Dolichorhynchops

Dolichorhynchops Temporal range: Late Cretaceous,
D. osborni, National Museum of Natural History, Washington D. C.
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	†Sauropterygia
Order:	†Plesiosauria
Family:	†Polycotylidae
Clade:	†Dolichorhynchia
Genus:	†Dolichorhynchops Williston, 1902
Type species
†Dolichorhynchops osborni Williston, 1902
Other species
†D. herschelensis Sato, 2005

Dolichorhynchops is an extinct genus of polycotylid plesiosaur from the Late Cretaceous of North America, containing the species D. osborni and D. herschelensis, with two previous species having been assigned to new genera. Definitive specimens of D. osborni have been found in the late Coniacian to early Campanian rocks, while those of D. herschelensis have been found in the late Campanian to early Maastrichtian rocks. Dolichorhynchops was a prehistoric marine reptile measuring around 3 metres (9.8 ft) long. Its Greek generic name means "long-nosed face".

Discovery and species

Mounted skeleton of the holotype of D. osborni (from Williston, 1903), in the University of Kansas Museum of Natural History

The holotype specimen of Dolichorhynchops osborni, KUVP 1300, was discovered in the upper Smoky Hill Chalk Logan County, Kansas, by George Fryer Sternberg, as a teenager, in around 1900. The remains were collected by him and his father, Charles Hazelius Sternberg, and then sold to the University of Kansas (Lawrence, Kansas). KUVP 1300 was prepared and mounted by H.T. Martin under the supervision of Dr. Samuel Wendell Williston, who described and named it in 1902. A more detailed description and photographs were provided by Williston 1903). The specimen has been on display in the KU Museum of Natural History since that time. Everhart 2004b estimated that the holotype had a skull measuring 57 cm (1.87 ft) long.

George Sternberg found a second, less complete specimen of D.osborni in 1926. In his effort to sell the specimen to a museum, Sternberg took detailed photographs of the skull. The specimen was eventually mounted in plaster and was acquired by the Harvard Museum of Comparative Zoology. MCZ 1064 was on display there until some time in the 1950s. This specimen was never completely described although the skull was figured by O'Keefe 2004. (See also Everhart 2004b)

The specimen of D. osborni on exhibit at the Sternberg, FHSM VP-404 was found by Marion Bonner near Russell Springs in Logan County in the early 1950s. Carpenter 1996 estimated that FHSM VP-404, with a skull measuring 51.3 centimetres (1.68 ft) long, had a total body length of approximately 3.07 metres (10.1 ft). The skull was crushed flat but is in very good condition. This specimen was initially reported by Sternberg & Walker 1957, and then was the subject of a Masters thesis by Bonner 1964. Note that it was described by Bonner as "Trinacromerum osborni" which was the accepted genus name at the time.

Skeleton in Canadian Fossil Discovery Centre

D. herschelensis was described as a new species by Tamaki Sato in 2005. It was discovered in the Bearpaw Formation of Saskatchewan, Canada, a Late Cretaceous (late Campanian to early Maastrichtian) rock formation. The fossil was found close to the town of Herschel in southwestern Saskatchewan, from which the species name is derived. The rock formation it was found in consists of sandstones, mudstones and shales laid down in the Western Interior Seaway, just before it began to revert to dry land.

The type specimen of D. herschelensis was discovered in a disarticulated state (i.e. the bones were scattered about the discovery site). The skull, lower jaw, ribs, pelvis and shoulder blades were all recovered, but the spine was incomplete, so the exact number of vertebrae the living animal would have had is unknown. All four limbs are missing, with the exception of nine small phalanges (finger bones) and a small number of limb bones found close by which may belong to the animal in question.

The specimen is believed to be an adult, due to the fusion of certain bones (it is generally assumed—not necessarily strictly correctly so—that other animals' skulls, much as humans', consist of dissociated bones interconnected by cartilage fontanelles that do not entirely close until full maturity). It is also believed to have been substantially smaller than its close relative, D. osborni, as some juvenile specimens of D. osborni are larger than the adult specimen of D. herschelensis. Assuming that only a few vertebrae are missing from the skeleton, the animal is estimated to be about 2.5–3 metres (8.2–9.8 ft) in length. The snout is long and thin, with numerous tooth sockets. However, very few of the thin, sharp teeth remain.

Formerly assigned species

Skeleton of Martinectes, which was formerly included in this genus

Two very large specimens of a polycotylid plesiosaur (KUVP 40001 and 40002) were collected from the Pierre Shale of Wyoming and later reported on by Adams in her 1977 Masters thesis. Later (1997), she officially described (1997) as a new species of Trinacromerum (T. bonneri). Unknown to her at the time, Carpenter (1996) had revised the Polycotylidae and separated Dolichorhynchops from Trinacromerum, raising the question as to whether or not the specimens represented a separate species or just larger individuals of D. osborni. A study in 2008 found that T. bonneri is a valid species of Dolichorhynchops, D. bonneri. Everhart (2017) suggested that KUVP 40001 would have measured up to 6–7 metres (20–23 ft) in length. A 2023 study assigns D. bonneri to a new genus, Martinectes. Other specimens previously reported as D. osborni by Carpenter 1996 (UNSM 50133 and AMNH 5834) were also referred to this taxon.

D. tropicensis was first named by Rebecca Schmeisser McKean in 2011. The specific name is derived from the name of the Tropic Shale, in which the two specimens of D. tropicensis were found. It is known from the holotype MNA V10046, an almost complete, well-preserved 3.2 metres (10 ft) long skeleton including most of the skull and from the referred specimen MNA V9431, fragmentary postcranial elements. It was collected by the Museum of Northern Arizona from a single locality within the Tropic Shale of Utah, dating to the early Turonian stage of the early Late Cretaceous, about 93.5-91 million years ago. D. tropicensis extended the known stratigraphic range for Dolichorhynchops back by approximately 7 million years, but the 2023 study assigns D. tropicensis to a new genus, Scalamagnus.

