Stance and gait in the flesh-eating dinosaur Tyrannosaurus

A study of the stance and locomotion of Tyrannosaurus was made for the mounting of the partial skeleton at the British Museum (Natural History). This shows that the posture was much more bird-like than is indicated by previous mounts, and also the tail is shorter. During walking the vertebral column was held nearly horizontal with the tail clear of the ground. The fore-limbs acted as struts to stop the body sliding forward as the animal raised its body from the resting position.     

Stance and gait in the flesh-eating dinosaur Tyrannosaurus

A study of the stance and locomotion of Tyrannosaurus was made for the mounting of the partial skeleton at the British Museum (Natural History). This shows that the posture was much more bird-like than is indicated by previous mounts, and also the tail is shorter. During walking the vertebral column was held nearly horizontal with the tail clear of the ground. The fore-limbs acted as struts to stop the body sliding forward as the animal raised its body from the resting position.     

The cranial anatomy and relationships of Secodontosaurus, an unusual mammal-like reptile (Synapsida: Sphenacodontidae) from the early Permian of Texas

The cranial anatomy of the Early Permian sphenacodontid synapsid Secodontosaurus is redescribed. There is no evidence for recognition of more than one species of Secodontosaurus, and S. willistoni is declared a junior subjective synonym of S. obtusidens. Numerous derived characters (autapomorphies), mainly related to the unusually slender and slightly elongated skull, distinguish Secodontosaurus. The cranial specializations are interpreted as an adaptation toward a feeding strategy which involved preying upon small tetrapods that attempted to avoid capture by hiding in crevices and burrows. A cladistic analysis supports the following hypotheses of relationships: (a) the Sphenacodontidae is the nearest sister taxon of Therapsida; (b) Secodontosaurus, Sphenacodon, Ctenospondylus and Dimetrodon share a more recent common ancestor with one another than any of them do with Haptodus, and (c) Secodontosaurus shares a more recent common ancestor with Dimetrodon than with either Sphenacodon or Ctenospondylus. The latter hypothesis suggests that the sphenacodont subfamily 'Sphenacodontinae' is paraphyletic and, therefore, invalid.     

Puberty in a Mesozoic reptile

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A Kantian Stance on the Intentional Stance

I examine the way in which Daniel Dennett (1987, 1995) uses his 'intentional'and 'design' stances to make the claim that intentionality is derived fromdesign. I suggest that Dennett is best understood as attempting to supplyan objective, nonintentional, naturalistic rationale for our use of intentionalconcepts. However, I demonstrate that his overall picture presupposesprior application of the intentional stance in a preconditional, ineliminable,'sense-giving' role. Construed as such, Dennett's account is almostidentical to the account of biological teleology offered by Kant in TheCritique of Judgement, with the consequence that Dennett's naturalism isuntenable. My conclusions lead to doubts concerning the legitimacy of anyaccount attempting to naturalise intentionality by extracting normativityfrom biology and also point to a novel account of biological function.     

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.     

Climate warming and the evolution of morphotypes in a reptile

Climate warming is known to have effects on population dynamics through variations in survival, fecundity and density. However, the impacts of climate change on population composition are still poorly documented. Morphotypes are powerful markers to track changes in population composition. In the common lizard, Lacerta vivipara , individuals display two types of dorsal patterns: reticulated (R individuals) and linear (L individuals). We examined how local warming affected intrapopulation frequencies of these morphotypes across 11 years. We observed changes in morph frequency of dorsal patterns across years, paralleling the rise of spring temperatures. The proportion of R individuals increased with June temperatures in juveniles, yearlings, and adult males and females. Three mechanisms could explain these changes: phenotypic plasticity, microevolution and/or dispersal between populations. We investigated the ontogenetic determinism, fitness and recruitment rates associated with dorsal morphotypes. Dorsal pattern ontogeny showed temperature dependence but this relationship was not associated with the warming trend during this study. We found variation by morphotype in survival and clutch size, but these factors did not explain R frequency increases. Among all the parameters considered in this study, only a decrease of immigration, which was more pronounced in the L morphotype, could explain the change in population composition. To our knowledge, this provides the first evidence of the impact of climate warming on population composition due to its effects on immigration.     

Oxygen storage capacity and tolerance of submergence of a non-aquatic reptile and an aquatic reptile

The oxygen storage capacities and the tolerance to submergence of an aquatic snake, Natrix sipedon, and a non-aquatic snake, Crotalus viridis, were determined and compared. C. viridis was found to have a larger oxygen storage capacity, hemoglobin content and blood volume than N. Sipedon. The submergence time for C. viridis was 30.13 min which was less than the estimated time for submergence based on the oxygen storage capacity. N. sipedon exceeded its estimated dive time of 24.00 min and remained submerged for 65.57 min without signs of stress. During submergence, the heart rate of N. sipedon fell to 9% (5 beats/min) of the resting rate, while the heart rate of C. viridis fell to only 75% (27 beats/min) of the resting rate during this activity. These data indicate that N. sipedon responds to submergence via a typical diving reflex and extends its oxygen stores beyond that expected of a non-diver such as C. viridis.     

