Belgian palaeontologist
Louis Dollo defined the genus in 1889, with the description of
Phosphorosaurus ortliebi from the upper Maastrichtian
Craie phosphateé of
Ciply in Belgium. The holotype is a fragmented and incomplete skull that is estimated to have been around 42 cm long. It was reclassified as
Halisaurus ortliebi in 1996, but this was not taken up by later authorities due to differences in the cranium. Below is a
cladogram following an analysis by Takuya Konishi and colleagues (
2015) done during the description of
P. ponpetelegans, which showcases the internal relationships within the
Halisaurinae. |label1=
Halisaurini}}
Species Two species are known,
P. ortliebi and
P. ponpetelegans, the latter from the oldest Maastrichtian beds located in Hokkaido, Japan. The skull of the latter species is thought to be around 50 cm long. The
etymology of
P. ponpetelegans derives from the words "
ponpet", which means "creek" in
Ainu (language of the indigenous peoples of
Hokkaido), and "
elegans",
Latin for "elegant", referencing the exceptional preservation of the holotype specimen of the species and the clean Pankerusano-sawa Creek where the fossil was discovered.
P. ortliebi and
P. ponpetelgans can be distinguished from each other by several fossil characters. For instance, the prefrontal postnarial medial lamina are smaller in
P. ponpetelgans than in
P. ortliebi and the development of prefrontal supraorbital tuberosity is minimal compared to
P. ortliebi. In
P. ponpetelgans the median dorsal ridge of the frontal becomes weak posterior to the orbits, which does not occur in
P. ortliebi. ==References==