Sigogneau-Russell named the species C. dolloi from remains found in the Paleocene of Belgium. In 1972, Bruce Erickson named the species C. gigas from SMM P71.2.1, a partial skeleton and skull found in the Sentinel Butte Formation, Golden Valley County, North Dakota. Erickson subsequently in 1981 named the species C. tenuis from SMM P79.14.1, a partial skeleton and skull found in the Bullion Creek Formation, North Dakota. In 1998 K. Q. Gao and Richard Carr Fox described the species C. lindoei from UALVP 931, a nearly complete skeleton with skull and jaws from the Dinosaur Park Formation in Alberta. The publication also thoroughly reviewed Champsosaurus, rediagnosing most species except for C. ambulator and C. laramiensis. Fossils of Champsosaurus have been found in North America (Alberta, Saskatchewan, Montana, New Mexico, Texas, Colorado, and Wyoming) and Europe (Belgium and France), dating from the Upper Cretaceous to the late Paleocene. Remains tenatively referred to Champsosaurus are known from the high Canadian Arctic, dating to the Coniacian–Turonian, a time of extreme warmth. Taxonomy Sixteen species of Champsosaurus have been named, of which seven are presently considered valid. The type species Champsosaurus annectens Cope, 1876 is considered to be dubious. The only named European species C. dolloi Sigogneau-Russell 1979 was considered to be too fragmentary to warrant a new species by Gao and Fox in 1998. Description Most species grew to about 1.50 m (5 ft) long, though Champsosaurus gigas, the largest species, reached 3–3.5 m (10–12 ft) in length. Anatomy The skull of Champsosaurus is dorsoventrally flattened, while the temporal arches are expanded posteriorly (towards the back of the skull) and laterally (away from the midline), giving the skull a heart shaped appearance when viewed from above. The snout is greatly elongated and gharial-like, making up around half the length of the skull, and at least four times as long as it is wide, with the opening of the nostrils at the end of the snout. The openings of the ears are located on the underside of the skull. The body is flat and streamlined, with heavy gastralia (rib-like bones situated in the belly). Compared to other choristoderes, the lacrimal bone is reduced in size to a small triangle, the postorbital bone does not form part of the orbit (eye socket), there is no contact between the premaxilla and the vomer bones, an internarial bone is present, the choanae are located posteriorly in correlation