Ben Creisler
Some recent Mesozoic and tetrapod-related papers and abstracts:
Free pdf:
Neil Brocklehurst, Elsa Panciroli, Gemma Louise Benevento & Roger B.J. Benson (2021)
Mammaliaform extinctions as a driver of the morphological radiation of Cenozoic mammals.
Current Biology (advance online publication)
DOI: https://doi.org/10.1016/j.cub.2021.04.044
https://www.cell.com/current-biology/fulltext/S0960-9822(21)00591-1
Free pdf:
https://www.cell.com/action/showPdf?pii=S0960-9822%2821%2900591-1
Highlights
The therian mammal radiation is usually associated with extinctions among dinosaurs
Mesozoic therians show greater morphological constraint than their close relatives
The release of this constraint occurred later than the extinction of the dinosaurs
The therian radiation was in part driven by extinctions among other mammaliaforms
Summary
Adaptive radiations are hypothesized as a generating mechanism for much of the morphological diversity of extant species. The Cenozoic radiation of placental mammals, the foundational example of this concept gave rise to much of the morphological disparity of extant mammals, and is generally attributed to relaxed evolutionary constraints following the extinction of non-avian dinosaurs. However, study of this and other radiations has focused on variation in evolutionary rates leaving the extent to which relaxation of constraints enabled the origin of novel phenotypes less well characterized. We evaluate constraints on morphological evolution among mammaliaforms (mammals and their closest relatives) using a new method that quantifies the capacity of evolutionary change to generate phenotypic novelty. We find that Mesozoic crown-group therians, which include the ancestors of placental mammals, were significantly more constrained than other mammaliaforms. Relaxation of these constraints occurred in the mid-Paleocene, post-dating the extinction of non-avian dinosaurs at the K/Pg boundary, instead coinciding with important environmental shifts and with declining ecomorphological diversity in non-theriimorph mammaliaforms. This relaxation occurred even in small-bodied Cenozoic mammals weighing <100 g, which are unlikely to have competed with dinosaurs. Instead, our findings support a more complex model whereby Mesozoic crown therian evolution was in part constrained by co-occurrence with disparate mammaliaforms, as well as by the presence of dinosaurs, within-lineage incumbency effects, and environmental factors. Our results demonstrate that variation in evolutionary constraints can occur independently of variation in evolutionary rate, and that both make important contributions to the understanding of adaptive radiations.
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Jean-David Moreau, Vincent Trincal, Jean-FranÃois Deconinck, Marc Philippe and Benjamin Bourel (2021)
Lowermost Jurassic dinosaur ecosystem from the Bleymard Strait (southern France): sedimentology, mineralogy, palaeobotany and palaeoichnology of the Dolomitic Formation.
Geological Magazine (advance online publication)
DOI: https://doi.org/10.1017/S001675682100039X
https://www.cambridge.org/core/journals/geological-magazine/article/abs/lowermost-jurassic-dinosaur-ecosystem-from-the-bleymard-strait-southern-france-sedimentology-mineralogy-palaeobotany-and-palaeoichnology-of-the-dolomitic-formation/003204F3F2504E219EEEAEFF09723A8E
Lowermost Jurassic dinosaur ecosystem from the Bleymard Strait (southern France): sedimentology, mineralogy, palaeobotany and palaeoichnology of the Dolomitic Formation.
