New papers about Triassic ichthyosaurs. All the pdfs are free:
Ryosuke Motani, Jiandong Huang, Da-yong Jiang, Andrea Tintori, Olivier Rieppel, Hailu You, Yuan-chao Hu & Rong Zhang (2016)
Separating sexual dimorphism from other morphological variation in a specimen complex of fossil marine reptiles (Reptilia, Ichthyosauriformes, Chaohusaurus).
Scientific Reports 8, Article number: 14978Â
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The Early Triassic Chaohu Fauna from Anhui Province, China, contains the oldest record of Mesozoic marine reptiles, such as Cartorhynchus and Sclerocormus. Most specimens from the fauna belong to the ichthyosauriform Chaohusaurus, more specifically resembling C. chaoxianensis. However, a wide range of morphological variation exists within about 40 skeletons that have been prepared, likely reflecting mixed signals from both sexual and taxonomic differences. We test whether the sexual and taxonomic signals are separable based on quantification, aided by the knowledge of sexual dimorphism in extant marine tetrapods. There are two different suites of dimorphism that divide the specimens differently from each other yet consistently within each suite, resulting in four morphotypes in combination, likely representing two sexes of two taxa. Presumed males have larger 'organ of prehension' sensu Darwin, specifically limbs in the present case, for a given body length. This sexing criterion is supported by the only specimen of a gravid female, which belongs to the morphotype with short limbs. Males also have larger skulls for the trunk length compared to females. This study demonstrates that sexual and taxonomic signals are separable in fossil reptiles, with a sufficient sample size and careful analyses.
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The new issue of Norwegian Journal of Geology is focused on Triassic ichthyosaurs from Svalbard in Norway. All of the article pdfs now have been posted but the supplements are not yet available. Again, many thanks to Jorn Hurum for contacting me about the special issue.
JÃrn H. Hurum, Victoria SjÃholt EngelschiÃn, Inghild Ãkland, Janne Bratvold, Christina Pokriefke Ekeheien, Aubrey Jane Roberts, Lene Liebe Delsett, Bitten Bolvig Hansen, Atle MÃrk, Hans Arne Nakrem, Patrick S. Druckenmiller & Ãyvind Hammer (2018)
The history of exploration and stratigraphy of the Early to Middle Triassic vertebrate-bearing strata of Svalbard (Sassendalen Group, Spitsbergen).
Norwegian Journal of Geology 98(2): 165-174
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The palaeontology of the Lower to Middle Triassic succession in Spitsbergen has been studied for more than a century and a half. Our ability to properly interpret the evolutionary and ecological implications of the faunas requires precise stratigraphic control that has only recently become available. Within such a detailed stratigraphic framework, the Spitsbergen fossil material promises to contribute to our understanding of the faunal recovery after the end-Permian mass extinction.
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Bitten Bolvig Hansen & Ãyvind Hammer (2018)
Stratigraphy and age of the Grippia niveau bonebed, Lower Triassic VikinghÃgda Formation, Spitsbergen.
Norwegian Journal of Geology 98(2): 175-187
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We report on a newly excavated Spathian (Lower Triassic) bonebed on Marmierfjellet, Central Spitsbergen. The bonebed contains a varied material of bones and teeth from marine vertebrates along with conodont elements. The fauna of the bonebed could prove interesting in a global context of recovery and speciation after the Late Permian mass extinction. For this reason it is important to place the bonebed in a stratigraphic and chronologic framework. The bonebed sits within the Grippia niveau and is likely to be the one first described by Stensià in 1921. The bonebed and the Grippia niveau are part of the Vendomdalen Member of the VikinghÃgda Formation. Based on the level in the stratigraphy, the bonebed most likely correlates to the Bajarunia euomphala Zone or the Parasibirites grambergi Zone which makes it either early or early/middle Spathian in age. Some conodont elements from the bonebed are reworked from older sediments but the youngest found are supporting a Spathian age. Vanadium data and TOC content from the bonebed indicate that it was formed under increasingly anoxic conditions.
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Inghild Ãkland, Lene Liebe Delsett, Aubrey Jane Roberts & JÃrn H. Hurum (2018)
A Phalarodon fraasi (Ichthyosauria: Mixosauridae) from the Middle Triassic of Svalbard.
