Pachythrissops is an extinctgenus of ray-finned fish. It contains two species, P. laevis from the Purbeckian of England and P. propterus from the Tithonian of Germany. A third species, P. vectensis, has been reassigned to the elopiform genus Arratiaelops.[1]Pachythrissops is often regarded as one of the most primitive members of the order Ichthyodectiformes;[2] however, a phylogenetic analysis by Cavin et al. (2013) placed it and the related genus Ascalabothrissops outside the group.[3]
^Cavin, L.; Forey, P. L.; Giersch, S. (2013). "Osteology of Eubiodectes libanicus (Pictet & Humbert, ) and some other ichthyodectiformes (Teleostei): phylogenetic implications". Journal of Systematic Palaeontology. 11 (2): 115–177. doi:10.1080/14772019.2012.691559. S2CID83807640.
Fossils (Smithsonian Handbooks) by David Ward (Page 215)