Geological Magazine (advance online publication)
DOI: https://doi.org/10.1017/S001675682100039X
https://www.cambridge.org/core/journals/geological-magazine/article/abs/lowermost-jurassic-dinosaur-ecosystem-from-the-bleymard-strait-southern-france-sedimentology-mineralogy-palaeobotany-and-palaeoichnology-of-the-dolomitic-formation/003204F3F2504E219EEEAEFF09723A8E
We report the first Hettangian theropod tracksite (~200 Ma) yielding a rich accumulation of plant remains from the Bleymard Strait (southern France). It constitutes an excellent opportunity to reconstruct lowermost Jurassic ecosystems hosting dinosaurs and which are still poorly documented in this area. Two morphotypes of tridactyl tracks are distinguished. They share similarities with Grallator and Kayentapus. Plant-bearing beds yield abundant leafy axes (Pagiophyllum peregrinum), male cones (Classostrobus sp.), wood (Brachyoxylon sp.) and pollen of conifers (Classopollis classoides). Sedimentological, petrological and mineralogical analyses demonstrated that, in the Dolomitic Formation from Bleymard, the palaeoenvironment progressively evolved from (1) a shoreface to a foreshore domain; to (2) a shallow environment that is restricted or occasionally open to the sea; then to (3) an intertidal to supratidal zone. The Hettangian theropod ecosystem of the Bleymard Strait was composed of tidal flats that were periodically emerged and bordered paralic environments inhabited by a littoral conifer-dominated forest in which Cheirolepidiaceae were the main component. The paucity of the palaeobotanical assemblage, as well as the xerophytic characteristics of Pagiophyllum, show that flora from Bleymard was adapted to withstand intense sunlight and coastal environments exposed to desiccant conditions coupled with salty sea spray, and dry conditions. These features are those of a conifer-dominated flora under a tropical to subtropical climate. The flora as well as the clay mineral analyses suggest contrasting seasons (cyclically dry then humid). This study supports that theropods were abundant and particularly adapted to this type of littoral environment bordering Cheirolepidiaceae-dominated forests.
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South America has few continental records of the Cretaceous-Paleogene boundary.
La Colonia Formation in Argentina may contain this interval of geological time.
New palynological, paleomagnetic, and geochronological results are presented.
Results show that the Cretaceous-Paleogene boundary interval is recorded here.
Abstract
The La Colonia Formation is an Upper Cretaceous to Paleogene shallow marine sedimentary unit in Chubut Province (Patagonia), Argentina that preserves important vertebrate and plant fossils. Despite good exposures and significant paleontological investigation, the precise age of the La Colonia Formation and its stratigraphic relationship to the Cretaceous-Paleogene (K-Pg) boundary are not well understood. The K-Pg boundary is associated with one of the largest mass extinctions in Earthâs history yet there are few continental stratigraphic records of the boundary in South America, resulting in poor understanding of its effects there. This study combines magnetostratigraphy, detrital zircon uraniumâlead (UâPb) geochronology, and preliminary palynological results to constrain the age of the La Colonia Formation and its fossils more precisely and determine whether it preserves the K-Pg boundary. U-Pb ages of detrital zircons from the directly underlying Puntudo Chico Formation indicate that the base of the La Colonia Formation is younger than â71.7 Ma. The studied palynological assemblage includes Quadraplanus brossus, which is restricted to the Maastrichtian in other southern hemisphere records. Paleomagnetic results show that the â125 meter Cerro Buitre Norte section of the La Colonia Formation and the overlying Cerro Bororà Formation has dominantly normal polarity except for a â5 meter zone of reversed polarity near the base that is interpreted to correlate to Chron C30R of the Geomagnetic Polarity Timescale (GPTS), and a â13 meter zone of reversed polarity near the top of the La Colonia Formation that is interpreted to correlate to Chron C29R. The presence of a magnetozone correlated to C29R in the La Colonia Formation suggests that it preserves the KâPg boundary, making it an important target for continued paleontological collection to better understand the K-Pg extinction and recovery dynamics in South America.
J. Matthias Starck, James R. Stewart & Daniel G. Blackburn (2021)
W.C. Clyde, J.M. Krause, F.De Benedetti, J. Ramezani, N.R. CÃneo, M.A. Gandolfo, P. Haber, C. Whelan & T. Smith (2021)
New South American record of the Cretaceous-Paleogene boundary interval (La Colonia Formation, Patagonia, Argentina).