The origin and early radiation of the therapsid mammal-like reptiles: a palaeobiological hypothesis

The replacement of the basal synapsid pelycosaurs by the more 'mammal-like' therapsids in the Permian was an important event in the history of tetrapods because it initiated the eventual transition to the mammals. It is also an example of taxon replacement in the fossil record that is unusually amenable to explanation, based on a combination of analysis of the biological significance of the inferred character changes, with the stratigraphic, palaeogeographic and palaeoecological circumstances of the time. An hypothesis is presented in which the origin of the therapsids resulted from a correlated progression of character evolution leading to higher levels of metabolic activity and homeostatic regulation of the body. It was a response to the availability of a seasonally arid, savanna-like biome. The subsequent explosive radiation of therapsids was associated with habitat expansion made possible by the Mid-Permian development of geographical continuity between that biome and the temperate biomes. The final extinction of the pelycosaurs was a case of incumbent replacement by the new therapsid lineages.     

三叠纪胎生主龙型海洋爬行动物（英文）

现代爬行动物的生殖方式包括卵生、卵胎生和"胎生"三种类型。总体而言,卵生即母体在陆地上产出羊膜卵,并依靠外界环境加以孵化;卵胎生系指羊膜卵在母体内孵化,随即产出幼子,其间胚胎的营养来源和代谢废物均限于羊膜卵内;所谓"胎生",是指某些类群的卵在母体内孵化后没有立刻产出,胚胎与母体建立了某种程度的营养乃至气体交换关系,此后再以幼体的形式娩出。卵胎生和"胎生"见于有鳞类。在化石中,由于无法识别胚胎与母体的营养联系等信息,通常只以"生产方式"加以定义,即除卵生以外,所有"含胚胎的化石"都统称为"胎生",目前"胎生"已有的准确记录包括鱼龙类、鳍龙类、沧龙类和离龙类。近期报道的"怀孕恐头龙"显示原龙类可能也有此种生殖方式,但标本的保存状态显示不能排除其"同类相食"之可能。本文记述了产自云南罗平地区中三叠系内一独立保存的、完整的圆胚状化石,标本的大小、形态、姿态和埋藏环境显示这是一个处于孵化后期、因某种原因而流产的胚胎。头后骨骼显示该标本代表了一种全新类型的海生原龙类,但是由于在个体发育中很多性状特征会有较大变化,因此胚胎乃至幼体标本不宜作为正型标本而建立新属种。这也是又一个主龙型爬行动物胎生的确切证据;同时这也进一步反映了盘县-罗平动物群中原龙类的高度多样性。     

Telomeres, age and reproduction in a long-lived reptile

A major interest has recently emerged in understanding how telomere shortening, mechanism triggering cell senescence, is linked to organism ageing and life history traits in wild species. However, the links between telomere length and key history traits such as reproductive performances have received little attention and remain unclear to date. The leatherback turtle Dermochelys coriacea is a long-lived species showing rapid growth at early stages of life, one of the highest reproductive outputs observed in vertebrates and a dichotomised reproductive pattern related to migrations lasting 2 or 3 years, supposedly associated with different environmental conditions. Here we tested the prediction of blood telomere shortening with age in this species and investigated the relationship between blood telomere length and reproductive performances in leatherback turtles nesting in French Guiana. We found that blood telomere length did not differ between hatchlings and adults. The absence of blood telomere shortening with age may be related to an early high telomerase activity. This telomere-restoring enzyme was formerly suggested to be involved in preventing early telomere attrition in early fast-growing and long-lived species, including squamate reptiles. We found that within one nesting cycle, adult females having performed shorter migrations prior to the considered nesting season had shorter blood telomeres and lower reproductive output. We propose that shorter blood telomeres may result from higher oxidative stress in individuals breeding more frequently (i.e., higher costs of reproduction) and/or restoring more quickly their body reserves in cooler feeding areas during preceding migration (i.e., higher foraging costs). This first study on telomeres in the giant leatherback turtle suggests that blood telomere length predicts not only survival chances, but also reproductive performances. Telomeres may therefore be a promising new tool to evaluate individual reproductive quality which could be useful in such species of conservation concern.     

Osteocytic osteolysis in a cretaceous reptile.

Bone resorption through osteocytic activity already recognized in all classes of Vertebrates, has been demonstrated in fragments of long bones from a non-identified reptile found in an Upper Cretaceous rock formation in Dinosaur National Park, Patricia, Alberta.     

