The first records of mollusks from mid-Cretaceous Hkamti amber (Myanmar), with the description of a land snail, Euthema myanmarica n. sp. (Caenogastropoda, Cyclophoroidea, Diplommatinidae)

Abstract

AbstractFive land snails and the borings of marine bivalves are reported from Hkamti (Khamti) amber whose age was recently uranium-lead dated to be ca. 110 Ma, in contrast to the nearby Kachin (‘Burmese’) amber considered to be ca. 99 Ma. Four of the snails belong to Cyclophoridae, and although their condition does not allow unambiguous identification or description of the species, one of them strongly resembles Archaeocyclotus plicatula Asato and Hirano in Hirano et al., 2019 from Kachin amber. The fifth snail, Euthema myanmarica n. sp. (Diplommatinidae), is a representative of a genus that was known exclusively from Kachin amber until now. The genus Euthema Yu, Wang, and Pan, 2018 is revised, with a new synonym, Xenostoma Bullis et al., 2020. The recently described ‘Truncatellina dilatatus’ Yu, 2020 from Kachin amber is placed in Euthema. A comparison of the distinguishing characters of the eight Euthema species is provided. The borings of bivalves in Hkamti amber correspond to the ichnospecies Teredolites clavatus Leymerie, 1842, associated with the bivalve genus Martesia Sowerby, 1824 (Pholadidae), and are common in Kachin amber. Similarity of the malacofauna from Hkamti and Kachin ambers, as well as the presence of numerous, similar Teredolites clavatus, indicates that these ambers were formed in very similar paleoenvironments. This indication suggests that forests with very similar conditions existed throughout the entire Albian to the early Cenomanian, or that the dating of at least one of these amber deposits is incorrect. In the latter case, it would mean that Kachin amber is at least 110 Ma or older.UUID: http://zoobank.org/142f10a2-307f-4053-9b29-8aa18db66219