Kronosaurus

Kronosaurus Temporal range: Aptian-Late Albian ~120–100 Ma PreꞒ Ꞓ 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]
Type species
†Kronosaurus queenslandicus Longman, 1924[1]
Other species
†K. boyacensis Hampe 1992[2]

Kronosaurus (/ˌkrɒnoʊˈsɔːrəs/ KRON-o-SAWR-əs; meaning "lizard of Kronos") is an extinct genus of short-necked pliosaur. With an estimated length of 9 to 10.9 meters (30 to 36 ft), it was among the largest pliosaurs, and is named after the leader of the Greek Titans, Kronos. It lived in the Early Cretaceous period (Aptian to Late Albian).^[2][3] Fossil material has been recovered from the Toolebuc Formation (middle to late Albian) and Wallumbilla Formations (Aptian) of Queensland and New South Wales in Australia, and from the upper Paja Formation (late Aptian) in Boyacá, Colombia, and assigned to two species.

Discovery and species

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][4] More Kronosaurus material, including a partial skull, was discovered in 1929, in the same location as Crombie's original find.^[4]

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.^[5] 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.^[5]

Harvard's completed skeleton

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

In 1931 the Harvard Museum of Comparative Zoology (MCZ) sent an expedition to Australia for the dual purpose of procuring specimens - the museum being "weak in Australian animals and...desires[ing] to complete its series" - and to engage in "the study of the animals of the region when alive."^[6] The Harvard Australian Expedition (1931–1932), as it became known, was a six-man venture led by Harvard Professor William Morton Wheeler, with the others being Dr. P. Jackson Darlington, Jr. (a renowned coleopterist),^[7][8] Dr. Glover Morrill Allen and his student Ralph Nicholson Ellis,^[9] medical officer Dr. Ira M. Dixon, and William E. Schevill (a graduate-student in his twenties and Associate Curator of Invertebrate Palaeontology).^[10][6][11] MCZ director Thomas Barbour said at the time "We shall hope for specimens' of the kangaroo, the wombat, the Tasmanian devil and Tasmanian wolf," and the mission was a success with over 300 mammal and thousands of insect specimens returning to the United States.^[7][10] Yet Mr. Schevill, the team's fossil enthusiast, remained in Australia after the others had departed and, in the winter of 1932, was told by the rancher R.W.H. Thomas of rocks with something "odd" poking out of them on his property near Hughenden.^{[4][12][10][13]} The rocks were limestone nodules containing the most complete skeleton of Kronosaurus ever discovered.^[4][14][15] After dynamiting the nodules out of the ground (and into smaller pieces weighing approximately four tons^[16][17]) with the aid of a British migrant trained in the use of explosives,^[18] William Schevill had the fossils 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 - most of the bones of which remained unexcavated within the limestone blocks - for 20 years.^[14]

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

This interim ended when they came to the attention of Godfrey Lowell Cabot - Boston industrialist, philanthropist, and founder of the Cabot Corporation - "who was then in his nineties" and "had been interested in sea serpents since childhood."^[10] Having formerly questioned MCZ director Alfred Romer about the existence and reports of sea serpents, it thus occurred to Dr. Romer to tell Mr. Cabot about the skeleton in the museum closet. Godfrey Cabot thus asked how much a restoration would cost and "Romer, pulling a figure out of the musty air, replied, 'Oh, about $10,000.'" Romer may not have been serious but the philanthropist clearly was because the check for said sum came shortly thereafter.^[10][18] Two years - and more than $10,000 - later, following the careful labor of the museum preparators, the restored and mounted skeleton was displayed at Harvard in 1959.^[4][14] However, Dr. Romer and MCZ preparator Arnold Lewis confirmed that same year in the institution's journal Breviora that "erosion had destroyed a fair fraction of this once complete and articulated skeleton...so that approximately a third of the specimen as exhibited is plaster restoration."^[19] Furthermore, the original (real) bones are also layered in plaster; a fact that, while keeping the fossils safe, makes it difficult for paleontologists to study it - an issue which factors into the controversial question of the true size of the Kronosaurus queenslandicus.^[18]

Size issues

Body-length estimates, largely based on the 1959 Harvard reconstruction, had previously put the total length of Kronosaurus at 12.8 meters (42 ft).^[20] 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 to 10.9 meters (30 to 36 ft).^[3][21]

Description

Restoration of K. queenslandicus

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. A feature of the genus Kronosaurus is that the first three maxillary teeth are enlarged to fangs.^[21] Current estimates put Kronosaurus at around 9 to 10.9 meters (30 to 36 ft) in length.^[3][21] In 2009, K. queenslandicus was estimated to weigh about 10.6 to 12.1 metric tons (11.7 to 13.3 short tons).^[21] The skull length of Kronosaurus was estimated to be 2.21–2.85 meters (7.3–9.4 ft).^[21][22]

All Sauropterygians had a modified pectoral girdle that supported a powerful swimming stroke.^[23] Kronosaurus and other plesiosaurs/pliosaurs had a similarly adapted pelvic girdle,^[24] 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.^[24] The strength of the limb girdles, combined with evidence of large, powerful swimming muscles, indicates that Kronosaurus was likely a fast, active swimmer.^[24]

Kronosaurus queenslandicus has four pairs of premaxillary teeth. The first three pairs of its maxillary teeth are large caniniform teeth, and in its lower jaw there are also three pairs of large caniniform teeth which are located immediately in front of the three maxillary caniniforms when the mouth is closed. Two pairs of the lower jaw caniniforms occlude between the last pair of premaxillary teeth and first pair of maxillary teeth in a diastema (gap in the tooth row). The enlargement of these two pairs of lower jaw teeth in K. queenslandicus may be related to the absence of a fifth pair of premaxillary teeth, which are present in a number of other pliosaurs.^[21]

Oliver Hampe described Kronosaurus boyacensis as having five pairs of premaxillary teeth. Colin Richard McHenry has said that the premaxillary tooth count of K. boyacensis requires confirmation and that if its premaxillary tooth count is confirmed to be five, it may be appropriate to place K. boyacensis into a different genus to K. queenslandicus. In addition to apparently having a different premaxillary tooth count, K. boyacensis differs from K. queenslandicus in postcranial features and possibly tooth ornamentation.^[21]

Teeth

Kronosaurus teeth exceed 7 centimeters (2.8 in) in length (the largest up to 30 centimeters (12 in) long with 12 centimeters (4.7 in) 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 formations from Australia.^[3][25]

Classification

Reconstructed skull of the Harvard specimen

Restoration of K. boyacensis

The cladogram below follows a 2011 analysis by paleontologists Hilary F. Ketchum and Roger B. J. Benson, and reduced to genera only.^[26]

Palaeobiology

Life restoration of K. queenslandicus preying on Woolungasaurus.

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.^[28]

Large, round bite-marks have been found on the skull of an Albian-age Australian elasmosaurid (Eromangasaurus) that could be from a Kronosaurus attack.^[29][30]

Paleoecology

Kronosaurus is known from Australia and Colombia. Both areas were covered by shallow inland seas when Kronosaurus inhabited them.^[5][28]

See also

• List of plesiosaur genera
• Timeline of plesiosaur research
• Platypterygius

References

External links

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