Cretaceous Research: 104889
doi:Âhttps://doi.org/10.1016/j.cretres.2021.104889
https://www.sciencedirect.com/science/article/abs/pii/S0195667121001361
Highlights
doi:Âhttps://doi.org/10.1016/j.cretres.2021.104889
https://www.sciencedirect.com/science/article/abs/pii/S0195667121001361
Highlights
South America has few continental records of the Cretaceous-Paleogene boundary.
La Colonia Formation in Argentina may contain this interval of geological time.
New palynological, paleomagnetic, and geochronological results are presented.
Results show that the Cretaceous-Paleogene boundary interval is recorded here.
Abstract
The La Colonia Formation is an Upper Cretaceous to Paleogene shallow marine sedimentary unit in Chubut Province (Patagonia), Argentina that preserves important vertebrate and plant fossils. Despite good exposures and significant paleontological investigation, the precise age of the La Colonia Formation and its stratigraphic relationship to the Cretaceous-Paleogene (K-Pg) boundary are not well understood. The K-Pg boundary is associated with one of the largest mass extinctions in Earthâs history yet there are few continental stratigraphic records of the boundary in South America, resulting in poor understanding of its effects there. This study combines magnetostratigraphy, detrital zircon uraniumâlead (UâPb) geochronology, and preliminary palynological results to constrain the age of the La Colonia Formation and its fossils more precisely and determine whether it preserves the K-Pg boundary. U-Pb ages of detrital zircons from the directly underlying Puntudo Chico Formation indicate that the base of the La Colonia Formation is younger than â71.7 Ma. The studied palynological assemblage includes Quadraplanus brossus, which is restricted to the Maastrichtian in other southern hemisphere records. Paleomagnetic results show that the â125 meter Cerro Buitre Norte section of the La Colonia Formation and the overlying Cerro Bororà Formation has dominantly normal polarity except for a â5 meter zone of reversed polarity near the base that is interpreted to correlate to Chron C30R of the Geomagnetic Polarity Timescale (GPTS), and a â13 meter zone of reversed polarity near the top of the La Colonia Formation that is interpreted to correlate to Chron C29R. The presence of a magnetozone correlated to C29R in the La Colonia Formation suggests that it preserves the KâPg boundary, making it an important target for continued paleontological collection to better understand the K-Pg extinction and recovery dynamics in South America.
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Also:
J. Matthias Starck, James R. Stewart & Daniel G. Blackburn (2021)
Phylogeny and evolutionary history of the amniote eggÂÂ
Journal of Morphology (advance online publication)
Journal of Morphology (advance online publication)
We review morphological features of the amniote egg and embryos in a comparative phylogenetic framework, including all major clades of extant vertebrates. We discuss 40 characters that are relevant for an analysis of the evolutionary history of the vertebrate egg. Special attention is given to the morphology of the cellular yolk sac, the eggshell and extraembryonic membranes. Many features that are typically assigned to amniotes, such as a large yolk sac, delayed egg deposition and terrestrial reproduction have evolved independently and convergently in numerous clades of vertebrates. We use phylogenetic character mapping and ancestral character state reconstruction as tools to recognize sequence, order and patterns of morphological evolution and deduce a hypothesis of the evolutionary history of the amniote egg. Besides amnion and chorioallantois, amniotes ancestrally possess copulatory organs (secondarily reduced in most birds), internal fertilization, and delayed deposition of eggs that contain an embryo in the primitive streak or early somite stage. Except for the amnion, chorioallantois, and amniote type of eggshell, these features evolved convergently in almost all major clades of aquatic vertebrates possibly in response to selective factors such as egg predation, hostile environmental conditions for egg development, or to adjust hatching of young to favorable season. A functionally important feature of the amnion membrane is its myogenic contractility that moves the (early) embryo and prevents adhering of the growing embryo to extraembryonic materials. This function of the amnion membrane and the liquid filled amnion cavity may have evolved under the requirements of delayed deposition of eggs that contain developing embryos. The chorioallantois is a temporary embryonic exchange organ that supports embryonic development. A possible evolutionary scenario is that the amniote egg presents an exaptation that paved the evolutionary pathway for reproduction on land. As shown by numerous examples from anamniotes, reproduction on land has occurred multiple times among vertebrates â the amniote egg presenting one âsolutionâ that enabled the conquest of land for reproduction.
