Mesosaurus bone microstructure + Blue Anchor Bay Triassic-Jurassic microvertebrate fossils + "Neogene" titanosaur eggshell + fossil disparity metrics
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Ben Creisler
Oct 22, 2024, 6:20:53 PMOct 22
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Ben Creisler
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Maxime Renaud, Christopher J. Duffin, Claudia Hildebrandt & Michael J. Benton (2024)
Microvertebrates from the Rhaetian bone beds at Blue Anchor Bay, Somerset
Geological Magazine 161: e8
DOI: https://doi.org/10.1017/S0016756824000268
https://www.cambridge.org/core/journals/geological-magazine/article/microvertebrates-from-the-rhaetian-bone-beds-at-blue-anchor-bay-somerset/ED645C8C7010AC07CFA61A577E9A2C26
The cliff and foreshore sections at Blue Anchor Bay, north Somerset, provide a detailed picture of the transitional Triassic–Jurassic succession. The site has been recorded as a location for fossil fishes for over 200 years, and yet the assemblages from the bone beds have not been described. Here, we present new observations on the two bone beds and find major faunal differences: the classic basal bone bed at Blue Anchor Bay contains an assemblage dominated by osteichthyan teeth, unexpected because elsewhere the ichthyofauna is usually dominated by chondrichthyans. The upper bone bed at Blue Anchor Bay is indeed more typical, being dominated by teeth of hybodont chondrichthyans. We report two unusual finds, first five teeth of the rare shark Parasycylloides turnerae, only the fifth such record in the UK. Further, we report here for the first time a tooth of the pycnodontiform Eomesodon, the first report of this taxon from the Triassic of the UK or Europe. The two bone beds are distinguished not only by different assemblages, but also by evidence of different degrees of anoxia and water depth: the upper bone bed contains abundant pyrite and marcasite, indicating highly anoxic conditions, and perhaps deposition in deeper water than the basal bone bed.
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Menna Jones & Roger Close (2024)
Standardizing fossil disparity metrics using sample coverage
Palaeontology 67(5): e12729
doi: https://doi.org/10.1111/pala.12729
https://onlinelibrary.wiley.com/doi/full/10.1111/pala.12729
Free pdf:
https://onlinelibrary.wiley.com/doi/epdf/10.1111/pala.12729
Estimating past biodiversity using the fossil record is a central goal of palaeobiology. Because raw estimates of biodiversity are biased by variation in sampling intensity across time, space, environments and taxonomic groups, sampling standardization is routinely applied when estimating taxonomic diversity (e.g. species richness). However, sampling standardization is less commonly used when estimating alternative currencies of biological diversity, such as morphological disparity. Here, we show the effects of standardizing fossil time series of morphological disparity to equal sample completeness, or ‘coverage’, of the underlying taxon-frequency distribution. We apply coverage-based standardization to three published datasets of discrete morphological characters (echinoderms, ichthyosaurs and ornithischian dinosaurs), and quantify disparity using two metrics: weighted mean pairwise dissimilarity (WMPD) and the sum of variance (SOV). We also compare the effects of coverage-based and sample-size-based standardization. Our results show that coverage standardization can yield estimates of disparity through time that dramatically deviate from raw estimates, both in magnitude and direction of changes. These findings demonstrate that future studies of morphological disparity should control for variation in sampling intensity to enable more reliable inferences.
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Some recent papers:
Thiago Carlisbino, Brodsky Dantas Macedo de Farias, Fernando Antonio Sedor & Cesar Leandro Schultz (2024)
Bone microstructure analyses in ontogenetic series of Mesosaurus tenuidens from the early Permian of Brazil
The Anatomical Record (advance online publication)
doi: https://doi.org/10.1002/ar.25591
https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.25591
Osteohistological evidence is widely used to infer paleobiological traits of fossil vertebrates, such as ontogeny and growth rates. Mesosaurs, an enigmatic group of aquatic reptiles from the early Permian, are the most well-known Paleozoic amniotes from Africa and South America. Their fossils are abundant in South America, ranging from the central-west region of Brazil to the southernmost areas, as well as parts of Paraguay and Uruguay. In this contribution, we examined the bone microstructure of Mesosaurus tenuidens by analyzing thin sections of axial and appendicular elements of several specimens collected from various Brazilian sites. The microstructure of the bones showed minimal histological variability among elements, predominantly composed of parallel-fibered tissues, indicating slow growth rhythm, along with increased bone density attributed to pachyosteosclerosis. The cortical area consists of poorly vascularized parallel-fibered bone tissue, which was interrupted by multiple cyclical growth marks, some of them being supernumerary, suggesting a strong influence of seasonality. Moreover, the organization of growth marks suggests distinct life history trajectories among individuals collected from different outcrops, reflecting environmental heterogeneity throughout the basin. Internally, the endosteal domain exhibits greater vascularization compared to the cortices and frequently contained calcified cartilage. In the ontogenetic series, there was a progressive filling of the medullary region from small to large individuals. The presence of the External Fundamental System (a proxy indicating somatic maturity) was observed in femora and ribs, suggesting that determinate growth was already occurring in Permian mesosaurs and may not be an exclusive specialization of crown amniotes.
