Ben Creisler
Some recent non-dino papers that may be interest:
Yesterday June 17th was World Crocodile Day...
Evan T. Whiting & Jason J. Head (2020)
Neogene crocodylians from the Central Great Plains: spatiotemporal histories and relationships with regional climatic and environmental changes.
Journal of Vertebrate Paleontology Article: e1764007
doi:
https://doi.org/10.1080/02724634.2020.1764007 https://www.tandfonline.com/doi/full/10.1080/02724634.2020.1764007
Crocodylian fossils are well documented from Upper Cretaceous and lower to middle Paleogene deposits in the mid-high latitudes of the Western Interior, whereas the only extant North American taxon, Alligator mississippiensis, is restricted to the lower-latitude wetlands of the southeastern United States. The departure of crocodylians from the Western Interior has been inferred to represent a major shift from more equable, warmer, wetter climates in the Paleogene to more seasonal, cooler, drier climates in the Neogene. The timing of further geographic range shifts during the Neogene, including the local extinction (extirpation) of crocodylians from the Great Plains, is poorly constrained. We document the Neogene crocodylian fossil record of the Central Great Plains (CGP) in order to constrain the timing of mid-continental crocodylian extinctions against a backdrop of climatic and environmental changes. The Neogene CGP crocodylian fossil record consists of mostly incomplete specimens, likely referable to the extant genus Alligator, and appears to document multiple latitudinal range shifts that are spatiotemporally consistent with regional climatic and environmental changes inferred from independent proxy evidence. The last appearance datum (LAD) for crocodylians in the CGP is â6 Ma, which suggests that climatic and environmental conditions in the region were unfavorable to crocodylians after this time. In general, Neogene crocodylian fossils throughout the Great Plains are not abundant. Barring taphonomic biases or sampling issues, this could imply low population densities, and/or that the fossil-bearing areas in this region were close to the northernmost limits of crocodylian (cf. Alligator) distributions during the Neogene.
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Igor J. Roberto, Pedro S. Bittencourt, Fabio L. Muniz, Sandra M. HernÃndez-Rangel, Yhuri C. NÃbrega, Robson W. Ãvila, Bruno C. Souza, Gustavo Alvarez, Guido Miranda-Chumacero, Zilca Campos, Izeni P. Farias & Tomas Hrbek (2020)
Unexpected but unsurprising lineage diversity within the most widespread Neotropical crocodilian genus Caiman (Crocodylia, Alligatoridae).
Systematics and Biodiversity (advance online publication)
doi:
https://doi.org/10.1080/14772000.2020.1769222https://www.tandfonline.com/doi/full/10.1080/14772000.2020.1769222Species discovery methods utilizing coalescent-based approaches are powerful tools for detecting cryptic lineages within morphological conservative groups, thus being an important methodology of integrative taxonomic research. Crocodilians are a classic example of morphologically conserved group where coalescence-based species delimitation analyses resulted in the discovery of cryptic lineages and potentially new species. In this study, we used several single locus species discovery methods to analyze the phylogenetic diversity of the most widespread alligatorid genus of the Neotropics, the genus Caiman. We analyzed 479 specimens representing all named taxa, with the exception of Caiman crocodilus apaporiensis, and known geographic distribution of these taxa. We observed high lineage diversity within the Caiman crocodilus/yacare complex, ranging from 7 to 10 lineages, and three lineages within Caiman latirostris. We also provide a new dated phylogeny for all the delimited lineages. Oligocene and Miocene events triggered the diversification of the major lineages, with latter Pleistocene events influencing the final diversification of the genus. We demonstrate that the discovered lineages within the Caiman complex are compatible with being species and as such are candidates for an integrated taxonomic analysis. However, it is important to highlight that independent of the future recognition of these lineages as species, it is extremely important to protect these cryptic lineages as unique evolutionary entities, many of which are highly threatened by habitat loss from dam construction projects, tailing dam collapses, mining, agriculture and agricultural run-off across all of South America.
