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This is the neonatal fossil located next to the fully formed Tylosaurus skull, measuring 1.2 m. Credit: Historical Biology
The smallest Tylosaurus mosasaure fossil ever found was revealed in a new study in the Journal of Vertebrate Paleontology and surprisingly, it lacks a trademark feature of the species.
The fossil, which could be that of a newborn, does not have the long recognizable snout typically seen in the species. The absence of this snout first surprised the researchers, who had trouble identifying which group of mosasaurs it belonged to.
After examining and comparing the fossil to young specimens of closely related species, such as T. nepaeolicus and T. Proriger who already had identifiable noses, the researchers eventually considered that it was a young person Tylosaurus.
Lead author, Professor Takuya Konishi, of the Department of Biological Sciences at the University of Cincinnati, said, "After examining the specimen in 2004 for the first time, it also took me almost 10 years to think about it was really a baby Tylosaurus still develop such a muzzle.
During those ten years or so, I had also believed that it was a newborn of Platecarpus, a medium-sized (5 to 6 m) mosasaur with a short snout, Tylosaurus, a giant mosasaur (up to 13 m) with a distinctly prominent snout. "
This picture shows from left to right a partial snout with teeth and tooth bases, a partial puzzle and a section of the upper jaw with tooth bases. Credit: Christina Byrd, head of paleontology collections at the Sternberg Museum of Natural History in Hays, Kansas.
The lack of muzzle in the found baby specimen suggests to researchers that the development of this function is extremely rapid, between birth and juvenile stage – what previous studies on the species did not notice .
Konishi added, "Again, we were challenged to fill our lack of knowledge by testing our preconceived idea, which in this case was that Tylosaurus have a pointed snout, a so-called "common knowledge".
Since individual development and the history of evolution are generally linked, the new revelation suggests the possibility that Tylosaurus adults from much older rock units may have been so muscular, something we can test in future discoveries. "
The found fragments include a partial snout with teeth and tooth bases, a partial jigsaw and a section of the upper jaw with tooth bases. From this they can estimate that the baby's skull was about 30 cm (1 ft) in total.
Tylosaurus belong to one of the largest known groups of mosasaurs, up to 13 m long, with a head at the front of 1.8 m. The baby was about 1/6 the size of such an adult.
Michael J. Everhart, a native of Kansas and special curator of paleontology at the Sternberg Museum of Natural History in Hays, Kansas, found the tiny specimens in 1991 in the lower part of the Niobrara Chalk, Kansas, which are now kept at the museum. The paper was co-authored by Paulina Jimenez-Huidobro and Michael W. Caldwell of the University of Alberta, Canada.
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