Bone microstructure analyses in ontogenetic series of Mesosaurus tenuidens from the early Permian of Brazil
The Anatomical Record (advance online publication)
doi: https://doi.org/10.1002/ar.25591
https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.25591
Osteohistological evidence is widely used to infer paleobiological traits of fossil vertebrates, such as ontogeny and growth rates. Mesosaurs, an enigmatic group of aquatic reptiles from the early Permian, are the most well-known Paleozoic amniotes from Africa and South America. Their fossils are abundant in South America, ranging from the central-west region of Brazil to the southernmost areas, as well as parts of Paraguay and Uruguay. In this contribution, we examined the bone microstructure of Mesosaurus tenuidens by analyzing thin sections of axial and appendicular elements of several specimens collected from various Brazilian sites. The microstructure of the bones showed minimal histological variability among elements, predominantly composed of parallel-fibered tissues, indicating slow growth rhythm, along with increased bone density attributed to pachyosteosclerosis. The cortical area consists of poorly vascularized parallel-fibered bone tissue, which was interrupted by multiple cyclical growth marks, some of them being supernumerary, suggesting a strong influence of seasonality. Moreover, the organization of growth marks suggests distinct life history trajectories among individuals collected from different outcrops, reflecting environmental heterogeneity throughout the basin. Internally, the endosteal domain exhibits greater vascularization compared to the cortices and frequently contained calcified cartilage. In the ontogenetic series, there was a progressive filling of the medullary region from small to large individuals. The presence of the External Fundamental System (a proxy indicating somatic maturity) was observed in femora and ribs, suggesting that determinate growth was already occurring in Permian mesosaurs and may not be an exclusive specialization of crown amniotes.
=======
Free pdf:
Maxime Renaud, Christopher J. Duffin, Claudia Hildebrandt & Michael J. Benton (2024)
Microvertebrates from the Rhaetian bone beds at Blue Anchor Bay, Somerset
Geological Magazine 161: e8
DOI: https://doi.org/10.1017/S0016756824000268
https://www.cambridge.org/core/journals/geological-magazine/article/microvertebrates-from-the-rhaetian-bone-beds-at-blue-anchor-bay-somerset/ED645C8C7010AC07CFA61A577E9A2C26
The cliff and foreshore sections at Blue Anchor Bay, north Somerset, provide a detailed picture of the transitional Triassic–Jurassic succession. The site has been recorded as a location for fossil fishes for over 200 years, and yet the assemblages from the bone beds have not been described. Here, we present new observations on the two bone beds and find major faunal differences: the classic basal bone bed at Blue Anchor Bay contains an assemblage dominated by osteichthyan teeth, unexpected because elsewhere the ichthyofauna is usually dominated by chondrichthyans. The upper bone bed at Blue Anchor Bay is indeed more typical, being dominated by teeth of hybodont chondrichthyans. We report two unusual finds, first five teeth of the rare shark Parasycylloides turnerae, only the fifth such record in the UK. Further, we report here for the first time a tooth of the pycnodontiform Eomesodon, the first report of this taxon from the Triassic of the UK or Europe. The two bone beds are distinguished not only by different assemblages, but also by evidence of different degrees of anoxia and water depth: the upper bone bed contains abundant pyrite and marcasite, indicating highly anoxic conditions, and perhaps deposition in deeper water than the basal bone bed.
====
Diego Brandoni, Javier Soffiantini, Lucas E. Fiorelli & Ernesto Brunetto (2024)
Paleogeographic implication of a titanosaur eggshell from the Neogene of the Entre Ríos Province, Argentina
Journal of South American Earth Sciences 105204
doi: https://doi.org/10.1016/j.jsames.2024.105204
https://www.sciencedirect.com/science/article/abs/pii/S0895981124004267
Highlights
A titanosaur eggshell from the Neogene of the Entre Ríos Province is described.
