Ben Creisler
Recent non-dino papers:
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The acquisition of terrestrial, limb-based locomotion during tetrapod evolution has remained a subject of debate for more than a century. Our current understanding of the locomotor transition from water to land is largely based on a few exemplar fossils such as Tiktaalik, Acanthostega, Ichthyostega and Pederpes. However, isolated bony elements may reveal hidden functional diversity, providing a more comprehensive evolutionary perspective. Here we analyse 40 three-dimensionally preserved humeri from extinct tetrapodomorphs that span the fin-to-limb transition and use functionally informed ecological adaptive landscapes to reconstruct the evolution of terrestrial locomotion. We show that evolutionary changes in the shape of the humerus are driven by ecology and phylogeny and are associated with functional trade-offs related to locomotor performance. Two divergent adaptive landscapes are recovered for aquatic fishes and terrestrial crown tetrapods, each of which is defined by a different combination of functional specializations. Humeri of stem tetrapods share a unique suite of functional adaptations, but do not conform to their own predicted adaptive peak. Instead, humeri of stem tetrapods fall at the base of the crown tetrapod landscape, indicating that the capacity for terrestrial locomotion occurred with the origin of limbs. Our results suggest that stem tetrapods may have used transitional gaits during the initial stages of land exploration, stabilized by the opposing selective pressures of their amphibious habits. Effective limb-based locomotion did not arise until loss of the ancestral 'L-shaped' humerus in the crown group, setting the stage for the diversification of terrestrial tetrapods and the establishment of modern ecological niches.
News
Water-to-land transition in early tetrapods
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New Bothremydini material discovered in the Olmos Formation of Coahuila, Mexico is described.
The characteristics of this material allow the recognition of a new genus and species, Palauchelys montellanoi.
Palauchelys montellanoi is the first Bothremydini turtle described from the late Campanian of Mexico.
The new specimen adds to the diversity of Bothremydini in North America.
ABSTRACT
During the Late Cretaceous, pleurodiran turtles were taxonomically diverse and, inhabited a variety of environments, within a practically worldwide distribution. Among this group, the most widespread at that time was Bothremydidae, which was represented in North America by four taxa: Algorachelus tibert, Chedighaii hutchisoni, Chedighaii barberi, and Bothremys cooki. Nevertheless, the presence of Bothremydidae in Mexico is so far very scarce, and the few reports were recognized at indeterminate generic level and have, not been analyzed in detail. In this paper we describe the first Bothremydini from Mexico, collected in a coal mine in Coahuila in the Late Cretaceous of the Olmos Formation (upper Campanian). The coal mines in this region are known for their paleoflora, but this turtle specimen is the first vertebrate to be notified. This specimen displays a unique combination of characters that allows its attribution to a new representative, Palauchelys montellanoi gen. et sp. nov., thus expanding knowledge about the diversity of this group in the American Cretaceous record.
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Also, posted earlier but now with free pdf:
Free pdf:
Rodolfo OtÃvio Santos, Michel Laurin & Hussam Zaher (2020)
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Free pdf:
Drilling into the Chicxulub crater (Yucatan, Mexico) reveals the dramatic aftermath of the dinosaurâkilling meteorite impact. Previous views of this event have mainly come from places well away from Ground Zero, where we see the extinction of ~70% of life, the fallout of a globeâspanning ejecta cloud, and the slumps and tsunamis that accompanied one of the biggest terrestrial earthquakes ever. The new view from the crater in a drill core records the collapse of the shattered and melted crater walls, the flood of the ocean back into the submarine crater, and the formation of hot vents over the pool of melt rock. The record shows that decades to centuries after the impact, the calm tropical marine lake was taken over by red tides and animals that colonized the previously sterile crater floor. The exact timing of appearance of the first newly evolved species is hard to pin down but probably occurred within a few centuries to several millennia based on evidence from the intensity of burrowing and estimates of sedimentation rates.
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An Os isotopic profile of the Carnian chert succession in Japan was determined.
Os isotope data indicate the Wrangellia LIP formed during the Julian.
Two negative Î13Corg shifts were detected in the Julian 2 in the study section.
Enrichment of redox-sensitive elements suggests oxygen-depleted conditions occurred in the Panthalassa in the Julian 2.
Abstract
The Carnian Pluvial Episode (CPE) was a global environmental change and biotic crisis that occurred during the Carnian (Late Triassic). The climate during the CPE was characterized by a short-lived period of extreme rainfall, and an extinction of marine taxa is known to have occurred during the latest Julian (i.e. Early Carnian). Although these events are considered to have been caused by the Wrangellia Flood Basalt (FB) volcanism, existing studies have found little direct evidence to support this. We investigated the temporal relationship between the eruption of Wrangellia FB and CPE using high-resolution microfossil biostratigraphy and paleo-seawater Os isotope data of an Upper Triassic bedded chert succession from an accretionary complex in Japan, which accumulated in a pelagic deep-sea environment in an equatorial region of the Panthalassa Ocean. Our biostratigraphic analysis, based on conodonts and radiolarians, and osmium isotope data show: (i) a continuous decline of initial Os isotope ratios (187Os/188Osi) in the early Julian; (ii) low 187Os/188Osi ratios during the late Julian; and (iii) an abrupt increase in 187Os/188Osi ratios at the end of the Julian. The decrease in 187Os/188Osi ratios throughout the Julian suggests an increased input of unradiogenic Os from the eruption of the Wrangellia FB into the ocean. Moreover, redox-sensitive elements, such as V and U, increased abruptly at the end of the Julian, which is the first evidence of reducing conditions during the CPE within the pelagic deep-sea Panthalassa Ocean. Marine anoxic event in the late Julian has been recognized from widespread deposition of black shales and organic-rich marls in intermediate to shallow water Tethyan sections. Thus, oxygen-depleted conditions occurred at the Tethyan shallow continental margin, as well as in the pelagic deep-sea Panthalassa Ocean, at the end of Wrangellia FB volcanism.