Faunal composition and paleoenvironment of the Arundel Clay (Potomac Formation; Early Cretaceous), Maryland, USA

Abstract

The Arundel Clay facies of the Potomac Group represents one of the few Lower Cretaceous vertebrate-bearing deposits in the Atlantic coastal plain. Vertebrate fossils from this unit have been known for more than 150 years, but thus far formal descriptions have mainly concentrated on its dinosaurs and mammals. Herein, we eport on a moderately diverse faunal assemblage (USNM 41614) from Dinosaur Park in Prince Georges County, Maryland. This assemblage is represented by 306 disarticulated macro-and microfossils that largely consist of teeth and scales (89%). This vertebrate fauna includes two species of hybodont sharks, multiple semionotid fishes, one species of lungfish, three species of turtle, three families of neosuchian crocodilians, six species of dinosaurs, and two species of mammals. Combined with other historical collections from this unit, these new additions to the fauna show that the Arundel was a far more robust and diverse ecosystem than previously envisaged, broadly similar in composition to contemporaneous units of western North America. The Arundel assemblage differs, however, from those in many other Lower Cretaceous sites in that it is dominated numerically by Hybodus and goniopholidid crocodylomorphs, which together comprise 58% of catalogued specimens. Similarly, this sample entirely lacks lissamphibians and lepidosaurs. Traditionally, the Arundel has been interpreted as being of fluvial origin, deposited in a freshwater system of stranded channels or oxbows. Based on faunal composition, together with published geological and sedimentological evidence, we propose that at least some of the Arundel facies was deposited in close proximity to the Atlantic Ocean.

Cranial osteology, taxonomic reassessment, and phylogenetic relationships of the Early Cretaceous (Aptian-Albian) turtle Trinitichelys hiatti (Paracryptodira)

“…Arundelemys dardeni and Trinitichelys hiatti were found in Aptian-Albian layers of Maryland and Texas, respectively, but a more constrained age is not known yet, which impedes synonymizing or clearly distinguishing both taxa based on temporal considerations. Arundelemys dardeni was originally described as being late Albian to early Aptian in age ( Lipka et al, 2006 ) but this was likely a typographical error, as a late Aptian to early Albian age was more recently mentioned for the layers in which the skull had been found ( Frederickson, Lipka & Cifelli, 2018 ). Trinitichelys hiatti was first described as Albian in age by Gaffney (1972) , although he also mentioned a slightly more precise age for the latter as being early Albian, based on Stephenson et al (1942) .…”

New data on the microvertebrate fauna from the Upper Jurassic or lowest Cretaceous of Ksar Metlili (Anoual Syncline, eastern Morocco)

“…The Valanginian–Aptian stratigraphic range of E. basanus (Biddle & Landemaine, 1988; Duffin & Sigogneau-Russell, 1993; Frederickson et al . 2018) would tend to confirm a Cretaceous age for the Ksar Metlili deposit, although it does not provide a full corroboration of the previously suggested Berriasian age (Duffin & Sigogneau-Russell, 1993). Moreover, E. basanus could be a synonym of E. duffini , described from the middle Bathonian of Great Britain (Rees & Underwood, 2008), so Egertonodus does not provide any precision on the biostratigraphic dating of the KM fossil locality.…”

Dinosaurs from the Santonian–Campanian Atlantic coastline substantiate phylogenetic signatures of vicariance in Cretaceous North America

“…Gould & Lewontin [136] famously noted the existence of 'just so' stories in evolutionary biology, and noted the various hypotheses then put forward about the function of the diminutive forelimbs of tyrannosaurids as an example. In the same vein, the anatomy of the Merchantville species and Dryptosaurus, which may form a monophyletic lineage that lived at exactly the same time as tyrannosaurids, filled large predator niches in ecosystems also dominated by potential prey species like hadrosaurids, ornithomimosaurs and ankylosaurs, and succeeded allosaurs as large predators in assemblages along the Atlantic Coastal Plain [137,138], warrants a critical look at current hypotheses about the reasons tyrannosaurids evolved large sizes, advances senses and odd postcranial features like a small, two-fingered arm so late in the Mesozoic.…”