Ichthyosaurs from the Upper Triassic (Carnian–Norian) of the New Siberian Islands, Russian Arctic, and their implications for the evolution of the ichthyosaurian basicranium and vertebral column

2021 ◽  
pp. 1-24
Author(s):  
Nikolay G. ZVERKOV ◽  
Dmitry V. GRIGORIEV ◽  
Andrzej S. WOLNIEWICZ ◽  
Alexey G. KONSTANTINOV ◽  
Evgeny S. SOBOLEV
Keyword(s):  
Vertebral Column ◽  
Cervical Vertebrae ◽  
Upper Triassic ◽  
Late Triassic ◽  
Phylogenetic Position ◽  
New Taxon ◽  
Russian Arctic ◽  
Micro Computed Tomography ◽  
New Siberian Islands ◽  
Group Relationships

ABSTRACT The first ichthyosaurian specimens discovered from the Upper Triassic of the Russian Arctic (Kotelny Island, New Siberian Islands) are described herein. They include the remains of large- to small-bodied ichthyosaurians originating from six stratigraphic levels spanning the lower Carnian to middle Norian. The material is mostly represented by isolated vertebrae and ribs, which are not possible to accurately diagnose, but also includes specimens comprising associated vertebrae and a fragmentary skeleton that preserves cranial remains (parabasisphenoid, fragmentary quadrate, partial mandible and hyoids). Based on vertebral and rib morphology, we identify the specimens as representatives of the following taxonomic groups: large-bodied shastasaurids, medium-sized indeterminate ichthyosaurians with a single rib facet in the presacral centra, and small euichthyosaurians with double rib facets present throughout the presacral vertebrae that likely represent toretocnemids and/or basal parvipelvians. In addition, the cranial and mandibular remains preserved in one of the specimens, ZIN PH 5/250, were studied using micro-computed tomography. Its mandible is highly similar to that of toretocnemids, whereas the parabasisphenoid demonstrates a peculiar combination of both plesiomorphic and derived character states, providing the first detailed data on this cranial element in a Late Triassic ichthyosaurian. Furthermore, the specimen also demonstrates a distinctive condition of rib articulation in the anteriormost presacral (cervical) vertebrae, which together with other features allows for the erection of a new taxon – Auroroborealia incognita gen. et sp. nov. Although the phylogenetic position of this taxon is uncertain due to its fragmentary nature, its anatomy, indicating toretocnemid or parvipelvian affinities, further supports the previously hypothesised sister-group relationships between these two clades. The morphology of the parabasisphenoid and vertebral column of the new taxon is discussed in broader contexts of the patterns of evolution of these skeletal regions in ichthyosaurs.

scholarly journals Osteology of the Late Triassic aetosaur Scutarx deltatylus (Archosauria: Pseudosuchia)

2016 ◽  
Author(s):  
William G Parker
Keyword(s):  
National Park ◽  
Vertebral Column ◽  
Upper Triassic ◽  
Late Triassic ◽  
Chinle Formation ◽  
Petrified Forest National Park ◽  
Petrified Forest

Aetosaurs are some of the most common fossils collected from the Upper Triassic Chinle Formation of Arizona, especially at the Petrified Forest National Park. Four partial skeletons collected from the park from 2002 through 2009 represent the holotype and referred specimens of Scutarx deltatylus. These specimens include much of the carapace, as well as the vertebral column, and shoulder and pelvic girldles. A partial skull represents the first aetosaur skull recovered from Arizona since the 1930s. Scutarx deltatylus can be distinguished from closely related forms Calyptosuchus wellesi and Adamanasuchus eisenhardtae not only morphologically, but also stratigraphically. Thus, Scutarx deltatylus is potentially an index taxon for the upper part of the Adamanian biozone.

Prosogynopora riseri, gen. et sp. nov., a phylogenetically problematic lithophoran proseriate (Platyhelminthes : Rhabditophora) with inverted genital pores from the New England coast

2014 ◽  
Vol 28 (3) ◽  
pp. 309 ◽  
Author(s):  
Christopher E. Laumer ◽  
Gonzalo Giribet ◽  
Marco Curini-Galletti
Keyword(s):  
New England ◽  
Sister Group ◽  
Optimality Criteria ◽  
Phylogenetic Position ◽  
28S Rrna ◽  
New Taxon ◽  
Taxonomic Rank ◽  
Molecular Phylogenetic ◽  
Pore Opening ◽  
Group Relationships

