[dinosaur] Microlestes microvertebrate quarry + Archegosaurus physiology + varanid growth + tar pits experiment

Ben Creisler

Some recent or not yet mentioned non-dino papers:

David I. Whiteside & Christopher J. Duffin (2017)

Late Triassic terrestrial microvertebrates from Charles Moore's ‘Microlestes’ quarry, Holwell, Somerset, UK.

Zoological Journal of the Linnean Society 179 (3): 677-705

https://academic.oup.com/zoolinnean/article-abstract/179/3/677/3058152/Late-Triassic-terrestrial-microvertebrates-from?redirectedFrom=fulltext

The fissure localities of the Bristol region and South Wales have yielded some of the most important Late Triassic and Early Jurassic small tetrapods. The ‘Microlestes’ quarry fissure at Holwell, which has produced the most diverse overall fauna, was originally investigated in the 1850s by the renowned amateur geologist, Charles Moore. The mammaliamorphs and marine fish have been well documented, but there are few reports and barely any descriptions of the terrestrial small reptile fossils. We address that deficiency with a description of the bones and teeth that can be assigned to the Reptilia, confirming the presence of Diphydontosaurus and describing two new rhynchocephalians. We recognise the presence of Variodens inopinatus Robinson, 1957 and Gephyrosaurus Evans, 1980: the first time that they have been recorded outside their original sites. Additionally, we record a procolophonid, elements of the actinopterygian Pholidophorus, and a number of unnamed lepidosaur specimens that show varying degrees of pleurodont–acrodont implantation, providing an insight into the evolution of rhynchocephalians. Our findings demonstrate that Holwell is a key link between the sauropsid and mammaliamorph fissure faunas of the Late Triassic and Early Jurassic of the south-west UK.

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Free pdf:

Florian Witzmann and Elizabeth Brainerd (2017)

Modeling the physiology of the aquatic temnospondyl Archegosaurus decheni from the early Permian of Germany.

Fossil Record 20: 105-127

doi:10.5194/fr-20-105-2017

http://www.foss-rec.net/20/105/2017/

Physiological aspects like heat balance, gas exchange, osmoregulation, and digestion of the early Permian aquatic temnospondyl Archegosaurus decheni, which lived in a tropical freshwater lake, are assessed based on osteological correlates of physiologically relevant soft-tissue organs and by physiological estimations analogous to air-breathing fishes. Body mass (M) of an adult Archegosaurus with an overall body length of more than 1 m is estimated as 7 kg using graphic double integration. Standard metabolic rate (SMR) at 20 °C (12 kJ h−1) and active metabolic rate (AMR) at 25 °C (47 kJ h−1) were estimated according to the interspecific allometry of metabolic rate (measured as oxygen consumption) of all fish (VO2 = 4. 8 M0. 88) and form the basis for most of the subsequent estimations. Archegosaurus is interpreted as a facultative air breather that got O2 from the internal gills at rest in well-aerated water but relied on its lungs for O2 uptake in times of activity and hypoxia. The bulk of CO2 was always eliminated via the gills. Our estimations suggest that if Archegosaurus did not have gills and released 100 % CO2 from its lungs, it would have to breathe much more frequently to release enough CO2 relative to the lung ventilation required for just O2 uptake. Estimations of absorption and assimilation in the digestive tract of Archegosaurus suggest that an adult had to eat about six middle-sized specimens of the acanthodian fish Acanthodes (ca. 8 cm body length) per day to meet its energy demands. Archegosaurus is regarded as an ammonotelic animal that excreted ammonia (NH3) directly to the water through the gills and the skin, and these diffusional routes dominated nitrogen excretion by the kidneys as urine. Osmotic influx of water through the gills had to be compensated for by production of dilute, hypoosmotic urine by the kidneys. Whereas Archegosaurus has long been regarded as a salamander-like animal, there is evidence that its physiology was more fish- than tetrapod-like in many respects.

Petra Frýdlová, Vendula NutilováJan, DudákJan Žemlička, Pavel Němec, Petr Velenský, Tomáš Jirásek & Daniel Frynta (2017)

Patterns of growth in monitor lizards (Varanidae) as revealed by computed tomography of femoral growth plates.

