Ptychodus Views
Generally teeth comprises a large robust crown, approximating a rounded square in plan view, with a blocky rounded-cube shaped root tucked underneath. Tooth form is highly variable and a perhaps surprising number of Ptychodus species are recognised from the Chalk, each defined on overall tooth form. The main species concepts can be summarised as follows:
2). Ptychodus decurrens; oral (biting surface) views of an exceptional articulated portion of the lower dentition, fused by pyrite / marcasite. The front of the animal presumably lies towards the top of the image. The single central row of larger teeth indicates that this is the lower dentition (Grey Chalk of Southerham, near Lewes, Sussex, Willett Collection, Booth Museum, BMB 007331, by kind permission of John Cooper); (A) general view of specimen (x0.9); (B) detail, with central row of enlarged teeth on the right (x1.5).
6). Ptychodus polygyrus - Low angle view of the specimen figure above - note flattened profile to the teeth (distinguishes Ptychodus polygyrus from Ptychodus concentricus (see below). Note also that teeth in the central row have well developed marginal areas, whilst marginal areas are highly reduced to absent in the more lateral rows (x0.7). Image used by kind permission of Ron Stilwell.
11). Ptychodus decurrens; a unique specimen with the articulated partial lower and upper dentitions of a moderate sized individual, the front of the animal presumably lying towards the top of the image. The teeth exposed in oral (biting surface) view are of the upper dentition, whilst the overlying teeth exposed in root view are of the lower dentition. The teeth are fused by pyrite / marcasite (White Chalk of Brighton, Sussex, Willett Collection, Booth Museum, BMB 008605, by kind permission of John Cooper); (A) general view of the specimen (x0.8); (B) detail, mainly showing the left hand side of the upper dentition (x1.5).
Ptychodus Images
