Helochelydridae Explained

The Helochelydridae are an extinct family of stem-turtles known from fossils found in North America and Europe spanning the Early to Late Cretaceous.^[1]

Description

The skull, shell and osteoderms of helochelydrids are covered in small, cylindrical protuberances, which are a distinctive characteristic of the group.^[2] They are thought to be terrestrial, based on the presence of limb osteoderms (granicones) and bone histology.^[3] Their skull morphology is dissimilar to that of extant tortoises, suggesting an omnivorous habit similar to that of box turtles.^[4]

Taxonomy

Helochelydridae includes all turtles that are more closely related to Helochelydra than Sichuanchelys, Meiolania, or extant turtles.^[5] Although referred to as Solemydidae in recent literature on extinct turtles, Helochelydridae has priority over Solemydidae. They are placed as part of the clade Perichelydia.^[6] Some recent studies have recovered them as paracryptodires,^{[7] [8]} though other studies have found them to be more basal than paracryptodires.^{[9] [10]}

Genera

• Aragochersis^[11] Escucha Formation, Spain, Early Cretaceous (Albian)
• Helochelydra Wessex Formation, England, Early Cretaceous (Barremian)
• “Helochelydra” anglica (Lydekker, 1889) Purbeck Group, United Kingdom, (Berriasian)
• “Helochelydra” bakewelli Mantell, 1833 Tunbridge Wells Sandstone, England, (Valanginian)
• Helochelys Grünsandstein Formation, Germany, Late Cretaceous (Cenomanian), Cambridge Greensand, England, Albian-Cenomanian, France, Spain, Cenomanian
• Trachydermochelys phlyctaenus Seeley 1869 (revised Joyce, 2022^[12]), Cambridge Greensand, England, Albian-Cenomanian
• Naomichelys Cretaceous (Aptian-Campanian) North America^[5]
• Plastremys Upper Greensand Formation, Cambridge Greensand, England, Albian-Cenomanian, Spain, Albian France, Cenomanian
• Solemys France, Spain, Late Cretaceous (Campanian-Maastrichtian)
• Trachyaspis turbulensis Bergounioux 1957 Gargallo, Spain, Early Cretaceous (Aptian-Albian) (possibly synonymous with Plastremys rutteri)^[12]

Indeterminate remains most similar to “Helochelydra” anglica and “Helochelydra” bakewelli have been reported from the Berriasian aged Angeac-Charente bonebed of France.^[13]

Notes and References

1. Joyce WG . Rabi M . Clark JM . Xu X. . 2016 . A toothed turtle from the Late Jurassic of China and the global biogeographic history of turtles . BMC Evolutionary Biology . 16 . 1 . 236 . 10.1186/s12862-016-0762-5 . 5084352 . 27793089 . free .
2. Gentry. Andrew D.. Ebersole. Jun A.. 2021-08-10. The first occurrence of the stem turtle Naomichelys from the Late Cretaceous of eastern North America. Historical Biology. 34 . 7 . en. 1129–1136. 10.1080/08912963.2021.1962855. 238677455 . 0891-2963.
3. Scheyer. T. M.. Pérez-García. A.. Murelaga. X.. March 2015. Shell bone histology of solemydid turtles (stem Testudines): palaeoecological implications. Organisms Diversity & Evolution. en. 15. 1. 199–212. 10.1007/s13127-014-0188-0. 18628827. 1439-6092.
4. WALTER, J.G., CHAPMAN S.D., MOODY R.T.J., and WALKER, C.A. 2011. The skull of the solemydid turtle Helochelydra nopcsai from the Early Cretaceous of the Isle of Wight (UK) and a review of Solemydidae IN BARRETT, P.M. and MILNER, A.R. (eds.) Studies on Fossil Tetrapods. Speicial Papers in Palaeontology, 86, 75-97.
5. Book: Hans-Dieter Sues . The Rise of Reptiles. 320 Million Years of Evolution . August 6, 2019 . Johns Hopkins University Press . 9781421428680 . 53.
6. Joyce . Walter G. . April 2017 . A review of the fossil record of basal Mesozoic turtles . Bulletin of the Peabody Museum of Natural History . 58 . 1 . 65–113 . 10.3374/014.058.0105 . July 9, 2017 . 54982901.
7. Rollot . Yann . Evers . Serjoscha W. . Joyce . Walter G. . December 2021 . A redescription of the Late Jurassic (Tithonian) turtle Uluops uluops and a new phylogenetic hypothesis of Paracryptodira . Swiss Journal of Palaeontology . en . 140 . 1 . 23 . 10.1186/s13358-021-00234-y . 34721284 . 8550081 . 1664-2376 . free .
8. Rollot . Yann . Evers . Serjoscha W. . Pierce . Stephanie E. . Joyce . Walter G. . 2022-11-02 . Cranial osteology, taxonomic reassessment, and phylogenetic relationships of the Early Cretaceous (Aptian-Albian) turtle Trinitichelys hiatti (Paracryptodira) . PeerJ . en . 10 . e14138 . 10.7717/peerj.14138 . 36345484 . 9636874 . 2167-8359 . free .
9. Tong . Haiyan . Tortosa . Thierry . Buffetaut . Eric . Dutour . Yves . Turini . Eric . Claude . Julien . January 2022 . A compsemydid turtle from the Upper Cretaceous of Var, southern France . Annales de Paléontologie . en . 108 . 1 . 102536 . 10.1016/j.annpal.2022.102536. 248792130 .
10. Tong . Haiyan . Buffetaut . Eric . Méchin . Patrick . Méchin-Salessy . Annie . Claude . Julien . 2023-01-03 . A Solemys Skull from the Late Cretaceous of Southern France . Diversity . en . 15 . 1 . 58 . 10.3390/d15010058 . 1424-2818. free.
11. A. Pérez-García . E. Espílez . L. Mampel . L. Alcalá . 2019 . A new basal turtle represented by the two most complete skeletons of Helochelydridae in Europe . Cretaceous Research . 107 . Article 104291 . 10.1016/j.cretres.2019.104291 . 210279023 .
12. Joyce . Walter G. . 2022-10-04 . A review of helochelydrid shell material from late Albian to early Cenomanian greensands of Southern England, United Kingdom . The Anatomical Record . en . ar.25086 . 10.1002/ar.25086 . 36193668 . 252693787 . 1932-8486. free .
13. Ronan Allain, Romain Vullo, Lee Rozada, Jérémy Anquetin, Renaud Bourgeais, et al.. Vertebrate paleobiodiversity of the Early Cretaceous (Berriasian) Angeac-Charente Lagerstätte (southwestern France): implications for continental faunal turnover at the J/K boundary. Geodiversitas, Museum National d’Histoire Naturelle Paris, In press. ffhal-03264773f