Greek
Greek may refer to:
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group
*Greek language, a branch of the Indo-European language family
**Proto-Greek language, the assumed last common ancestor of all kno ...
''Pachys'', "Thick" and ''Strophaios'', Vertebrae) is a
genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
reptile
Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...
, from the
Rhaetian
The Rhaetian is the latest age (geology), age of the Triassic period (geology), Period (in geochronology) or the uppermost stage (stratigraphy), stage of the Triassic system (stratigraphy), System (in chronostratigraphy). It was preceded by the N ...
(
Late Triassic
The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...
) of southwestern
England
England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...
. It is the youngest known thalattosaur.
Taxonomy
''Pachystropheus'' was named by Erika von Huene in 1935; Huene described ''Pachystropheus'' as a
choristodere
Choristodera (from the Greek χωριστός ''chōristos'' + δέρη ''dérē'', 'separated neck') is an extinct order of semiaquatic diapsid reptiles that ranged from the Middle Jurassic, or possibly Triassic, to the Miocene (168 to 20 or p ...
, but this was overlooked for decades until its redescription by Storrs and Gower in 1993. This reevaluation would extend the fossil record of choristoderes back 45 million years. However, other authors consider attribution of ''Pachystropheus'' to Choristodera problematic, stating that it depends on vertebral and girdle characters that are also found in the skeletons of aquatic reptiles other than choristoderes; most of the diagnostic features of choristoderes are skull features, but the presence of these cannot be confirmed in ''Pachystropheus'', as there is no confirmed skull material for this taxon. Silvio Renesto (2005) found similarities in the postcranial skeleton of ''Pachystropheus'' and the
thalattosaur
Thalattosauria (Greek for "sea lizards") is an extinct order of marine reptiles that lived during the Triassic Period. Thalattosaurs were diverse in size and shape, and are divided into two superfamilies: Askeptosauroidea and Thalattosauroidea.
...
genus ''
Endennasaurus
''Endennasaurus'' is an extinct genus of thalattosaurian from the Upper Triassic of Italy. It was found in and named after the Endenna cave, composed of Zorzino Limestone in Lombardia.convergent evolution
Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...
triggered by the aquatic lifestyle of both taxa. The placement as a thalattosaur has been supported by other researchers, including a thorough analysis published in 2024, which found it to be a thalattosaur based on postcranial characters, including the presence of a "finely striated blade of the ilium", and a member of the subclade
Askeptosauroidea
Askeptosauroidea is a superfamily of thalattosaurs, a Triassic group of marine reptiles. Askeptosauroidea is one of two major subgroups of Thalattosauria, the other being Thalattosauroidea. It includes the family Askeptosauridae and a more basa ...
based on its dumbbell-shaped radius. The phylogenetic analysis recovered it as closely related to ''
Endennasaurus
''Endennasaurus'' is an extinct genus of thalattosaurian from the Upper Triassic of Italy. It was found in and named after the Endenna cave, composed of Zorzino Limestone in Lombardia.
pachyostosis
Pachyostosis is a non-pathological condition in vertebrate animals in which the bones experience a thickening, generally caused by extra layers of lamellar bone. It often occurs together with bone densification ( osteosclerosis), reducing inner c ...
and the vertebrae exhibit thickening, likely as an adaptation to living in a marine environment. As no teeth are known for ''Pachystropheus'', it may have been toothless like its close relative ''Endennasaurus.''
Ecology
The Westbury Mudstone where ''Pachystropheus'' was found represents a shallow shelf marine environment. ''Pachystropheus'' likely used its limbs as paddles along with propulsion from the tail. It probably fed on small fish and cephalopods. Finds in coprolites suggests that ''Pachystropheus'' was fed upon by larger marine reptiles.