A new lithophoran proseriate flatworm, Prosogynopora riseri, gen. et sp. nov. (Platyhelminthes: Rhabditophora: Proseriata), is described from the New England coast (USA). The species shares characters with members of the families Calviriidae and Coelogynoporidae, e.g. the presence of paracnida, the short common female duct, a septum and diaphragm at the base of the pharynx. However, the inverted topology of the genital system, presenting an anterior female pore shortly behind the mouth and a male pore opening nearly on the caudal terminus, is unique within the Proseriata, and permits inclusion into neither family on morphological grounds. We investigated the phylogenetic position of the new species within the available diversity of proseriate 18S and 28S rRNA sequences. However, an exploration of diverse homology schemes, alignment conditions and optimality criteria proved the position of P. riseri, gen. et sp. nov. to be remarkably unstable, particularly with respect to the method of alignment, variously suggesting sister-group relationships with (or within) Coelogynoporidae, with Calviriidae, or with a clade composed of all other Lithophora. Despite its unique morphology and the absence of molecular phylogenetic evidence for its inclusion within any family as currently defined, we refrain from assigning a higher taxonomic rank to the new lineage, pending critical re-assessment of homology in several character systems and the availability of further taxon- and gene-rich enquiries into the phylogeny of Proseriata. Apingospermata, new taxon and Dolichogynoducta, new taxon are proposed as two rankless taxonomic names of Lithophora, corresponding to well-supported clades in our molecular phylogenetic hypothesis.

scholarly journals Revision of Erpetosuchus (Archosauria: Pseudosuchia) and new erpetosuchid material from the Late Triassic ‘Elgin Reptile’ fauna based on μCT scanning techniques

2020 ◽  
pp. 1-25
Author(s):  
Davide FOFFA ◽  
Richard J. BUTLER ◽  
Sterling J. NESBITT ◽  
Stig WALSH ◽  
Paul M. BARRETT ◽  
...  
Keyword(s):  
Computed Tomography ◽  
Phylogenetic Relationships ◽  
Late Triassic ◽  
New Taxon ◽  
Micro Computed Tomography ◽  
Fossil Remains ◽  
New Information ◽  
Sandstone Formation ◽  
Shed Light

ABSTRACT The Late Triassic fauna of the Lossiemouth Sandstone Formation (LSF) from the Elgin area, Scotland, has been pivotal in expanding our understanding of Triassic terrestrial tetrapods. Frustratingly, due to their odd preservation, interpretations of the Elgin Triassic specimens have relied on destructive moulding techniques, which only provide incomplete, and potentially distorted, information. Here, we show that micro-computed tomography (μCT) could revitalise the study of this important assemblage. We describe a long-neglected specimen that was originally identified as a pseudosuchian archosaur, Ornithosuchus woodwardi. μCT scans revealed dozens of bones belonging to at least two taxa: a small-bodied pseudosuchian and a specimen of the procolophonid Leptopleuron lacertinum. The pseudosuchian skeleton possesses a combination of characters that are unique to the clade Erpetosuchidae. As a basis for investigating the phylogenetic relationships of this new specimen, we reviewed the anatomy, taxonomy and systematics of other erpetosuchid specimens from the LSF (all previously referred to Erpetosuchus). Unfortunately, due to the differing representation of the skeleton in the available Erpetosuchus specimens, we cannot determine whether the erpetosuchid specimen we describe here belongs to Erpetosuchus granti (to which we show it is closely related) or if it represents a distinct new taxon. Nevertheless, our results shed light on rarely preserved details of erpetosuchid anatomy. Finally, the unanticipated new information extracted from both previously studied and neglected specimens suggests that fossil remains may be much more widely distributed in the Elgin quarries than previously recognised, and that the richness of the LSF might have been underestimated.

scholarly journals Osteology of the Late Triassic aetosaur Scutarx deltatylus (Archosauria: Pseudosuchia)

2016 ◽  
Author(s):  
William G Parker
Keyword(s):  
National Park ◽  
Vertebral Column ◽  
Upper Triassic ◽  
Late Triassic ◽  
Chinle Formation ◽  
Petrified Forest National Park ◽  
Petrified Forest

Aetosaurs are some of the most common fossils collected from the Upper Triassic Chinle Formation of Arizona, especially at the Petrified Forest National Park. Four partial skeletons collected from the park from 2002 through 2009 represent the holotype and referred specimens of Scutarx deltatylus. These specimens include much of the carapace, as well as the vertebral column, and shoulder and pelvic girldles. A partial skull represents the first aetosaur skull recovered from Arizona since the 1930s. Scutarx deltatylus can be distinguished from closely related forms Calyptosuchus wellesi and Adamanasuchus eisenhardtae not only morphologically, but also stratigraphically. Thus, Scutarx deltatylus is potentially an index taxon for the upper part of the Adamanian biozone.

