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

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

Description

The skull, shell and

osteoderm Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct amp ...

s of helochelydrids are covered in small, cylindrical protuberances, which are a distinctive characteristic of the group. They are thought to be terrestrial, based on the presence of limb

s and bone histology. Their skull morphology is dissimilar to that of extant tortoises, suggesting an omnivorous habit similar to that of box turtles.

Taxonomy

Helochelydridae includes all turtles that closely related to '' Helochelydra'' than '' Sichuanchelys'', '' Meiolania'', or extant turtles. 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 Perichelydia (from Greek ''peri'' "near" and ''chelys'' "turtle") is a clade within Pantestudines (turtles and their extinct relatives) known from the Middle Jurassic to Holocene. Alongside crown group Testudines, it also contains Helochelydrida ...

. Some recent studies have recovered them as paracryptodires, though other studies have found them to be more basal than paracryptodires.

Genera

* '' Aragochersis''

Escucha Formation The Escucha Formation is a geological formation in La Rioja and Teruel provinces of northeastern Spain whose strata date back to the late Aptian to middle Albian stages of the Early Cretaceous. Dinosaur remains are among the fossils that have bee ...

, Spain, Early Cretaceous ( Albian) * '' Helochelydra'' Wessex Formation, England, Early Cretaceous (

Barremian The Barremian is an age in the geologic timescale (or a chronostratigraphic stage) between 129.4 ± 1.5 Ma (million years ago) and 121.4 ± 1.0 Ma). It is a subdivision of the Early Cretaceous Epoch (or Lower Cretaceous Series). It is preceded ...

) *''“Helochelydra” anglica'' (Lydekker, 1889)

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 ...

, United Kingdom, (

Berriasian In the geological timescale, the Berriasian is an age/stage of the Early/Lower Cretaceous. It is the oldest subdivision in the entire Cretaceous. It has been taken to span the time between 145.0 ± 4.0 Ma and 139.8 ± 3.0 Ma (million years ago) ...

) *''“Helochelydra” bakewelli'' Mantell, 1833 Tunbridge Wells Sandstone, England, (

Valanginian In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 139.8 ± 3.0 Ma and 132.9 ± 2.0 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretaceou ...

) * '' Helochelys'' Grünsandstein Formation, Germany, Late Cretaceous (

Cenomanian The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in the s ...

), Cambridge Greensand, England, Albian-Cenomanian, France, Spain, Cenomanian * ''Trachydermochelys phlyctaenus'' Seeley 1869 (revised Joyce, 2022), Cambridge Greensand, England, Albian-Cenomanian * '' Naomichelys'' Cretaceous (Aptian-Campanian) North America *'' Plastremys'' Upper Greensand Formation, Cambridge Greensand, England, Albian-Cenomanian, Spain, Albian France, Cenomanian * '' Solemys'' France, Spain, Late Cretaceous ( Campanian-

Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...

) * ''Trachyaspis turbulensis'' Bergounioux 1957 Gargallo, Spain, Early Cretaceous (Aptian-Albian) (possibly synonymous with ''Plastremys rutteri'') Indeterminate remains most similar to ''“Helochelydra” anglica'' and ''“Helochelydra” bakewelli'' have been reported from the Berriasian aged Angeac-Charente bonebed of France.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

References

{{Taxonbar, from=Q3489339 Testudinata Prehistoric reptile families