1,721,016 research outputs found
The cranial osteology of Tyrannoneustes lythrodectikos (Crocodylomorpha: Metriorhynchidae) from the Middle Jurassic of Europe
Full text linkTyrannoneustes lythrodectikos is one of numerous metriorhynchid crocodylomorph species known from the Oxford Clay Formation of England (Callovian-Oxfordian; Middle-Late Jurassic). This taxon is of evolutionary importance, as it is the oldest and most basal known macrophagous metriorhynchid. It has a mosaic of plesiomorphic and derived feeding related characteristics, including: teeth with microscopic, poorly formed and non-contiguous denticles; increased tooth apicobasal length; ventrally displaced dentary tooth row (increased gape); reduced dentary tooth count; and a proportionally long mandibular symphysis. However the type specimen, and current referred specimens, all lack a preserved cranium. As such, the craniofacial morphology of this taxon, and its potential feeding ecology, remains poorly understood. Here we describe two skulls and two lower jaws which we refer to T. lythrodectikos. Previously these specimens were referred to ‘Metriorhynchus’ brachyrhynchus. They share with the T. lythrodectikos holotype: the in-line reception pits on the dentary, dorsal margin of the surangular is strongly concave in lateral view, and the most of the angular ventral margin is strongly convex. Based on our description of these specimens, the skull of T. lythrodectikos has three autapomorphies: very long posterior processes of the premaxilla terminating in line with the 4th or 5th maxillary alveoli, deep lateral notches on the lateral surface of the maxillary with reception pits for dentary teeth, and the premaxilla forms the anterior margin of the first maxillary alveoli. Our description of the cranial anatomy of Tyrannoneustes lythrodectikos confirms that some macrophagous characteristics evolved during the Middle Jurassic, and were not exclusive to the clade Geosaurini. Moreover, the skulls further highlight the mosaic nature of Tyrannoneustes lythrodectikos and wide-gape macrophagous evolution in Geosaurinae
Figure 6. Thalattosuchus superciliosus lectotype MNHN.F RJN 256. A in Cutting the Gordian knot: a historical and taxonomic revision of the Jurassic crocodylomorph Metriorhynchus
No full textFigure 6. Thalattosuchus superciliosus lectotype MNHN.F RJN 256. A, dorsal view; B, palatal view; C, left lateral view. Scale bar = 10 cm.Published as part of Young, Mark T., Brignon, Arnaud, Sachs, Sven, Hornung, Jahn J., Foffa, Davide, Kitson, James J. N., Johnson, Michela M. & Steel, Lorna, 2021, Cutting the Gordian knot: a historical and taxonomic revision of the Jurassic crocodylomorph Metriorhynchus, pp. 510-553 in Zoological Journal of the Linnean Society 192 (2) on page 541, DOI: 10.1093/zoolinnean/zlaa092, http://zenodo.org/record/701700
Reappraisal of the thalattosuchian crocodylomorph record from the Middle-Upper Jurassic Rosso Ammonitico Veronese of northeastern Italy: Age calibration, new specimens and taphonomic biases
Full text linkDespite their extremely rare and fragmentary record, aquatic crocodylomorphs from the Middle to Upper Jurassic (Bajocian-Tithonian) Rosso Ammonitico Veronese (RAV) of northeastern Italy have sparked interest since the late 18th century. Among marine reptiles, Thalattosuchia is by far one of the best represented groups from the RAV units, especially in the Middle Jurassic. Although some specimens have been the subject of multiple studies in recent times, most of them still lack precise stratigraphic assignment and taphonomic assessment, while others remain undescribed. Here we provide a comprehensive revision of the thalattosuchian record from the RAV, alongside the most up-to-date age determination, by means of calcareous nannofossils, when available. Three new metriorhynchoid specimens are described for the first time from the Middle Jurassic of Asiago Plateau (Vicenza province). While the taphonomy of the newly described specimens hampers any taxonomic attribution below superfamily/family level, all three were confidently assigned to a precise interval between the upper Bajocian and the upper Bathonian. This revised record has major paleobiogeographical implications: the new specimens confirm an early origin and distribution of Metriorhynchoidea in the Tethys area and suggest a fast colonization of the open-ocean environment since the upper Bajocian
Thalattosuchus Young & Brignon & Sachs & Hornung & Foffa & Kitson & Johnson & Steel 2021, GEN. NOV.
No full textTHALATTOSUCHUS GEN. NOV. (FIG. 6) Type species Crocodilus superciliosus Blainville in Eudes- Deslongchamps, 1852 (following Recommendation 67B of the ICZN Code) (nomen protectum). Now referred to as Thalattosuchus superciliosus (Blainville in Eudes- Deslongchamps, 1852) comb. nov. Type by designation. Thalattosuchus superciliosus is a junior subjective synonym of Steneosaurus rostrominor Geoffroy Saint- Hilaire, 1825 (nomen oblitum). Etymology ‘Sea crocodile’, given that the species superciliosus is perhaps the best-known thalattosuchian, it is fitting that the genus be established for this species. Diagnosis Same as the only species (see below).Published as part of Young, Mark T., Brignon, Arnaud, Sachs, Sven, Hornung, Jahn J., Foffa, Davide, Kitson, James J. N., Johnson, Michela M. & Steel, Lorna, 2021, Cutting the Gordian knot: a historical and taxonomic revision of the Jurassic crocodylomorph Metriorhynchus, pp. 510-553 in Zoological Journal of the Linnean Society 192 (2) on page 538, DOI: 10.1093/zoolinnean/zlaa092, http://zenodo.org/record/701700
Reappraisal of the thalattosuchian crocodylomorph record from the Middle-Upper Jurassic Rosso Ammonitico Veronese of northeastern Italy: Age calibration, new specimens and taphonomic biases.
