Donald J. Morgan III & F. Robin O'Keefe (2018)
The cranial osteology of two specimens of Dolichorhynchops bonneri (Plesiosauria, Polycotylidae) from the Campanian of South Dakota, and a cladistic analysis of the Polycotylidae
Cretaceous Research (advance online publication)
This paper describes the cranial morphology of two undescribed specimens of the polycotylid plesiosaur Dolichorhynchops bonneri from the Pierre Shale of South Dakota. Based on the axial osteology of the juvenile specimen (UNSM 55810), it was most likely a neonate at the time of death. The juvenile material exhibits well-defined suture lines in its cranium and exhibits cranial characters that typify a young polycotylid plesiosaur. The adult specimen UNSM 50133 preserves a complete palate and comparisons to KUVP 40002 illustrate intraspecific variation in the osteology of D. bonneri. A linear regression analysis performed on the rostral lengths of D. bonneri specimens, found that the rostrum exhibits negative allometry relative to overall skull length. A phylogenetic analysis positioned D. bonneri within the Polycotylidae. The analysis found resolution for the clade of derived polycotylids, Polycotylinae, and revealed that D. bonneri is part of a clade that contains D. osborni and D. herschelensis. This suggests that similarities between the morphology of D. bonneri and P. latipinnis are due to convergence rather than homology. The phylogenetic analysis did not recover Dolichorhynchops tropicensis within the Dolichorhynchops clade, as it was recovered as a basal member of the Polycotylinae. This suggests that the taxonomy of Turonian polycotylids from the western interior seaway requires further analysis.
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Jeremy E. Martin, RaphaÃl Sarr & Lionel Hautier (2018)
A dyrosaurid from the Paleocene of Senegal.
Journal of Paleontology (advance online publication)
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We describe a partial dyrosaurid skeleton recently prepared out of a limestone block discovered in the 1930s from Danian strata along the Atlantic coast of Senegal. The specimen, from a single individual, comprises nicely preserved elements of the appendicular and axial skeleton from the abdominal and sacral region, which enables us to refine our knowledge on some postcranial characteristics of the Dyrosauridae. Although Dyrosauridae are abundant in early Eocene deposits of North Africa, the present discovery in the Danian of Senegal fills a patchier record early after the K/Pg boundary and provides an important comparative data point with the few other Danian dyrosaurid records such as Atlantosuchus from nearby Morocco or Guarinisuchus and Hyposaurus from Brazil and the USA, respectively.
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Viktoriia Kamska, Edward B. Daeschler, Jason P. Downs, Per E. Ahlberg, Paul Tafforeau and Sophie Sanchez (2018)
Long-bone development and life-history traits of the Devonian tristichopterid Hyneria lindae
Earth and Environmental Science Transactions of The Royal Society of Edinburgh (advance online publication)
Hyneria lindae is one of the largest Devonian sarcopterygians. It was found in the Catskill Formation (late Famennian) of Pennsylvania, USA. The current study focuses on the palaeohistology of the humerus of this tristichopterid and supports a low ossification rate and a late ossification onset in the appendicular skeleton. In addition to anatomical features, the large size of the cell lacunae in the cortical bone of the humerus mid-shaft may suggest a large genome size and associated neotenic condition for this species, which could, in turn, be a partial explanation for the large size of H. lindae. The low metabolism of H. lindae revealed here by bone histology supports the hypothesis of an ambush predatory behaviour. Finally, the lines-of-arrested-growth pattern and late ossification of specimen ANSP 21483 suggest that H. lindae probably had a long juvenile stage before reaching sexual maturity. Although very few studies address the life-history traits of stem tetrapods, they all propose a slow limb development for the studied taxa despite different ecological conditions and presumably distinct behaviours. The bone histology of H. lindae would favour the hypothesis that a slow long-bone development could be a general character for stem tetrapods.