'' with a dorsal fringe ''
1900s ====
1902 ==== • Williston publicly acknowledged that the supposed fringe running down the back of a mosasaur he had reported was actually misidentified tracheal rings. ====
1904 ==== • Dollo reported the presence of the remains of a large
turtle preserved in the stomach of
Hainosaurus. ====
1905 ==== • Fossil hunters Dennis Halvorson and Mike Hanson discovered the largest known specimen of
Plioplatecarpus in the
Pierre Shale of
North Dakota. The skeleton was about 70% complete. ====
1907 ==== • The excavation of the
North Dakota Plioplatecarpus specimen concluded.
1910s '' skeleton '' '' ====
1911 ==== • The "Bunker"
Tylosaurus specimen was discovered in Kansas. At almost 45 feet in length it was one of the largest specimens ever classified in the genus and is the largest mosasaur skeleton in the United States to have been mounted for a museum exhibit, which is on display at the
University of Kansas museum. ====
1912 ==== •
Charles Whitney Gilmore described the new genus and species
Globidens alabamaensis. This unusual mosasaur had rounded teeth specialized for cracking shell and probably fed on the abundant ammonites of the Cretaceous seas. •
Robert Broom described a new
Tylosaurus species,
T. capensis from
Pondoland,
South Africa. ====
1914 ==== • Williston interpreted the mosasaur
Clidastes as inhabiting the waters near the surface of its marine home. ====
1917 ==== •
Charles Sternberg discovered a skeleton left behind by a 25 foot long
Tylosaurus in Kansas with preserved skin. He observed that the skin was "covered with small, overlapping scales". ====
1918 ==== • Charles and
Levi Sternberg excavated a
Platecarpus and a
Clidastes sternbergii specimen in Kansas, which were sold to the
Paleontological Museum in
Uppsala,
Sweden. • A
Tylosaurus specimen was discovered in
Logan County, Kansas.
1920s ====
1920 ==== •
Carl Wiman described the new species
Clidastes sternbergii. He noticed evidence for tail bends in the species
Halisaurus sternbergi and
Platecarpus tympaniticus. He compared them to the tail bend in ichthyosaurs that support their tail flukes. In one figure, he restored the mosasaur's tail with an upper lobe like ichthyosaurs have. This prescient observation would be confirmed in the early 21st century. ====
1922 ==== • Sternberg reported the remains of a young
polycotylid plesiosaur preserved in the remains of the 1918 Logan County
Tylosaurus specimen.
1930s '' ====
1930 ==== •
W. E. Swinton described the new species
Mosasaurus nigeriensis from
Nigeria. ====
1935 ==== •
Otto Zdansky reported that eight species of mosasaurs had been discovered in
Egypt and ten species were known from Africa overall. ====
1937 ==== • A high school student named Allan Bennison discovered the future type specimen of
Plotosaurus bennisoni in
Moreno Formation rocks of the
San Joaquin Valley in
California. • Another major mosasaur discovery occurred in
California when a rancher named Frank Paiva and a
Fresno State College professor named William M. Tucker discovered the future type specimen of
Plotosaurus tuckeri. ====
1939 ==== • Robert Leard discovered the future type specimen of
Plesiotylosaurus crassidens in Moreno Formation rocks of the
Panoche Hills in California.
1940s '' ====
1942 ==== •
Charles Camp described the new genera
Kolposaurus and
Plesiotylosaurus, although the genus
Kolposaurus had already been used for a different kind of animal and Camp would later rename the mosasaur
Plotosaurus. Along with describing the genus itself, Camp named two "
Kolposaurus", "
K."
bennisoni and "
K."
tuckeri. At least one specimen of these species was found to have fish preserved in its stomach. Camp observed that
Plotosaurus was a very evolutionarily advanced mosasaur with an especially stiff torso and powerful tail.
Plesiotylosaurus Camp found to be very similar to the original
Tylosaurus. •
George Gaylord Simpson reported that the possible mosasaur fossils discovered by the Lewis and Clark expedition had been lost. ====
1945 ==== •
Rainer Zangerl of the
Chicago Field Museum led an expedition to collect fossils from the
Selma Formation of Alabama and acquired several mosasaur specimens.
1950s ====
1951 ==== • Camp renamed the mosasaur genus
Kolposaurus to
Plotosaurus because the former name had been used previously for a
nothosaur.