Full text linkDespite their extremely rare and fragmentary record, aquatic crocodylomorphs from the Middle to Upper Jurassic (Bajocian-Tithonian) Rosso Ammonitico Veronese (RAV) of northeastern Italy have sparked interest since the late 18th century. Among marine reptiles, Thalattosuchia is by far one of the best represented groups from the RAV units, especially in the Middle Jurassic. Although some specimens have been the subject of multiple studies in recent times, most of them still lack precise stratigraphic assignment and taphonomic assessment, while others remain undescribed. Here we provide a comprehensive revision of the thalattosuchian record from the RAV, alongside the most up-to-date age determination, by means of calcareous nannofossils, when available. Three new metriorhynchoid specimens are described for the first time from the Middle Jurassic of Asiago Plateau (Vicenza province). While the taphonomy of the newly described specimens hampers any taxonomic attribution below superfamily/family level, all three were confidently assigned to a precise interval between the upper Bajocian and the upper Bathonian. This revised record has major paleobiogeographical implications: the new specimens confirm an early origin and distribution of Metriorhynchoidea in the Tethys area and suggest a fast colonization of the open-ocean environment since the upper Bajocian
Convergent evolution and possible constraint in the posterodorsal retraction of the external nares in pelagic crocodylomorphs
Full text linkAmongst Mesozoic marine reptiles, metriorhynchid crocodylomorphs were unique in evolving into pelagically adapted forms with little-to-no posterodorsal retraction of the external nares. Narial retraction is a common adaptation seen in sustained swimmers, notably occurring during cetacean evolution. Mesosaurids and the basalmost known members of ichthyosauriforms, thalattosaurians, saurosphargids, sauropterygians, pleurosaurids and mosasauroids had the external nares divided by an ossified bar, bound by multiple cranial bones and were positioned back from the tip of the rostrum. However, metriorhynchids evolved from taxa with a single external naris bound solely by the premaxilla, and positioned near the tip of an elongate rostrum. We posit that metriorhynchids were uniquely disadvantaged in evolving into sustained swimmers. Herein we describe three Late Jurassic metriorhynchid cranial rostra that display differing degrees of narial retraction. In our new phylogenetic analyses, the backwards migration of the narial fossa posterior margin occurred independently at least four times in Metriorhynchidae, whereas the backwards migration of the anterior margin only occurred twice. Although Rhacheosaurini share the backwards migration of the anterior and posterior narial margins, posterodorsal retraction occurred differently along three lineages. This culminated in the Early Cretaceous, where a rhacheosaurin evolved nares bound by the premaxilla and maxilla, and significantly posterodorsally retracted.Fil: Young, Mark. University of Edinburgh; Reino UnidoFil: Sachs, Sven. Museum Bielefeld; AlemaniaFil: Abel, Pascal. Eberhard Karls Universität Tübingen. Institute for Archaeological Sciences; AlemaniaFil: Foffa, Davide. National Museums Scotland; Reino UnidoFil: Herrera, Laura Yanina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; ArgentinaFil: Kitson, James J. N.. University of Newcastle; Reino Unid
Tough to digest: first record of Teleosauroidea (Thalattosuchia) in a regurgitalite from the Upper Jurassic of north‐eastern Italy
No full textPostcranial remains of a small teleosauroid from the Upper Jurassic of north-eastern Italy are described in detail. The specimen, discovered in 1980 on a slab of Rosso Ammonitico Veronese (RAV Fm.; Bajocian–Tithonian), is represented by partially articulated thoracic, sacral and anterior caudal vertebrae, fractured and displaced osteoderms and pelvic girdle elements. Additional bone elements overlap one another in a densely packed cluster. The
peculiar arrangement of this specimen is here interpreted as the result of regurgitation of the animal carcass from a pelagic predator or scavenger. Microstructural and geo-
chemical evidence from bone and surrounding matrix support this hypothesis. A dearth of phosphorus in the matrix near the bone mass corroborates the interpretation of the specimen as a regurgitalite rather than a coprolite. Calcareous nannofossil and stratigraphic data allow us to assign the fossil to the latest Kimmeridgian or earliest Tithonian. The specimen is here tentatively referred to the teleosauroid subfamily Aeolodontinae based on the alternating pattern of the osteoderm ornamentation; this attribution is supported by stratigraphical and palaeoenvironmental evidence. If confirmed, this represents the first occurrence of Aeolodontinae in Italian outcrops of the western Tethys margin and represents the first marine crocodylomorph described as a bromalite
Marine tethysuchian crocodyliform from the ?Aptian-Albian (Lower Cretaceous) of the Isle of Wight, UK
Full text linkA marine tethysuchian crocodyliform from the Isle of Wight, most likely from the Upper Greensand Formation (upper Albian, Lower Cretaceous), is described. However, we cannot preclude it being from the Ferruginous Sands Formation (upper Aptian), or more remotely, the Sandrock Formation (upper Aptian-upper Albian). The specimen consists of the anterior region of the right dentary, from the tip of the dentary to the incomplete fourth alveolus. This specimen increases the known geological range of marine tethysuchians back into the late Lower Cretaceous. Although we refer it to Tethysuchia incertae sedis, there are seven anterior dentary characteristics that suggest a possible relationship with the Maastrichtian-Eocene clade Dyrosauridae. We also review ‘middle’ Cretaceous marine tethysuchians, including putative Cenomanian dyrosaurids. We conclude that there is insufficient evidence to be certain that any known Cenomanian specimen can be safely referred to Dyrosauridae, as there are some cranial similarities between basal dyrosaurids and Cenomanian–Turonian marine ‘pholidosaurids’. Future study of middle Cretaceous tethysuchians could help unlock the origins of Dyrosauridae and improve our understanding of tethysuchian macroevolutionary trends
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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