Hexanchiformes Buen 1926
Teeth, which can be at a glance identified to the genus, and, in addition, uppers can be clearly distinguished from lowers.
Quite rare teeth. Complete specimens are very rare. Two genera from Hexanchidae family are represented: Hexanchus Rafinesque, 1810 and Notorynchus Ayres, 1855 — sixgill and sevengill sharks respectively.
Notorynchus. Lower left.
Still alive (as well as Hexanchus), but nowadays absent in Mediterranean and all Northern Atlantic.
Stereopair
The same genus, tooth of similar position.
Somewhat more eroded one.
An upper left from the same genus.
Tiny cusplets indicate anterior (but not first) position.
Symphyseal!
Such teeth comprise several percent of their dentition.
For Notorynchus, with rate of finding about 2 teeth/year (taken more or less complete), you can expect 1 symphyseal in 10 years. For Hexanchus the rate must be several times bigger.
Another specimen.
This one seems to be reliably Hexanchus.
Hexanchus. Lower right one.
Much more common in Kyiv than Notorynchus. And always smaller.
The root edge here is about 1/3 mm thick. In spite of this, it survived a journey through sand-sucking pipe.
Same genus, same position.
But significantly different appearance.
Hexanchus, lower left.
It seems, from a young shark, judging from absence of serrations on the acrocone and big number of cusps per tooth width (see Adnet, 2006). According to this paper, parameters of this tooth indicate shark's body length about 50 cm.
Upper right anterior.
Perfectly preserved one.
Similar one.
Upper left anterior. More lateral one: first small cusplet appears.
Slightly bilobate flat root and short second cutting edge. Such teeth help to understand, why some early researchers ascribed Xiphodolamia to Hexanchidae.
Upper left lateral
Links and references:
Adnet, S. 2006. Biometric analysis of the teeth of fossil and Recent hexanchid sharks and its taxonomic implications. Acta Palaeontologica Polonica 51 (3): 477–488.
a profound article about Hexanchus teeth morphology, it's relations to species identification, shark's size etc.
about Notorynchus and Hexanchus on www.fossilguy.com
teeth with different positions: Notorhynchus primigenius on belgiansharkteeth
Hexanchiformes' teeth diversity and tooth sets on J-elasmo
recent Notorynchus with it's teeth on discoverlife.org