1960s '', showing putative mosasaur toothmarks ====
1960 ==== • Erle Kauffman and Robert Kesling reported a fossil ammonite of the genus
Placenticeras exhibiting damage they interpreted as tooth marks from a mosasaur, probably a
platecarpine. ====
1963 ==== • George Sternberg discovered a mostly complete mosasaur specimen with skin impressions near
WaKeeney, Kansas. The specimen is now recognized as the best preserved specimen of the genus
Ectenosaurus. ====
1967 ==== •
Dale Russell published a monograph on American mosasaurs. This monograph contained significant taxonomic revisions for the family. Among these were his conclusion that
Platecarpus coryphaeus and
Platecarpus ictericus were likely junior synonyms of
P. tympaniticus while
P. planfirons was too poorly preserved to be classified confidently at all. Russell also dismissed the species
Tylosaurus dyspelor described by Cope as a dubious probable-synonym of
Tylosaurus proriger. Russell also published additional information and speculation on mosasaur biostratigraphy. He reported the presence of mosasaur vertebrae up to 90 million years old among the
Turonian fossils curated by the University of Kansas Museum of Natural History. Another of this work's significant contributions to mosasaur biostratigraphy concerned the mosasaurs of the Smoky Hill Chalk. Russell devised two biostratigraphic zones based on the Chalk's mosasaur fossils. The lower zone was characterized by
Clidastes liodontus,
Platecarpus coryphaeus, and
Tylosaurus nepaeolicus. The upper was home to
Clidastes,
Platecarpus ictericus, and
Tylosaurus proriger. He regarded
Platecarpus and
Tylosaurus as deep water animals but concluded that the biostratigraphic evidence from the Smoky Hill mosasaurs suggested that the Chalk's depositional environment was becoming shallower and nearer to the ancient coastline over time. Russell also argued that by the end of the Late Cretaceous, mosasaurs were converging on the body plan that characterized the first ichthyosaurs during the Triassic period and gradually replacing these older marine reptiles. ====
1969 ==== • A
University of Florence team embarked on a fossil hunting expedition to Nigeria. This expedition would discover a large quantity of mosasaur fossils in the
Dukamaje Formation.
1970s '' from the
Selma Group of Alabama ====
1970 ==== • Russell published a paper on the mosasaurs of the Selma Formation, including those collected by the Zangerl expedition in 1945. The paper contained several taxonomic advances including the description of the new species
Tylosaurus zangerli and the reclassification of "
Clidastes"
sternbergii in the genus
Halisaurus. Russell considered the
Mosasaurus species
M. lemonnieri and
M. conodon to be synonyms. Overall he concluded that the known mosasaurs of the Selma Formation were
Clidastes propython,
Halisaurus sternbergi,
Globidens alabamaensis,
Platecarpus,
Prognathodon, and
T. zangerli. He noted that the biostratigraphic distribution of mosasaurs in the Selma Formation were different than the mosasaurs of the Smoky Hill Chalk. • The University of Florence team continued searching for mosasaur fossils in Nigeria. ====
1972 ==== • Azzaroli and others erected the new genus
Goronyosaurus for the species "
Mosasaurus"
nigeriensis. ====
1975 ==== • Russell claimed that unlike all other mosasaurs,
Globidens dakotensis didn't have teeth on its pterygoid, although this claim has been subsequently dismissed. ====
1977 ==== • Martin and Stewart argued that some fossils discovered in
Cenomanian rocks in Kansas represented the oldest known mosasaur fossils.