scholarly journals Non-dinosaurian dinosauromorphs from the Chinle Formation (Upper Triassic) of the Eagle Basin, northern Colorado: Dromomeron romeri (Lagerpetidae) and a new taxon, Kwanasaurus williamparkeri (Silesauridae)

PeerJ ◽  
2019 ◽  
Vol 7 ◽  
pp. e7551 ◽  
Author(s):  
Jeffrey W. Martz ◽  
Bryan J. Small
Keyword(s):  
Articular Surface ◽  
Upper Triassic ◽  
Late Triassic ◽  
New Taxon ◽  
Dietary Specialization ◽  
Sister Clade ◽  
Chinle Formation ◽  
Northern Colorado ◽  
Land Vertebrate ◽  
Early Late

The “red siltstone” member of the Upper Triassic Chinle Formation in the Eagle Basin of Colorado contains a diverse assemblage of dinosauromorphs falling outside of Dinosauria. This assemblage is the northernmost known occurrence of non-dinosaurian dinosauromorphs in North America, and probably falls within the Revueltian land vertebrate estimated biochronozone (215–207 Ma, middle to late Norian). Lagerpetids are represented by proximal femora and a humerus referable to Dromomeron romeri. Silesaurids (non-dinosaurian dinosauriforms) are the most commonly recovered dinosauromorph elements, consisting of dentaries, maxillae, isolated teeth, humeri, illia, femora, and possibly a scapula and tibiae. These elements represent a new silesaurid, Kwanasaurus williamparkeri, gen. et sp. nov., which possesses several autapomorphies: a short, very robust maxilla with a broad ascending process, a massive ventromedial process, a complex articular surface for the lacrimal and jugal, and 12 teeth; 14 dentary teeth; an ilium with an elongate and blade-like preacetabular process and concave acetabular margin; a femur with an extremely thin medial distal condyle and a depression on the distal end anterior to the crista tibiofibularis. The recognition of K. williamparkeri further demonstrates the predominantly Late Triassic diversity and widespread geographic distribution across Pangea of the sister clade to Asilisaurus, here named Sulcimentisauria. Silesaurid dentition suggests a variety of dietary specializations from faunivory and omnivory in the Middle Triassic and early Late Triassic (Carnian), to herbivory in the Late Triassic (Carnian and Norian), with the latter specialization possibly coinciding with the radiation of Sulcimentisauria across Pangea. The extremely robust maxilla and folidont teeth of K. williamparkei may represent a strong herbivorous dietary specialization among silesaurids.

scholarly journals Osteology of the Late Triassic aetosaurScutarx deltatylus(Archosauria: Pseudosuchia)

PeerJ ◽  
2016 ◽  
Vol 4 ◽  
pp. e2411 ◽  
Author(s):  
William G. Parker
Keyword(s):  
Morphological Feature ◽  
National Park ◽  
Vertebral Column ◽  
Dorsal Surface ◽  
Upper Triassic ◽  
Late Triassic ◽  
Naming Convention ◽  
Holotype Specimen ◽  
Posteromedial Corner ◽  
Chinle Formation

Aetosaurians are some of the most common fossils collected from the Upper Triassic Chinle Formation of Arizona, especially at the Petrified Forest National Park (PEFO). Aetosaurians collected from lower levels of the park includeDesmatosuchus spurensis,Paratypothorax,Adamanasuchus eisenhardtae,Calyptosuchus wellesi, andScutarx deltatylus. Four partial skeletons collected from the park between 2002 and 2009 represent the holotype and referred specimens ofScutarx deltatylus. These specimens include much of the carapace, as well as the vertebral column, and shoulder and pelvic girdles, and a new naming convention proposed for osteoderms descriptions better differentiates portions of the carapace and ventral armor. A partial skull from the holotype specimen represents the first aetosaur skull recovered and described from Arizona since the 1930s. The key morphological feature distinguishingScutarx deltatylusis the presence of a prominent, triangular boss located in the posteromedial corner of the dorsal surface of the dorsal paramedian osteoderms.Scutarx deltatyluscan be distinguished from closely related formsCalyptosuchus wellesiandAdamanasuchus eisenhardtaenot only morphologically, but also stratigraphically. Thus,Scutarx deltatylusis potentially an index taxon for the upper part of the Adamanian biozone.

scholarly journals A new pleurodire turtle (Chelonii) from Adamantina Formation (Bauru Group), Upper Cretaceous of Brazil

