Rare clutch of Cretaceous turtle eggs preserved in the Kaiparowits Formation of southern Utah

Abstract

Although turtles are common Mesozoic fossils, their eggs and nests are rare. Here, we describe an in-situ clutch of turtle eggs from the Campanian (Upper Cretaceous) Kaiparowits Formation of southern Utah. The clutch is preserved in a green mudstone associated with aquatic terrestrial gastropods. Eggshell is broadly distributed across an area of 3.75 m2 with three nearly complete, spherical eggs ∼2.9 cm in diameter, and another three partial eggs identified. The aragonitic eggshell is 0.7–1.2 mm thick and consists of closely packed, slightly domed shell units with a height to width ratio of 3.7:1 and nodular ornamentation 53–71 μm in diameter. Eggshell orientation (concave up/concave down) of 54:46 is consistent with in-situ preservation. An eggshell porosity of 42.5 mm correlates to a humid nesting environment. Extrapolating from egg size, the producing adult carapace length is estimated at 24.45 cm with an average clutch size of 9.91 eggs. The unique attributes of the eggshell warrant naming of a new oospecies, Testudoolithus tuberi. This fossil occurrence is another example of exceptional preservation in the Western Interior Basin associated with the Campanian “taphozone.”