within German native reptiles and amphibians. However, as expected, a reliable identification of the hybridogenetic species complex in the frog genus Pelophylax was not possible. Deep conspecific lineages resulting in the identification of more than one BIN were found in Lissotriton vulgaris, Natrix natrix and the hybridogenetic Pelophylax complex. A high variety of lineages with different BINs was also found in the barcodes of wall lizards (Podarcis muralis), confirming the existence of many introduced lineages and the frequent occurrence of multiple introductions. Besides the reliable species identification of all life stages and even of tissue remains, our study highlights other potential applications of DNA barcoding concerning German amphibians and reptiles, such as the detection of allochthonous lineages, monitoring of gene flow and also noninvasive sampling via environmental DNA. DNA barcoding based on COI has now proven to be a reliable and efficient tool for studying most amphibians and reptiles as it is already for many other organism groups in zoology.     

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.     

Classification and phylogeny of the diapsid reptiles

Reptiles with two temporal openings in the skull are generally divided into two groups–the Lepidosauria (lizards, snakes, Sphenodon , 'eosuchians') and the Archosauria (crocodiles, thecodontians, dinosaurs, pterosaurs). Recent suggestions that these two are not sister-groups are shown to be unproven, whereas there is strong evidence that they form a monophyletic group, the Diapsida, on the basis of several synapomorphies of living and fossil forms. A cladistic analysis of skull and skeletal characters of all described Permo-Triassic diapsid reptiles suggests some significant rearrangements to commonly held views. The genus Petrolacosaurus is the sister-group of all later diapsids which fall into two large groups–the Archosauromorpha (Pterosauria, Rhynchosauria, Prolacertiformes, Archosauria) and the Lepidosauromorpha (Younginiformes, Sphenodontia, Squamata). The pterosaurs are not archosaurs, but they are the sister-group of all other archosauromorphs. There is no close relationship between rhynchosaurs and sphenodontids, nor between Prolacerta or Tanystropheus and lizards. The terms 'Eosuchia', 'Rhynchocephalia' and 'Protorosauria' have become too wide in application and they are not used. A cladistic classification of the Diapsida is given, as well as a phylogenetic tree which uses cladistic and stratigraphic data.     

On the phylogenetic relationships of Vincelestes neuquenianus

This short review paper compares the lower jaw and lower dentition of the small Mesozoic mammal Vincelestes neuquenianus with some other Laurasian and Gondwanan taxa. On this basis a set of 90 characters recognised by recent authors was assembled and used to construct a cladogram. The topology suggests that the early Cretaceous mammal from Patagonia, Vincelestes, is nested within a clade comprising ‘other Gondwanan mammals’, separated from Laurasian taxa. In general, because there is a lack of Mesozoic mammal skulls from Gondwana, meaning that the skull of Vincelestes can only be compared with cranial material from Laurasia, an incomplete understanding of relationships has resulted in earlier studies. The prototribosphenic condition of Vincelestes is supported by the cladistic analysis presented here and permits a number of interesting speculations because it is of later age than Jurassic tribosphenic mammals from Gondwana. It is proposed that the tribosphenic condition may have developed first amongst taxa on Pangea, before the separation of Laurasia and Gondwana.     

AMONG-FAMILY VARIATION FOR ENVIRONMENTAL SEX DETERMINATION IN REPTILES

Unlike birds and mammals, in many reptiles the temperature experienced by a developing embryo determines its gonadal sex. To understand how temperature-dependent sex determination (TSD) evolves, we must first determine the nature of genetic variation for sex ratio. Here, we analyze among-family variation for sex ratio in three TSD species: the American alligator (Alligator mississipiensis), the common snapping turtle (Chelydra serpentina) and the painted turtle (Chrysemys picta). Significant family effects and significant temperature effects were detected in all three species. In addition, family-by-temperature interactions were evident in the alligator and the snapping turtle, but not in the painted turtle. Overall, the among-family variation detected in this study indicates potential for sex-ratio evolution in at least three reptiles with TSD. Consequently, climate change scenarios that are posited on the presumption that sex-ratio evolution in TSD reptiles is genetically constrained may require reevaluation.     

The Liassic ichthyosaur<Emphasis Type="Italic">Stenopterygius</Emphasis> cf.<Emphasis Type="Italic">quadriscissus</Emphasis> from the lower Toarcian of Dobbertin (northeastern Germany) and some considerations on lower Toarcian marine reptile palaeobiogeography

An incomplete skull of the lower Toarcian ichthyosaurStenopterygius cf.quadriscissus is described from the lower Toarcian of Dobbertin (Mecklenburg, northeastern Germany). It represents both the northeasternmost occurrence of this ichthyosaur genus and the first diagnostic specimen from East Germany. It therefore extends the palaeobiogeographic range ofStenopterygius considerably and demonstrates that this ichthyosaur also inhabited the Germanic Basin east of the Rhenish Massif by Early Jurassic times. A palaeobiogeographical pattern is evident within the genusStenopterygius, with the ubiquitous speciesS. longifrons andS. hauffianus on one hand, andS. megalorhinus andS. quadriscissus on the other hand, which appear not to have ranged northwest of the London-Brabant Massif. It is suggested that, whereas the Rhenish Massif was not an effective barrier for dispersal of ichthyosaurs in Western Europe during early Toarcian times, the London-Brabant Massif played a rather significant role, as is also shown by the fossil record of other marine reptile groups. A provincialism of early Toarcian marine reptiles is suggested for Western Europe, with a northwestern province which contains the British occurrences, an intermediate, Subgermanic province in France and the Benelux countries, and a southeastern province in the Germanic Basin. The British and Germanic provinces are each characterized by a typical assemblage of ichthyosaurs, plesiosaurs, and marine crocodiles, wheres the intermediate Subgermanic region shows an intermingling of faunal elements.