2015 ◽  
Author(s):  
Edio-Ernst Kischlat
Keyword(s):  
Cervical Vertebrae ◽  
New Combination ◽  
Southeastern Brazil ◽  
Phylogenetic Position ◽  
South American ◽  
New Taxon ◽  
Close Phylogenetic Relationship ◽  
Long Time ◽  
The City ◽  
Bauru Group

Background. A new podocnemidid taxon from the Adamantina Formation (Campanian to Maastrichtian), Bauru Group - Paraná Basin (southeastern Brazil) is presented. Some multifragmented specimens were discovered near 30 years ago, in the region of Álvarez Machado (State of São Paulo) on the farm of Mr. Yoshitoshi Myzobuchi (a.k.a "Myzobuchi Site"), and they were mounted piece by piece of a huge puzzle. The remains comprise two incomplete carapace, 4 fragmented plastra, some cervical vertebrae, scapular and pelvic girdles, and limb bones of at least 4 specimens. The sauropod Gondwanatitan faustoi was described from this same site that also provided some crocodile remains. Methods. This new Adamantina taxon was codified according Gabriel S. Ferreira’s pleurodire dataset (unpublished MSc thesis) which comprises an extensive taxonomic sampling (85 taxa, 226 characters, some multistate), including fossil and recent taxa from all pleurodiran lineages. Three software packages (PAUP*, WinClada and TNT) were used to evaluate its phylogenetic position. Results. All searches resulted on most parsimonious trees of same lenght (1011 steps), and similar strict consensus topology. The new Adamantina taxon is in Bairdemys-Stereogenys lineage, after the Podocnemis split and sequentially between the eocenic Egyptian fossil Neochelys fajumensis and the recent South American Peltocephalus dumerilianus. Discussion. The plastral bones of this new taxon are relatively thick and the most striking feature is the ankylosed suture between the pubis and the xiphiplastron. In any other pleurodire the articular faces between the pubis and the xiphiplastron have several osseous lamellae but in the new taxon this ankylosed articulation is simply broken (to the contrary, the articular faces between the ischium and xiphisplastron are preserved and have these lamellae). This apparently is also the case for Podocnemis harrisi Pacheco, 1910, which is considered a nomen dubium by several authors. It also has a thick xiphiplastron, which is the only holotypic bone preserved (but lost long time ago) and shows the pubic articular face apparently with no lamellae, but the ischiadic one clearly showing them, as illustrated in Pacheco (1910). It also shows some minor differences in the morphology with an intumescence mainly in the region of the pubic articular face which is absent in the present specimens. Podocnemis harrisi is also from Adamantina Formation, but from the City of Colina away 300 km NE from the City of Álvarez Machado, and the ankylosed puboxiphiplastral suture suggest a close phylogenetic relationship between both that is here expressed as a new combination with the Álvarez Machado new nominative genus.

scholarly journals An enigmatic Arthropoda from the Upper Triassic (Carnian) southwestern Gondwana (Argentina)

2019 ◽  
Vol 94 (2) ◽  
pp. 279-290 ◽  
Author(s):  
María B. Lara ◽  
Bárbara Cariglino ◽  
Ana M. Zavattieri ◽  
Iracema Zacarías
Keyword(s):  
New Genus ◽  
Upper Triassic ◽  
Late Triassic ◽  
New Taxon ◽  
Delta Plain ◽  
Ecological Implications ◽  
Fish Remains ◽  
Potrerillos Formation ◽  
Warm Temperate ◽  
Early Late

AbstractThe presence of a new taxon, Duraznovis gallegoi new genus new species is reported and described from an early Late Triassic (Carnian) deposit in Argentina. Two specimens, recovered from the Quebrada del Durazno locality, uppermost levels of the Potrerillos Formation, Cuyana Basin (Mendoza), are represented by the molds of their shield and imprints of soft parts. The identity of these specimens appears enigmatic but closely resembles in the possession of a generalized arthropod morphology and a distinctive combination of characters, to living and fossil representatives of xiphosurans (Chelicerata) and notostracans (Branchiopoda). The new fossils are associated with a rich biota comprising abundant insects, spinicaudatans, plants, and scarce fish remains living in semipermanent swamps and/or ponds within a delta plain environment with intermittent episodes of flooding, in a warm temperate and humid megamonsoonal climate during Triassic times. In this context, we analyze the taphonomic and ecological implications of their presence. Lastly, these unique specimens at the Quebrada del Durazno locality adds to the diversity of the biota, revealing the importance of this site as an exceptional paleontological Triassic deposit.UUID: http://zoobank.org/8d1194c2-170c-4b7a-b0c6-5c08b0974d95

scholarly journals Homeotic shift at the dawn of the turtle evolution

2017 ◽  
Vol 4 (4) ◽  
pp. 160933 ◽  
Author(s):  
Tomasz Szczygielski
Keyword(s):  
Vertebral Column ◽  
Phylogenetic Analyses ◽  
Cervical Vertebrae ◽  
Expression Patterns ◽  
Cervical Vertebra ◽  
Late Triassic ◽  
Cervical Region ◽  
Crown Group ◽  
Dorsal Vertebra ◽  
Shift Hypothesis

