New research by Brockport College Professor Judy Massare and University of Manchester paleontologist Dean Lomax confirms that two species of ichthyosaurs — Ichthyosaurus communis and I. intermedius – are actually one and the same species.
Ichthyosaurs. Image credit: Julio Lacerda.
Ichthyosaurs — predatory marine reptiles that ranged in size from 1 to 69 feet (0.3 – 21 m) long — swam the world’s oceans for millions of years during the Triassic, Jurassic and Cretaceous periods.
Despite their profound adaptations to the aquatic realm and their apparent success throughout Triassic and Jurassic periods, these reptiles disappeared roughly 30 million years before the end-Cretaceous mass extinction (65 million years ago) that marked the end for dinosaurs and the beginning of the age of mammals.
Ichthyosaurs were the first, large extinct reptiles brought to the attention of the scientific world.
Many ichthyosaur fossils were found in England during the early 19th century, but it was not until 1821 that the first ichthyosaur species, Ichthyosaurus communis, was described.
This species has become one of the most well-known and iconic of all the British fossil reptiles.
In 1822, three other species were described, based on differences in the shape and structure of their teeth. Two of the species were later re-identified as other types of ichthyosaur, whereas one of these species, called Ichthyosaurus intermedius, was still considered closely related to I. communis.
In the years that followed, many eminent paleontologists, including Sir Richard Owen (the man who coined the word dinosaur), studied ichthyosaur fossils collected in England.
Their studies and observations of Ichthyosaurus communis and I. intermedius resulted in confusion with the species, with many skeletons identified on unreliable grounds.
“The early accounts of ichthyosaurs were based on very scrappy, often isolated, remains. This resulted in a very poor understanding of the differences between species and thus how to identify them,” Lomax said.
“To complicate matters further, the original specimen of Ichthyosaurus communis is lost and was never illustrated.”
“Similarly, the original specimen of I. intermedius is also lost, but an illustration does exist.”
“This has caused a big headache for paleontologists trying to understand the differences between the species.”
In the 1970s, paleontologist Dr. Chris McGowan was the first to suggest that Ichthyosaurus communis and I. intermedius may represent the same species.
He could not find reliable evidence to separate the two species. Subsequent studies argued for and against the separation of the species.
In a new study, published in the Journal of Systematic Palaeontology, Lomax and Prof. Massare have reviewed all of the research for and against the separation of the two species.
This is the most extensive scientific study ever published comparing the two.
The authors confirm the species are the same and that features of Ichthyosaurus intermedius can be found in other ichthyosaur species, including I. communis.
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Judy A. Massare & Dean R. Lomax. A taxonomic reassessment of Ichthyosaurus communis and I. intermedius and a revised diagnosis for the genus. Journal of Systematic Palaeontology, published online March 7, 2017; doi: 10.1080/14772019.2017.1291116