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Abstracts only:
John Fortner, Alec Wilken, Kaleb Sellers, Ian Cost, ÂKevin Middleton & Casey Holliday (2021)
The Role of the Intramandibular Joint, Symphyseal Tissues, and Wrapping Muscles on Theropod Dinosaur Mandibular Function.
The FASEB Journal 35(S1) Special Issue: Experimental Biology 2021 Meeting Abstracts (abstract only)
doi: Âhttps://doi.org/10.1096/fasebj.2021.35.S1.03068
https://faseb.onlinelibrary.wiley.com/doi/10.1096/fasebj.2021.35.S1.03068
NSF IOS 1457319, NSF EAR 1631684
Sauropsids, unlike mammals, possess an intramandibular joint (IMJ) separating the dentary and postdentary bones, with different lineages either rigidifying (turtles & crocodilians) or maintaining compliance (lepidosaurs & birds) about the joint. IMJ construction and its role on mandibular performance is unclear, impeding our understanding of its function in extinct animals with extreme feeding behaviors like Tyrannosaurus rex. Sauropsids like T. rex pose a particular biomechanical paradox; feeding traces, coprolites, and their robust crania and teeth indicate that they regularly bit through and ingested bone, but their dorsoventrallyâtall and mediolaterallyâthin hemimandibles, IMJ, and patent mandibular symphyses suggest their mandibles were illâsuited for boneâcrushing bites. Extant sauropsids also exhibit wrapping intramandibularis (mIRA) and pterygoideus ventralis (mPTv) muscles, whose effect on mandibular performance and interaction with the IMJ are unknown. Here we model the effect of the IMJ, symphyseal tissue properties, and wrapping muscle orientation on T. rex mandible biomechanical performance in order to give insight into the biomechanical constraints faced by sauropsids, and the link between their mandibular form and function. Joint tissue histology, gross dissection, and iodine contrast data of extant sauropsids were performed to inform model tissue properties, IMJ construction and muscle orientation. We imported a 3D STL model of the T. rex "STAN" and modeled the IMJ by differing material properties of modeled joint tissues to test the influence of linkage materials on mandibular performance. Muscles were mapped onto the model, and their corresponding muscle moments calculated from area centroids, muscle architecture, and volumes. Wrapping mIRA and mPTv muscles were simulated by directing their force vectors to appropriately positioned dummy points using extant sauropsids as a guide. The mandible was then constrained at the jaw joint and in a series of points along the tooth row from rostral to caudal, simulating both unilateral and bilateral bites. We find that while strains are quite high (>6000 Âstrains) about the intramandibular joint, mediolateral bending stresses and strain are markedly reduced by the prearticular, which exhibits greater strain than the surrounding bone. Our results suggest the prearticular of T. rex acted as a strain sink to counteract bending about the IMJ and thereby rigidifying the mandible during feeding. We hypothesize that differences in IMJ articulation and prearticular construction may differentially facilitate or impede prearticular streptognathy, and thus intramandibular kinesis about the IMJ, in sauropsids. Forthcoming models will simulate other theropods within and without Tyrannosauridae to test this hypothesis.
