The genus Onchosaurus is a sclerorhynchid (extinct family of sawfish-like batoids) reported on the basis of isolated rostral spines.
An historical review of the published record includes:
Gervais (1852) erected Onchosaurus radicalis for a specimen (Turonian, Paris Basin, France) thought to be a reptile tooth (mosasaur) at the time. A redrawn example of this 'tooth' was provided by Cappetta (1987:154, fig. 131)
Leidy (1856a: 221) described Onchosaurus mirus from the Campanian "Green Sand" of New Jersey (teleost related to Sphyraena) and (1856b: 256) Ischyrhiza antiqua from North Carolina. He later (1860:120) synonymized the two as Ischyrhiza mira. Cope 1875: 280 includes Ischyrhiza as a Haplomi (pike).
Dames (1887b) erected Titanichthys pharao; H. Woodward (1888: 157) noted the genus was preoccupied and Dames (1887c) renamed it Gigantichthys pharao (Santonian of Egypt, see Fig. ).
A. S. Woodward (1889) erected Sclerorhynchus atavus based on complete skeletons (to 1 meter in length) from the Late Santonian of Syria - as a or .
Jaekel (1890) argued that S. atavus should actually be included as Pristiophorus.
Eastman (1904:298) included in Onchosaurus, both Ischyrhiza and Gigantichthys as pike.
Haug (1905) erected Gigantichthys numidus and Platyspondylus foureaui (Upper Albian, Algeria).
Garman (1913: 244-48) included no fossil taxa in ; he did include within : Propristis DAMES 1883 (Lower Tertiary, Egypt), Sclerorhynchus (Upper Cretaceous, Syria) and Amblypristis DAMES 1888 (Eocene, Egypt).
Priem (1914) reported Onchosaurus numidus from the Cretaceous of Egypt (as a teleost).
Stromer (1917) erected Onchopristis and moved Gigantichthys numidus to it (having found a relatively complete rostrum; Cenomanian, Egypt). He included as "sawfishes" ( or ) Gigantichthys, Onchopristis and Sclerorhynchus.
Arambourg (1935) referred to the 'ganopristines', the rostral spines that include and . In addition, he described Ganopristis leptodon and Onchosaurus maroccanus (Maas., Morocco)
Arambourg (1940) erected additional "sawfish" taxa, synonymized Dalpiazia with Ischyrhiza, included Ischyrhiza as a subgenus of Onchosaurus, and separated the members of Ganopristinae into two groups (the first limited to Onchosaurus and its subgenera).
Schaeffer (1963) erected Pucapristis branisi (Maas., Bolivia). The author noted that Onchosaurus and Ischyrhiza spines differed in histology: the former, osteodentine [Onchosaurus group] and the latter, orthodentine [Onchopristis group].
Cappetta (1972) included all sawfishes in with two subfamilies: Pristinae (Tertiary, spines set in sockets) and Ganopristinae (Late Cretaceous, spines fixed to rostrum by ligaments). The latter was divided into two groups: osteodentine (including Onchosaurus & Pucapristis) and orthodentine (including Dalpiazia, Ischyrhiza & Sclerorhynchus). He went on to note that Onchosaurus maroccanus had orthodentine and synonymized it with Dalpiazia stromeri.
Cappetta (1987) included observations and conclusions from his 1974 and 1980b papers as well. All Late Cretaceous sawfishes were included in the suborder Sclerorhynchoides CAPPETTA 1980b and the family CAPPETTA 1974 (=Ganopristinae); genera were sub-grouped as noted in Cappetta (1972). Onchosaurus (=Titanichthys DAMES 1887b = Gigantichthys DAMES 1887c; p 154) included two species, O. radicalis (fig. 131) and O. pharao - the genus ranging from the Turonian-Santonian of France, Africa and South America.
Lehman (1989) reported as Onchosaurus pharao, a group of peduncles (all missing caps) from the San Carlos Fm. (E-L Camp., ammonites suggested M. Camp.) of Presidio Co., TX. Based on anteroposterior width (up to 3.6 cm), the author estimated the rostral spine length as 9 cm. Specific determination aside, this would be the youngest (and ?largest) reported example of the genus.
Williamson et al. (1989: 241) reported as cf Onchosaurus sp. four rostral spine fragments from the Hosta Tongue, Pt. Lookout Ss. (E. Sant.) of Bernalillo Co., New Mexico.
Welton & Farish (1993) included this genus by reference to Lehman 1989 only, suggesting an underlying rarity in Texas.
Nelson (1994) raised the extant sawfishes, (), to the ordinal level -- Pristiformes.
Compagno (1999) included Recent sawfishes as Pristiformes.
Kriwet (2004) wrote that using cladistic principles and phylogenic analysis, appeared to represent a sister group to the Pristiformes and proposed the order Sclerorhynchiformes. Certain taxa (Ptychotrygon, Celtipristis, Texatrygon & Kiestus) deemed Rajiformes incertae sedis by Cappetta (1987), Cappetta & Case (1999) and Kriwet (1999b), were included in Sclerorhynchiformes. Kriwet et al. (2009) would move that latter group to a newly erected .
Bourdon et al (2011) speculated on the presence of Onchosaurus oral teeth in the Pt. Lookout Sandstone (E-M Santonian) of New Mexico. The basis for this hypothesis was the presence of Onchosaurus rostral spines and 3 undescribed oral teeth. Cappetta (pers. com 2009) acknowledged seeing a similar tooth-design in Morocco from sediments that yielded Onchosaurus rostral spines.
The published record appears to have coalesced upon an Onchosaurus rostral spine-design, although it took over 125-years. Systematically, it's certainly to be expected that more than one family will finally emerge, and there continue to be more than one opinion on ordinal position. Kriwet (2004) provided a good overview of the diverse opinions, particularly of ichthyologists, on this matter. Only Bourdon et al 2011 speculated upon the Onchosaurus oral tooth-design.
Likely similar to extant sawfishes: a flattened shark-like body with a spine-edged rostrum; unlike Tertiary taxa, the rostral spines are surface-mounted. They have been reported from the Late Cretaceous of France, Africa and South & North America.
Rostral spines. Histology: osteodentine, no pulp cavity. The cap is much shorter than the peduncle, the enameloid is smooth and limited to the cap. Viewed laterally, the cap is strongly inclined anteriorly and somewhat erect posteriorly; there is a complete anteroposterior carina. Laterally, the cap extends beyond the peduncle and each margin may (O. pharao type) or may not (O. radicalis type) be barbed (basally). The peduncle is high, anteroposteriorly elongated basally and dorsoventrally compressed, particularly apically. The ventral and dorsal faces are tightly folded in the lower half, more so basally. The anterior edge is generally rounded and the posterior flatter with a depression extending towards the cap. Basally, the root has a distinct anteroposterior depression; the anterior and posterior portions slightly flare relative to the medial.
? Onchosaurus Oral teeth.
Teeth, as found, are small (3-4 mm class) but robust with inflated lobes. The crown is strongly cuspidate and mesodistally compressed; enameloid smooth; shoulders low and thick, not particularly long; transverse carina complete; apron long and thick, rounded basally; and uvula short and thick. The root is high, wider laterally than the crown. The nutritive groove is narrow, parallel and complete, with a lingually positioned pore.
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