Ben Creisler
Some recent non-dino papers, many with free pdfs:
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Free pdf:
The physiological demands of flight exert strong selection pressure on avian morphology and so it is to be expected that the evolutionary loss of flight capacity would involve profound changes in traits. Here, we investigate morphological consequences of flightlessness in a bird family where the condition has evolved repeatedly. The Rallidae include more than 130 recognized species of which over 30 are flightless. Morphological and molecular phylogenetic data were used here to compare species with and without the ability to fly in order to determine major phenotypic effects of the transition from flighted to flightless. We find statistical support for similar morphological response among unrelated flightless lineages, characterized by a shift in energy allocation from the forelimbs to the hindlimbs. Indeed, flightless birds exhibit smaller sterna and wings than flighted taxa in the same family along with wider pelves and more robust femora. Phylogenetic signal tests demonstrate that those differences are independent of phylogeny and instead demonstrate convergent morphological adaptation associated with a walking ecology. We found too that morphological variation was greater among flightless rails than flighted ones, suggesting that relaxation of physiological demands during the transition to flightlessness frees morphological traits to evolve in response to more varied ecological opportunities.
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Paywalled:
Acosta Hospitaleche and Reguero (2020) report the discovery of two mandibular fragments collected during 2016 and 2017 in Seymour Island, Antarctica, and assign them as Pelagornithidae indet. Morpho-Type 1. However, based on the published pictures of both specimens, it is clear that only IAA-PV 175 can be tentatively assigned to Pelagornithidae, whereas IAA-PV 823 truly belongs to a bony fish. Although this reasignation does not invalidate the general content and conclusions of their publication, we consider this reply important in order to clarify the assignation of IAAPV 823 and bring attention to the implications of this new interpretation in regards to the fossil record of fishes in the Southern Hemisphere.
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Free pdf:
Free pdf:
https://www.annualreviews.org/doi/abs/10.1146/annurev-earth-072619-060126A remarkable diversity of plant-eating mammals known as South American native ungulates (SANUs) flourished in South America for most of the Cenozoic. Although some of these species likely filled ecological niches similar to those of modern hoofed mammals, others differed substantially from extant artiodactyls and perissodactyls in their skull and limb anatomy and probably also in their ecology. Notoungulates and litopterns were the longest-lived and most diverse SANU clades and survived into the Quaternary; astrapotheres went extinct in the late Miocene, whereas other SANU groups were restricted to the Paleogene. Neogene notoungulates were quite specialized in craniodental structure, but many were rather unspecialized postcranially; in contrast, litopterns evolved limb specializations early in their history while maintaining more conservative dentitions. In this article, we review the current understanding of SANU evolutionary relationships and paleoecology, provide an updated compilation of genus temporal ranges, and discuss possible directions for future research.
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South American native ungulates (SANUs) were a diverse, long-lived, and independent radiation of mammals into varied terrestrial plant-eater niches.
We review origins, evolution, and paleoecology of the major SANU clades: Notoungulata, Litopterna, Astrapotheria, Xenungulata, and Pyrotheria.
At their peak, during the Eocene and Oligocene, more than 40 genera of native ungulates inhabited South America at any one time.
SANUs ranged from <1 kg to several tons and evolved many combinations of diet and locomotor adaptations not seen in living ungulates.
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Free pdf:
Fossil melanosomes, micron-sized granules rich in melanin in vivo, provide key information for investigations of the original coloration, taxonomy and internal anatomy of fossil vertebrates. Such studies rely, in part, on analysis of the inorganic chemistry of preserved melanosomes and an understanding of melanosome chemical taphonomy. The extent to which the preserved chemistry of fossil melanosomes is biased by biotic and abiotic factors is, however, unknown. Here we report the discovery of hierarchical controls on the inorganic chemistry of melanosomes from fossil vertebrates from nine biotas. The chemical data are dominated by a strong biota-level signal, indicating that the primary taphonomic control is the diagenetic history of the host sediment. This extrinsic control is superimposed by a biological, tissue-level control; tissue-specific chemical variation is most likely to survive in fossils where the inorganic chemistry of preserved melanosomes is distinct from that of the host sediment. Comparative analysis of our data for fossil and modern amphibians reveals that most fossil specimens show tissue-specific melanosome chemistries that differ from those of extant analogues, strongly suggesting alteration of original melanosome chemistry. Collectively, these findings form a predictive tool for the identification of fossil deposits with well-preserved melanosomes amenable to studies of fossil colour and anatomy.
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Free pdf:
Melanin and other pigments are now well known to be important in exceptional preservation of soft tissues in vertebrates and other animals. Because pigments confer coloration and even structural colors, they have opened a new field of paleocolor reconstruction. Since its inception about a decade ago, reconstruction of color patterns has been performed on several vertebrates, including feathered and scale-clad dinosaurs. Iridescence and other types of structural color can also be identified through melanosome shape and arrangement. How pigments and melanosomes fossilize and are altered has become an important research subject. Ancient color patterns that may range from crypsis to brilliant displays have revealed insights into the evolution and escalation of visual systems, the nature of ancient animal interactions, and how several unique characteristics of birds already arose among dinosaurs.
