[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

[dinosaur] Polycotylid Long Bone Microanatomy and Histology + alligator diving + Stenoplacosaurus + more free pdfs






Ben Creisler

Some recent non-dino papers with free pdfs:

Free pdf:


F. R. OâKeefe, P. M. Sander, T. Wintrich & S. Werning (2019)
Ontogeny of Polycotylid Long Bone Microanatomy and Histology.Â
Integrative Organismal Biology 1(1): oby007


Plesiosauria is an extinct clade of diapsid marine reptiles that evolved in the Late Triassic and radiated globally for the remainder of the Mesozoic. The recent description of a pregnant specimen of Polycotylus latipinnis demonstrates that some plesiosaurs were viviparous. To establish a baseline of histological data on plesiosaur ontogeny, we sampled the mother and fetus of the gravid plesiosaur specimen. To widen the base of data concerning ontogeny and life history of plesiosaurs, we gathered additional morphologic and histologic data from a securely identified growth series of polycotylids from the Pierre Shale of South Dakota. Paleohistological thin sections were prepared from the three humeri. Both adults show a dense, heavily remodeled cortex consisting entirely of longitudinally oriented secondary osteons, except for a thin rind of superficial primary bone. The mother exhibits an external fundamental system, indicating it was fully mature; the other adult does not. In both adults the cortex grades into a spongy medulla, comprising large vascular canals and erosion rooms surrounded by secondary lamellar trabecular bone, and lacking a marrow cavity. The fetal humerus possesses a medullary region similar to that of the Dolichorhynchops bonneri adult, although its lamellar bone is primary and deposited around calcified cartilage. The medulla is demarcated from the cortex by a prominent Kastschenkoâs line. The cortex of the fetus is a relatively thin layer of periosteal woven bone, longitudinally to radially vascularized, and interfingered with columns of osteoblasts surrounded by rapidly-deposited extracellular matrix. The neonate humerus resembles the fetus, with its trabeculae identical in both size and histology, although it lacks calcified cartilage. The cortex is also similar but much thicker, consisting entirely of rapidly deposited, radially vascularized, woven to fibrolamellar bone. The cortex carries a line near its surface. This feature is not a line of arrested growth, but a sudden change in vascular angle and increase in bone density. We argue this feature is a birth line indicating a change in growth regime, possibly in response to increased hydrodynamic forces after birth. The birth line indicates that the neonate was about 40% of maternal length when born. Our histological data demonstrate that polycotylids had very high fetal growth rates, and that birth size was large. Comparison with the geologically oldest plesiosaur confirms that rapid growth evolved in the Triassic, although histological details differ, and the degree to which the polycotylid ontogenetic pattern is generalizable to other plesiosaurs is currently unknown. Further histological research utilizing full growth series is needed, particularly for Jurassic taxa.


==============

Additional non-dino papers that may be of interest:

Free pdf:


T. J. Uriona, M. Lyon & C. G. Farmer (2019)
Lithophagy Prolongs Voluntary Dives in American Alligators (Alligator mississippiensis )Â
Integrative Organismal Biology 1(1): oby008


Many vertebrates ingest stones, but the function of this behavior is not fully understood. We tested the hypothesis that lithophagy increases the duration of voluntary dives in juvenile American alligators (Alligator mississippiensis). After ingestion of granite stones equivalent to 2.5% of body weight, the average duration of dives increased by 88% and the maximum duration increased by 117%. These data are consistent with the hypothesis that gastroliths serve to increase specific gravity, and that the animals compensate by increasing lung volume, thereby diving with larger stores of pulmonary oxygen.


====


Free pdf:

J. G. Capano, S. Moritz. R. L. Cieri, L. Reveret & E. L. Brainerd (2019)
Rib Motions Donât Completely Hinge on Joint Design: Costal Joint Anatomy and Ventilatory Kinematics in a Teiid Lizard, Salvator merianae.Â
Integrative Organismal Biology 1(1): oby004


