Molecular evidence for a terrestrial origin of snakes

Biologists have debated the origin of snakes since the nineteenth century. One hypothesis suggests that snakes are most closely related to terrestrial lizards, and reduced their limbs on land. An alternative hypothesis proposes that snakes are most closely related to Cretaceous marine lizards, such as mosasaurs, and reduced their limbs in water. A presumed close relationship between living monitor lizards, believed to be close relatives of the extinct mosasaurs, and snakes has bolstered the marine origin hypothesis. Here, we show that DNA sequence evidence does not support a close relationship between snakes and monitor lizards, and thus supports a terrestrial origin of snakes.     

Evolution and ecology of lizard body sizes

Aim Body size is instrumental in influencing animal physiology, morphology, ecology and evolution, as well as extinction risk. I examine several hypotheses regarding the influence of body size on lizard evolution and extinction risk, assessing whether body size influences, or is influenced by, species richness, herbivory, island dwelling and extinction risk. Location World‐wide. Methods I used literature data and measurements of museum and live specimens to estimate lizard body size distributions. Results I obtained body size data for 99% of the world's lizard species. The body size–frequency distribution is highly modal and right skewed and similar distributions characterize most lizard families and lizard assemblages across biogeographical realms. There is a strong negative correlation between mean body size within families and species richness. Herbivorous lizards are larger than omnivorous and carnivorous ones, and aquatic lizards are larger than non‐aquatic species. Diurnal activity is associated with small body size. Insular lizards tend towards both extremes of the size spectrum. Extinction risk increases with body size of species for which risk has been assessed. Main conclusions Small size seems to promote fast diversification of disparate body plans. The absence of mammalian predators allows insular lizards to attain larger body sizes by means of release from predation and allows them to evolve into the top predator niche. Island living also promotes a high frequency of herbivory, which is also associated with large size. Aquatic and nocturnal lizards probably evolve large size because of thermal constraints. The association between large size and high extinction risk, however, probably reflects a bias in the species in which risk has been studied.     

Correlations between lizard cranial shape and diet: a quantitative, phylogenetically informed analysis

Although the relationship between dietary and phenotypic specialization has been well documented for many vertebrate groups, it has been stated that few such general trends can be established for lizards. This is often thought to be due to the lack of dietary specialization in many lizards. For example, many species that are reported to be insectivorous may also consume a variety of plant materials, and the reverse is often true as well. In this study, we investigate whether a correlation exists between general cranial form and dietary niche in lizards. Additionally, we test previously proposed hypotheses suggesting that herbivorous lizards should be larger bodied than lizards with other diets. Our data indicate that lizards specializing in food items imposing different mechanical demands on the feeding system show clear patterns of morphological specialization in their cranial morphology. True herbivores (diet of fibrous and tough foliage) are clearly distinguished from omnivorous and carnivorous lizards by having taller skulls and shorter snouts, likely related to the need for high bite forces. This allows herbivores to mechanically reduce relatively less digestible foliage. Carnivores have relatively longer snouts and retroarticular processes, which may result in more efficient capture and processing of elusive prey. When analysed in an explicit phylogenetic context, only snout length and skull mass remained significantly different between dietary groups. The small number of differences in the phylogenetic analyses is likely the result of shared evolutionary history and the relative paucity of independent origins of herbivory and omnivory in our sample. Analyses of the relationship between diet and body size show that on average herbivores have a larger body size than carnivores, with omnivores intermediate between the two other dietary groups. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 86 , 433–466.     