1980s ====
1980 ==== •
Joan Wiffen described the new genus
Moanasaurus. ====
1982 ==== •
Sankar Chatterjee and Zinsmeister reported the discovery of mosasaur fossils from islands off the coast of
Antarctica. ====
1985 ==== • Suzuki described the new species
Mosasaurus hobetsuensis. ====
1986 ==== '' • Bell and SHeldon reported the discovery of subadult mosasaur fossils. ====
1987 ==== • Judy Massare studied the anatomy of mosasaur teeth and its implication for their diet. She argued that the "slender", recurved teeth of
Platecarpus were adapted to feeding on relatively small, soft prey like
squid. • James Martin and Phillip Bork reported the fossilized stomach contents of a
Tylosaurus proriger skeleton discovered in South Dakota: a bony fish in the genus
Bananogmius,
Hesperornis, a
lamnid shark, and
Clidastes. '' • Rothschild and Martin looked for evidence that mosasaurs suffered from the bends as a result of their diving and ascent activities. Avascular necrosis resulting from the bends was completely absent in fossils of the genus Clidastes, suggesting that it preferred to stay near the surface. In contrast, Rothschild and Martin observed
avascular necrosis in nearly every specimen of
Platecarpus and
Tylosaurus that they surveyed. The presence and ubiquity of the avascular necrosis is consistent with the idea that these were deep diving animals. • Russell described the new genus Ectenosaurus for the species "Platecarpus" clidastoides. '' ====
1988 ==== • Kenneth Wright and Samuel Shannon described the new genus and species
Selmasaurus russelli from the
Mooreville Chalk near
Selma, Alabama. • Lingham-Soliar reexamined
Goronyosaurus from Nigeria. • Betsy Nicholls described a new species of
Hainosaurus,
H. pembinensis, from a Pembina Mining Company mine in the Pierre Shale of
Manitoba,
Canada. • Massare concluded that mosasaurs were slow swimmers that had to hunt by ambushing prey rather than chasing it down directly. • Stewart disputed Russell's 1967 mosasaur-based biostragraphic scheme for the Smoky Hill Chalk because he had observed fossils preserved outside of their purported "zones". ====
1989 ==== • Martin and Rothschild interpreted
Clidastes as an inhabitant of shallow waters, while
Tylosaurus may have been the Cretaceous paleoecological equivalent to a
sperm whale, diving deep in the
Western Interior Seaway to hunt the giant squid that lived there. • Russell suggested that mosasaurs may have reproduced by laying eggs on remote island beaches.
1990s '' ====
1990 ==== • Wiffen described the new genus
Rikkisaurus. • Michael Everhart discovered two
Platecarpus skulls that had been "co-mingled and partially digested". • Stewart used a recently proposed biostratigraphic scheme for the Smoky Hill Chalk to propose stratigraphic ranges for its mosasaur taxa. ''. ====
1991 ==== • Lingham-Soliar rejected the idea that "
Halisaurus"
sternbergi belonged to the genus. However, he thought that the genus
Phosphorosaurus should be sunk in that genus. He also dismissed the supposed
Mosasaurus species
M. nigeriensis as a chimera of multiple mosasaur species. • Lingham-Soliar attempted to reconstruct how mosasaurs swam by studying their vertebral column. He found that the front part of column was stiffened and only the rear portion flexed during swimming. This more similar to the way a modern
Alligator swims rather than snakes, which many previous researchers had put forth as mosasaur analogs. ====
1992 ==== • Robert Carroll and Michael DeBraga published a discussion about
aigialosaurs and their evolutionary affinities. They noted that aigialosaur skulls are virtually indistinguishable from those of primitive mosasaurs. However they found the vertebrae in their back and their limb bones to more closely resemble those belonging to the precursors of living monitor lizards. • Lingham-Soliar regarded the question of how the
Hainosaurus reported in 1904 by Dollo to contain a turtle in its stomach could have swallowed a prey item of that size as mysterious. • Lingham-Soliar hypothesized that
Plioplatecarpus marshi "flew" underwater primarily using its powerful fore-flippers rather than using its tail like other mosasaurs due to
P. marshi's well-developed shoulder region. He argued that this unusual style of swimming increased its maneuverability, allowing this species to flourish in shallow habitats. • Nathalie Bardet published a discussion of the possible causes for the extinction of the ichthyosaurs. She expressed doubt that ichthyosaurs were replaced by mosasaurs because they would not be in direct competition with each other. Instead she posited a connection to an extinction event that affected cephalopods at the boundary between the Cenomanian and Turonian ages. She proposed that the disappearance of these many cephalopod species may have deprived ichthyosaurs of their food source and caused their extinction. '' ====
1993 ==== • According to Russell, by this time at least 1,823 mosasaur specimens had been recovered from the Niobrara Chalk of Kansas alone. • Phosphate diggers in the
