Placenticeratidae Hyatt, 1900
Key morphological features: Shells of this group are large with inner whorls involute lacking ornamentation, while the outer whorls are strongly ornamented and evolute. Suture lines have wide lobes that branch off into rounded, long, and frilly elements.
MOBILITY: Mobile (swim)
FEEDING MODE: Predator
Wright, C. W., 1996. Ammonoidea, in Kaesler, R. L., ed., Treatise on Invertebrate Paleontology, Part L, Mollusca 4 Revised, Volume 4. The University of Kansas and Geological Society of America. 362 pp.