Proceedings of the Geologists Association最新文献

Locally within the Charmouth Mudstone Formation (Sinemurian, Lower Jurassic) of the Dorset coast fatally bitten ammonites with ventral bite marks are common. Ventral bite marks occur at the rear of the body-chamber. The predator probably severed attachment muscles, thus removing its prey more easily. We report the first ventrally bitten fossil nautiloid, which is unusual in that the large bite mark is entirely within the phragmocone. The nautiloid is juvenile with a very short body-chamber extending 46° back from the apparently undamaged aperture. The whorl cross-section is nearly circular, giving the predator little to grip when biting. Nautiloid shells are also thicker than ammonite shells. Despite these difficulties, the predator bit repeatedly and damaged both the shell and septa. Five rounded bites occur on the left side, separated by sharp points. This suggests the predator was probably another cephalopod with suckered arms and powerful jaws. The centre of the bite is 160.5° back from the aperture, close to the mean value for ammonites (184.5°), suggesting the predator located the position of the first bite opposite the victim's aperture. Thus, we think the predator attacked an incomplete nautiloid shell which explains why the damage affects only the phragmocone.

New trilobite material and the first graptolites from outcrop are described from the Am5 member of the Amdeh Formation near Al Fleij in northeast Oman. The sediments in which these faunas occur are interpreted as distal-shelf deposits with storm beds packed with brachiopods and orthoconic nautiloids. The deposits and its faunas are considered of late Darriwilian age and younger than the shallower-water Am5 deposits known from other outcrops. No palynomorphs could be recovered to confirm this due to the increased burial temperature the Al Fleij area has experienced.

The trilobites are of considerable palaeo-biogeographic interest as few faunas of this age are known from the Arabian Plate, though their preservation precludes the establishment of new species. They include Isabelinia aff. glabrata, Liomegalaspides sp., Neseuretus tristani, Neseuretinus sp. and the deeper-water forms, Cyclopyge cf. C. bohemica, Arthrorhachis sp. and Brachypleura sp. The graptolites are pendent Didymograptus spp. of later Darriwilian type.

Rare elements of the conodonts Nordiora, Amorphognathus and Microzarkodina have been recovered from shell beds that occur interbedded with the faunas. They too indicate a late Darriwilian age and differ from richer, restricted, shallow-water faunas known from the Am5 at other locations, and the more cosmopolitan shelf fauna from the Ayim Member of the Rann Formation of the United Arab Emirates.

A coarser, 80 m-thick, terrestrial sequence containing igneous pebbles, included in the Am5 in the 1980s, is shown from the occurrence of fossil plants to be of Permian age and probably equivalent to the Basal Saiq Clastics of Jabal al Akhdar.

Four isolated cervical vertebrae from the Kimmeridge Clay Formation (Upper Jurassic, Kimmeridgian) of Abingdon, Oxfordshire, England are identified as from a pliosaurid plesiosaurian sauropterygian on account of their shortness relative to width and height, their near platycoelous nature and the location of tall rib facets on the centrum body. They are noteworthy for their size, with a maximum width of 269 mm, maximum height of 222 mm and maximum length of 103 mm. Simple scaling and comparisons with cervical vertebrae of Mid Jurassic pliosaurs Peloneustes and Liopleurodon, and the Early Cretaceous Stenorhynchosaurus and Sachicasaurus suggest a total body length of between ~ 9.8 m and 14.4 m for the Abingdon Kimmeridge Clay pliosaur. Likely the true length was towards the higher end of this range.

A genus and species cannot be confidently determined on the basis of the described material, but they likely belong to Pliosaurus sp. or a similar animal, for which a precise neck length is not known. We estimate a neck length of 0.77 m for Pliosaurus ?brachyspondylus based on the average cervical lengths provided for specimen CAMSM J.35991.

Rare, isolated teeth of Corysodon multicristatus sp. nov. are described from two levels in the Atherfield Clay Formation (Early Aptian, Early Cretaceous) of Atherfield Point on the Isle of Wight, UK. Ten teeth of the new species were recovered from 1095 kg of washed and graded sediment residues. The teeth themselves are very small (around 0.5 mm high) and possess a distinctive crown bearing a tiered series of transverse crests adapted for rasping. Details of the dental architecture of the Atherfield Clay Formation specimens clearly indicate that the Cretaceous material differs significantly from the teeth of the type species for the genus, Corysodon cirinensis, recorded from the Kimmeridgian of northern France and Switzerland. C. multicristatus is the first substantiated record of the genus from the Early Cretaceous, thereby extending the stratigraphic range of the genus from the latest Jurassic, and the geographical range from continental Europe to the UK.

The Inferior Oolite Formation, 'Wild Bed' of Quarr Hill, Chideock, Dorset is described in terms of ammonite biostratigraphy down to the resolution of biohorizons for a segment of the Aalenian Stage of the Middle Jurassic. A section is presented and descriptions of the ammonites of the families Graphoceratidae, Erycitidae, Hammatoceratidae and Lytoceratidae are made in conjunction with an assessment of available types along with new illustrations of specimens collected in-situ. Examples of other molluscs are cited and imaged. Lectotypes are designated for some of the species erected by S. S. Buckman from Chideock. Comparisons are made with successions in other areas of North-West Europe thus providing an improved correlation and relationships between different ammonite morpho-taxa.

An isolated jaw fragment from the Late Cretaceous (Cenomanian) Cambridge Greensand Member of the West Melbury Marly Chalk Formation previously identified as a cestraciontid shark fin spine is referred to the pterosaur clade Azhdarchoidea on account of its lateral and occlusal foramina and edentuly. The specimen differs from the azhdarchoid Ornithostoma sedgwicki from the same deposit in having flat lateral surfaces and an acute dorsal/ventral apex. The specimen is similar in overall morphology to CAMSM B40085 from the same horizon and probably represents the corresponding jaw but from a different individual. Likely these specimens represent a new taxon but are considered too fragmentary to diagnose at present. A remarkably similar and distinctive morphology is found in unnamed pterosaur jaws from the Kem Kem Group (?Albian-Cenomanian) of Morocco, supporting the idea of faunal similarity between these two distant localities.

Spyway Quarry in Dorset contains >100 tracks made by large sauropod dinosaurs walking across what was a shelly beach in the Early Cretaceous. It is the largest in situ easily accessible UK dinosaur tracksite, a unique location for the public to directly engage with dinosaurs. Following consultation on how best to open and manage the site considering its 'value', longevity, and resources available, it was left unstaffed with the track surface directly accessible. The site has been open to the elements since 2013 and to the public since 2016. We created a new photogrammetric model of the site in 2021, for comparison with an existing 2014 model to identify any changes in the trackway surface and to assess the sustainability of direct public access and weathering to the surface. To understand public use of the site, we installed a visitor counter, compiled social media reviews, and analysed photographs of visitor's movement on the quarry surface. We provide quantitative evidence for exfoliation of the track surface and reduction in the prominence of individual tracks over time primarily due to natural processes. Visitor data suggest ~10,000 people visit annually, and feedback suggests potential improvements to visitor directions and information. We do not recommend substantial changes to the site management plan given resource constraints. Our work highlights the importance of using 3D imaging techniques to document sites upon discovery and thereafter and making these data openly available to all for conservation monitoring, communication and to preserve sites' legacies.