Classification

Life restoration of D. osborni

D. osborni in Vienna

Below is a cladogram of polycotylid relationships from Ketchum & Benson, 2011.

Plesiosauroidea	Cryptoclididae  Leptocleidia  Leptocleididae  Polycotylidae  Edgarosaurus Plesiopleurodon QM F18041 Eopolycotylus Polycotylus Thililua Trinacromerum Manemergus Dolichorhynchops herschelensis Dolichorhynchops Palmulasaurus

See also

• List of plesiosaur genera
• Timeline of plesiosaur research

References

• Adams, D. A. (1977), Trinacromerum bonneri, a new polycotylid plesiosaur from the Pierre Shale of South Dakota and Wyoming, Unpublished Masters thesis, University of Kansas, 97 pages
• Adams, D. A. (1997). "Trinacromerum bonneri, new species, last and fastest pliosaur of the Western Interior Seaway". Texas Journal of Science. 49 (3): 179–198.
• Albright III, L. B.; Gillette, D. D.; Titus, A. L. (2007b). "Plesiosaurs from the Upper Cretaceous (Cenomanian-Turonian) Tropic Shale of southern Utah, part 2: polycotylidae" (PDF). Journal of Vertebrate Paleontology. 27 (1): 41–58. doi:10.1671/0272-4634(2007)27[41:PFTUCC]2.0.CO;2. S2CID 130268187. Archived from the original (PDF) on 2011-09-28.
• Bonner, O. W. (1964), An osteological study of Nyctosaurus and Trinacromerum with a description of a new species of Nyctosaurus, Unpub. Masters Thesis, Fort Hays State University, 63 pages
• Carpenter, K. (1996). "A Review of short-necked plesiosaurs from the Cretaceous of the western interior, North America" (PDF). Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen. 201 (2): 259–287. doi:10.1127/njgpa/201/1996/259.
• Everhart, M. J. (2003). "First records of plesiosaur remains in the lower Smoky Hill Chalk Member (Upper Coniacian) of the Niobrara Formation in western Kansas". Transactions of the Kansas Academy of Science. 106 (3–4): 139–148. doi:10.1660/0022-8443(2003)106[0139:FROPRI]2.0.CO;2. S2CID 86541758.
• Everhart, M. J. (2004a). "Plesiosaurs as the food of mosasaurs; new data on the stomach contents of a Tylosaurus proriger (Squamata; Mosasauridae) from the Niobrara Formation of western Kansas". The Mosasaur. 7: 41–46.
• Everhart, M. J. (2004b). "New data regarding the skull of Dolichorhynchops osborni (Plesiosauroidea: Polycotylidae) from rediscovered photos of the Harvard Museum of Comparative Zoology specimen". Paludicola. 4 (3): 74–80.
• Everhart, M. J. (2005). Oceans of Kansas - A Natural History of the Western Interior Sea. Indiana University Press.
• Everhart, M.J.; Decker, R.; Decker, P. (2006). "Earliest remains of Dolichorhynchops osborni (Plesiosauria: Polycotylidae) from the basal Fort Hays Limestone, Jewell County, Kansas". Transactions of the Kansas Academy of Science. 109 (3–4): 261. doi:10.1660/0022-8443(2006)109[247:AOTTAM]2.0.CO;2. S2CID 198152472. (abstract)
• Everhart, M. J. (2007). Sea Monsters: Prehistoric Creatures of the Deep. National Geographic. ISBN 978-1-4262-0085-4.
• O'Keefe, F. R. (2004). "On the cranial anatomy of the polycotylid plesiosaurs, including new material of Polycotylus latipinnis Cope, from Alabama". Journal of Vertebrate Paleontology. 24 (2): 326–340. Bibcode:2004JVPal..24..326O. doi:10.1671/1944. S2CID 46424292.
• Sato, T. (2005). "A new Polycotylid Plesiosaur (Reptilia: Sauropterygia) from the Upper Cretaceous Bearpaw Formation in Saskatchewan, Canada". Journal of Paleontology. 79 (5): 969–980. doi:10.1666/0022-3360(2005)079[0969:ANPPRS]2.0.CO;2. S2CID 131128997.
• Schmeisser McKean, Rebecca (2011). "A new species of polycotylid plesiosaur (Reptilia: Sauropterygia) from the Lower Turonian of Utah: extending the stratigraphic range of Dolichorhynchops". Cretaceous Research. 34: 184–199. Bibcode:2012CrRes..34..184S. doi:10.1016/j.cretres.2011.10.017.
• Sternberg, C. H. (1922). "Explorations of the Permian of Texas and the chalk of Kansas, 1918". Transactions of the Kansas Academy of Science. 30 (1): 119–120. doi:10.2307/3624047. JSTOR 3624047.
• Sternberg, G. F.; Walker, M. V. (1957). "Report on a plesiosaur skeleton from western Kansas". Transactions of the Kansas Academy of Science. 60 (1): 86–87. doi:10.2307/3627008. JSTOR 3627008.
• Williston, S. W. (1902). "Restoration of Dolichorhynchops osborni, a new Cretaceous plesiosaur". Kansas University Science Bulletin. 1 (9): 241–244.
• Williston, S. W. (1903). "North American plesiosaurs". Field Columbian Museum, Pub. 73. Geological Series. 2 (1): 1–79.