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- Title
Geologically oldest oysters were epizoans on Early Triassic ammonoids.
- Authors
Hautmann, Michael; Ware, David; Bucher, Hugo
- Abstract
Ammonoids that lived in the wake of the end-Permian mass extinction are frequently encrusted by the shells of cementing bivalves, but the majority of these epizoans are too poorly preserved for a precise taxonomic identification. However, our huge collection of Griesbachian -- Dienerian (Early Triassic, c. 252-251 Ma) ammonoids from east Greenland, the Salt Range (Pakistan) and Spiti (India) includes three ammonoid specimens with epizoans that can reliably be identified as oysters, based on their attachment by the left valve and the morphology of their ligament area. Some of these oysters have their right (upper) valve preserved, which shows the characteristic morphology of Liostrea. These finds predate (1) the previously known first occurrence of oysters by c. 5Myr, (2) that of Gryphaeidae by c. 15Myr and (3) that of Liostrea by c. 20Myr. Moreover, the stratigraphic polarity indicates that Liostrea is a candidate ancestor of Gryphaea and not vice versa. The open-marine habitat of the Liostrea epizoans described herein provides an explanation for the unusual ecology of its putative descendent Gryphaea as a fully marine soft-bottom dweller with a preference for relatively deep water environments during the Triassic. The revised timing of the early phylogeny of oysters suggests that this bivalve clade underwent rapid morphological divergence during the initial phase of its evolution.
- Subjects
AMMONOIDEA; OYSTERS; BIVALVES; TAXONOMY; HABITATS; TYPE specimens (Natural history)
- Publication
Journal of Molluscan Studies, 2017, Vol 83, Issue 3, p253
- ISSN
0260-1230
- Publication type
Article
- DOI
10.1093/mollus/eyx018