• journal_title：Journal of Paleontology
• Contributor：Lloyd N. Glawe ; Dennis E. Bell ; David T. Dockery III ; John F. Anderson
• Publisher：Paleontological Society
• Date：2011-
• Format：text/html
• Language：en
• Identifier：10.1666/09-143.1
• journal_abbrev：Journal of Paleontology
• issn：0022-3360
• volume：85
• issue：5
• firstpage：977
• section：ARTICLE

Assemblages of the boat-shaped bivalve Odontogryphaea thirsae (bibr">Gabb, 1861) from southwestern Alabama are used to define three ontogenetic growth stages that are bounded by major discontinuities in either mineral structure or growth-line prominence. Features of the larval and juvenile stages are described here for the first time and are compared with the well-known morphologic features that distinguish adults (late dissoconchs).

The larval stage is represented by prodissoconch valves which are about 0.4 mm in height with suborbicular outlines, commarginal striations, and ridge-like, opisthogyral beaks. The juvenile (early dissoconch) stage is expressed by dissoconch valves up to 19 mm in height with elliptical outlines (height > length), indistinct commarginal growth lines, flat commissural planes, and tiny attachment areas on left valves; the valve interiors exhibit a posterior adductor muscle scar, a resilifer, and chomata. The adult (late dissoconch) stage is characterized by dissoconch valves >19 mm in height with subtriangular outlines, prominent commarginal growth lines, wavy commissural planes, and a keel-like terebratuloid fold.

Paleonvironmental and stratigraphic studies of the diversely fossiliferous Odontogryphaea thirsae beds indicate 0. thirsae (bibr">Gabb, 1861) thrived in a shallow, normal-marine, tropical sea that extended from Texas to Georgia about 57 million years ago.