The evolution of the lepidosaurian lower temporal bar: new perspectives from the Late Cretaceous of South China

Until recently, it was considered axiomatic that the skull of lizards and snakes arose from that of a diapsid ancestor by loss of the lower temporal bar. The presence of the bar in the living New Zealand Tuatara, Sphenodon, was thus considered primitive, corroborating its status as a ‘living fossil’. A combination of new fossils and rigorous phylogeny has demonstrated unequivocally that the absence of the bar is the primitive lepidosaurian condition, prompting questions as to its function. Here we describe new material of Tianyusaurus, a remarkable lizard from the Late Cretaceous of China that is paradoxical in having a complete lower temporal bar and a fixed quadrate. New material from Jiangxi Province is more complete and less distorted than the original holotype. Tianyusaurus is shown to be a member of the Boreoteiioidea, a successful clade of large herbivorous lizards that were dispersed through eastern Asia, Europe and North America in the Late Cretaceous, but disappeared in the end-Cretaceous extinction. A unique combination of characters suggests that Tianyusaurus took food items requiring a large gape.     

A tiny lizard (Lepidosauria,Squamata) from the Lower Cretaceous of Spain

Abstract: The smallest living amniotes are all lizards, but the fossil history of this size trait in Squamata is difficult to follow because small skeletons have low preservation potential and are often hard to detect in the field. A new squamate taxon, Jucaraseps grandipes gen. et sp. nov., is here described on the basis of an articulated skeleton from the Early Cretaceous Spanish lagerstätten of Las Hoyas. It differs from other known Mesozoic lizards in combining very small body size with a short rostrum, low maxillary tooth count, a relatively slender and elongated body, and short limbs with large hind feet. Phylogenetic analysis using TNT places it on the stem of a clade encompassing scincomorphs, gekkotans, snakes, amphisbaenians and anguimorphs. Comparison with modern lizards suggests it was probably a cryptic surface or subsurface ground dweller but not a burrower.     

Frugivory in polychrotid lizards: effects of body size

As more data have become available on lizard diets in the past few decades, researchers have stressed the importance of lizards as pollinators and seed dispersers. Whereas large body size has been traditionally put forward as a major biological factor allowing herbivory and frugivory in lizards, a recent review of frugivory and seed dispersal by lizards showed that frugivory might be considered to be a typical island phenomenon, independent of body size. Here we show that frugivory is correlated with lizard body size among a group of syntopic Anolis species in Jamaica, with larger species eating more fruit. Additionally, the size of the fruits consumed is significantly related to lizard body size. Multiple regression analyses show that this is largely a pure body size effect as head shape or residual bite force are uncorrelated to overall fruit size. Moreover, we demonstrate that among polychrotid (Anolis-like) lizards in general, those that consume fruit are on average larger than those that do not. Lizards from the mainland were not significantly different in body size from island species. We thus suggest that fruit consumption in polychrotid lizards is mediated by large body size whether living on islands or not.     

A new basal ornithuromorph bird (Aves: Ornithothoraces) from the Early Cretaceous of China with implication for morphology of early Ornithuromorpha

Ornithuromorpha is the most derived avian group in the Early Cretaceous, advanced members of which encompass all living birds (Neornithes). Here we report on a new basal ornithuromorph bird, Bellulia rectusunguis gen. et sp. nov., represented by a nearly complete skeleton from the Early Cretaceous Jehol Biota in northeastern China. A comprehensive phylogenetic analysis resolved the new taxon in a basal position that is only more derived than Archaeorhynchus and Jianchangornis among ornithuromorphs, increasing the morphological diversity of basal ornithuromorphs. The new specimen has a V‐shaped furcula with a short hypocleidium, a feature otherwise known only in Schizooura among Cretaceous ornithuromorphs. We discuss the implications of the new taxon on the evolution of morphology of primitive ornithuromorphs, particularly of pectoral girdle, sternum and limb proportion pertaining to powered flight. The preserved gastroliths and pedal morphology indicate herbivory and lakeshore adaption for this new species. © 2015 The Linnean Society of London     

Palaeobiogeographic significance of the Deccan infra‐ and intertrappean biota from peninsular India

