A NEOSELACHIAN SHARK FROM THE NON-MARINE WESSEX FORMATION (WEALDEN GROUP: EARLY CRETACEOUS, BARREMIAN) OF THE ISLE OF WIGHT, SOUTHERN ENGLAND

Abstract:  Bulk screening of Early Cretaceous (Barremian) Wessex Formation strata exposed on the south-east coast of the Isle of Wight, southern England, has resulted in the recovery of neoselachian shark teeth referred to the scyliorhinid Palaeoscyllium . These are the first neoselachian remains from the British Wealden Group and represent the geologically oldest neoselachian yet recovered from a freshwater deposit. This is also the only known example of a non-marine occurrence of a member of the Scyliorhinidae.     

Adaptive origins of primates revisited

Interpretation of the adaptive profile of ancestral primates is controversial and has been constrained for decades by general acceptance of the premise that the first primates were very small. Here we show that neither the fossil record nor modern species provide evidence that the last common ancestor of living primates was small. Instead, comparative weight distributions of arboreal mammals and a phylogenetic reconstruction of ancestral primate body mass indicate that the reduction of functional claws to nails -- a primate characteristic that had up until now eluded satisfactory explanation - resulted from an increase in body mass to around 1000 g or more in the primate stem lineage. The associated shift to a largely vegetarian diet coincided with increased angiosperm diversity and the evolution of larger fruit size during the Late Cretaceous.     

DOES NICHE CONSERVATISM PROMOTE SPECIATION? A CASE STUDY IN NORTH AMERICAN SALAMANDERS

Recent speciation research has generally focused on how lineages that originate in allopatry evolve intrinsic reproductive isolation, or how ecological divergence promotes nonallopatric speciation. However, the ecological basis of allopatric isolation, which underlies the most common geographic mode of speciation, remains poorly understood and largely unstudied. Here, we explore the ecological and evolutionary factors that promote speciation in Desmognathus and Plethodon salamanders from temperate eastern North America. Based on published molecular phylogenetic estimates and the degree of geographic range overlap among extant species, we find strong evidence for a role for geographic isolation in speciation. We then examine the relationship between climatic variation and speciation in 16 sister-taxon pairs using geographic information system maps of climatic variables, new methods for modeling species' potential geographic distributions, and data on geographic patterns of genetic variation. In contrast to recent studies in tropical montane regions, we found no evidence for parapatric speciation along climatic gradients. Instead, many montane sister taxa in the Appalachian Highlands inhabit similar climatic niches and seemingly are allopatric because they are unable to tolerate the climatic conditions in the intervening lowlands. This temporal and spatial-ecological pattern suggests that niche conservatism, rather than niche divergence, plays the primary role in promoting allopatric speciation and montane endemism in this species-rich group of vertebrates. Our results demonstrate that even the relatively subtle climatic differences between montane and lowland habitats in eastern North America may play a key role in the origin of new species.     

Size analyses of the coccolith species Biscutum constans and Watznaueria barnesiae from the Late Albian “Niveau Breistroffer” (SE France): taxonomic and palaeoecological implications

The size variability of the coccolith species Biscutum constans and Watznaueria barnesiae has been studied in 50 samples of the Late Albian “Niveau Breistroffer” black shales (Col de Palluel section, SE France). For each species, length and width of the total coccolith and the central unit have been measured in 60 specimens per sample. In addition, ellipticity and central unit length/total coccolith length ratio have been calculated. This study aims to improve our understanding of the taxonomic concepts of B. constans and W. barnesiae, and to test whether the size changes correspond to palaeoceanographic changes interpreted from other proxies. Two morphotypes (varieties) were differentiated for each of the two taxa studied. B. constans includes morphotypes with a narrow (B. constans var. constans) and a wide central unit (B. constans var. ellipticum). Between these two morphotypes no significant size differentiation has been observed. They seem to represent end members of a size continuum, relating to both the total coccolith- and central unit size distribution. The two morphotypes of W. barnesiae differ only in the absence (W. barnesiae var. barnesiae) and the presence of a narrow central opening (W. barnesiae var. fossacincta). No significant size differences have been observed between these two morphotypes, and both show similar distributions of the measured characteristics. We recommend that the studied morphotypes of both B. constans and W. barnesiae should not be assigned to different morphospecies. Throughout the studied black shale succession the measured parameters show mostly statistically insignificant, short-term fluctuations, but significant long-term trends have been observed for B. constans. These show a trend to smaller forms with a narrower central unit in the upper part of the succession. This change coincides with a cooling trend, as indicated by a nannofossil based temperature index. Therefore the two morphotypes of B. constans are interpreted to represent ecophenotypic varieties rather than two different morphospecies. No clear relationship has been recognized between the size of W. barnesiae and the palaeoenvironmental conditions.     

Juvenile ornithopod (Dinosauria: Rhabdodontidae) remains from the Upper Cretaceous (Lower Campanian, Gosau Group) of Muthmannsdorf (Lower Austria)

The fragmentary remains of a juvenile rhabdodontid ornithopod from the Coal-bearing Complex of the Gosau Group (Lower Campanian, Grünbach syncline) at Muthmannsdorf near Wiener Neustadt, Lower Austria are revised. The material, probably belonging to a single individual, includes a right dentary (lectotype of Iguanodon suessi Bunzel, 1871, designated herein), teeth, a fragmentary parietal, fragments of scapula, ?radius, femur, tibia, two vertebrae (lost) and a manual ungual.The lectotype dentary does not provide clear autapomorphies or sufficient diagnostic features to determine its position within the Rhabdodontidae at generic level. By this “Iguanodon suessi” Bunzel, 1871 and the genus “Mochlodon” Seeley, 1881, to which it was latter referred as type species, cannot be characterized sufficiently by differential diagnosis and these are best considered nomina dubia. Based upon combined character comparisons (mainly postcranial features) the Muthmannsdorf ornithopod is referred herein to Zalmoxes Weishampel, Jianu, Csiki and Norman, 2003, a genus so far known from the late Maastrichtian of Romania. It probably but not evidently represents a yet unnamed species, most closely related to Zalmoxes shqiperorum Weishampel, Jianu, Csiki and Norman, 2003. At the present state of knowledge the Austrian material is not further diagnostic at the species level and kept in open nomenclature as Zalmoxes sp.     

