Ben Creisler
Some recent non-dino papers with free pdfs:
Free pdf:
The origin of phenotypic diversity among higher clades is one of the most fundamental topics in evolutionary biology. However, due to methodological challenges, few studies have assessed rates of evolution and phenotypic disparity across broad scales of time to understand the evolutionary dynamics behind the origin and early evolution of new clades. Here, we provide a total-evidence dating approach to this problem in diapsid reptiles. We find major chronological gaps between periods of high evolutionary rates (phenotypic and molecular) and expansion in phenotypic disparity in reptile evolution. Importantly, many instances of accelerated phenotypic evolution are detected at the origin of major clades and body plans, but not concurrent with previously proposed periods of adaptive radiation. Furthermore, strongly heterogenic rates of evolution mark the acquisition of similarly adapted functional types, and the origin of snakes is marked by the highest rates of phenotypic evolution in diapsid history.
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Free pdf:
Joshua W. Bonde, Peter A. Druschke, Richard P. Hilton, Amy C. Henrici & Stephen M. Rowland (2020)
Preservation of latest Cretaceous (Maastrichtian)âPaleocene frogs (Eorubeta nevadensis) of the Sheep Pass Formation of east-central Nevada and implications for paleogeography of the Nevadaplano.
PeerJ 8:e9455
doi:
https://doi.org/10.7717/peerj.9455https://peerj.com/articles/9455/
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Here we report on exceptional preservation of remains of the frog Eorubeta nevadensis in deposits of the Sheep Pass Formation, ranging from Late Cretaceous to Eocene, in the south Egan Range, Nevada. This formation represents a lacustrine basin within the Sevier retroarc hinterland. The formation is subdivided into six members (AâF); of interest here are members B and C. The base of member B is ?uppermost Cretaceous-Paleocene, while member C is Paleocene. Member B frogs are preserved in three taphonomic modes. Mode 1 frogs are nearly complete and accumulated under attritional processes, with frogs settling on microbial mats, as evidenced by crenulated fabric of entombing limestone. Mode 2 involves accumulation of frogs as a result of attritional processes. These frogs are mostly complete with some showing evidence of invertebrate scavenging. Possible scavengers are gastropods, ostracods, and decapods. Mode 3 is represented by isolated, reworked remains of frogs as a result of storm activity, supported by the association of elements with disarticulated bivalves and mud rip-up clasts. Member C preserves frogs in two taphonomic modes. Mode 4 are nearly complete frogs that accumulated during discrete mass mortality events. Numerous individuals are preserved along bedding planes in identical preservational states. Mode 5 is beds of frog bone hash, which represent increased energy to the depositional system (likely tempestites) and reworking of previously buried frog remains. Taphonomy of the frogs, along with the associated fauna and flora, are consistent with preservation in a cool, temperate lake basin, supporting previous interpretations that the Nevadaplano was an elevated plateau during the late Cretaceous through the Eocene. This is a period of time coincident with a climatic thermal optimum, thus the most parsimonious explanation for a temperate lake at the latitude of east-central Nevada is to invoke high elevation, which is consistent with independent structural and clumped stable isotope studies.
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Amphibian caecilians have tooth-related glands in both upper and lower jaws
The glands have the same origin of reptile venom glands
The secretion contains proteins with enzymatic activities commonly found in venoms
Caecilians might have developed the ability to inject oral toxins early in evolution
Summary
Amphibians are known for their skin rich in glands containing toxins employed in passive chemical defense against predators, different from, for example, snakes that have active chemical defense, injecting their venom into the prey. Caecilians (Amphibia, Gymnophiona) are snake-shaped animals with fossorial habits, considered one of the least known vertebrate groups. We show here that amphibian caecilians, including species from the basal groups, besides having cutaneous poisonous glands as other amphibians do, possess specific glands at the base of the teeth that produce enzymes commonly found in venoms. Our analysis of the origin of these glands shows that they originate from the same tissue that gives rise to teeth, similar to the venom glands in reptiles. We speculate that caecilians might have independently developed mechanisms of production and injection of toxins early in their evolutionary history.
News:
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Free pdf:
The first "complete" paradigm of extinction was proposed as "the multigenerational, attritional loss of reproductive fitness," for which MALF is a suitable acronym. A "complete" paradigm must encompass cause, effect, and a mechanism. The primary goal of this study is to verify the new paradigm. We cite four independent tests of the paradigm employing observational, experimental, and wholly theoretical techniques, utilizing phyletically diverse organisms from disparate parts of the Earth. All of these analyses confirmed the new paradigm. This new paradigm was originally derived from studies of MALF on six species of higher plants. We now report seven additional, worldwide examples from the earlier literature of higher plants (and a small mammal) that support the new paradigm. We also note the stark deficiencies in comparing "mass" and "background" extinctions and the unique case of the end-Cretaceous mass extinction. To provide context for the new paradigm, we explore the long history of linguistic and philosophical contradiction or misconception that prevented the construction of a complete extinction paradigm for approximately 200 years. We also discuss the inadequacy of "incomplete" paradigms based largely on "cause-alone" explanations. We then consider logical inconsistencies and difficulties inherent in the usage of the term "extinction" itself and propose a new term for extinction. We then discuss cases of relict species that are the last survivors of their lineage and are essentially "functionally" extinct, thus making them excellent subjects for the study of MALF. Anthropogenic extinctions are exceptionally rapid when compared to typical MALF extinctions. For extinctions occurring at least within the life span of a species we suggest the term "quasi-catastrophic."
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