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Achelonia formosa

Reptilia

Discussion

(From Anquetin et al. 2017:330): Achelonia formosa is based on two specimens from the late Kimmeridgian locality of Cerin, France (Meyer 1860). The first specimen (MHNL 20015606) consists of a fragment of the anterior rim of a carapace (partial nuchal, left peripherals I–III, and partial left costal I), parts of the pectoral girdle, remains of the left forelimb, and a crushed skull. The second specimen (MHNL 20015608) consists of two manus exposed in palmar view on a slab of limestone. In a relatively ambiguous statement, Meyer (1860) noted that Victor Thiollière, who communicated this material to him, declared that the two specimens were found at the same time and belonged to the same turtle. It is rather unclear, however, whether Thiollière and Meyer were suggesting that the two remains belong to the same individual or simply pertain to the same species. Rütimeyer (1873a) referred the two specimens to the same taxon, whereas Lortet (1892) clearly stated that the aspect of the sediment suggests they belong to the same animal. However, it is difficult to confirm whether or not the two specimens belong to the same individual since there is no connection between the slabs. For clarity, we designate the first specimen (MHNL 20015606) as the lectotype of Achelonia formosa.

Taxonomy
Achelonia formosa was named by von Meyer (1860). Its type specimen is MHNL 20015606, a partial skeleton (fragment of the anterior rim of a carapace plus associated partial left forelimb and skull), and it is a 3D body fossil. Its type locality is Cerin, Jura, which is in a Kimmeridgian terrestrial horizon in France. It is the type species of Achelonia.

Synonymy list
YearName and author
1860Achelonia formosa von Meyer
1873Achelonia formosa Rütimeyer p. 134
2017Achelonia formosa Anquetin et al. pp. 329-330
2020Achelonia formosa Joyce and Mäuser

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RankNameAuthor
kingdomAnimalia()
—Bilateria
—EubilateriaAx 1987
—Deuterostomia
phylumChordataHaeckel 1874
subphylumVertebrata
superclassGnathostomata
—Osteichthyes()
subclassSarcopterygii()
subclassDipnotetrapodomorpha(Nelson 2006)
subclassTetrapodomorpha()
—Tetrapoda
RankNameAuthor
—Reptiliomorpha
—Anthracosauria
subclassAmphibiosauriaKuhn 1967
—Cotylosauria()
—Amniota
—Sauropsida
classReptilia
—Testudinata(Oppel 1811)
—Thalassochelydia
genusAchelonia
speciesformosa

If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.

†Achelonia formosa von Meyer 1860
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Diagnosis
ReferenceDiagnosis
J. Anquetin et al. 2017Achelonia formosa can be differentiated from all other “eurysternids” by having well-developed costo-peripheral fontanelles, reduced ossification of the costal bones partly revealing the underlying thoracic ribs, insertion of thoracic rib II between peripherals III and IV, anterior contact of vertebral I with cervical scutes only, a shallow nuchal notch, and stout manual digits.
W. G. Joyce and M. Mäuser 2020Achelonia formosa can differentiated from all other known representatives of Thalassochelydia by the following combination of characteristics: large size (i.e., a carapace length of more than 60cm), poorly imprinted carapacial scutes, eight pairs of elongated and flattened costal rib ends associated with nine pairs of carapacial fontanelles, and a ligamentous bridge with lateral plastral fontanelles.