Mammalian lower jaw (Metatheria) from the Late Cretaceous Lance Formation (Wyoming, USA)

The public excavation and preparation of sixteen sediment blocks of a Late Cretaceous Lance Formation bonebed (Eastern Wyoming, USA) yielded a well-preserved mammalian lower jaw. The sediment blocks were transported to the Senckenberg Forschungsinstitut und Naturmuseum in Frankfurt am Main (Germany) in 2018 and 2019 as part of the public “Edmond’s prehistoric Realm” event (“Edmonds Urzeitreich”, Senckenberg Naturmuseum Frankfurt 2020 to 2021). Here we highlight that public outreach projects can serve as valuable tools for engaging the public interest while contributing to science with the discovery and description of new material. The partial fossil jaw was professionally excavated and prepared from the surrounding sediment matrix and subsequently μCT scanned. Morphological characters like dental formula, occlusal surface characteristics, and jaw shape suggest affinities to Mesozoic Marsupialia or Marsupialiaformes. Abundant metatherian taxa known from the Lance Formation are the didelphimorph alphadontids and pediomyids. Position and form of the oblique cristid (i.e. cristid obliqua) in relation to the protocristid notch are key features that distinguish alphadontids and pediomyids. Even though the specimen shows heavily worn tooth surfaces, the identification of genus and species appears possible, and we tentatively assign the specimen to the pediomyid genus ?Leptalestes due to the following characters: both entoconid and hypoconulid are distally wing-like expanded, the oblique cristid connects to the trigonid at the protocristid notch, and the entocristid is a sharp crest rather than cusp-shaped. The strong dental wear indicates that the animal was likely fully adult to senile.