The Kinzers Formation (Pennsylvania, USA): the most diverse assemblage of Cambrian Stage 4 radiodonts

Radiodonta, apex Cambrian predators such as Anomalocaris have been known from the Kinzers Formation (Cambrian Series 2, Stage 4 - Pennsylvania, USA) for nearly 100 years. Work over the last ten years, mainly on radiodont material from the Chengjiang (Cambrian Series 2, Stage 3 - Yunnan, China) and Burgess Shale (Miaolingian, Wuliuan - British Columbia, Canada), has greatly improved our knowledge of the diversity and disparity of radiodonts and their frontal appendages, including the description of new species, genera and families. Previous work identified two species of radiodonts from the Kinzers Formation: Anomalocaris pennsylvanica Resser, 1929 and Anomalocaris? cf. pennsylvanica based on isolated frontal appendage material (Briggs, 1979). A restudy of Kinzers Formation material shows that only some of the specimens can be confirmed as Anomalocaris pennsylvanica, and a number of specimens previously attributed to Anomalocaris in fact belong to other more recently discovered radiodont genera Amplectobelua and Tamisiocaris. This reinterpretation makes the Kinzers Formation the most diverse Cambrian Stage 4 Burgess Shale Type Lagerstatten in terms of number of radiodont species. This assemblage includes the youngest known Tamisiocaris and the first from outside Greenland, the only Amplectobelua from Stage 4 and the oldest from Laurentia, two specimens tentatively assigned to the recently described Chengjiang genus Laminacaris, and the endemic Anomalocaris pennsylvanica. The identification of these new radiodont taxa increases the total known diversity of the Kinzers Formation to more than ten species, and so it should now be considered a Tier 2 Lagerstatte.