Melanin and other pigments preserve in exceptional fossils; this opens paths for reconstructing coloration of extinct organisms, such as dinosaurs.
The most abundant pigment is melanin, which can be identified chemically and through preserved melanosome microbodies.
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Melanosome shape reveals clues to original hue ranging from reddish brown and black to gray and structural coloration.
Other pigments may preserve, such as porphyrin pigments in theropod dinosaur eggshells.
Fossil color patterns contribute new insights into the evolution of visual systems, predator-prey interactions, and key innovations.
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Free pdf:
Interpretations of the tempo of mass extinctions and recoveries often rely on the distribution of fossils in a stratigraphic column. These interpretations are generally compromised when they are not based on a knowledge of marine ecological gradients and sequence-stratigraphic architecture. Crucially, last and first occurrences of species do not record times of extinction and origination. A face-value interpretation of the stratigraphic record leads to incorrect inferences of pulsed extinction, underestimates of the duration of mass extinction, and overestimates of local recovery times. An understanding of the processes of extinction and recovery is substantially improved by knowledge of the distribution of species along marine environmental gradients, interpreting sequence-stratigraphic architecture to show how those gradients are sampled through time, and sampling along regional transects along depositional dip. Doing so suggests that most ancient mass extinctions were substantially longer and local recoveries substantially shorter than generally thought.
The concepts that let geologists find petroleum allow paleontologists to reinterpret ancient mass extinctions and their recoveries.
Most ancient mass extinctions were longer than the fossil record suggests, lasting hundreds of thousands of years to a few million years.
Ancient recoveries from mass extinctions were shorter than thought and likely overlapped with extinction during a period of turnover.
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Paywalled:
Jun Liu, Jian Yia & Jian-Ye Chen (2020)
Constraining assembly time of some blocks on eastern margin of Pangea using Permo-Triassic non-marine tetrapod records.
Earth-Science Reviews 103215 (advance online publication)
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https://doi.org/10.1016/j.earscirev.2020.103215https://www.sciencedirect.com/science/article/abs/pii/S0012825220302610The supercontinent Pangea was mainly formed during the Permian, but when it reached maximum land is unsure because the configuration of the East Asian blocks during the Permo-Triassic is still highly debated. Fossil tetrapods provide one of the best calibrations to the time of connection between continents, but the data of Permo-Triassic tetrapods have rarely been applied in the previous reconstructions. Here we review the oldest records of non-marine tetrapods on the East Asia blocks and use them to discuss the timing of connection between continents during the Permian and Triassic. The distribution of Seymouriamorpha shows the Kazakhstanian was connected to the Baltica by land from the Cisuralian. The diverse Dashankou Fauna indicates that the Alxa Block amalgamated to Pangea at least in the Guadalupian (older than 266âMa). The questionable footprints and late Permian dicynodont assemblage from the North China show the North China Craton may have been connected to the main part of Pangea from the Guadalupian, and became part of Pangea at least by 256âMa. The late Permian Laotian tetrapods support the hypothesis that the South China Block already collided with the North China and the Indochina blocks by the end of the Permian, and there was a land route for the migration of non-marine tetrapods.
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Free pdf:
The consequences of the Cretaceous-Paleogene (K-Pg) boundary (KPB) mass extinction for the evolution of plant diversity remain poorly understood, even though evolutionary turnover of plant lineages at the KPB is central to understanding assembly of the Cenozoic biota. The apparent concentration of whole genome duplication (WGD) events around the KPB may have played a role in survival and subsequent diversification of plant lineages. To gain new insights into the origins of Cenozoic biodiversity, we examine the origin and early evolution of the globally diverse legume family (Leguminosae or Fabaceae). Legumes are ecologically (co-)dominant across many vegetation types, and the fossil record suggests that they rose to such prominence after the KPB in parallel with several well-studied animal clades including Placentalia and Neoaves. Furthermore, multiple WGD events are hypothesized to have occurred early in legume evolution. Using a recently inferred phylogenomic framework, we investigate the placement of WGDs during early legume evolution using gene tree reconciliation methods, gene count data and phylogenetic supernetwork reconstruction. Using 20 fossil calibrations we estimate a revised timeline of legume evolution based on 36 nuclear genes selected as informative and evolving in an approximately clock-like fashion. To establish the timing of WGDs we also date duplication nodes in gene trees. Results suggest either a pan-legume WGD event on the stem lineage of the family, or an allopolyploid event involving (some of) the earliest lineages within the crown group, with additional nested WGDs subtending subfamilies Papilionoideae and Detarioideae. Gene tree reconciliation methods that do not account for allopolyploidy may be misleading in inferring an earlier WGD event at the time of divergence of the two parental lineages of the polyploid, suggesting that the allopolyploid scenario is more likely. We show that the crown age of the legumes dates to the Maastrichtian or early Paleocene and that, apart from the Detarioideae WGD, paleopolyploidy occurred close to the KPB. We conclude that the early evolution of the legumes followed a complex history, in which multiple auto- and/or allopolyploidy events coincided with rapid diversification and in association with the mass extinction event at the KPB, ultimately underpinning the evolutionary success of the Leguminosae in the Cenozoic.
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