Helochelydra is an extinct genus of extinct stem turtle known from the Early Cretaceous (Barremian) of the Isle of Wight, southern England.A. R. Milner. 2011. Turtles. Palaeontological Association Field Guide to Fossils 14:295-304.
Phylogeny Helochelydra is a member of the stem turtle family Helochelydridae, 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 of the Isle of Wight that Lydekker (1889) had referred to Tretosternon punctatum, a turtle taxon from the Purbeck Group of Dorset, but no species name was provided.LYDEKKER, R. (1889). Catalogue of the Fossil Reptilia and Amphibia in the British Museum (Natural History). III. Chelonia. Trustees Brit. Mus. (Nat. Hist.), London, pp. 1-239.NOPCSA, F. (1928). Palaeontological notes on the reptiles. 4. Helochelydra and Hylaeochelys, two little known tortoises from the Wealden and Purbeck Formations. Geol. Hungar., Ser. Palaeont. 1(1): 44-50. Lapparent de Broin and Murelaga (1999) recognized Helochelydra as closely related to the Late Cretaceous stem turtle Solemys, and erected the type species epithet nopcsai for NHMUK R171, even as they considered Tretosternon a possible synonym of Pleurosternon.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).
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