三叠纪胎生主龙型海洋爬行动物

现代爬行动物的生殖方式包括卵生、卵胎生和“胎生”三种类型.总体而言,卵生即母体在陆地上产出羊膜卵,并依靠外界环境加以孵化;卵胎生系指羊膜卵在母体内孵化,随即产出幼子,其间胚胎的营养来源和代谢废物均限于羊膜卵内;所谓“胎生”,是指某些类群的卵在母体内孵化后没有立刻产出,胚胎与母体建立了某种程度的营养乃至气体交换关系,此后再以幼体的形式娩出.卵胎生和“胎生”见于有鳞类.在化石中,由于无法识别胚胎与母体的营养联系等信息,通常只以“生产方式”加以定义,即除卵生以外,所有“含胚胎的化石”都统称为“胎生”,目前“胎生”已有的准确记录包括鱼龙类、鳍龙类、沧龙类和离龙类.近期报道的“怀孕恐头龙”显示原龙类可能也有此种生殖方式,但标本的保存状态显示不能排除其“同类相食”之可能.本文记述了产自云南罗平地区中三叠系内一独立保存的、完整的圆胚状化石,标本的大小、形态、姿态和埋藏环境显示这是一个处于孵化后期、因某种原因而流产的胚胎.头后骨骼显示该标本代表了一种全新类型的海生原龙类,但是由于在个体发育中很多性状特征会有较大变化,因此胚胎乃至幼体标本不宜作为正型标本而建立新属种.这也是又一个主龙型爬行动物胎生的确切证据;同时这也进一步反映了盘县—罗平动物群中原龙类的高度多样性.     

Thermal benefits from familiarity with the environment in a reptile

Summary The tortoise Testudo hermanni Gmelin is non-territorial, frequents non-personal shelters and is generalist in diet, but stays within a home range very stable in time. Analysis of shell temperatures obtained at set intervals by radiothermometers showed that while tortoises resident in the study area behave as homoiotherms, animals imported from a similar environment appear relatively poikilotherms. Moreover, residents are more efficient in basking, reaching the daily thermal maxima systematically earlier than the unfamiliar animals. These observations support the hypothesis that its home range stability and the associated familiarity with the microenvironment facilitates the behavioural thermoregulation in T. hermanni.     

Implications of flexible-shelled eggs in a Cretaceous choristoderan reptile

Flexible, or soft-shelled, eggs are almost unknown in the fossil record, leaving large gaps in our knowledge of the reproductive biology of many tetrapod clades. Here, we report two flexible-shelled eggs of the hyphalosaurid choristodere Hyphalosaurus baitaigouensis from the Early Cretaceous of China, one containing an embryo and the second associated with a neonate. Choristoderes are an enigmatic group of aquatic reptiles that survived the K–T extinction but died out in the Miocene. Hyphalosaurids, a specialized clade of Choristodera, resemble miniature plesiosaurs and are considered to be primarily aquatic in habit. Scanning electron microscopy of samples from the eggs reveals a thin, non-columnar external mineralized layer characterized by rounded nodes and tentatively identified poorly structured irregular pores, with an underlying amorphous layer presumably representing decomposed protein fibrils. While the relationships of Choristodera remain controversial, eggshell microstructure more closely resembles that of Lepidosauromorpha (the lineage including lizards) as opposed to that of Archosauromorpha (the lineage including birds and crocodiles).     

Family and population effects on disease resistance in a reptile

Despite its importance in evolutionary biology, studies of the pattern of disease resistance in natural populations are rare. In this paper, we report patterns of infection of a viral eye disease in juvenile Swedish common lizards (Lacerta vivipara). Females were sampled at random from natural populations immediately prior to parturition with equal exposure of pathogens for all lizards once in captivity. No causative agents could be found that linked risk of disease to maternal/interfollicular transfer of pathogens. The results show that a major factor influencing offspring susceptibility is family identity, suggesting heritable variation in pathogen resistance. Our interpopulation comparison provides additional support for a link between genetics and disease resistance. Lizards in northern Sweden were not only more susceptible to the disease but were also more health compromised once infected, with relatively more reduced growth rate and increased mortality than lizards from the south. This scenario suggests that southern lizards have been under selection for resistance to this pathogen, whereas northern lizards have not, or at least not to the same degree. Thus, this study confirms the importance of genetic (family) effects on pathogen resistance with variation in this trait among natural populations.     

Heterospecific alarm call recognition in a non-vocal reptile

The ability to recognize and respond to the alarm calls of heterospecifics has previously been described only in species with vocal communication. Here we provide evidence that a non-vocal reptile, the Galápagos marine iguana (Amblyrhynchus cristatus), can eavesdrop on the alarm call of the Galápagos mockingbird (Nesomimus parvulus) and respond with anti-predator behaviour. Eavesdropping on complex heterospecific communications demonstrates a remarkable degree of auditory discrimination in a non-vocal species.