non-dino...
The recent The 150th Annual Meeting of the Kansas Academy of Science had a few Mesozoic vertebrate related items. The abstracts book for all the talks and posters is free:
First description of axial histology for the genus Dolichorhynchops (Sauropterygia; Plesiosauria)Â
Holman, P.L. and Wilson, L.E. (2018)Â
Dolichorhynchops osborni is a species of polycotylid plesiosaur that roamed the Western Interior Seaway during the Campanian age of the Late Cretaceous. FHSM VP-404 is a nearly complete specimen from the Niobrara Formation, Smoky Hill Chalk Member of Logan Co., KS. The purpose of this study is to test if ontogeny can be assessed for D. osborni by using the microanatomy of thoracic ribs. From this specimen the mid-thoracic rib was histologically sectioned at the midpoint and proximal part of the shaft. Previous research shows that the most complete record of growth is retained in the proximal 20% to 30% of the rib in some reptiles. The medullary cavity is small with endosteal trabeculae composed of fibrolamellar bone. The cortex is relatively thick on the lateral and medial horns of the shaft and is composed almost entirely of cancellous bone tissue that appears isometric under cross polarized light. The cortex is also dominated by secondary osteons showing extensive remodeling. There is a very thin layer of non-continuous lamellar bone near the periosteal surface that is often interrupted by secondary osteons. This result mirrors the osteoporotic condition that has previously been seen in the ribs of some adult plesiosaurs and is not consistent with the compact cortex of lamellar bone and growth marks seen in an adult elasmosaur specimen. Due to the highly remodeled nature of these rib sections, they cannot be used to estimate ontogeny in this specimen of D. osborni.Â
Â====Â
New specimens of the hesperornithiform bird Fumicollis from the Upper Cretaceous of Western Kansas.Â
Garofalo, I. and Bell, A.K. (2018)Â
Hesperornithiforms are an extinct group of foot-propelled diving birds from the Cretaceous Period. Currently, four genera are known from the Smoky Hill Chalk of Kansas: Hesperornis, Parahesperornis, Baptornis, and Fumicollis. While Hesperornis is represented by hundreds of specimens, the remaining three genera are only known from a handful of individuals. A collection of previously undescribed hesperornithiform fossils housed at the Fick Fossil and History Museum in Oakley, Kansas includes a left femur (FFHM 1972.121.7f.1) and left tarsometatarsus (FFHM 1972.121.7f.4), which display features consistent with Fumicollis. FFHM 1972.121.7f.1 shows a curved shaft, similar to Fumicollis and unlike Baptornis, but has enough differences from the holotype of Fumicollis that it cannot be confidently assigned to Fumicollis hoffmanni. Due to the isolated nature of FFHM 1972.121.7f.1, we do not consider it appropriate to erect a new taxon, so the specimen is designated Fumicollis sp. FFHM 1972.121.7f.4 is very similar to the holotype of F. hoffmani and is here assigned to this species. These remains demonstrate the morphological variability in hesperornithiforms and emphasize the need for additional specimens to clarify our understanding of this variation.ÂÂ
===Â
Osteohistology and skeletochronology in an ontogenetic series of Clidastes (Squamata: Mosasauridae)Â
ÂGreen, C.C. and Wilson, L.E. (2018)Â
Clidastes was a large, predatory reptile that inhabited the Western Interior Seaway during the Late Cretaceous. Isotopic studies indicate Clidastes maintained body temperatures closer to endothermic animals, leading to speculation they were gigantothermic and able to keep a high body temperature due to size. Based on vascularity, previous studies have also hypothesized higher growth rates in Clidastes than in modern varanids, mosasaurs closest living relative. Whether the growth rates in Clidastes are comparable to endothermic or ectothermic animals has not been studied. Osteohistology and skeletochronology are well-documented techniques used to investigate growth and life histories of extinct animals. This study used these tools to investigate ontogenetic changes in internal microstructure, determine age at the time of death, and estimate growth rates in Clidastes. Four humeri representing a size gradient in Clidastes were histologically analyzed. Skeletochronology calculations age the four specimens as a neonate (>1 year), juvenile (3-4 years), sub-adult (6-7 years), and adult (18-19 years). No growth marks are visible in the neonate, so exact growth rates cannot be calculated. The juvenile and subadult humeri had growth rates averaging 1.7Îm/day and 1.6Îm/day respectively. The largest humerus had a growth rate averaging 0.4Îm/day. Because growth slows after sexual maturity, only the largest humerus is considered sexually mature. No humeri show a cessation of growth or evidence of skeletal maturity. Overall, these growth rates indicate Clidastes grew more like ectothermic varanid lizards which grow 0.0 to 2.0Îm/day. This evidence, coupled with previous isotopic temperature evidence, supports the gigantothermic metabolic hypothesis for Clidastes.Â