Multi-taxic palaeohistological analyses of vertebrates originating from the Upper Triassic at Krasiejów (SW Poland) and an assessment of growth patterns in comparative taxa

Palaeohistology is a good source of information about the biology of extinct animals as it provides insight into skeletochronology, metabolic rate or mode of life. The Polish Krasiejów locality recovers a unique Upper Triassic ecosystem with the aquatic temnospondyl amphibians Metoposaurus krasiejowensis, and Cyclotosaurus intermedius, the aquatic to semi-aquatic phytosaur Parasuchus cf. arenaceus, the terrestrial aetosaur Stagonolepis olenkae and the volant proterosaur Ozimek volans. This is the first study sampling phylogenetically distant, ectotherm taxa originating from one locality, with consideration of bone adaptation, phylogenetic relationship or ontogenetic stage, as a possible growth pattern alteration. Humeri and femora of all above-mentioned taxa were sampled in order to study the histological growth pattern and to analyse if the external, e.g., environmental and/or palaeoclimatic factors influenced the growth. Independent of the phylogenetic position or the ontogenetic stage, the temnospondyls, phytosaurs and aetosaur bones from Krasiejów grew with a lamellar-zonal bone type (LZB) consisting of parallel-fibred bone, grading into lamellar bone. A complete growth mark consists of a vascularised zone and an (almost) avascular annulus, but lacking the deposition of a Line of Arrested Growth (LAGs). Surprisingly, both the amphibians and reptiles grew with a similar pattern, despite their distant phylogeny, or different modes of life, implying a strong influence of external features on the growth pattern over the primary genotypic signal. The only herein studied taxon from Krasiejów showing, beside zones and annuli, the deposition of LAGs is O. volans; however, its unique pattern is most probably linked with the biomechanical bone adaptation to gliding. In addition, the comparative taxa sampled from German localities, namely the phytosaur Nicrosaurus sp. and the aetosaur Aetosaurus ferratus, and the Indian temnospondyl amphibian Panthasaurus maleriensis, showed that the animals grew also with LZB, the same as the Polish taxa, but either showed deposition of LAGs (Nicrosaurus) or revealed the ontogenetic influence, thus, the Aetosaurus were too young to be able to deposit growth marks. A comparison with literature data showed, that aetosaurs and phytosaurs from North and South America are characterised by a rapid deposited of fibro-lamellar bone type with multiple LAGs preserved, which is distinctly different from the specimens sampled herein. Further, the Moroccan metoposaurid, Dutuitosaurus ouazzoui, beside growing with LZB, similar to the taxa sampled herein, preserved multiple LAGs. This implies a strong influence of the external factors on the growth pattern on animals at the family level (e.g., Metoposaurus and Panthasaurus vs. Dutuitosaurus), occupying the same ecological niche but separated geographically; similar to aetosaurs and phytosaurs. Finally, this suggests strong climatic differences during the Upper Triassic between today’s Europe and Asia and that of North and South America and Africa. Moreover, it is astonishing, that animals from one locality, occupying different ecological niches seem to copy a growth pattern influenced by climatic and/or environmental conditions, rather than grow with the genetically induced signal

An Upper Triassic terrestrial vertebrate assemblage from the forgotten Kocury locality (Poland) with a new aetosaur taxon

