We describe remains of freshwater turtles from the Upper Cretaceous of Chilean Patagonia. The fossils, which comprise isolated shell fragments and incomplete appendicular bones, were recovered from meandering fluvial deposits of the Dorotea Formation (upper CampanianâDanian), in the RÃo de Las Chinas Valley, Magallanes region. These remains represent the first records of Upper Cretaceous pan-chelid pleurodiran turtles in the Magallanes-Austral Basin. The shell fragments show a strong ornamentation of irregular polygons distributed over their entire dorsal surface, and one of the peripheral plates is narrow and elongated. These features are consistent with traits described in Yaminuechelys, a chelid genus from the Upper Cretaceous and Paleogene of Argentinian Patagonia. In addition, the suprapygal plate presents sulci that mark the limits of the vertebral scute 5 and the marginal scutes 12 as in Yaminuechelys sulcipeculiaris. This finding represents the southernmost record of a species conferred to Yaminuechelys, extending the distribution of this genus to the Magallanes-Austral basin during the CampanianâMaastrichtian.
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JÃrÃmy Anquetin & Christian PÃntener (2020)
A new species of the large-headed coastal marine turtle Solnhofia (Testudinata, Thalassochelydia) from the Late Jurassic of NW Switzerland
PaleorXiv Preprint (under review for PeerJ)
DOI: 10.31233/
osf.io/wap2zhttps://paleorxiv.org/wap2z/
Background.Â
The large-headed turtle Solnhofia parsonsi is known by a handful of specimens from the Late Jurassic of Germany and Switzerland (maybe also France). Solnhofia parsonsi is traditionally regarded as a eurysternid Thalassochelydia, a group of small to medium sized, mostly lagoonal or marginal turtles found almost exclusively from the Late Jurassic of Europe. More recently, Solnhofia parsonsi has been proposed to be a close relative of Sandownidae, an enigmatic group of Cretaceous to Paleogene turtles characterized by a derived cranial anatomy and a wider geographical distribution. Sandownids may therefore have evolved from thalassochelydian ancestors such as Solnhofia parsonsi.
Methods.Â
We herein describe new material of Solnhofia from the Kimmeridgian (Late Jurassic) of Porrentruy, NW Switzerland. The bulk of the material consists of an association of a cranium and over 180 shell bones found together in a block of marly limestone. A second cranium and a mandible from slightly younger, but nearby localities are also described.
Results.Â
We refer the new material to Solnhofia [edited] n. sp. The new species shares with Solnhofia parsonsi a relatively large head, an extensive secondary palate formed primarily by the maxillae, a greatly developed processus trochlearis oticum with a contribution from the parietal and quadratojugal, a large jugal-palatine contact in the floor of the fossa orbitalis, and a posteromedial process of the jugal running on the dorsal surface of the maxilla and pterygoid. Some of these characteristics are also present in sandownids, but our morphological study clearly shows that Solnhofia [edited] is closer to Solnhofia parsonsi than to any sandownids.
Discussion.
Solnhofia [edited] differs from Solnhofia parsonsi in many aspects, notably: a shortened and broader cranium, a shorter and posteriorly broader upper triturating surface with a slightly sinusoidal lateral margin and without contribution from the palatine, a processus trochlearis oticum more oblique in dorsal or ventral view and less concave in anterior view, choanae that do not extend posteriorly on the pterygoids, a more developed processus pterygoideus externus, a condylus mandibularis situated anterior to the level of the occipital plane, a greater ventral exposure of the parabasisphenoid, a mandible about as wide as long, a relatively short symphysis, a lower triturating surface widened posterolaterally thanks to the presence of large laterally projecting dentary tubercles, a stouter and shorter coronoid process, a splenial positioned more anteriorly along the mandibular ramus, costo-peripheral fontanelles extending more anteriorly and posteriorly along the costal series, and an escutcheon shaped central plastral fontanelle formed mostly by the hypoplastra. In addition to the morphology of the new species, we also briefy discuss about observable ontogenetic variations and possible taphonomic origin of the assemblage.
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JÃrÃmy Anquetin & Charlotte Andrà (2020)
The last surviving Thalassochelydia--A new turtle cranium from the Early Cretaceous of the Purbeck Group (Dorset, UK).
PaleorXiv Preprint (under review)
DOI: 10.31233/
osf.io/7pa5chttps://paleorxiv.org/7pa5c/Background.Â
The mostly Berriasian (Early Cretaceous) Purbeck Group of southern England has produced a rich turtle fauna dominated by the freshwater paracryptodires Pleurosternon bullockii and Dorsetochelys typocardium. Each of these species is known by numerous relatively complete shells and by a single cranium. The two other turtles found in the Purbeck Group (Hylaeochelys belli, a species of uncertain affinities, and the terrestrial helochelydrid "Helochelydra" anglica) are known only from shell remains.
Methods.
In the present contribution, we describe a new turtle cranium from the Purbeck Group of Swanage, Dorset (southern England). We also explore the phylogenetic relationships of this new cranium and of Hylaeochelys belli in the context of a recently published global turtle matrix.
Results.Â
Before complete preparation, the new Purbeck cranium was provisionally referred to Dorsetochelys typocardium, but our analysis clearly contradicts a referral to this species in particular and to paracryptodires in general. In contrast, the new cranium shares a number of features with the Late Jurassic, coastal marine Thalassochelydia, including a posterolaterally open foramen posterius palatinum, a strong ridge on the posterior surface of the processus articularis of the quadrate, a strong posterior orientation of the processus articularis in ventral view, and a processus trochlearis oticum limited to the medial part of the otic chamber and bordered by a deep recess laterally. Our phylogenetic analysis confirms a placement of the new Purbeck cranium within the clade Thalassochelydia.
Discussion.Â
In terms of morphology, the new Purbeck cranium does not correspond to any known taxon. However, we refrain from naming a new species based on it because there is a good chance that this cranium actually belongs to the shell-based species Hylaeochelys belli (also recovered as a thalassochelydian in our phylogenetic analysis). Unfortunately, we lack any objective evidence to support this conclusion for the moment. In any case, the new Purbeck cranium confirms what others have previously suggested based on Hylaeochelys belli: thalassochelydian turtles survived the Jurassic-Cretaceous transition.
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A proximal distributary channel deposit in the Turonian Ferron Sandstone of central Utah contains a trace-fossil assemblage comprised of turtle tracks (Chelonipus), vertebrate swim trace fossils (Characichnos), repichnial traces of mollusks (Archaeonassa), Rhizocorallium, and Teredolites. Mayflies are abundant producers of horizontal, spreiten, U-shaped burrows in modern freshwater channels, but rarely ascribed as producers of Rhizocorallium in the rock record. The in situ trace fossils studied are interpreted as a freshwater assemblage. Teredolites occurs within allochthonous debris reworked from stratigraphically lower brackish-water deposits. This Ferron Sandstone assemblage provides an example of the juxtaposition of freshwater ichnocoenose with exhumed brackish-water clasts. Caution must be exercised in environmental interpretation when taking into consideration both adjacent floodplain and the sedimentary structures surrounding the clasts. Complex trace-fossil relationships such as these may play a role in the scarcity of Rhizocorallium reports from freshwater deposits in the rock record, and may be more common than presently recognized. This study illustrates the importance of addressing the detailed ichnology above and below the base of channel deposits in progradational environments (e.g., delta plain), where reworked, brackish-water deposits (and bored clasts) may be entrained within overlying lower salinity facies.
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