Journal
PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY
Volume 585, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.palaeo.2021.110741
Keywords
Aragonite; EBSD; Eggshell; Judith River Formation; Raman spectroscopy; Turtle
Funding
- National Research Foundation of Korea - Ministry of Education [2020R1A6A3A03038316]
- National Research Foundation of Korea - Ministry of Science and ICT [2020R1A3B2079815]
- National Research Foundation of Korea [2020R1A3B2079815, 2020R1A6A3A03038316] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
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Turtles are the only amniotes that lay aragonitic eggs. A discovery in Montana, USA, confirmed the existence of aragonite in turtle eggs dating back to at least the Campanian period, around 76 million years ago. This finding supports the hypothesis that aragonitic eggshell is a unique feature of all turtles and suggests high-quality, unaltered paleoenvironmental information can be obtained from localities with aragonitic turtle eggs.
Among amniotes, turtles are the only clade that lay aragonitic eggs. Because aragonite is a metastable mineral, unequivocal preservation of aragonite in fossil turtle eggs has only been reported from Pliocene deposits. Here, we report in situ preservation of aragonite in a turtle egg from the Judith River Formation (Campanian) of Montana, USA. We utilized electron backscatter diffraction (EBSD) and Raman spectroscopy to explore the carbonate mineral polymorphs in the eggshell. The EBSD maps show the presence of both aragonite and calcite with the former preserved as needle-like crystal, a feature of all turtle eggshells. The presence of aragonite is independently validated by Raman maps. This dual approach provides direct, unambiguous evidence that the record of aragonitic turtle eggshell dates back at least to the Campanian (ca. 76 Ma) and supports the hypothesis that aragonitic eggshell is a synapomorphy of all turtles. The presence of pristine aragonite also indicates minimal taphonomic alteration at the fossil locality. Consequently, diverse invertebrate or vertebrate fossils from localities with aragonitic turtle eggs may provide high quality, unaltered palaeoenvironmental information.
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