Extensive work done in the last decade on the sedimentary beds intercalated with the Deccan volcanic flows (infra‐ and intertrappean) has demonstrated the vast potential of these rocks for vertebrate, invertebrate and plant fossils. The infra‐ and intertrappean beds, especially those exposed on the eastern margin of the Deccan Traps, produced a large number of fossils which made it possible to establish the age and duration of Deccan volcanism (late Cretaceous—early Palaeocene) with some degree of confidence. Affinities of the late Cretaceous infratrappean vertebrates, such as pelomedusid turtles and sauropod dinosaurs, lie with those of Gondwanan landmasses. It seems more likely that these taxa are relicts of the Gondwanan stock that boarded the Indian plate well before its separation from Madagascar 70–80 Ma ago. Remnants of the former Gondwanaland fauna, such as pelomedusid turtles, leptodactylid frogs and titanosaurid dinosaurs did persist in relatively younger (latest Cretaceous) intertrappean beds. In addition to these Gondwanan elements, the intertrappean beds register many North American, European and Central Asiatic taxa (pelobatid and discoglossid frogs, anguid lizards, alligatorid crocodiles, palaeoryctid mammals, ostracodes and charophytes) suggesting that a contact between India and southern Asia was already established by the end of Cretaceous. An early India/Asia collision, long before the widely accepted early to middle Eocene date, is favoured to explain the presence of Laurasian elements in the late Cretaceous of India.     

The molecular evolutionary tree of lizards,snakes, and amphisbaenians

Squamate reptiles (lizards, snakes, amphisbaenians) number approximately 8200 living species and are a major component of the world's terrestrial vertebrate diversity. Recent molecular phylogenies based on protein-coding nuclear genes have challenged the classical, morphology-based concept of squamate relationships, requiring new classifications, and drawing new evolutionary and biogeographic hypotheses. Even the key and long-held concept of a dichotomy between iguanians (～1470 sp.) and scleroglossans (all other squamates) has been refuted because molecular trees place iguanians in a highly nested position. Together with snakes and anguimorphs, iguanians form a clade – Toxicofera – characterized by the presence of toxin secreting oral glands and demonstrating a single early origin of venom in squamates. Consequently, neither the varanid lizards nor burrowing lineages such as amphisbaenians or dibamid lizards are the closest relative of snakes. The squamate timetree shows that most major groups diversified in the Jurassic and Cretaceous, 200–66 million years (Myr) ago. In contrast, five of the six families of amphisbaenians arose during the early Cenozoic, ～60–40 Myr ago, and oceanic dispersal on floating islands apparently played a significant role in their distribution on both sides of the Atlantic Ocean. Among snakes, molecular data support the basic division between the small fossorial scolecophidians (～370 sp.) and the alethinophidians (all other snakes, ～2700 sp.). They show that the alethinophidians were primitively macrostomatan and that this condition was secondarily lost by burrowing lineages. The diversification of alethinophidians resulted from a mid-Cretaceous vicariant event, the separation of South America from Africa, giving rise to Amerophidia (aniliids and tropidophiids) and Afrophidia (all other alethinophidians). Finally, molecular phylogenies have made it possible to draw a detailed evolutionary history of venom among advanced snakes (Caenophidia), a key functional innovation underlying their radiation (～2500 sp.). To cite this article: N. Vidal, S.B. Hedges, C. R. Biologies 332 (2009).     

A LONG-BODIED LIZARD FROM THE LOWER CRETACEOUS OF JAPAN

Abstract:  Platynotan lizards underwent a dramatic Late Cretaceous radiation into marine habitats. Beginning with small-bodied forms, the lineage culminated with the mosasaurs, large predatory lizards with a world-wide distribution in the Santonian–Campanian. Moreover, the marine squamate radiations of the Cenomanian–Turonian are remarkable in having produced a range of long-bodied, reduced-limbed swimmers (dolichosaurs, adriosaurs, coniasaurs and limbed snakes) that seem to have thrived in the shallow coastal environments of the Western Tethys region. Until now, none of these long-bodied aquatic squamates has been recorded prior to the Cenomanian, none has been recovered from a non-marine locality and none is known from Asia. Here we describe a small, gracile, long-bodied mosasauroid lizard from a swampy continental deposit in the Lower Cretaceous of Japan.     

