Kronosaurus

Kronosaurus Temporal range: Early Cretaceous, 125–99 Ma PreЄ Є O S D C P T J K Pg N
K. boyacensis in Villa de Leyva, Boyaca, Colombia
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Superorder:	†Sauropterygia
Order:	†Plesiosauria
Family:	†Pliosauridae
Subfamily:	†Brachaucheninae
Genus:	†Kronosaurus Longman, 1924[1]
Species
†K. queenslandicus (type) Longman, 1924[1] †K. boyacensis Hampe, 1992[2]

Kronosaurus (/ˌkrɒnoʊˈsɔːrəs/ KRON-o-SAWR-əs; meaning "lizard of Kronos") is an extinct genus of short-necked pliosaur. It was among the largest pliosaurs, and is named after the leader of the Greek Titans, Cronus. It lived in the Early Cretaceous Period (Aptian-Albian).^[2][3]

Description

Restoration of K. queenslandicus by Dmitry Bogdanov, 2007.

Like other pliosaurs, Kronosaurus was a marine reptile. It had an elongated head, a short neck, a stiff body propelled by four flippers, and a relatively short tail. The posterior flippers were larger than the anterior. Kronosaurus was carnivorous, and had many long, sharp, conical teeth. Current estimates put Kronosaurus at around 9–10.5 meters (30–34 feet) in length.^[3][4] In 2009, K. queenslandicus was estimated to weigh up to 11,000 kilograms (11 metric tons).^[4]

All Sauropterygians had a modified pectoral girdle that supported a powerful swimming stroke.^[5] Kronosaurus and other plesiosaurs/pliosaurs had a similarly adapted pelvic girdle,^[6] allowing them to push hard against the water with all four flippers. Between its two limb girdles was a massive mesh of gastralia (belly ribs) that provided additional strength and support.^[6] The strength of the limb girdles, combined with evidence of large, powerful swimming muscles, indicates that Kronosaurus was likely a fast, active swimmer.^[6]

Size issues

K. queenslandicus scale diagram, showing the size of the restored Harvard skeleton along with a more accurate estimate

Body-length estimates, largely based on the 1959 Harvard reconstruction, had previously put the total length of Kronosaurus at 12.8 meters (42 feet).^[7] However, more recent studies, comparing fossil specimens of Kronosaurus to other pliosaurs suggests that the Harvard reconstruction may have included too many vertebrae, exaggerating the previous estimate, with the true length probably only 9–10.5 meters (30–34 feet).^[3][4]

Teeth

Kronosaurus teeth exceed 7 cm in length (the largest up to 30 cm long with 12 cm crowns). However, they lack carinae (cutting edges) and the distinct trihedral (three facets) of Pliosaurus and Liopleurodon teeth. The combination of large size, conical shape and lack of cutting edges allows for easy identification of Kronosaurus teeth in Cretaceous deposits from Australia.^[3][8]

Discovery and species

K. queenslandicus at Harvard University which may have been reconstructed with too many vertebrae

In 1899, Andrew Crombie of Hughenden discovered a "scrap of bone" containing six conical teeth, and gave this fragmentary fossil to the Queensland Museum. Twenty-five years later, then-director Heber Longman formally described the specimen as the holotype of a new species: Kronosaurus queenslandicus.^[1][9] More Kronosaurus material, including a partial skull, was discovered in 1929, in the same location as Crombie's original find.^[9]

While touring Australia in 1932, a fossil-hunting expedition from Harvard University led by William E. Schevill was told of some interesting rocks on some property near Hughenden.^[9] The rocks were limestone nodules containing the most complete skeleton of Kronosaurus ever discovered.^[9][10] After dynamiting the nodules out of the ground (and into smaller pieces), Scheville had them shipped back to Harvard for examination and preparation. The skull—which matched the holotype jaw fragment of K. queenslandicus—was prepared right away, but time and budget constraints put off restoration of the nearly complete skeleton for 20 years.^[10] The restored and mounted skeleton was displayed at Harvard in 1959.^[9][10]

In 1977, a Colombian peasant farmer from Moniquirá turned up an enormous stone while tilling his field, which he later recognized as a possible fossil. Excavation revealed a nearly complete Kronosaurus skeleton, one of the best preserved fossils to come from Colombia.^[11] Oliver Hampe formally described the specimen in 1992, assigning it to a second species, K. boyacensis.^[2]

The people of Villa de Leyva built a museum, El Fósil, around the spot where the skeleton was excavated, and the K. boyacensis skeleton is on display there.^[11]

Classification

Skull of the Harvard specimen

Restoration of K. boyacensis by Dmitry Bogdanov, 2008.

The cladogram below follows a 2011 analysis by paleontologists Hilary F. Ketchum and Roger B. J. Benson, and reduced to genera only.^[12]

Paleobiology

Life restoration of K. queenslandicus preying on Woolungasaurus by Dmitry Bogdanov, 2008.

Fossil stomach contents from Northern Queensland show that Kronosaurus preyed on turtles and plesiosaurs. Fossil remains of giant squid have been found in the same area as Kronosaurus; it may have fed on them, but no direct evidence for this exists.^[14]

Large, round bite-marks have been found on the skull of an Albian-age Australian elasmosaurid (Eromangasaurus) that could be from a Kronosaurus attack.^[15][16]

Palaeoecology

Kronosaurus is known from Australia and Colombia. Both areas were covered by shallow inland seas when Kronosaurus inhabited them.^[11][14]

See also

• List of plesiosaur genera
• Timeline of plesiosaur research

References

External links

• Genus Kronosaurus. The Plesiosaur Directory.
• Media related to Kronosaurus at Wikimedia Commons