Pachycostasaurus
genus of plesiosaur
Pachycostasaurus (meaning 'thick-ribbed lizard') is an extinct Pliosauroid from the Oxford Clay formation of Peterborough, England.
History and naming
The holotype fossil of Pachycostasaurus was discovered by Alan Dawn, an amateur geologist and museum volunteer, in what is now a quarry in Peterborough. The fossil was described in 1996 by Palaeontologists Arthur Cruickshank, David Martill and Leslie Noè, due to its distinct set of features not present in contemporary pliosaurids Liopleurodon and Simolestes.
Description
The type species, P. dawni, is represented by a single near complete specimen (PETMG R338) which was approximately 3 metres (9.8 ft) long.
Perhaps the most defining feature of this genus is the large, pachyostic ribs and gastralia described as ‘sausage-like’ in profile. Pachyostosis is known from a number of Pliosaurid genera (for example Monquirasaurus), and is present in modern animals such as Sirenians (Dugong and Manatees). This robust, barrel shaped torso, coupled with a relatively short neck and small flippers, indicate that it was not an agile swimmer. Histological sections taken from these elements show that they are osteosclerotic as well (combined, this represents the condition pachyosteosclerosis).
The holotypic specimen possessed five stout and conical tooth pairs on the mandibular symphysis (the length of which is a clear characteristic of the genus in comparison to other contemporary Pliosaurids Simolestes and Liopleurodon). Its head was about 20% of overall body length, typical for most Pliosaurids of its time.
The public source identifies “Pachycostasaurus” as genus of plesiosaur. This brief keeps that definition visible, then builds a research path around Pachycostasaurus, genus and plesiosaur.
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The date and method of observation matter as much as the stated conclusion, especially where classification or consensus has changed. The source revision retrieved here is dated Mar 30, 2025. The linked authority identifier is Q3888477. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1996.
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This entry incorporates text from “Pachycostasaurus” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.