All derived turtles are characterized by one of the strongest reductions of the dorsal elements among Amniota, and have only 10 dorsal and eight cervical vertebrae. I demonstrate that the Late Triassic turtles, which represent successive stages of the shell evolution, indicate that the shift of the boundary between the cervical and dorsal sections of the vertebral column occurred over the course of several million years after the formation of complete carapace. The more generalized reptilian formula of at most seven cervicals and at least 11 dorsals is thus plesiomorphic for Testudinata. The morphological modifications associated with an anterior homeotic change of the first dorsal vertebra towards the last cervical vertebra in the Triassic turtles are partially recapitulated by the reduction of the first dorsal vertebra in crown-group Testudines, and they resemble the morphologies observed under laboratory conditions resulting from the experimental changes of Hox gene expression patterns. This homeotic shift hypothesis is supported by the, unique to turtles, restriction of Hox-5 expression domains, somitic precursors of scapula, and brachial plexus branches to the cervical region, by the number of the marginal scute-forming placodes, which was larger in the Triassic than in modern turtles, and by phylogenetic analyses.

scholarly journals A new pleurodire turtle (Chelonii) from Adamantina Formation (Bauru Group), Upper Cretaceous of Brazil

2015 ◽  
Author(s):  
Edio-Ernst Kischlat
Keyword(s):  
Cervical Vertebrae ◽  
New Combination ◽  
Southeastern Brazil ◽  
Phylogenetic Position ◽  
South American ◽  
New Taxon ◽  
Close Phylogenetic Relationship ◽  
Long Time ◽  
The City ◽  
Bauru Group

Background. A new podocnemidid taxon from the Adamantina Formation (Campanian to Maastrichtian), Bauru Group - Paraná Basin (southeastern Brazil) is presented. Some multifragmented specimens were discovered near 30 years ago, in the region of Álvarez Machado (State of São Paulo) on the farm of Mr. Yoshitoshi Myzobuchi (a.k.a "Myzobuchi Site"), and they were mounted piece by piece of a huge puzzle. The remains comprise two incomplete carapace, 4 fragmented plastra, some cervical vertebrae, scapular and pelvic girdles, and limb bones of at least 4 specimens. The sauropod Gondwanatitan faustoi was described from this same site that also provided some crocodile remains. Methods. This new Adamantina taxon was codified according Gabriel S. Ferreira’s pleurodire dataset (unpublished MSc thesis) which comprises an extensive taxonomic sampling (85 taxa, 226 characters, some multistate), including fossil and recent taxa from all pleurodiran lineages. Three software packages (PAUP*, WinClada and TNT) were used to evaluate its phylogenetic position. Results. All searches resulted on most parsimonious trees of same lenght (1011 steps), and similar strict consensus topology. The new Adamantina taxon is in Bairdemys-Stereogenys lineage, after the Podocnemis split and sequentially between the eocenic Egyptian fossil Neochelys fajumensis and the recent South American Peltocephalus dumerilianus. Discussion. The plastral bones of this new taxon are relatively thick and the most striking feature is the ankylosed suture between the pubis and the xiphiplastron. In any other pleurodire the articular faces between the pubis and the xiphiplastron have several osseous lamellae but in the new taxon this ankylosed articulation is simply broken (to the contrary, the articular faces between the ischium and xiphisplastron are preserved and have these lamellae). This apparently is also the case for Podocnemis harrisi Pacheco, 1910, which is considered a nomen dubium by several authors. It also has a thick xiphiplastron, which is the only holotypic bone preserved (but lost long time ago) and shows the pubic articular face apparently with no lamellae, but the ischiadic one clearly showing them, as illustrated in Pacheco (1910). It also shows some minor differences in the morphology with an intumescence mainly in the region of the pubic articular face which is absent in the present specimens. Podocnemis harrisi is also from Adamantina Formation, but from the City of Colina away 300 km NE from the City of Álvarez Machado, and the ankylosed puboxiphiplastral suture suggest a close phylogenetic relationship between both that is here expressed as a new combination with the Álvarez Machado new nominative genus.

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