Carbon is one of the most important elements on Earth. It is the basis of life, it is stored and mobilized throughout the Earth from core to crust and it is the basis of the energy sources that are vital to human civilization. This issue will focus on the origins of carbon on Earth, the roles played by large-scale catastrophic carbon perturbations in mass extinctions, the movement and distribution of carbon in large igneous provinces, and the role carbon plays in icehouse–greenhouse climate transitions in deep time. Present-day carbon fluxes on Earth are changing rapidly, and it is of utmost importance that scientists understand Earth's carbon cycle to secure a sustainable future.

Auroraceratops rugosus from the Lower Cretaceous Zhonggou Formation, Gansu Province, China is characterized by exquisite external preservation of articulated, often ventrolaterally curled remains found in discrete locations several to hundreds of meters apart. This has prompted a hypothesis that the remains are the result of recurring die-offs and rapid burial in burrows. To test this, rare earth element (REE) concentrations were measured from Auroraceratops bones and surrounding red-bed mudstones via inductively coupled plasma mass spectrometry. Petrographic analysis was conducted to understand the preservation of the bones and surrounding rock. Results suggest early postmortem deterioration of the bone by bacteria and/or fungal hyphae (Wedl type I tunneling and mineralized remains) and mineralization of hyphae in acidic/reducing conditions. This is supported by Ce-enriched, filamentous ferromanganese oxide coatings on the external and internal bone cavities. Deterioration/dissolution of the bone must have ceased for a period of time, and we suggest that desiccation of the carcasses halted the deterioration of bone. A second mineralization phase occurred as remains came into contact with vadose water, as evident by precipitation of micritic calcite, recrystallization of filamentous apatite in the bone matrix, and bone REE patterns indicating equilibration with alkaline/oxidized fluids. Despite poor histologic preservation, the well-articulated, curled-up positioning of the remains, and similarity to remains from the Upper Cretaceous Nemegt Formation of Mongolia, suggests that the Auroraceratops beds are the result of death in burrows in a seasonally arid environment. The similar taphonomic mode to remains from Nemegt may represent a common preservation mode for faunas from extensional basin deposits. SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP Citation for this article: Suarez, C. A., E. M. Morschhauser, M. B. Suarez, H. You, D. Li, and P. Dodson. 2019. Rare earth element geochemistry of bone beds from the Lower Cretaceous Zhonggou Formation of Gansu Province, China; pp. 22–35 in Hailu You, Peter Dodson, and Eric Morschhauser (eds.), Auroraceratops rugosus (Ornithischia, Ceratopsia) from the Early Cretaceous of northwestern Gansu Province, China. Society of Vertebrate Paleontology Memoir 18. Journal of Vertebrate Paleontology 38(Supplement). DOI: 10.1080/02724634.2017.1400441.

An ostracode fauna is described from lacustrine sediments of the Hettangian, Lower Jurassic, Whitmore Point Member of the Moenave Formation. The Moenave is well known for its rich, Late Triassic?–Early Jurassic fossil record, which includes fossil fishes, stromatolites, ostracodes, spinicaudatans, and a diverse ichnofauna of invertebrates and vertebrates. Four ostracode species, all belonging to the suborder Darwinulocopina, were recovered from these sediments:Suchonellina globosa,S. stricta,Whipplella? sp. 1, andW.? sp. 2. The diversity and composition of the Whitmore Point Member ostracode fauna agree with previous interpretations about Lake Dixie and nearby paleoenvironments as shallow lakes inhabited by darwinulocopine species that survived the effects of the Central Atlantic Magmatic Province and the subsequent end-Triassic extinction and quickly recolonized these areas, thanks to asexual reproduction by parthenogenesis. The Lake Dixie region, in its geographical isolation, could represent the last episode of darwinulocopine dominance in nonmarine environments before the Late Jurassic diversification of the cypridocopine/cytherocopine modern ostracodes.

Lanzhousaurus magnidens, a large non-hadrosauriform iguanodontian dinosaur from the Lower Cretaceous Hekou Group of Gansu Province, China has the largest known herbivorous dinosaur teeth. Unlike its hadrosauriform relatives possessing tooth batteries of many small teeth, Lanzhousaurus utilized a small number (14) of very large teeth (~10 cm long) to create a large, continuous surface for mastication. Here we investigate the significance of Lanzhousaurus in the evolutionary history of iguanodontian-hadrosauriform transition by using a combination of stable isotope analysis and CT imagery. We infer that Lanzhousaurus had a rapid rate of tooth enamel elongation or amelogenesis at 0.24 mm/day with dental tissues common to other Iguanodontian dinosaurs. Among ornithopods, high rates of amelogenesis have been previously observed in hadrosaurids, where they have been associated with a sophisticated masticatory apparatus. These data suggest rapid amelogenesis evolved among non-hadrosauriform iguanodontians such as Lanzhousaurus, representing a crucial step that was exapted for the evolution of the hadrosaurian feeding mechanism.

We present a previously discovered but undescribed late Early Cretaceous vertebrate fauna from the Holly Creek Formation of the Trinity Group in Arkansas. The site from the ancient Gulf Coast is dominated by semi-aquatic forms and preserves a diverse aquatic, semi-aquatic, and terrestrial fauna. Fishes include fresh- to brackish-water chondrichthyans and a variety of actinopterygians, including semionotids, an amiid, and a new pycnodontiform,Anomoeodus caddoisp. nov. Semi-aquatic taxa include lissamphibians, the solemydid turtleNaomichelys, a trionychid turtle, and coelognathosuchian crocodyliforms. Among terrestrial forms are several members of Dinosauria and one or more squamates, one of which,Sciroseps pawhuskaigen. et sp. nov., is described herein. Among Dinosauria, both large and small theropods (Acrocanthosaurus,Deinonychus, andRichardoestesia) and titanosauriform sauropods are represented; herein we also report the first occurrence of a nodosaurid ankylosaur from the Trinity Group. The fauna of the Holly Creek Formation is similar to other, widely scattered late Early Cretaceous assemblages across North America and suggests the presence of a low-diversity, broadly distributed continental ecosystem of the Early Cretaceous following the Late Jurassic faunal turnover. This low-diversity ecosystem contrasts sharply with the highly diverse ecosystem which emerged by the Cenomanian. The contrast underpins the importance of vicariance as an evolutionary driver brought on by Sevier tectonics and climatic changes, such as rising sea level and formation of the Western Interior Seaway, impacting the early Late Cretaceous ecosystem.