Helochelydridae

The skull, shell and osteoderms of helochelydrids are covered in small, cylindrical protuberances, which are a distinctive characteristic of the group.[3] They are thought to be terrestrial, based on the presence of limb osteoderms (granicones) and bone histology.[4] Their skull morphology is dissimilar to that of extant tortoises, suggesting an omnivorous habit similar to that of box turtles.[5]

Helochelydridae includes all turtles that are more closely related to Helochelydra than Sichuanchelys, Meiolania, or extant turtles.[6] 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.[7] Some recent studies have recovered them as paracryptodires,[8][9] though other studies have found them to be more basal than paracryptodires.[10][11]

• Aragochersis[12] 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[13]), Cambridge Greensand, England, Albian-Cenomanian
• Naomichelys Cretaceous (Aptian-Campanian) North America[6]
• 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)[13]

Indeterminate remains most similar to “Helochelydra” anglica and “Helochelydra” bakewelli have been reported from the Berriasian aged Angeac-Charente bonebed of France.[14]