Helochelydridae, Nopcsa, 1928
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publication ID |
https://doi.org/ 10.5252/geodiversitas2022v44a25 |
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publication LSID |
urn:lsid:zoobank.org:pub:EA12DCB7-A5BE-4763-B805-25087EBD726D |
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DOI |
https://doi.org/10.5281/zenodo.6928883 |
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persistent identifier |
https://treatment.plazi.org/id/03C887B9-FFA6-FFF8-76C9-A509FD6AF85D |
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treatment provided by |
Felipe |
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scientific name |
Helochelydridae |
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Helochelydridae indet.
( Fig. 12A, B View FIG )
DESCRIPTION
In Angeac-Charente, helochelydrids are mostly represented by incomplete isolated shell elements covered by typical tubercles, pustules and crests ( Fig. 12A, B View FIG ) that diagnose this clade ( Lapparent de Broin & Murelaga 1999; Joyce 2017). Probably based on the previous stratigraphical claim by Néraudeau et al. (2012) that Angeac-Charente was Hauterivian-Barremian in age, Joyce (2017) provisionally referred this material to Helochelydra nopcsai , a species otherwise diagnosed by a shell surface ornamentation consisting of distinct, easily dislocated tubercles. Our observations reveal, however, that the helochelydrid material from Angeac-Charente usually displays distinct tubercles that do not easily dislocate. This ornamentation is more similar to the morphotypes of “ Helochelydra ” anglica and “ Helochelydra ” bakewelli ( Joyce 2017), respectively from the Purbeck Group (Berriasian) of Dorset and the Wealden (Valanginian) of Sussex, United Kingdom ( Joyce et al. 2011). That being said, the systematics of Early Cretaceous helochelydrids remains highly confused. For that reason, the helochelydrid material from Angeac-Charente is herein conservatively referred to Helochelydridae indet.
The posterior part of a large carapace collected in 2018 and 2020 provides new information on the morphology of the helochelydrid from Angeac-Charente. However, the material is not fully prepared yet and will be described in more detail elsewhere. A raised midline keel on the posterior neurals is clearly observable, which is a character shared with other helochelydrids ( Lydekker 1889; Lapparent de Broin & Murelaga 1999; Milner 2004; Vullo et al. 2010; Joyce et al. 2014; Joyce 2017; Pérez-García et al. 2020). The general morphology resembles that of other species in which this region is sufficiently known, such as “ Helochelydra ” anglica, Naomichelys speciosa , Aragochersis lignitesta , and Solemys vermiculata ( Lydekker 1889; Lapparent de Broin & Murelaga 1999; Milner 2004; Joyce et al. 2014; Joyce 2017; Pérez-García et al. 2020). Neurals V and VI are elongate and hexagonal. Neurals VII and VIII are probably fused. They are wide and hexagonal anteriorly and posteriorly, and narrower on the midline. There are three suprapygals, which are reminiscent of the condition in FMNH PR273, a nearly complete specimen referred to the North American species Naomichelys speciosa . However, the number of suprapygals is known to be rather variable in basal turtles. The morphology of the suprapygals and pygal differs from other known helochelydrids, but detailed comparisons are needed in order to assess the systematic value of these characters. The shell surface sculpturing is less prominent on the neurals and becomes more pronounced on the distal part of the costals and on the peripherals, suprapygals, and pygal.
Helochelydrids are considered by numerous authors to be terrestrial forms ( Lapparent de Broin & Murelaga 1999; Joyce et al. 2011; Scheyer et al. 2015). They are known to have limbs and neck covered with osteoderms ( Barrett et al. 2002; Joyce et al. 2014; Scheyer et al. 2015). Such osteoderms have also been found at Angeac-Charente. Known cranial material suggests a durophagous diet, although it is still unclear exactly which hard-shelled food elements these turtles fed on ( Joyce et al. 2011, 2014).
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