figures of various
eugeneodont fossils, the
holotype of
H. davisii (WAMAG 9080) being shown at the top (fig. 1) The first known specimen of
Helicoprion consists of a partial tooth whorl preserving 15 teeth, 14 of which are visible. It was discovered in
Western Australia in a
tributary of the
Gascoyne River by a
gold prospector named Mr. Davis, his
first name being unknown. Now housed in the
Western Australian Museum under the catalogue WAMAG 9080, the fossil was not found
in situ, thus its precise
stratigraphic origin remains uncertain. tooth whorl of
H. bessonowi (TsNIGR 1/1865) More complete tooth whorls were discovered in the late 19th century by Alexander G. Bessonov of the
Russian Academy of Sciences, in a quarry near the town of
Krasnoufimsk in
Sverdlovsk Oblast. He sent them to geologist
Alexander Karpinsky, who first described them in a monograph published in Russian in 1899, followed later that year by a German translation. As the fossils he examined were sufficiently distinct from those of
Edestus, Karpinsky assigned them to a new genus, which he named
Helicoprion, with
H. bessonowi as the
type species. The
generic name Helicoprion derives from the
Ancient Greek (
hélikos, "spiral") and (
príōn, "saw"), in reference to the characteristic morphology of the tooth whorls, while the
specific epithet bessonowi honors their discoverer. In his 1899 observations, Karpinsky also noted that the specimen described by Woodward in 1886 showed sufficient similarities with the Krasnoufimsk material to justify its provisional reassignment to
Helicoprion, renaming it
H. davisii. A few years later, in 1909, his colleague
Oliver Perry Hay transferred the species once again, this time to
Toxoprion, another newly established, related genus. In later publications, Karpinsky reaffirmed the position he had argued in 1899, an interpretation followed by several authors in the subsequent decades. His interpretation was finally confirmed in 1940, when German–American paleontologist
Curt Teichert described much more complete fossils of
H. davisii, which like the holotype, were also discovered in Western Australia. Since the genus
Helicoprion was established by Karpinsky in 1899, numerous additional species have been described from fossils found across the world, although most originate from North America. In a
morphometric revision published in 2013, American paleontologists Leif Tapanila and Jesse Pruitt reassessed all of these historical species assignments. Their analysis showed that, among the roughly 10 named species, only three possess features distinctive enough to be considered
valid:
H. bessonowi,
H. davisii, and
H. ergassaminon, with the remaining taxa regarded as either
synonymous or
doubtful.
H. ergassaminon was first described in 1966 by Danish ichthyologist Svend Erik Bendix-Almgreen in a monograph devoted to several
Helicoprion fossils housed in the paleontological collections of various universities in Idaho, USA. As with the generic name, the specific epithet derives from the Ancient Greek (
ergasamenon), meaning "the one who has done work", in reference to the distinctive wear marks observed on the holotype. This latter, nicknamed "Idaho 5" and discovered in a now-abandoned mine near
Fort Hall, was reported by Bendix-Almgreen to be stored at the
University of Idaho in
Moscow, Idaho. However, later searches failed to locate the specimen at that institution, and the fossil was subsequently considered lost. For nearly a century, this species was distinguished on the basis of tooth angle and height. However, in their 2013 revision, Tapanila and Pruitt demonstrated that these traits
vary naturally within a single
Helicoprion species, so regarded
H. ferrieri as a junior synonym of
H. davisii. In their 2013 revision, Tapanila and Pruitt demonstrated that the characters attributed to
H. sierrensis fall within the natural range of variation seen in
H. davisii, while those of
H. nevadensis correspond to the
growth stage of
H. bessonowi. The two species named by Wheeler were thus synonymized with
H. davisii and
H. bessonowi. Although the holotype of this species has since been reported lost, Tapanila and Pruitt noted that its anatomy closely resembles that of the largest known
Helicoprion specimen. Nevertheless, neither specimen can be assigned to any of the three recognised species due to their incomplete preservation. Consequently, in the absence of more complete material attributable to the taxon,
H. mexicanus is regarded as a
nomen dubium. Contrary to
ICZN requirements, though, the author provided no
diagnosis establishing the distinctiveness of the taxon. As the specimen is also considered lost, Tapanila and Pruitt classified this species as a
nomen nudum. Tapanila and Pruitt interpreted these observations as an artefact of the holotype’s partial preservation, since only the central portions of its teeth are preserved. The authors of the 2013 revision considered
H. svalis to be strongly similar to
H. bessonowi, but could not formally synonymise the two due to the incompleteness of the fossil material, so regarded it as a doubtful taxon. In their 2013 revision, though, Tapanila and Pruitt pointed out that the specimen is partially obscured by its surrounding
matrix, which likely led to an underestimation of tooth height. Taking this into account, along with intraspecific variation, they regarded
H. jingmenense as a junior synonym of
H. davisii.
, which was originally assigned to Helicoprion'' In 1916, Karpinsky erected the species
H. clerci on the basis of fragmentary remains of a large tooth whorl discovered near Krasnoufimsk, the same locality that yielded the original fossils of
H. bessonowi. In his description, however, he noted that the taxon might be sufficiently distinct to warrant its own genus. He formalised this proposal in 1924 by transferring the species to the genus
Parahelicoprion, a name he had already used informally in several earlier publications. In 1986, a second species,
P. mariosuarezi, was described by Bolivian geologist Dagmar Merino-Rodo and French palaeontologist
Philippe Janvier on the basis of fossils recovered in
Bolivia. In the same publication, however, the authors were the first to question the taxonomic status of the genus, noting the likely absence of clearly defined
autapomorphies. This cast doubt on the
monophyly of
Parahelicoprion and complicated the assignment of additional species. In 2018 and 2023, Russian palaeontologists Sergey V. Naugolnykh and Dmitry V. Naumkin proposed that
Parahelicoprion may, in fact, represent a junior synonym of
Helicoprion, suggesting that the genus may have been named on the basis of fossils belonging to exceptionally large and old individuals of the latter. Other authors have continued to consider the genus to be distinct from
Helicoprion. == Description ==