Ptychodus (teeth)

Object/Artifact

-

Crater Rock Museum

Name/Title

Ptychodus (teeth)

Entry/Object ID

78.57.110

Description

Description: Kingdom: Animalia Phylum: Chordata Class: Chondrichthyes Subclass: Elasmobranchii Superorder: Selachimorpha Order: Hybodontiformes Superfamily: Hybodontoidea Family: Ptychodontidae Genus: Ptychodus Common Name: Shark Tooth Age: Eocene Location: Lower Chalk, in either Kent or Sussex, England Description: One group of three shark teeth in concretion. The teeth have wave-like ridges and are fairly flat. The teeth are fused by pyrite / marcasite (White Chalk of Brighton, Sussex). Physical Characteristics: The distinctive crushing / grinding teeth of Ptychodus are amongst the most familiar of Chalk fossils, but the taxonomic placement of the Ptychodontid sharks is an ongoing point of controversy. They possess a problematic combination of characters which suggest a number of non-compatible affinities - their tooth microstructure like Hybodontids, their tooth morphology like rays (Batomorphii), their jaw structure like Heterodontiformes, and their vertebrae like Lamniformes. They are widely thought of as rays by amateur collectors, though the academic community seems to have dismissed this option, largely viewing them as relatively 'primitive' euselachians, close to the Hybodontids. However, recent work based on vertebra from well preserved US material has concluded that they are neoselachians (Everhart & Caggiano, 2004). Generally teeth comprise of 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: - P. decurrens – This is the common form from the Grey Chalk and lowest White Chalk and is highly variable. Flattened to bulbous in lingual profile, but without a depressed marginal area. Crown crossed by a large number of transverse ridges, often finely bifurcated towards the margins, and passing diffusely into a narrow and poorly defined marginal area with granular ornament. [Cenomanian to Turonian] - P. marginalis – Central area is broad, flattened and moderately elevated in lingual profile, with a broad depressed marginal area. The central area is crossed by a large number of longitudinal ridges. [White Chalk: Turonian to Coniacian]. - P. mammillaris – Central area is narrow, rounded and highly elevated in lingual profile, with a depressed marginal area. The central area is crossed by a small number of longitudinal ridges. [White Chalk: Turonian to Coniacian]. - P. rugosus – Like P. mammilaris, but with poorly defined ridges on the central area passing into a rugose ('lumpy') ornament. [White Chalk: Coniacian to Santonian]. - P. latissimus – Low rounded profile in lingual view. The central area is crown crossed by a relatively small number of highly pronounced longitudinal ridges, triangular in section. Relatively wide marginal area, not depressed, and with fine granular ornament. P. 'dixoni' form with finer ridges to central area, P. 'paucisulcatus' form with very few ridges. [White and grey Chalk: Cenomanian to Santonian]. - P. polygyrus - Low in profile, with broad, highly flattened central area, and typically very narrow marginal area. Central area ornamented by a relatively small number of pronounced longitudinal ridges, often joined to one another at the ends giving concentric ringed effect. [White Chalk: Coniacian to Santonian]. - P. concentricus - Like P. polygyrus, but with a highly domed central area. Scarce in the UK. [Grey Chalk: Cenomanian]. - P. oweni - Low and rounded in lingual profile, with no depression of the narrow marginal area. Ridged ornament of the central area passes into a finer ridged ornament of the marginal area, all loosely arranged in a part-radial, part-longitudinal fashion. [Grey Chalk: Cenomanian]. - P. mortoni - A US form, virtually unknown from the UK. Rounded to sub-triangular in side profile. Central area bears a radial ornament of coarse ridges converging towards a central apex, with a broad margin with granular ornament. Family: Ptychodontidae Genus: Ptychodus Kingdom: Animalia (Animals) Class: Chondrichthyes Order: Hybodontiformes Phylum: Chordata

Collection

Fossil Collection

Acquisition

Accession

78.57

Source or Donor

Delmar Smith Fossil Collection

Acquisition Method

Donation

Dimensions

Width

1-5/8 in

Depth

1-1/8 in

Length

2-5/8 in

Location

Location

Room

Fossil Room

Building

Crater Rock Museum

Category

Exhibit