Glandulocalyx upatoiensis, a fossil flower of Ericales (Actinidiaceae/Clethraceae) from the Late Cretaceous (Santonian) of Georgia, USA

Background and Aims

Ericales are a major group of extant asterid angiosperms that are well represented in the Late Cretaceous fossil record, mainly by flowers, fruits and seeds. Exceptionally well preserved fossil flowers, here described as Glandulocalyx upatoiensis gen. & sp. nov., from the Santonian of Georgia, USA, yield new detailed evidence of floral structure in one of these early members of Ericales and provide a secure basis for comparison with extant taxa.

Methods

The floral structure of several fossil specimens was studied by scanning electron microscopy (SEM), light microscopy of microtome thin sections and synchrotron-radiation X-ray tomographic microscopy (SRXTM). For direct comparisons with flowers of extant Ericales, selected floral features of Actinidiaceae and Clethraceae were studied with SEM.

Key Results

Flowers of G. upatoiensis have five sepals with quincuncial aestivation, five free petals with quincuncial aestivation, 20–28 stamens arranged in a single series, extrorse anther orientation in the bud, ventral anther attachment and a tricarpellate, syncarpous ovary with three free styles and numerous small ovules on axile, protruding-diffuse and pendant placentae. The calyx is characterized by a conspicuous indumentum of large, densely arranged, multicellular and possibly glandular trichomes.

Conclusions

Comparison with extant taxa provides clear evidence for a relationship with core Ericales comprised of the extant families Actinidiaceae, Roridulaceae, Sarraceniaceae, Clethraceae, Cyrillaceae and Ericaceae. Within this group, the most marked similarities are with extant Actinidiaceae and, to a lesser degree, with Clethraceae. More detailed analyses of the relationships of Glandulocalyx and other Ericales from the Late Cretaceous will require an improved understanding of the morphological features that diagnose particular extant groups defined on the basis of molecular data.     

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.     

Biomechanical trade-offs bias rates of evolution in the feeding apparatus of fishes

Morphological diversification does not proceed evenly across the organism. Some body parts tend to evolve at higher rates than others, and these rate biases are often attributed to sexual and natural selection or to genetic constraints. We hypothesized that variation in the rates of morphological evolution among body parts could also be related to the performance consequences of the functional systems that make up the body. Specifically, we tested the widely held expectation that the rate of evolution for a trait is negatively correlated with the strength of biomechanical trade-offs to which it is exposed. We quantified the magnitude of trade-offs acting on the morphological components of three feeding-related functional systems in four radiations of teleost fishes. After accounting for differences in the rates of morphological evolution between radiations, we found that traits that contribute more to performance trade-offs tend to evolve more rapidly, contrary to the prediction. While ecological and genetic factors are known to have strong effects on rates of phenotypic evolution, this study highlights the role of the biomechanical architecture of functional systems in biasing the rates and direction of trait evolution.     

Marine planktonic microbes survived climatic instabilities in the past

In the geological past, changes in climate and tectonic activity are thought to have spurred the tempo of evolutionary change among major taxonomic groups of plants and animals. However, the extent to which these historical contingencies increased the risk of extinction of microbial plankton species remains largely unknown. Here, I analyse fossil records of marine planktonic diatoms and calcareous nannoplankton over the past 65 million years from the world oceans and show that the probability of species' extinction is not correlated with secular changes in climatic instability. Further supporting these results, analyses of genera survivorship curves based on fossil data concurred with the predictions of a birth-death model that simulates the extinction of genera through time assuming stochastically constant rates of speciation and extinction. However, my results also show that these marine microbes responded to exceptional climatic contingencies in a manner that appears to have promoted net diversification. These results highlight the ability of marine planktonic microbes to survive climatic instabilities in the geological past, and point to different mechanisms underlying the processes of speciation and extinction in these micro-organisms.     

Evidence for determinism in species diversification and contingency in phenotypic evolution during adaptive radiation

Adaptive radiation (AR) theory predicts that groups sharing the same source of ecological opportunity (EO) will experience deterministic species diversification and morphological evolution. Thus, deterministic ecological and morphological evolution should be correlated with deterministic patterns in the tempo and mode of speciation for groups in similar habitats and time periods. We test this hypothesis using well-sampled phylogenies of four squamate groups that colonized the New World (NW) in the Late Oligocene. We use both standard and coalescent models to assess species diversification, as well as likelihood models to examine morphological evolution. All squamate groups show similar early pulses of speciation, as well as diversity-dependent ecological limits on clade size at a continental scale. In contrast, processes of morphological evolution are not easily predictable and do not show similar pulses of early and rapid change. Patterns of morphological and species diversification thus appear uncoupled across these groups. This indicates that the processes that drive diversification and disparification are not mechanistically linked, even among similar groups of taxa experiencing the same sources of EO. It also suggests that processes of phenotypic diversification cannot be predicted solely from the existence of an AR or knowledge of the process of diversification.