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New, well-preserved specimens of the Upper Pennsylvanian synapsid Haptodus garnettensis from Garnett, Kansas, represent more mature individuals than those available previously and indicate that H. garnettensis is diagnosed by several autapomorphies: septomaxilla with small facial exposure; prefrontal pocket shallow; pineal ridge present; supratemporal notched; anterior end of angular overlapped dorsally and ventrally by splenial; robust, chisel-shaped teeth; teeth present on palatal ramus of premaxilla. A phylogenetic analysis of early synapsids indicates that H. garnettensis is not a sphenacodontid.
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Michel Laurin (1993) studied this question.
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