A phytosaur osteoderm from a late middle Rhaetian bone bed of Bonenburg (North Rhine-Westphalia, Germany): Implications for phytosaur extinction

Although there are problematic earliest Jurassic records, phytosaurs are thought to have become extinct during the Rhaetian. A newly-discovered left paramedian phytosaur osteoderm from a clay pit in Bonenburg, Kreis Höxter, North Rhine-Westphalia, Germany, is the youngest, well-dated phytosaur record. This osteoderm was found in a bone bed (Bone Bed 2) in the Contorta Beds of the Rhaetian Exter Formation. Palynology constrains the age of Bone Bed 2 to the late middle Rhaetian (ca. 203.5 million years ago). The Bonenburg osteoderm cannot be assigned to any named species. It most closely resembles some osteoderms from the Rhaetian of Halberstadt in Central Germany. Phytosaurs survived in Europe to at least the late middle Rhaetian, probably falling victim to the end-Triassic extinction event about two million years later.