A new paracryptodiran turtle, Arundelemys dardeni, gen. et sp. nov., is described on the basis of an isolated, nearly complete skull from the Early Cretaceous Arundel Clay facies of Maryland, USA. The basicranial region exhibits the paracryptodiran condition of a single foramen for the canalis caroticus internus located midway along the basisphenoid. As revealed by CT scans, the basicranial region of Arundelemys is unusual in that the right and left canales carotici interni merge just before reaching the sella turcica and the canalis caroticus lateralis is very small or absent. A phylogenetic analysis places Arundelemys dardeni as the basal-most member of the Paracryptodira. Within the Paracryptodira, Arundelemys dardeni is most similar to Compsemys victa in general proportions.

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Multituberculates, though among the most commonly encountered mammalian fossils of the Mesozoic, are poorly known from the North American Early Cretaceous, with only one taxon named to date. Herein we describe Argillomys marylandensis, gen. et sp. nov., from the Early Cretaceous of Maryland, based on an isolated M2. Argillomys represents the second mammal known from the Arundel Clay facies of the Patuxent Formation (Lower Cretaceous: Aptian). Though distinctive in its combination of characters (e.g., enamel ornamentation consisting of ribs and grooves only, cusp formula 2:4, presence of distinct cusp on anterobuccal ridge, enlargement of second cusp on buccal row, central position of ultimate cusp in lingual row, great relative length), the broader affinities of Argillomys cannot be established because of non-representation of the antemolar dentition. Based on lack of apomorphies commonly seen among Cimolodonta (e.g., three or more cusps present in buccal row, fusion of cusps in lingual row, cusps strongly pyramidal and separated by narrow grooves), we provisionally regard Argillomys as a multituberculate of “plagiaulacidan” grade. Intriguingly, it is comparable in certain respects to some unnamed Paulchoffatiidae, a family otherwise known from the Late Jurassic – Early Cretaceous of the Iberian Peninsula.

Previous authors have noted the general scarcity of Early Cretaceous vertebrate fossils, and mammals in particular (e.g., Clemens et al., 1979). The Arundel Clay facies of the Patuxent Formation (Potomac Group), Maryland, is one of a small number of Early Cretaceous units that has produced a vertebrate assemblage, and is the only vertebrateproducing unit of this age in eastern North America (Kranz, 1996(Kranz, , 1998. Isolated bones and teeth of dinosaurs have been known from the Arundel for more than a century (e.g.

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.

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