Abstract
Abstract. Several British specimens of relatively complete and partial shells of small pleurosternid turtles, found in the Purbeck Limestone Group (Berriasian, Lower Cretaceous), are analysed in detail here. Despite having been found more than a century ago, most of them remained unpublished until now. Due to the scarce knowledge available to date about the small individuals of Pleurosternidae from the British record, their taxonomic status was doubtful. Thus, some authors proposed their attribution to a new but not defined taxon of small size, whereas others suggested that they could represent juvenile individuals of Pleurosternon bullockii, the adults of which were also found in the Purbeck Limestone Group but at different levels. Knowledge about the shell of the adult individuals of Pleurosternon bullockii has notably increased recently, abundant information on its intraspecific variability being currently available. In this context, a detailed study of the small specimens through qualitative and quantitative approaches is performed here. The results are evidence a significant range of shape variability because of ontogenetic development, as well as other types of intraspecific variation such as inter-individual variation. As a consequence, their attribution to juvenile individuals of Pleurosternon bullockii is justified, providing new data on the ontogenetic development of a basal form.
Highlights
The European uppermost Jurassic to lowermost Cretaceous (Tithonian to Berriasian) Pleurosternon bullockii (Owen, 1853) corresponds to the best-represented member of Pleurosternidae (Guerrero and Pérez-García, 2021), a relatively diverse group of Upper Jurassic–Lower Cretaceous North American and European freshwater to brackish turtles (Gaffney, 1979; Pérez-García and Ortega, 2011; PérezGarcía, 2014; Pérez-García et al, 2014, 2015)
Pérez-García: Ontogenetic development of the turtle Pleurosternon bullockii this study is to evaluate if these small forms belong to a new small taxon or justify their attribution to P. bullockii and, to provide data on the ontogenetic development of this basal form
Minor modifications in the carapace ornamentation pattern comparable with those recognized here for P. bullockii have been recognized as resulting from the ontogenetic variation in several species of extinct and extant turtles (Hay, 1908; Zangerl, 1953; de Broin, 1977; Somers et al, 2000; Danilov and Parham, 2008; Jansen and Klein, 2014; Cadena, 2015; Szczygielski et al, 2018)
Summary
The European uppermost Jurassic to lowermost Cretaceous (Tithonian to Berriasian) Pleurosternon bullockii (Owen, 1853) corresponds to the best-represented member of Pleurosternidae (Guerrero and Pérez-García, 2021), a relatively diverse group of Upper Jurassic–Lower Cretaceous North American and European freshwater to brackish turtles (Gaffney, 1979; Pérez-García and Ortega, 2011; PérezGarcía, 2014; Pérez-García et al, 2014, 2015) This lineage of Paracryptodira, together with its exclusively North American sister group Baenidae, constitutes the clade Baenoidea (Joyce et al, 2020; Pérez-García, 2020a). The British collection of P. bullockii had not been analysed and figured in detail until recently (Guerrero and Pérez-García, 2020, 2021) In these last studies, a detailed approach to the knowledge about the inter-individual variation (i.e. polymorphisms and sexual dimorphism) for the adult stage of P. bullockii was obtained, an emended diagnosis for this species having been proposed. They show a controversial taxonomic status due to some authors proposing their attribution to a putative and undefined new genus of small size (Lapparent de Broin and Murelaga, 1999), whereas others suggested that they probably are juvenile individuals of P. bullockii (Lydekker, 1889a; Milner, 2004)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
