Environmental controls on the distribution of neoselachian sharks and rays within the British Bathonian (Middle Jurassic).

Extensive sampling from a range of facies within the Bathonian (Middle Jurassic) of southern England has allowed the palaeoenvironmental distribution of a number of taxa of neoselachian sharks and rays to be assessed. Faunas were collected from a number of recurrent facies, with different assemblages being characteristic of particular palaeoenvironments. Palaeoenvironmental specificity occurred at both ordinal and specific level. Samples from offshore facies contain high diversity faunas containing members of all neoselachian groups known to have been present in the Middle Jurassic. Shallower water assemblages contain lower diversity faunas lacking Synechodontiformes and Hexanchiformes. Samples from lagoonal facies contain low diversity faunas typically comprising different species from open marine settings. The presence of different taxa within different palaeoenvironments suggests that by the Bathonian neoselachians had differentiated into a wide range of niches and ecologically more diverse than has previously been recognised. Implications for early neoselachian palaeoecology, salinity tolerance and diversification are discussed

Interstipe webbing in the Silurian graptolite Cyrtograptus murchisoni and its palaeobiological significance.

Although it has long been recognized that the Graptoloidea constituted a diverse group of planktic organisms, the precise hydrodynamics of the various colony morphotypes has been a source of debate. Recent discoveries of specimens of Cyrtograptus murchisoni with a complex suite of webs or vanes between the central coiled stipe and the cladial branches have shown that the hydrodynamic modifications of at least this taxon were considerably more complex than previously thought. These webs are composed of very thin peridermal tissue and stretch between the first or second order cladial branches and the main stipe, the webs overlapping to give a screw-type morphology to the rhabdosome. The form of the webbing also has implications for the mode of life and mobility of individual zooids within the colony, as the main areas of web construction are in regions in which the zooids were enclosed within restricted thecal apertures

Sharks, Rays and a Chimaeroid from the Kimmeridgian (Late Jurassic) of Ringstead, Southern England

Sampling of a lenticular concentration of vertebrate debris and associated sediments from the lower Kimmeridgian of southern England has allowed the study of a diverse and abundant assemblage of chondrichthyan remains. A number of previously undescribed species are recorded, of which three new species are named; Squatina? frequens, Synechodus plicatus and Protospinax planus. Additional diagnosis of the genus Paracestracion Koken is given to allow its identification from dental remains. Several nominal batoid species are synonymised with Spathobatis bugesiacus Thiolliere. This assemblage is considered to be typical of Middle–Late Jurassic neritic environments, and is compared to other contemporaneous selachian faunas

Diversification of the Neoselachii (Chondrichthyes) during the Jurassic and Cretaceous

The Neoselachii are a monophyletic group including all of the extant sharks and rays. They underwent rapid diversification throughout the Jurassic and Cretaceous, going from low-diversity assemblages of members of extinct orders in the Late Triassic to diverse assemblages containing representatives of most extant clades by the end of the Cretaceous. The known fossil record of Mesozoic neoselachians is composed largely of isolated teeth, with articulated skeletal remains being known from a limited number of sites. The small tooth size of a large proportion of neoselachians, including almost all taxa in existence prior to the mid Cretaceous, led to very poor representation in older publications. Their state of knowledge has improved dramatically since 1970 with the increased use of bulk sampling for isolated dental remains. Despite this, the high proportion of Lazarus taxa from some stages suggests that the state of knowledge is still intermittent. Increase in assemblage diversity throughout the Jurassic and Cretaceous suggests that radiation events resulted in real and dramatic increases in diversity, and that the perceived diversification is not an artefact of poor knowledge. Cladogenesis inferred from the fossil record typically compares more favourably with divergence predicted from molecular analysis, where Batoidea form a discrete basal clade, than with divergence predicted from morphological analysis, where Batoidea are considered a derived crown group within the Squalea. The timing of diversification events is discussed in light of the known fossil record, cladistically generated divergence times, and the paleoenvironmental distribution of faunas

Selachian faunas from the earliest Cretaceous Purbeck Group of Dorset, southern England.

Abundant selachian remains have been recovered from a number of horizons through the Purbeck Group at Durlston Bay, Lulworth Cove and Stair Hole in southern England. The remains, primarily teeth, but additionally fin spines and dermal denticles, belong to selachians from two major groups, the Hybodontoidea and the Rhinobatoidei. The assemblage of hybodont sharks is quite diverse, comprising six species from the four genera ‘Hybodus’, Egertonodus, Polyacrodus and Lonchidion. The rhinobatoid rays include two species, one belonging to the genus Belemnobatis and another, larger, indeterminate ray. Within the Purbeck fauna, two species are new: Lonchidion inflexum sp. nov. and Belemnobatis variabilis sp. nov. Within the entirely non-marine succession of the Purbeck Group, the beds containing ray teeth also contain molluscs indicative of more saline intervals. In all of the sampled beds, the hybodont faunas recovered were relatively homogenous

The development of aerodynamic uncertainties for the space shuttle orbiter

The Shuttle Program development schedule and the management decision to perform an orbital, manned mission on the first launch resulted in a requirement to develop realistic aerodynamic uncertainties for the preflight aerodynamic predictions. This paper addresses the methodology in developing two types of aerodynamic uncertainties. One involves the ability to reproduce aerodynamic results between various wind tunnel tests. The second addresses the difference between preflight aerodynamic predictions and flight results derived from analysis of past aircraft programs. Both types of uncertainties for pitching moment, lateral-directional stability, rudder power, and aileron power are presented. In addition, the application of uncertainties to flight control design and fight test planning is briefly reviewed

Environmental distribution of Bathonian (Middle Jurassic) neoselachians in southern England

Within the Bathonian (Middle Jurassic) a wide range of depositional environments were present across Britain. Within this dominantly carbonate shelf setting, there is a general palaeoenvironmental transition from open marine shelf in the south of England, to marine and non-marine lagoons in south-central England. Isolated teeth of neoselachians are frequent at several localities within a range of marine and lagoonal facies. Extensive bulk sampling has allowed teeth from over 20 neoselachian taxa to be recovered from several distinct facies. The distributions of many species suggest that they were strongly environmentally controlled, with few taxa being commonly present within both open marine and lagoonal settings. Some taxonomic groups appear to have been restricted to specific environments, with hexanchids and palaeospinacids only being recorded within open marine facies. Within other groups, environmental segregation is at generic and specific level, with different species of Protospinax, orectolobids, batoids and scyliorhinids being recorded within different facies. The differential distribution of neoselachians within the Bathonian demonstrates that the initial phase of neoselachian radiation during the late Early and Middle Jurassic was accompanied by diversification into a wide range of ecological niches. This greatly increases our understanding of the mechanisms and timing of neoselachian radiation and Jurassic fish palaeoecolog

Sharks, bony fishes and endodental borings from the Miocene Montpelier Formation (White Limestone Group) of Jamaica

Bulk samples of Miocene carbonate sediments (deep-water chalks and shallow-water-derived calcarenites) from the Montpelier Formation (White Limestone Group) in Duncans Quarry, Jamaica, have yielded a small, but diverse, fauna of disassociated fish remains. Shark remains include the teeth of five species, four of which are squalids. A diverse, but taxonomically indeterminate, osteichthyan tooth assemblage is also present. A number of the teeth contain microborings of two ichnotaxa. The assemblage is considered to be typical of a deep-water continental slope fauna, and indicates an abrupt northern margin of the Miocene shallow-water carbonate platforms