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][2]
Description
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]
Taxonomy
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]
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]
^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. doi:10.1016/j.cretres.2019.104291. S2CID210279023.
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