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Megamphicyon
Herein, we present a study of an interesting sample of fossils of the giant amphicyonid Megamphicyon giganteus (Schinz, 1825) from the Spanish middle Miocene (MN6) site of Carpetana (Madrid city), obtained during public works for the Madrid underground in 2008. Although the dentition of this species is known from other sites, the postcranial bones are very poorly known, and the new material provides new data on the locomotor adaptations of this spectacular predator, and allows an estimation of its body mass, which would be around 600 kg. Surprisingly, despite this giant size, the morphology of both femur and tibia shows that this animal exhibited higher cursorial capacity than large extant carnivorans, such as bears, which together with a high degree of pronation/supination movement of the forearm, reveals adaptations of M. giganteus to occupy the niche of active top predator in middle Miocene ecosystems.
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Three-dimensional Late Cretaceous elasmobranch endoskeletal elements (including palatoquadrates, ceratohyals, braincase fragments, and a series of anterior vertebrae) are described from the Late Cretaceous University of Alabama Harrell Station Paleontological Site (HSPS), Dallas County, Alabama. The material is referred to the extant elasmobranch Family Squatinidae on the basis of several distinctive morphological features. It also exhibits features not shared by any modern or fossil Squatina species or the extinct Late Jurassic squatinid Pseudorhina. A new genus and species is erected, despite there being some uncertainty regarding potential synonymy with existing nominal species previously founded on isolated fossil teeth (curiously, no squatinid teeth have been documented from the HSPS). A preliminary phylogenetic analysis suggests that the new genus falls on the squatinid stem, phylogenetically closer to Squatina than Pseudorhina. The craniovertebral articulation in the new genus exhibits features considered convergent with modern batomorphs (skates and rays), including absence of contact between the posterior basicranium and first vertebral centrum, and a notochordal canal which fails to reach the parachordal basicranium. Supporting evidence that similarities in the craniovertebral articulation of squatinoids and batomorphs are convergent rather than synapomorphic (as "hypnosqualeans") is presented by an undescribed Early Jurassic batomorph, in which an occipital hemicentrum articulates with the first vertebral centrum as in all modern sharklike (selachimorph) elasmobranchs. The fossil suggests instead that the batomorph synarcual evolved by fusion of the anterior basiventral and basidorsal cartilages prior to the reduction of the anterior centra and loss of the occipital hemicentrum, not afterward as predicted by the hypnosqualean hypothesis.
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Many angiosperm fossils can be dated to the Early Cretaceous (~135 million years ago), which has led paleobotanists to reason that they originated during that era. It is now increasingly recognized that angiosperms are probably older than the oldest fossils, but how much older remains controversial. When angiosperms originated is key to understanding the origin and evolution of pollinators, particularly insects such as bees, butterflies, moths, and flies.
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Supposed "living fossil" lycopsid plant from the Triassic is more recent.
Free pdf:
Daniel Wood, Guillaume Besnard, David J. Beerling, Colin P. Osborne & Pascal-Antoine Christin (2020)
Phylogenomics indicates the "living fossil" Isoetes diversified in the Cenozoic.
PLoS ONE 15(6): e0227525.
doi:
https://doi.org/10.1371/journal.pone.0227525https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0227525The fossil record provides an invaluable insight into the temporal origins of extant lineages of organisms. However, establishing the relationships between fossils and extant lineages can be difficult in groups with low rates of morphological change over time. Molecular dating can potentially circumvent this issue by allowing distant fossils to act as calibration points, but rate variation across large evolutionary scales can bias such analyses. In this study, we apply multiple dating methods to genome-wide datasets to infer the origin of extant species of Isoetes, a group of mostly aquatic and semi-aquatic isoetalean lycopsids, which closely resemble fossil forms dating back to the Triassic. Rate variation observed in chloroplast genomes hampers accurate dating, but genome-wide nuclear markers place the origin of extant diversity within this group in the mid-Paleogene, 45-60 million years ago. Our genomic analyses coupled with a careful evaluation of the fossil record indicate that despite resembling forms from the Triassic, extant Isoetes species do not represent the remnants of an ancient and widespread group, but instead have spread around the globe in the relatively recent past.