Norwegian Journal of Geology 98(2): 267-288
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A new specimen of Phalarodon from the Middle Triassic Botneheia Formation on Svalbard, although not complete, is well preserved with both cranial and postcranial elements. Uncompressed preservation of the rostrum reveals the dental groove divided by alveolar bone between the teeth. The right opisthotic has a thin and plate-like paroccipital process, a structure which has only been observed in Mixosaurus cornalianus among mixosaurids. The rare preservation of the atlas-axis complex, being nearly complete and articulated, is very similar to that of Phalarodon callawayi. The interclavicle, although not complete, is preserved with detailed structures which have previously not been described in Mixosauridae. Contrary to earlier studies, the shoulder girdle, with an articulated scapula and coracoid, reveals a coracoid facet on the scapula. Using comparative morphological and phylogenetic analyses, similarities between the new specimen and the known species of Mixosauridae are addressed. We assign the new specimen to Phalarodon fraasi. With its uncompressed preservation, the new specimen contributes to the knowledge of our morphology of the species. This study suggests a reassignment of the specimen PMO 219.250 to the genus Mixosaurus, and opens up for the possibility of Mixosaurus on Svalbard. This would imply a wider geographical distribution of the genus than previously recognised. Additionally, it would prove the coexistence of Mixosaurus and Phalarodon in a shared habitat at the same point in time, a hypothesis that is strengthened by the differences in dentition which reflects separate feeding habits, and thus different niches.
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Christina Pokriefke Ekeheien, Lene Liebe Delsett, Aubrey Jane Roberts & JÃrn H. Hurum (2018)
Preliminary report on ichthyopterygian elements from the Early Triassic (Spathian) of Spitsbergen.
Norwegian Journal of Geology 98(2): 219-238
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Jaw elements of Omphalosaurus sp. are described from the Early Triassic (Spathian) of Marmierfjellet, Spitsbergen. The elements are from the Grippia and the Lower Saurian niveaus in the Vendomdalen Member of the VikinghÃgda Formation. In the Grippia niveau a bonebed was excavated in 2014â15 and a large number of ichthyopterygian elements were recovered. Together with the omphalosaurian jaw elements a collection of large vertebral centra were recognized as different from the smaller Grippia centra and more than 200 large vertebral centra are referred to Ichthyopterygia indet. and tentatively assigned to regions of the vertebral column. We refrain from further assignment due to the systematic position and the difficulty of defining criteria for recognizing postcranial elements of Omphalosaurus.
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Victoria SjÃholt EngelschiÃn, Lene Liebe Delsett, Aubrey Jane Roberts & JÃrn H. Hurum (2018)
Large-sized ichthyosaurs from the Lower Saurian niveau of the VikinghÃgda Formation (Early Triassic), Marmierfjellet, Spitsbergen.
Norwegian Journal of Geology 98(2): 239-265
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Humeri of Pessopteryx nisseri and vertebrae referred to Cymbospondylus sp. are described from the Lower Saurian niveau at Marmierfjellet, Spitsbergen. This is the most well-preserved Cymbospondylus material described from the Early Triassic so far, and the first description of new material of Pessopteryx nisseri since the species was established. The taxa are not represented by articulated or overlapping material. Herein, the most diagnostic material of both taxa is described and discussed, and the possibility that there is only one large-sized taxon present is suggested. Several specimens of Ichthyosauria indet. are also described. Comparisons are made to previously described specimens from the Lower Saurian niveau, including the disputed Merriamosaurus hulkei. The Boreal Ocean of Svalbard is of particular interest due to its position at the northern margin of Pangea, between the Early Triassic localities of todayâs British Colombia and Nevada, and South China. More than 2000 three-dimensional and disarticulated fragments show that large-sized ichthyosaurs had evolved and were numerous by the Early Triassic.
This is the first time since the collections of Carl Wiman that the Lower Saurian niveau has been systematically sampled and placed in the modern stratigraphy.
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Janne Bratvold, Lene Liebe Delsett & JÃrn H. Hurum (2018)
Chondrichthyans from the Grippia bonebed (Early Triassic) of Marmierfjellet, Spitsbergen.
Norwegian Journal of Geology 98(2): 189-217
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The Grippia bonebed is located at Marmierfjellet in Flowerdalen, Isfjorden area of Spitsbergen. The bonebed occurs in the Vendomdalen Member, Vikinghogda Formation, Early Triassic (Spathian). It is unique in Spitsbergen because of the richness of chondrichthyans, osteichthyes, amphibians and ichthyopterygians. This paper focuses on the chondrichthyans with more than 550 chondrichthyan teeth studied, together with three fin spines and one cephalic spine, assigned to 7 genera and 15 species, 8 of which are new from the Grippia niveau. The Hybodontiformes represent five of the identified genera, where most of the identified species belong to Hybodus and Acrodus. Hybodus sasseniensis, previously recorded from the older Dienarian substage, and is now shown to occur in the younger Spathian substage, and suggested to be the senior synonym of H. rapax. The possibility of Acrodus scaber and A. spitzbergensis being morphospecies, and the Acrodus genus in general, is further discussed. The occurrence of Hybodus microdus in the material is uncertain since it is shown that the mesio-distal length of the teeth is much larger than described by Stensio in 1921. The Neoselachii (modern shark), previously only known from a fin spine of Nemacanthus from the Triassic of Spitsbergen, is now described from teeth belonging to possibly two new neoselachian species. They are referred to Synechodontiformes 1 and 2, awaiting more material to be processed.