Omnivory in lacertid lizards: adaptive evolution or constraint?

Feeding specializations such as herbivory are an often cited example of convergent and adaptive evolution. However, some groups such as lizards appear constrained in the evolution of morphological specializations associated with specialized diets. Here we examine whether the inclusion of plant matter into the diet of omnivorous lacertid lizards has resulted in morphological specializations and whether these specializations reflect biomechanical compromises as expected if omnivores are constrained by functional trade-offs. We examined external head shape, skull shape, tooth structure, intestinal tract length and bite performance as previous studies have suggested correlations between the inclusion of plants into the diet and these traits. Our data show that omnivorous lacertid lizards possess modifications of these traits that allow them to successfully exploit plant material as a food source. Conversely, few indications of a compromise phenotype could be detected, suggesting that the evolution towards herbivory is only mildly constrained by functional trade-offs.     

Effect of fragmentation on predation pressure of insect herbivores in a north temperate deciduous forest ecosystem

1. Forest fragmentation affects many ecosystem processes by spatially altering relationships among organisms. Herbivory by arthropods is an important ecosystem processes in forests that fragmentation alters by changing relationships among herbivores, their predators, and their hosts. The relative importance of these factors remains unclear. 2. It was tested whether the exclusion of vertebrate predators affected the arthropod abundance or amounts of herbivory in a fragmented, deciduous forest landscape in southern Quebec. Differences in the abundance of arthropod herbivores and amounts of herbivory in forest patches with different landscape characteristics (small isolated patches versus large connected ones), on sugar maple saplings with or without exclosures that restricted access by large vertebrate predators were measured. 3. Saplings protected from predators with exclosures had greater abundances of all arthropods (herbivores and invertebrate predators) than those without, indicating potential top‐down effects of vertebrate predators on arthropods. Analysis of effect sizes between exclosure treatments and controls suggests the magnitude of predation effects may be affected by fragmentation. 4. Strong top‐down effects of predators on arthropods, and weak effects of fragmentation on predation or amounts of herbivory were found. As a result, herbivory may be regulated by factors other than vertebrate predation in this system.     

Huehuecuetzpalli mixtecus gen. et sp. nov: a basal squamate (Reptilia) from the Early Cretaceous of Tepexi de Rodríguez,Central México

Huehuecuetzpalli mixtecus gen. et sp. nov. is characterized by a combination of characters unlike those of any of the previously described Late Jurassic or Early Cretaceous lizards. It has most of the synapomorphies common to modern squamates, but still retains primitive features rare in living taxa. Autapomorphic characters include an anteroposteriorly elongated premaxilla that results in the elongation of the snout and the apparent retraction of the external nares. A small rounded postfrontal and a parietal foramen on the frontoparietal suture suggest affinities with iguanians, but the retention of divided premaxillae, amphicoelous vertebrae, thoracolumbar intercentra, entepicondylar foramen, and a second distal tarsal supports the hypothesis that Huehuecuetzpalli has a more basal position relative to the extant squamates. Although its appearance is late in the fossil record of lizards, Huehuecuetzpalli is the first report of a basal squamate. It provides important information on early transformation of characters in lizard evolution. Many primitive characters present in some modern squamates are usually explained by paedomorphosis; however, these characters are common in early lizards suggesting that derived states may have been fixed later in lizard evolution. If Huehuecuetzpalli is an iguanian, then it would be the earliest known representative of this lineage and extends their fossil record into the Albian. This paper presents an extensive review of the characters and character states used in previously published cladistic analyses of the Squamata.     

