PYRITIZED IN SITU TRILOBITE EGGS FROM THE ORDOVICIAN OF NEW YORK (LORRAINE GROUP): IMPLICATIONS FOR TRILOBITE REPRODUCTIVE BIOLOGY

Despite a plethora of exceptionally preserved trilobites, trilobite reproduction has remained a mystery. No trilobite has preserved unambiguous eggs or genitalia. This study reports on the first occurrence of preserved, in situ trilobite eggs from Triarthrus eatoni from the Lorraine Group in upstate New York. Like other exceptionally preserved trilobites from the Lorraine Group, the trilobites are replaced with pyrite on their exoskeletons and ventral appendages. The eggs (presumably representing unfertilized eggs) are spherical to elliptical in shape, about 50 µm in size, and are clustered in the genal area of the cephalon near the lateral border. The eggs are only visible ventrally with no dorsal brood pouch or recognized sexual dimorphism. This location is consistent with how modern horseshoe crabs carry their unfertilized eggs. Trilobites likely released their gametes (eggs and sperm) through a genital pore of as-yet unknown location (likely near the posterior boundary of the head). If T. eatoni’s reproductive biology is representative of other trilobites, they spawned rather than mated.