Zoomorphology 136 (1): 95-106

DOI: 10.1007/s00435-016-0338-3

https://link.springer.com/article/10.1007/s00435-016-0338-3

Growth plate cartilage (GPC) is responsible for the growth of long bones due to endochondral ossification, which is the main mechanism of longitudinal skeletal growth in tetrapods. Degradation of GPC is a sign of determinate growth as it arrests the growth irreversibly. By contrast, indeterminate growth requires the persistence of GPC throughout the entire life. Monitor lizards (Varanidae) were previously reported to exhibit a dual type of growth, determinate as well as indeterminate. To reinvestigate this highly unexpected finding, we examined 13 species of varanids and their close relatives (Shinisauridae and Helodermatidae). In order to visualize GPC on the proximal part of the femur, we employed micro-radiography and micro-computed tomography. In large-bodied species, an extended capability of longitudinal growth was demonstrated; GPC was preserved for most of their lives. On the other hand, GPC senescence with complete disappearance of cartilage was found in adults of small-bodied varanids. These results confirm previous finding and, together with the absence of GPC in the outgroup species, challenge the universality of indeterminate growth in squamates. Moreover, we observed disappearance of GPC in an extremely old Varanus indicus, implying that GPC degradation is not entirely absent but only delayed to senescence in this large-bodied species. These findings raise the intriguing possibility that it is the timing, rather than other underlying mechanisms, what sets apart determinate from indeterminate growth. We therefore suggest that this dual type of growth represents an extreme case of heterochrony and is a consequence of strong sexual selection pressure to large-bodied varanids.

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Lichtig, Asher J. & Lucas, Spencer G. (2017)

Sutures of the shell of the Late Cretaceous-Paleocene baenid turtle Denazinemys.

Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 283(1): 1-8

DOI: https://doi.org/10.1127/njgpa/2017/0622

http://www.ingentaconnect.com/content/schweiz/njbgeol/2017/00000283/00000001/art00001

The sutures of the Late Cretaceous-Paleocene turtle Denazinemys are described in detail and sexual dimorphism recognized based on historical specimens and newly studied, unfused shells. The carapace is remarkable in the possession of an unfused paired nuchal. While it has been observed in turtle embryology that this bone has two ossification centers, this is the first adult turtle known to show this morphology. Furthermore, the pustules on the surface of the carapace of Denazinemys do not align with the sutures, crossing them with no change. Conversely, the pustules are clearly interrupted by the sulci. Histological examination reveals that the pustules on the dorsal surface are composed of an expanded external cortex with no noticeable expansion of the cancellous bone layer. The plastron of Denazinemys is particularly similar to Boremys in the intersection of the gular-humeral sulcus at the widest point of the entoplastron. Overall, the sutures are consistent with what would be expected from the proposed sister group relationship ofDenazinemys with Boremys based on sulci and skull anatomy.

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Caitlin Brown, Emily Curd & Anthony Friscia (2017)

An actualistic experiment to determine skeletonization and disarticulation in the La Brea tar seeps.

PALAIOS 32(3): 119-124

DOI: 10.2110/palo.2016.074

http://palaios.sepmonline.org/content/32/3/119.abstract

http://palaios.geoscienceworld.org/content/32/3/119

The famous Rancho La Brea tar seeps of Southern California trapped thousands of Pleistocene and early Holocene vertebrates, preserving them as jumbled columns of millions of disarticulated bones. Previous work has contributed to a hypothetical entrapment scenario, however, it lacks detail in the period between the time the animals perished and the permeation of their bones with tar. Additionally, previous work has shown that skeletal elements moved apart from each other at least 1–3 meters but it is unclear whether this movement occurred near the surface of the tar, soon after submersion, or later after burial by sediment and compaction. To help answer these questions of disarticulation and transport, we conducted an actualistic experiment to record the progress of microbial succession and skeletonization of specimens in tar. We submerged dismembered bobcat (Lynx rufus) carcasses in an undisturbed tar seep and recorded the progress of microbial faunal changes and tissue decay. Microbial communities differed between tar environments and tissue decay, and changes in microbial communities across the stages of decay indicate rapid microbial succession, with the microbes most involved in the decay likely originating from the liquid surface tar. The minimum time to achieve clean bone was 40 days, from which we conclude that a surficial process may have been responsible for the movement of bones in the La Brea tar seeps.