Negev Desert of
Israel discovered the remains of a 40-foot mosasaur that was sent to
Copenhagen,
Denmark for preparation. This mosasaur was nicknamed "
Oronosaurus" after the phosphate field in which it was discovered, but would be formally named as a new species of
Prognathodon,
P. currii, in 2002. • Lingham-Soliar re-examined the mosasaur genus
Liodon. • Schumacher published additional research on mosasaur biostratigraphy based on Stewart's 1990 paper. ====
1994 ==== '' • Lingham-Soliar published a review of Turonian mosasaur fossils that were discovered in
Angola. Commenting on the evolutionary origins of the mosasaurs, he remarked that while aigialosaurs had the correct anatomy to be the ancestors of the mosasaurs they were only known from rocks of the same age as the mosasaurs themselves. Until the presence of aigialosaurs earlier in the Cretaceous could be confirmed, Lingham-Soliar noted that there would be room to doubt this hypothesized connection even if it seemed plausible. • Stewart and Bell argued that the supposed oldest known mosasaur fossils reported by Martin and Stewart from Kansas were not even the remains of mosasaurs. Instead, they attributed the fossils to several kinds of
ichthyodectiform fishes. • Judy Massare observed that mosasaurs exhibited adaptations for rapid acceleration and probably employed this capability as ambush hunters. • Lingham-Soliar reported the presence of abundant mosasaur remains in Angola and
Zaire and observed that Africa was a hotspot of mosasaur discoveries on the same scale as western North America and the Netherlands-Belgium region. He identified four species from Zaire:
Halisaurus,
Mosasaurus,
Plioplatecarpus, and
Prognathodon. He also synonymized
Angolasaurus with
Platecarpus. He considered this genus to be the most widespread of any mosasaur. He interpreted
Plioplatecarpus as a snake-like ratchet feeder that "walked" its jaws across large prey to swallow it. He also hypothesized that it swam using its flippers rather than relying on its tail fin. • Nicholls and Godfrey rejected Lingham-Soliar's reinterpretation of
Plioplatecarpus marshi locomotion as underwater flight because there was no reason to believe that its tail was a less developed or effective means of propulsion than those of other mosasaurs. They suggested that its powerful shoulder region was actually an adaptation for shaking prey, like some modern shark species do. • Massare argued that mosasaurs were cold blooded, like their relatives the monitor lizards.
January • Patrick Antuzzi discovered a mosasaur skull in the
Chico Formation of California. The specimen is now catalogued as SC-VR59 and may have belonged to a species of Clidastes resembling members of this genus previously from
New Zealand. ====
1995 ==== • Theagarten Lingham-Soliar published the first truly thorough description of
Mosasaurus hoffmani. He interpreted its preferred habitat as biodiverse coastal waters of depths from 40–50 m. In this paper he also argued that mosasaurs went extinct rapidly. • Gordon Bell and Martin reported a
Mosasaurus conodon skull fossil bearing bite marks apparently inflicted by another
M. conodon. •
Michael Everhart discovered a series of five large mosasaur vertebrae with two
Cretoxyrhina teeth embedded in it. He found evidence the bone material had been partially dissolved where it had not been exposed to the elements. This implies that these vertebrae had been partially digested before fossilization by the shark that fed upon it. The shark probably only scavenged the specimen, but Everhart could not rule out predation. • Pete Bussen discovered a specimen of
Globidens in the Pierre Shale of Kansas. This was the first specimen of the genus to be documented in Kansas.
. Squalicorax'' teeth are often associated with mosasaur fossils ====
1996 ==== • Gordon Bell reported the discovery of a specimen of
Plioplatecarpus primaevus accompanied by two embryos of the same species. Both the remains of mother and young were accompanied more than two thousand of teeth shed by shark of the genus
Squalicorax. These sharks probably only scavenged the mosasaurs and were likely responsible for the disarticulated state of the skeletons. This discovery proved that mosasaurs gave live birth. • Sheldon published additional research on mosasaur biostratigraphy based on Stewart's 1990 paper. One notable find was a
P. planifrons fossil in the upper Smoky Hill Chalk, the uppermost known remains of this species. • Cowen disagreed with Lingham-Soliar's claim that
Plioplatecarpus marshi was an underwater flyer and suggested that
P. marshi's unusual traits were actually specializations for swimming near the surface of the water column by overcoming Carrier's constraint. •
Steve Johnson discovered a complete
Platecarpus planifrons skull. • Schumacher and Varner observed more evidence for tail bends in the genera
Clidastes,
Platecarpus, and
Tylosaurus.
September • Michael and Pam Everhart excavated the skull and neck of a mosasaur in Kansas.
