ODONTASPIDIDS [Sand Sharks]
It seems accepted in academic circles that the Odontaspids, including the living Sand Sharks, are not a natural grouping (polyphyletic, containing forms that are not closely related) and there are difficulties separating some taxa from the Mitsukurinids.
Taxonomic difficulties aside, there are shared morphological characters that characterise the Odontaspids as currently defined. The group possesses small- to medium-sized tearing teeth, typically tall and slender, with a sygmoidal character to the cusps. The main cusp is tall, sided by small and often slightly hook-like accessory cusps. The root is forked, with strongly pointed root halves and a deep, narrow basal notch. There is a lingual protrusion with a deep nutritive cleft (medial vertical groove through the lingual protrusion). The base of the crown is often wrinkled.
Odontaspid teeth are encountered with moderate frequency in the field.
1). (A) "Carcharias" sp. - Labial view of an anterior tooth exhibiting Odontaspid characteristics - strongly forked root halves, tall slender main cusp, and narrow, slightly hooked accessory cusps (x5.0, White Chalk, Booth Museum, BMB 024344, by kind permission of John Cooper); (A) Carcharias sp. - Labial view of another isolated anterior tooth, again exhibiting forked root halves and narrow accessory cusps (x5.8, Grey Chalk, Samphire Hoe, near Dover, Joe Shimmin collection, image used by kind permission).
2). "Carcharias" sp.? - (A) Labial and (B) lingual views of a small lateral Odontaspid tooth encased in hard phosphatic chalk - note nutritive cleft (vertical groove across the lingual protrusion (x10, Grey Chalk (channel lag deposit in West Melbury Marly Chalk), Southerham, near Lewes, Randell Collection RR0046).
3). "Carcharias" sp.? - Lingual view of a small anterior tooth (x9.5, Seaford Chalk, Thanet Coast, Randell Collection RR1569).
4). Modern sand sharks for illustration; (A) Sand Tiger Shark (Carcharias taurus) (image sourced from ARKive, © Andy Murch / Elasmodiver.com); (B) Smalltooth Sand Tiger (Odontaspis ferox) (image sourced from ARKive, © Yves Lefèvre / Biosphoto).