Rib rotations contribute to lung ventilation in most extant amniotes. These rotations are typically described as bucket-handle rotation about a dorsoventral axis, caliper rotation about a craniocaudal axis, and pump-handle rotation about a mediolateral axis. A synapomorphy for Lepidosauria is single-headed costovertebral articulations derived from the ancestral double-headed articulations of most amniotes. With a single articular surface, the costovertebral joints of squamates have the potential to rotate with three degrees-of-freedom (DOFs), but considerable variation exists in joint shape. We compared the costovertebral morphology of the Argentine black and white tegu, Salvator merianae, with the green iguana, Iguana iguana, and found that the costovertebral articulations of I. iguana were hemispherical, while those of S. merianae were dorsoventrally elongated and hemiellipsoidal. We predicted that the elongate joints in S. merianae would permit bucket-handle rotations while restricting caliper and pump-handle rotations, relative to the rounded joints of I. iguana. We used X-ray reconstruction of moving morphology to quantify rib rotations during breathing in S. merianae for comparison with prior work in I. iguana. Consistent with our hypothesis, we found less caliper motion in S. merianae than in I. iguana, but unexpectedly found similar pump-handle magnitudes in each species. The dorsoventrally elongate costovertebral morphology of S. merianae may provide passive rib support to reduce the conflict between locomotion and ventilation. Moreover, the observation of multiple DOFs during rib rotations in both species suggests that permissive costovertebral morphology may be more related to the biological roles of ribs outside of ventilation and help explain the evolution of this trait.

======

2018 papers not yet mentioned:

Free pdf:

Stenoplacosaurus n. gen.

Robert M. Sullivan and Liping Dong (2018)
Stenoplacosaurus mongoliensis, a new generic name for "Placosaurus" mongoliensis (Anguidae, Glyptosaurinae) from the Shara Murun Formation, Nei Mongol (Inner Mongolia), China.
in Lucas, S.G. and Sullivan, R.M., eds., 2018, Fossil Record 6. New Mexico Museum of Natural History and Science Bulletin 79: 691-694


The genus Stenoplacosaurus (n. gen.) is established for the holotype of "Placosaurus" mongoliensis. The holotype of Stenoplacosaurus mongoliensis, from the middle Eocene Shara Murun Formation (Sharamurunian age), is distinct from the European Placosaurus rugosus and P. estesi based, in part, onhaving slender unfused frontalsand fewer osteoderms covering the frontal bones. A nearly complete pair of frontals from the Rencun Member, Heti Formation (Sharamurunian), bears a near identical morphology and osteoderm distribution on the frontals, and is thus considered to be an exemplar of this species. Recent phylogenetic analyses have confirmed the distinct nature of the taxon Placosaurus rugosus. However, P. estesi is here retained in the genus Placosaurus, based on having concave frontal orbital borders and a W-shaped frontonasal suture, two characters that were misinterpreted in recent studies. The retention of P. estesi in the genus Placosaurus is consistent with its age and geographic proximity to the holotype, P. rugosus. Morphological differences between P. rugosus and P. estesi are considered specific and not generic.


=======

Free pdf:

Spencer G. Lucas, Emily D. Thorpe, David S. Berman, Larry F. Rinehart, Vincent L Santucci and Amy C. Henrici (2018)
Discovery of a tetrapod body fossil in the Lower Permian Yeso group, central New Mexico.
in Lucas, S.G. and Sullivan, R.M., eds., 2018, Fossil Record 6. New Mexico Museum of Natural History and Science Bulletin 79: 493-497.


The lower Permian Yeso Group records arid coastal plain, shallow marine and evaporitic deposition across much of central New Mexico during Leonardian time. Generally considered to have few fossils, recent study of Yeso Group strata has uncovered a diverse fossil record of marine microorganisms (mostly algae and foraminiferans), terrestrial plants and tetrapod footprints. We document the discovery of a tetrapod body fossil in the Yeso Groupâa partial skeleton of a varanopid eupelycosaur. The fossil consists of the natural molds of articulated bones in two pieces, part and counterpart, that were preserved in a sandstone bed of the lower part of the Arroyo de Alamillo Formation in the southern Manzano Mountains. The fossil-bearing sandstone is interpreted as an eolian sheet sand. The casts preserve part of the pelvis(?), 18 caudal vertebral centra, both femora, tibia-fibulae, and most of the pedes, largely in close articulation, of a single individual. The skeleton is of a relatively small (femur length = 62 mm, total length of the preserved cast from the pelvis to tip of the incomplete tail = 325 mm) and gracile eupelycosaur most similar to Varanops. In New Mexico, various early Permian eupelycosaurs are known from the older strata of the Bursum Formation, Abo Formation, and Cutler Group, so this discovery extends the eupelycosaur fossil record in the state into younger early Permian strata. It also indicates that a substantial community must have been present on the arid coastal plain during deposition of the Arroyo de Alamillo Formation, as the varanopid is a generally large, early Permian predator that likely fed on smaller vertebrates and arthropods. Furthermore, this discovery indicates the potential for additional discoveries of tetrapod body fossils in Yeso Group strata.

=====


Virus-free. www.avg.com