We thank D. Mazurek who was the first to draw our attention to the Velocipes guerichi material, and members of the popular science website Dinozaury.com who were engaged in the preliminary study of that historical material. We thank the mayor of Kocury, D. Maleska, the forest ranger K. Wójcik and the forestry management of Lubliniec for their help in performance of our field work. We are grateful to participants of the excavations in Kocury in seasons 2012 to 2019, including G. Niedźwiedzki and R. Piechowski. We thank G. Racki for help in obtaining the archival literature, as well as A. and U. Gaedke for helping us to translate some of these publications. We thank V. Dutra Paes-Neto for discussion and comments on a new aetosaur. We are grateful to Editor M. Young and reviewers S. Dias-da-Silva and R. T. Müller for important suggestions that improved our manuscript.Since 1990, several localities within the Keuper (upper Middle to Upper Triassic) strata in southern Poland have yielded remains of numerous terrestrial vertebrate species. Here we report a new Upper Triassic vertebrate assemblage from the rediscovered Kocury locality. An incomplete theropod dinosaur fibula named Velocipes guerichi described in 1932 was found there. The site was then forgotten and not explored until our excavations initiated in 2012, that yielded material of a lungfish, a proterochersid turtle, and a new typothoracin aetosaur Kocurypelta silvestris gen. et sp. nov. The new taxon is characterized by autapomorphies of the maxilla: an elongated edentulous posterior portion longer than 80% of the posterior maxillary process, a short medial shelf restricted to the posterior portion of the bone, an anteriorly unroofed maxillary accessory cavity, and lack of a distinct groove for choanal recess on the anteromedial surface of the bone. These new finds improve our knowledge on the vertebrate diversity of the Germanic Basin in the Late Triassic, evidencing the presence of yet unrecognized taxa. Additionally, the partial cranial aetosaur material emphasizes the issues with the aetosaurian taxonomy that is focused mostly on the osteoderm morphology.NC

Rotten Hill: A Late Triassic Bonebed In The Texas Panhandle, USA

The Rotten Hill bonebed is a Late Triassic fossil locality in the Texas Panhandle discovered by Floyd V. Studer in 1926, and collected primarily by WPA-funded excavations during the late 1930s and early 1940s. This locality is in the lower part of the Tecovas Formation (Chinle Group) and is of Adamanian (late Carnian) age. Forensic taphonomic analysis indicates it is a mass death assemblage that was hydraulically concentrated. The Rotten Hill bonebed is a low diversity multitaxic and monodominant bonebed; the vast majority of the bones are of the metoposaurid Koskinonodon perfectum. It closely resembles other Chinle Group metoposaurid-dominated bonebeds that suggest aggregation of a group of metoposaurids, followed by catastrophic mortality, complete disarticulation and disassociation of the skeletons, culminated by rapid transport and burial. Fossil taxa from the Rotten Hill bonebed are the unionoidan bivalve Plesioelliptio sp., the coprolite ichnogenera Alacocopros, Eucoprus and Heteropolacopros; various fishes known from ichthyoliths; a rhynchosaur; a sphenodontid; the archosauriform Vancleavea; the trilophosaurs Trilophosaurus and Spinosuchus; the phytosaur Smilosuchus; a probable poposaurid (cf. Postosuchus), the aetosaurs Desmatosuchus and cf. Stagonolepis; a shuvosaurid; and the metoposaurids Apachesaurus gregorii and K. perfectum. K. perfectum is represented by numerous skulls, lower jaws, vertebrae, girdle and limb bones representing a minimum number of 68 individuals based on recovered interclavicles. We describe the osteology and variation of these bones, which allows us to present a revised diagnosis of Koskinonodon that employs new postcranial characters to differentiate it from other metoposaurid genera. We also compiled and analyzed a morphometric database of the Rotten Hill Koskinonodon to conclude that bone growth varied from isometry to allometry and suggests a loss in limb robustness during ontogeny that likely indicates a transition from a partly terrestrial to a more aquatic lifestyle. Probability plotting to test for size groups in the Rotten Hill Koskinodonon identifies 10-11 groups that we interpret as yearly age cohorts and use to plot a growth curve. This indicates indeterminate growth in K. perfectum and that the Rotten Hill sample represents a population of breeding adults, some of which survived at least 10-11 years after reaching sexual maturity. This is a growth curve also characteristic of some living salamanders. We infer that K. perfectum employed some mechanism, such as disparate feeding strategies, or another ecological factor that enforced separation of adults and juveniles, to reduce predation on juveniles by conspecifics and minimize the competition for food resources between the ontogenetic stages

Comparative bone histology of two thalattosaurians (Diapsida: Thalattosauria): Askeptosaurus italicus from the Alpine Triassic (Middle Triassic) and a Thalattosauroidea indet. from the Carnian of Oregon (Late Triassic)

