Ben Creisler
Some recent non-dino papers:
The ÎCT data for this study, including the tiff stacks (slices) and mesh files (in .ply format), are available via MorphoSource:
http://www.morphosource.org/Detail/MediaDetail/Show/media_id/63541Data supporting this study, including the data matrix, results of IterPCR procedure, the complete timeâcalibrated MRC tree from the Bayesian analysis and a list of DOIs for MorphoSource ÎCT data for AMNH FARB 3158, as well as additional notes and results, are available in the Dryad Digital Repository:
https://doi.org/10.5061/dryad.xsj3tx9bt
Caimaninae is one of the few crocodylian lineages that still has living representatives. Today, most of its six extant species are restricted to South and Central America. However, recent discoveries have revealed a more complex evolutionary history, with a fossil record richer than previously thought and a possible North American origin. Among the oldest caimanines is Eocaiman cavernensis, from the Eocene of Patagonia, Argentina. It was described by George G. Simpson in the 1930s, representing the first caimanine reported for the Palaeogene. Since then, E. cavernensis has been ubiquitous in phylogenetic studies on the group, but a more detailed morphological description and revision of the taxon were lacking. Here, we present a reassessment of E. cavernensis, based on firstâhand examination and microâcomputed tomography of the holotype, and reinterpret different aspects of its morphology. We explore the phylogenetic affinities of E. cavernensis and other caimanines using parsimony and Bayesian inference approaches. Our results provide evidence for a monophyletic Eocaiman genus within Caimaninae, even though some highly incomplete taxa (including the congeneric Eocaiman itaboraiensis) represent significant sources of phylogenetic instability. We also found Culebrasuchus mesoamericanus as sister to all other caimanines and the North American globidontans (i.e. Brachychampsa and closer relatives) outside Caimaninae. A timeâcalibrated tree, obtained using a fossilized birth-death model, shows a possible Campanian origin for the group (76.97 Â 6.7 Ma), which is older than the age estimated using molecular data, and suggests that the earliest cladogenetic events of caimanines took place rapidly and across the KâPg boundary.
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Here, we review the development, morphology, genes, and proteins of claws in reptiles. Claws likely form owing to the inductive influence of phalangeal mesenchyme on the apical epidermis of developing digits, resulting in hyperâproliferation and intense protein synthesis in the dorsal epidermis, which forms the unguis. The tip of claws results from prevalent cell proliferation and distal movement along most of the ungueal epidermis in comparison to the ventral surface forming the subâunguis. Asymmetrical growth between the unguis and subâunguis forces betaâcells from the unguis to rotate into the apical part of the subâunguis, sharpening the claw tip. Further sharpening occurs by scratching and mechanical wearing. Ungueal keratinocytes elongate, form an intricate perimeter and cementing junctions, and remain united impeding desquamation. In contrast, thin keratinocytes in the subâunguis form a smooth perimeter, accumulate less corneous beta proteins and cysteineâpoor intermediate filament (IF)âkeratins, and desquamate. In addition to prevalent glycineâcysteineâtyrosine rich corneous beta proteins, special cysteineârich IFâkeratins are also synthesized in the claw, generating numerous âSâSâ bonds that harden the thick and compact corneous material. Desquamation and mechanical wear at the tip ensure that the unguis curvature remains approximately stable over time. Reptilian claws are likely very ancient in evolution, although the unguis differentiated like the outer scale surface of scales, while the subâunguis might have derived from the inner scale surface. The few hairâlike IFâkeratins synthesized in reptilian claws indicate that ancestors of sauropsids and mammals shared cysteineârich IFâkeratins. However, the number of these keratins remained low in reptiles, while new types of corneous beta proteins function to strengthen claws.
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Free pdf:
Lorenzo MARCHETTI, Sebastian VOIGT, Spencer G. LUCAS, Matthew R. STIMSON, Olivia A. KING & John H. CALDER (2020)
Footprints of the earliest reptiles:ÂNotalacerta missouriensis -- Ichnotaxonomy, potential trackmakers, biostratigraphy, palaeobiogeography and palaeoecology.
The origin of reptiles in the tetrapod footprint record has always been a debated topic, despite the great potential of fossiliferous ichnosites to shed much light on reptile origins when compared to the much less extensive skeletal record. This is in part due to an unclear ichnotaxonomy of the earliest tracks attributed to reptiles that has resulted in unreliable trackmaker attributions. We comprehensively revise the earliest supposed reptile ichnotaxon, Notalacerta missouriensis, based on a neotype and a selection of well-preserved material from the type locality and other sites. A synapomorphy-based track-trackmaker attribution suggests eureptiles and, more specifically, 'protorothyridids' such as Paleothyris as the most probable trackmakers. A revision of the entire Pennsylvanian Cisuralian record of this ichnotaxon unveils an unexpected abundance and a wide palaeogeographical distribution. The earliest unequivocal occurrence of Notalacerta is in the middle Bashkirian (early Langsettian) at the UNESCO World Heritage Site, Joggins Fossil Cliffs (Joggins, Nova Scotia, Canada). This occurrence also coincides with the earliest occurrence of reptile body fossils (Hylonomus lyelli), which are found at the same site. Notalacerta is abundant and widely distributed during the Bashkirian, mostly in sediments deposited in tidal palaeoenvironments, and less common in the Moscovian and Kasimovian. During the Gzhelian and Asselian, Notalacerta occurrences are unknown, but it occurs again during the Sakmarian and is widespread but not abundant during the Artinskian, mostly in fully continental palaeoenvironments.ÂÂ
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Also:
Free pdf:
Kenshu Shimada, Martin A. Becker & Michael L. Griffiths (2020)
Body, jaw, and dentition lengths of macrophagous lamniform sharks, and body size evolution in Lamniformes with special reference to 'off-the-scale' gigantism of the megatooth shark, Otodus megalodon.
Historical Biology (advance online publication)
doi:
https://doi.org/10.1080/08912963.2020.1812598 https://www.tandfonline.com/doi/full/10.1080/08912963.2020.1812598Free pdf:
https://www.tandfonline.com/doi/pdf/10.1080/08912963.2020.1812598?needAccess=trueExtinct lamniform sharks (Elasmobranchii: Lamniformes) are well represented in the late MesozoicâCenozoic fossil record, yet their biology is poorly understood because they are mostly represented only by their teeth. Here, we present measurements taken from specimens of all 13 species of extant macrophagous lamniforms to generate functions that would allow estimations of body, jaw, and dentition lengths of extinct macrophagous lamniforms from their teeth. These quantitative functions enable us to examine the body size distribution of all known macrophagous lamniform genera over geologic time. Our study reveals that small body size is plesiomorphic for Lamniformes. There are four genera that included at least one member that reached >6 m during both the Mesozoic and Cenozoic, most of which are endothermic. The largest form of the genus Otodus, O. megalodon ('megatooth shark') that reached at least 14 m, is truly an outlier considering that all other known macrophagous lamniforms have a general size limit of 7 m. Endothermy has previously been proposed to be the evolutionary driver for gigantism in Lamniformes. However, we contend that ovoviviparous reproduction involving intrauterine cannibalism, a possible synapomorphy of Lamniformes, to be another plausible driver for the evolution of endothermy achieved by certain lamniform taxa.
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