Abstract

Alokistocare subcoronatum (Hall and Whitfield, 1877) is the type species of Alokistocare Lorenz, 1906, the nominal genus for the diverse Middle Cambrian Alokistocaridae Resser, 1939b. New collections from the Ehmaniella Biozone contain cranidia, librigenae, hypostomes, rostral plates, thoracic segments, and pygidia, which allow a more complete understanding of the morphological range and character of this important species. Cladistic analyses using this new information about A. subcoronatum suggest that: 1) Ehmaniellidae Sundberg, 1994, is synonymous with Alokistocaridae; 2) Alokistocaridae is a monophylectic clade and not synonymous with Papyriaspididae Whitehouse, 1939; 3) Pseudoalokistocare Sundberg, 1994, is synonymous with Alokistocare; and 4) Taxa previously assigned to the older "Alokistocare"/Amecephalus group (Plagiura to Glossopleura biochrons) form a separate clade and should not be included in Alokistocare or the Alokistocaridae. These older species are assigned to Amecephalus Walcott, 1924, which is restricted to the Delamaran Stage. Alokistocaridae as recognized here is restricted to the Marjuman Stage. A morphometric analysis of Alokistocare subcoronatum shows minor but significant differences among collections, indicating population differences. In addition, the cranidium displays both positive and negative allometric growth as well as isometric growth. Allometric growth is present in both meraspid and holaspid stages. The pygidium shows only isometric growth.

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