Here, we present the first bone histological and microanatomical study of thalattosaurians, an enigmatic group among Triassic marine reptiles. Two taxa of thalattosaurians, the askeptosauroid Askeptosaurus italicus and one as yet undescribed thalattosauroid, are examined. Both taxa have a rather different microanatomy, tissue type, and growth pattern. Askeptosaurus italicus from the late Anisian middle Besano Formation of the southern Alpine Triassic shows very compact tissue in vertebrae, rib, a gastralium, and femora, and all bones are without medullary cavities. The tissue shows moderate to low vascularization, dominated by highly organized and very coarse parallel-fibred bone, resembling interwoven tissue. Vascularization is dominated by simple longitudinal vascular canals, except for the larger femur of Askeptosaurus, where simple vascular canals dominate in a radial arrangement. Growth marks stratify the cortex of femora. The vertebrae and humeri from the undescribed thalattosauroid from the late Carnian of Oregon have primary and secondary cancellous bone, resulting in an overall low bone compactness. Two dorsal vertebral centra show dominantly secondary trabeculae, whereas a caudal vertebral centrum shows much primary trabecular bone, globuli ossei, and cartilage, indicating an earlier ontogenetic stage of the specimens or paedomorphosis. The humeri of the thalattosauroid show large, simple vascular canals that are dominantly radially oriented in a scaffold of woven and loosely organized parallel-fibred tissue. Few of the simple vascular canals are thinly but only incompletely lined by parallel-fibered tissue. In the Oregon material, changes in growth rate are only indicated by changes in vascular organization but no distinct growth marks were identified. The compact bone of Askeptosaurus is best comparable to some pachypleurosaurs, whereas its combination of tissue and vascularity is similar to eosauropterygians in general, except for the coarse nature of its parallel-fibred tissue. The cancellous bone of the Oregon thalattosauroid resembles what is documented in ichthyosaurs and plesiosaurs. However, in contrast to these its tissue does not consist of fibro-lamellar bone type. Tissue types of both thalattosaurian taxa indicate rather different growth rates and growth patterns, associated with different life history strategies. The microanatomy reflects different life styles that fit to the different environments in which they had been found (intraplatform basin vs. open marine). Both thalattosaurian taxa differ from each other but in sum also from all other marine reptile taxa studied so far. Thalattosaurian bone histology documents once more that bone histology provides for certain groups (i.e., Triassic Diapsida) only a poor phylogenetic signal and is more influenced by exogenous factors. Differences in lifestyle, life history traits, and growth rate and pattern enabled all these Triassic marine reptiles to live contemporaneously in the same habitat managing to avoid substantial competition

Growth and limb bone histology of aetosaurs and phytosaurs from the Late Triassic Krasiejów locality (sw Poland) reveals strong environmental influence on growth pattern

Abstract The growth pattern of the Polish phytosaur Parasuchus cf. arenaceus and the aetosaur Stagonolepis olenkae (both Krasiejów; Norian) was studied. Results were compared to published data of other members of these two groups and to a new sample of the German (Heslach; Norian) phytosaur Nicrosaurus sp. All three herein studied taxa display lamellar-zonal bone consisting predominately of parallel-fibred tissue and on average a low to moderate vascular density. Towards the outer cortex the thickness of annuli increases in most samples and becomes distinctly wider than the zones. Therefore, most of the appositional growth in adults was achieved during phases of prolonged slow growth. All bones show a diffuse growth pattern, without well demarcated zones and annuli. Distinct lines of arrested growth (lag) are not identified in the Krasiejów sample, only the Nicrosaurus femur shows one distinct lag as do other taxa outside Krasiejów. Instead, the Krasiejów taxa display multiple rest lines and sub-cycles. Thus, identification and count of annual growth cycles remains difficult, the finally counted annual growth cycles range (two to six) is quite large despite the low size range of the samples. A correlation between age and bone length is not identified, indicating developmental plasticity. Although both are archosaurs, Stagonolepis and Parasuchus are phylogenetically not closely related, however, they show a very similar growth pattern, despite different life styles (terrestrial vs. semi-aquatic). Based on the new data, and previously histological studies from Krasiejów, the local environmental conditions were special and had a strong influence on the growth pattern.</jats:p