. Cretoxyrhina'' teeth are often associated with mosasaur fossils. ====
1997 ==== • Gordon Bell favorably assessed the mosasaur fossil record, finding its documentation of their evolutionary history nearly as complete as the fossil record of horses. • Bell published a detailed review of mosasaur biostratigraphy. • In contrast to Williston and Martin and Rothschild, Amy Sheldon interpreted Clidastes as a deep water diver because its bones were less dense than those of other mosasaurs, lending it neutral buoyancy during descents. Meanwhile, she argued that Platecarpus preferred shallower waters. • Michael Lee argued that mosasaurs and snakes were sister groups. • Caldwell and Lee argued that the new snake genus and species
Pachyrhachis problematicus was more evidence for a close evolutionary affinity between mosasaurs and snakes. • Tom Caggiano discovered a partial jaw once belonging to a young mosasaur in Kansas. This specimen had been partially digested, possibly by the shark
Cretoxyrhina mantelli. • Shimada reported evidence that mosasaurs were fed upon by sharks, although this may have been scavenging rather than active predation. • Richard P. Hilton and Antuzzi reported the possible
Clidastes skull SC-VR59 from California to the scientific literature. '' '', showing putative mosasaur toothmarks ====
1998 ==== • Fossils of a mosasaur related to
Tylosaurus were discovered on
Vega Island, Antarctica. • Bardet and others reported the discovery of a partial
Plioplatecarpus marshi near
Liège, Belgium with a tail vertebra bearing grooves apparently inflicted by the shark
Centrophorodes appendiculatus, which scavenged the mosasaurs remains before burial. • Ruud Dortangs discovered the skeleton of a new species of
Prognathodon,
P. saturator, in a Maastricht cement quarry. • Lingham-Soliar reported evidence of damage to the skull and braincase of an immature
Mosasaurus hoffmanni. He observed that the area of trauma was similar in size and shape to the bony prow at the tip of the snout of a
Hainosaurus. Lingham-Soliar believed that the larger
Hainosaurus rammed the young
Mosasaurus to death with this snout prow. •
Peter Ward argued that the supposed toothmarks on a
Placenticeras shell described in 1960 by Kauffman and Kesling were actually
limpet boreholes. He described how a graduate student named Erica Roux was unable replicate tooth-shaped punctures in the shells of modern
Nautilus with a mechanical "jaw" because the shells were too brittle. • Kase and others also attributed the rounded indentations and puncture marks to limpets rather than mosasaurs. • Seilacher provided a third voice in favor of the limpet interpretation of punctured ammonite shells. • Bell and VonLoh reported the discovery of mosasauroids from the
Boquillas Formation of
Texas and the
Greenhorn Formation of South Dakota. • Lingham-Soliar reported the discovery of a mosasaur called
Pluridens walkeri from Africa with unusually long, toothy jaws.
August 8th • An additional nearly complete skeleton of
Mosasaurus hoffmani was discovered in the St. Pietersburg quarry of Masstricht and excavated by crews under the auspices of the Dutch Geological Society and Natural History Museum of Maastricht. '' ====
1999 ==== • Holmes Caldwell and Cumbaa rejected the idea that
Plioplatecarpus swam using its flippers to "fly" underwater. They noted however, that a specimen of the genus from
Scabby Butte,
Alberta, Canada seems to have been preserved in a relatively inland and freshwater environmental context, possibly an
estuary. • Lingham-Soliar regarded
Goronyosaurus as the most derived mosasaurid. He also speculated on the ecological conditions that allowed the mosasaurs to achieve dominance of the ichthyosaurs and plesiosaurs. Lingham-Soliar observed that the evolution of swifter swimming fishes in the mid-Cretaceous would have challenged predators that actively chased them while yielding a competitive advantage to sneakier ambush hunters. He thought these conditions gave an advantage to mosasaurs and plesiosaurs over the ichthyosaurs and led to the latter group's extinction. • Lingham Soliar reconstructed the
heterodont dentition of
Carinodens. Teeth near the tip of the jaw were pointed, teeth near the rear were roughly rectangular and triangular teeth could be found between them. • Everhart reported physical evidence of shark bite in the mosasaur genera
Clidastes,
Platecarpus, and
Tylosaurus. • Lingham-Soliar argued that the disappearance of the mosasaurs at their peak of size and diversity was evidence that the mass extinction at the end of the Cretaceous was a rapid event. • Lee and others argued that snakes were the descendants of mosasaurs. • Lee, Bell, and Caldwell argued that mosasaurs were the closest relatives of snakes among the traditional lizards. • Polcyn, Tchernov, and Jacobs described the new genus and species
Haasia gittelmani. • Sakurai and Shibuya described the new species
Mosasaurus prismaticus. • Kass described the species
Prognathodon stadtmani. ==21st century==