Two species of ichthyosaurs might actually be one and the same

Diagram of the skeletal anatomy of Ichthyosaur communis from 1824
Diagram of the skeletal anatomy of Ichthyosaur communis from 1824

An article published in the “Journal of Systematic Palaeontology” describes a research that proposes a taxonomic revision among ichthyosaurs, marine reptiles that lived in the Triassic and Cretaceous periods. Dean Lomax, a paleontologist at the University of Manchester, and Professor Judy Massare of Brockport College studied fossils of the species Ichthyosaurus communis and Ichthyosaurus intermedius concluding that they are actually the same species.

Ichthyosaur fossil have been known for centuries but only in the 19th century serious taxonomic studies began and in the case of these marine reptiles in 1821 a species was described that was named Ichthyosaurus communis. In the following years many other species of ichthyosaurs were described but confusion also began following the description of another species that was named Ichthyosaurus intermedius.

From the beginning Ichthyosaurus communis and Ichthyosaurus intermedius were seen as two closely related species but assigning fossils to one or the other species quickly became a major problem. As often happens in the field of paleontology, the specimens found were in many cases incomplete and that made it even more difficult to identify their species.

This situation has been going on for over a centur, but in the 1970s paleontologist Chris McGowan suggested the possibility that Ichthyosaurus communis and Ichthyosaurus intermedius were actually the same species, in technical terms synonymous. This began a series of discussions among scholars that went on for decades but now Dean Lomax and Judy Massare believe they found evidence that McGowan was right.

The two researchers accumulated significant experience examining thousands of fossils of various species of ichthyosaurs, in recent years described three new species belonging to this group of reptiles and suggested a revision of historical species. In essence, they have the proper specialized knowledge to best examine ichthyosaur fossil  and the research on the fossils discovered so far.

The distinction between Ichthyosaurus communis and Ichthyosaurus intermedius was based on their teeth’s morphology. The specimens originally described got lost so the new exams were conducted based on the documentation that survived from that era and other fossils.

Reading the descriptions of the differences between the two species, Dean Lomax and Judy Massare explained their objections providing counter-examples that show inconsistencies. Basically, the different characteristics of the teeth found in the first fossils studied nearly two centuries ago that led to the classification of two species were found together in other fossils.

The research reports a number of examples that show a variety of individual characteristics that convinced Dean Lomax and Judy Massare that the distinction between Ichthyosaurus communis and Ichthyosaurus intermedius was a mistake. If there are no objections, a discussion that went on for a long time may be ending.

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