The northernmost sauropod record in the Northern Hemisphere

Isolated sauropod teeth from the Early Cretaceous Teete locality in Yakutia (Eastern Siberia, Russia) are the only evidence that sauropods lived in high latitudes (palaeolatitude estimate of N 62°) in the Northern Hemisphere. The spatulate broad tooth crowns of adult individuals lack marginal denticles while these are present in a juvenile tooth. The teeth have overlapping facets and likely belong to a basal macronarian. The juvenile tooth indicates that sauropods reproduced in high latitudes and possibly stayed there around the year. The Teete vertebrate assemblage comprises both endothermic, or presumably endothermic tetrapods (theropod dinosaurs, tritylodontids and mammals), and ectothermic tetrapods (salamanders, turtles, choristoderes and lizards), but no crocodyliforms. This suggests a temperate climate, with an annual mean temperature well above freezing level but below 14°C.     

A new kogaionid multituberculate mammal from the Maastrichtian of the Transylvanian Basin,Romania

The Latest Cretaceous (Maastrichtian) terrestrial sedimentary sequences of the Haţeg Basin in Transylvania are well known for the so-called “Haţeg Island” vertebrate faunas, which evolved in endemic (insular?) conditions. In addition to frogs, lizards, turtles, crocodilians, birds and dinosaurs, peculiar multituberculate mammals have been recorded, all belonging to the family Kogaionidae. Here, a new species of the genus Barbatodon is reported from the Maastrichtian Şard Formation in the Transylvanian Basin (Alba County, Romania). Barbatodon oardaensis n. sp. is characterized by M1 cusp formula 3:4:2 and is much smaller than the two other Maastrichtian kogaionids from Transylvania, Barbatodon transylvanicus and Kogaionon ungureanui. The origin and paleobiogeography of kogaionids are discussed.     

Top-down control of herbivory by birds and bats in the canopy of temperate broad-leaved oaks (Quercus robur)

The intensive foraging of insectivorous birds and bats is well known to reduce the density of arboreal herbivorous arthropods but quantification of collateral leaf damage remains limited for temperate forest canopies. We conducted exclusion experiments with nets in the crowns of young and mature oaks, Quercus robur, in south and central Germany to investigate the extent to which aerial vertebrates reduce herbivory through predation. We repeatedly estimated leaf damage throughout the vegetation period. Exclusion of birds and bats led to a distinct increase in arthropod herbivory, emphasizing the prominent role of vertebrate predators in controlling arthropods. Leaf damage (e.g., number of holes) differed strongly between sites and was 59% higher in south Germany, where species richness of vertebrate predators and relative oak density were lower compared with our other study site in central Germany. The effects of bird and bat exclusion on herbivory were 19% greater on young than on mature trees in south Germany. Our results support previous studies that have demonstrated clear effects of insectivorous vertebrates on leaf damage through the control of herbivorous arthropods. Moreover, our comparative approach on quantification of leaf damage highlights the importance of local attributes such as tree age, forest composition and species richness of vertebrate predators for control of arthropod herbivory.     

Predation by an exotic lizard,Anolis sagrei,alters the ant community structure in betelnut palm plantations in southern Taiwan

Abstract 1. Predators can affect prey directly by reducing prey abundance and indirectly by altering behavioural patterns of prey. From previous studies, there is little evidence that ant community structure is affected by vertebrate predation. 2. Researchers tend to consider the interactions between vertebrate predators and ants to be weak. The present study examined the impact of the exotic invasive lizard, Anolis sagrei, on the ant community structure by manipulating the density of lizards within enclosures. The natural density of A. sagrei in the field was surveyed and used as the stocking density rate in the lizard‐present sub‐enclosures. 3. Before the lizard density was manipulated, there was no difference in the ant diversity between sub‐enclosures. After the lizard density manipulation, the ant diversity in sub‐enclosures with A. sagrei present was significantly different from that of enclosures where the lizards were absent, although the overall ant abundance did not differ significantly. 4. The ant diversity difference was generated by a significant reduction of the ant species Pheidole fervens in sub‐enclosures with A. sagrei present. Such an abundance change might be the result of direct predation by the lizards, or it might be generated by a foraging site shift by this ant. 5. The results of this study thus demonstrated that the invasion of an exotic vertebrate can significantly alter the community structure of ants, perhaps through the combined direct and indirect effects of lizards on ants.