Titanosauria eggshells are frequent in units of the Upper Cretaceous of western Uruguay
The eggshell herein described would come from the eastern area of the basin (western Uruguay)
Abstract
The Lower Member of the Ituzaingó Formation (LMIF), fluvial in origin and assigned to the Upper Miocene, contains a conglomerate level known as “Mesopotamiense” or “Conglomerado osífero” that has yielded a rich fauna of vertebrates. The aim of this contribution is to describe a titanosaurian dinosaur eggshell fragment recovered from the LMIF at the locality of Toma Vieja (western Entre Ríos Province), discussing its paleogeographic history and implications. Fragments of eggshells referred to Titanosauria are frequent from litostratigraphic units of the Upper Cretaceous of western Uruguay (e.g., Guichón, Mercedes, and Queguay Formations). Besides, a fragment of eggshell recovered from the Puerto Yeruá Formation (Upper Cretaceous) at eastern Entre Ríos Province was described. Geophysical data from the Entre Ríos Province allow to propose the presence of a Lower Cretaceous field of extensional tectonic stresses that generated structural lineaments with a E-W and ENE-WSW trend. This ancient penetrative Cretaceous tectonic framework would have exerted control on the shape of the basin and sediment flow patterns and subsequent sedimentation, by promoting the generation of accommodation space over the late Paleogene and the Neogene. The phenomenon would have conditioned the deposition of the Fray Bentos Formation, the subsequent marine Paraná Formation, and the sedimentation of the LMIF, with source materials coming from the east. Thus, it is hypothesized that the fragment of eggshell of Titanosauria would come from the eastern area of the basin (western Uruguay) as a consequence of the existence of a paleohydric system with predominantly E-W and ENE-WSW directions. This late Neogene system would have been controlled by inherited Cretaceous structural lineaments with orientations similar to those that also govern the current fluvial systems of western Uruguay, developed on the Mesozoic substrate.
===
Paleogeographic implication of a titanosaur eggshell from the Neogene of the Entre Ríos Province, Argentina
Journal of South American Earth Sciences 105204
doi: https://doi.org/10.1016/j.jsames.2024.105204
https://www.sciencedirect.com/science/article/abs/pii/S0895981124004267
Highlights
A titanosaur eggshell from the Neogene of the Entre Ríos Province is described.
Titanosauria eggshells are frequent in units of the Upper Cretaceous of western Uruguay
The eggshell herein described would come from the eastern area of the basin (western Uruguay)
Abstract
The Lower Member of the Ituzaingó Formation (LMIF), fluvial in origin and assigned to the Upper Miocene, contains a conglomerate level known as “Mesopotamiense” or “Conglomerado osífero” that has yielded a rich fauna of vertebrates. The aim of this contribution is to describe a titanosaurian dinosaur eggshell fragment recovered from the LMIF at the locality of Toma Vieja (western Entre Ríos Province), discussing its paleogeographic history and implications. Fragments of eggshells referred to Titanosauria are frequent from litostratigraphic units of the Upper Cretaceous of western Uruguay (e.g., Guichón, Mercedes, and Queguay Formations). Besides, a fragment of eggshell recovered from the Puerto Yeruá Formation (Upper Cretaceous) at eastern Entre Ríos Province was described. Geophysical data from the Entre Ríos Province allow to propose the presence of a Lower Cretaceous field of extensional tectonic stresses that generated structural lineaments with a E-W and ENE-WSW trend. This ancient penetrative Cretaceous tectonic framework would have exerted control on the shape of the basin and sediment flow patterns and subsequent sedimentation, by promoting the generation of accommodation space over the late Paleogene and the Neogene. The phenomenon would have conditioned the deposition of the Fray Bentos Formation, the subsequent marine Paraná Formation, and the sedimentation of the LMIF, with source materials coming from the east. Thus, it is hypothesized that the fragment of eggshell of Titanosauria would come from the eastern area of the basin (western Uruguay) as a consequence of the existence of a paleohydric system with predominantly E-W and ENE-WSW directions. This late Neogene system would have been controlled by inherited Cretaceous structural lineaments with orientations similar to those that also govern the current fluvial systems of western Uruguay, developed on the Mesozoic substrate.
===
Free pdf:
Menna Jones & Roger Close (2024)
Standardizing fossil disparity metrics using sample coverage
Palaeontology 67(5): e12729
doi: https://doi.org/10.1111/pala.12729
https://onlinelibrary.wiley.com/doi/full/10.1111/pala.12729
Free pdf:
https://onlinelibrary.wiley.com/doi/epdf/10.1111/pala.12729
Estimating past biodiversity using the fossil record is a central goal of palaeobiology. Because raw estimates of biodiversity are biased by variation in sampling intensity across time, space, environments and taxonomic groups, sampling standardization is routinely applied when estimating taxonomic diversity (e.g. species richness). However, sampling standardization is less commonly used when estimating alternative currencies of biological diversity, such as morphological disparity. Here, we show the effects of standardizing fossil time series of morphological disparity to equal sample completeness, or ‘coverage’, of the underlying taxon-frequency distribution. We apply coverage-based standardization to three published datasets of discrete morphological characters (echinoderms, ichthyosaurs and ornithischian dinosaurs), and quantify disparity using two metrics: weighted mean pairwise dissimilarity (WMPD) and the sum of variance (SOV). We also compare the effects of coverage-based and sample-size-based standardization. Our results show that coverage standardization can yield estimates of disparity through time that dramatically deviate from raw estimates, both in magnitude and direction of changes. These findings demonstrate that future studies of morphological disparity should control for variation in sampling intensity to enable more reliable inferences.
======
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