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Abstract only:
David Kay, Haley O'Brien & Paul Gignac (2021)
Alveolar Trough: Formalizing an Arcus Alveolaris Analog in a Sauropsid Model
Volume 35(S1) Special Issue: Experimental Biology 2021 Meeting Abstracts (abstract only)
doi: https://doi.org/10.1096/fasebj.2021.35.S1.05014
https://faseb.onlinelibrary.wiley.com/doi/10.1096/fasebj.2021.35.S1.05014
Mammals and crocodylians share thecodont tooth implantation, wherein bony sockets (alveoli) enclose tooth roots. Mammalian alveoli are composed of a thin layer of remodeled haversian bone forming the socket, and cancellous bone filling the space between the socket and the jaw elements, together forming an arcus alveolaris. The sockets act as an anchoring attachment for the periodontal ligament and support the dentition, and recent research has shown that alveoli have a role in tooth formation. Complexity in mammal heterodonty depends, in part, on alveoli mechanically constraining the developing crown: high alveolar constraint produces more complex crowns. Previously, we have shown a significant relationship between alveolar and dental crown morphologies in Alligator mississippiensis: as each new tooth contributes tissue to the socket wall, the alveoli limit shape variation of subsequent crown generations. In yearling caimans, alveolar bone type is identified as lamellar bundle bone; however, there is toâdate no complete morphological description of the alveolar anatomy of crocodylians. In this study, we describe the unique alveolar anatomy in extant crocodylians and evaluate the need for specific anatomical terminology based on deviations from the mammalian standard.
From microâcomputed tomography (ÎCT) data, we digitally reconstructed the jaws of embryonic, hatchling, juvenile, and subadult life stages of Alligator, parsing alveolar bone from other jaw elements. We compared these ÎCT datasets with those of model rodent species (Microtus, Rattus, Napaeozapus) and to the dental literature.
Our results show alligators lack the mammalianâtype arcus alveolus. Instead, they have a thick trough of lamellar bundle bone connected to adjacent jaw elements by thin osseous struts and direct fusion on buccal and lingual contacts. Notably, cancellous bone is absent. The trough is retained throughout ontogeny and is the foundation onto which interdental septa are added. Both trough and septa thicken with age as replacementâtooth size increases.
Current anatomical terminology for alveoli fits the integrated mammalian jaw type well, but the crocodylian type is markedly different. The crocodylian alveolar condition is principally composed of a thickened trough of lamellar bundle bone, indicating a need for sauropsidâspecific terminology to reflect this analogous configuration. The term alveolar trough is suggested as it has been used previously to describe alveolar features in fossil reptiles but lacks a formal definition, which we now erect. Alveus alveolaris (L., âalveolar troughâ)âa thick channel of lamellar bundle bone in the jaws of, for example, crocodylians that provides the surface for gomphotic thecodonty and connects to jaw elements through direct fusion, but without cancellous bone.
The delineation of the alveolar trough has farâreaching implications to dental form and function. Primarily, it calls attention to this apparently unique feature of crocodylian jaws, which should inform future research directions to more discretely address its development, function, and evolution. In addition, the troughâalongside interdental septa and rootednessâmay help to clarify the role of tooth socket configurations as potential key innovations in tetrapod dental evolution.
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Abstract only:
Arjan Mann, Thomas W. Dudgeon, Amy C. Henrici, Dave S. Berman and Stephanie E. Pierce (2021)
Digit and ungual morphology suggest adaptations for scansoriality in the late Carboniferous eureptile Anthracodromeus longipes.
doi: 10.3389/feart.2021.675337
https://www.frontiersin.org/articles/10.3389/feart.2021.675337/abstract
A new skeleton of the exceedingly rare, late Carboniferous eureptile Anthracodromeus longipes Carroll and Baird, 1972, reveals the presence of a reduced phalangeal count in the manus and pedes and uniquely recurved claws. With these data, we quantitatively evaluate the locomotor ecology of Anthracodromeus using morphometric analyses of the phalangeal proportions, claw curvature, and claw shape. Our findings indicate that the anatomy of Anthracodromeus likely facilitated scansorial clinging to some degree via recurved claws and increased surface area of the large manus and pes. This suggests that Anthracodromeus was among the earliest amniotes to show climbing abilities, pushing back the origins of scansoriality by at least 17 million years. It further suggests that scansoriality arose soon after the origin of amniotes, allowing them to exploit a wide range of novel terrestrial niches.
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