''Helochelydra'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of extinct stem

turtle Turtles are an order of reptiles known as Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Cryptodira (hidden necked tu ...

known from the

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pro ...

(Barremian) of the

Isle of Wight The Isle of Wight ( ) is a county in the English Channel, off the coast of Hampshire, from which it is separated by the Solent. It is the largest and second-most populous island of England. Referred to as 'The Island' by residents, the Isle of ...

, southern England.

Phylogeny

''Helochelydra'' is a member of the stem turtle family

Helochelydridae The Helochelydridae are an extinct family of stem-turtles known from fossils found in North America and Europe spanning the Early to Late Cretaceous. Description The skull, shell and osteoderms of helochelydrids are covered in small, cylindric ...

, which is known from Late Jurassic to Late Cretaceous deposits in North America and Europe. Cladistic analysis recovers Helochelydridae outside the clade leading to crown turtles (Testudines).W. G. Joyce, S. D. Chapman, R. T. J. Moody, C. A. Walker (2011) The skull of the solemydid turtle ''Helochelydra nopcsai'' from the Early Cretaceous of the Isle of Wight (UK) and a review of Solemydidae. ''Special Papers in Palaeontology'': 75-97.

Taxonomy

''Helochelydra'' was named in 1928 by Franz Baron Nopcsa for a partial shell ( NHMUK R171) from the Early Cretaceous

Wessex Formation The Wessex Formation is a fossil-rich English geological formation that dates from the Berriasian to Barremian stages (about 145–125 million years ago) of the Early Cretaceous. It forms part of the Wealden Group and underlies the younger Vecti ...

of the Isle of Wight that

Lydekker Richard Lydekker (; 25 July 1849 – 16 April 1915) was an English naturalist, geologist and writer of numerous books on natural history. Biography Richard Lydekker was born at Tavistock Square in London. His father was Gerard Wolfe Lydekker, ...

(1889) had referred to ''Tretosternon punctatum'', a turtle taxon from the

Purbeck Group The Purbeck Group is an Upper Jurassic to Lower Cretaceous lithostratigraphic group (a sequence of rock strata) in south-east England. The name is derived from the district known as the Isle of Purbeck in Dorset where the strata are exposed in the ...

of Dorset, but no species name was provided. Lapparent de Broin and Murelaga (1999) recognized ''Helochelydra'' as closely related to the Late Cretaceous stem turtle ''

Solemys ''Solemys'' is an extinct genus of stem turtle known from the Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epo ...

'', and erected the type species epithet ''nopcsai'' for NHMUK R171, even as they considered ''Tretosternon'' a possible synonym of ''

Pleurosternon ''Pleurosternon'' is an extinct genus of freshwater pleurosternid turtle from the latest Jurassic to earliest Cretaceous of Europe. Its type species, ''P. bullocki'' was described by the paleontologist Richard Owen (noted for coining the word ' ...

''.F. de Lapparent and X. Murelaga. 1999. Turtles from the Upper Cretaceous of Lano (Iberian Peninsula). Estudios del Museo de Ciencias Naturales de Alava 14(1):135-211. The turtles ''"Trionyx" bakewelli'' and ''"Platychelys" anglica'' were referred to ''Helochelydra'' by Milner (2004) based on morphological similarities with the shell of the type species, but were placed in Compsemyidae by Joyce et al. (2012).

References

{{Taxonbar, from=Q41154180 Fossil taxa described in 1928 Early Cretaceous turtles Extinct turtles Testudinata