Lobsters come with their own set of armor, but apparently that wasn’t always enough. Paleontologists have found three tiny lobster fossils inside the fossil shell of a Jurassic mollusk. Adiel Klompmaker of Kent State University (Ohio) and Rene Fraaije from Oertijmusueum De Groene Poort in The Netherlands recently examined these three mini-lobsters, belonging to the group Eryonidae, to determine exactly what kind of relationship they had with Harpoceras falciferum, the 180-million-year-old ammonoid in which they took residence. The outer organic layer of the ammonoid shell, the periostracum, was preserved, and the inner calcareous layer disintegrated, leaving a translucent covering that allowed the paleontologists to look inside the shell, where they discovered the crustaceans. Apparently the ammonoid shell was empty at the time that the lobsters lived inside. The three lobsters, each measuring just an inch long by 10 mm wide, were splayed out tail-to-tail in the shell – a position that suggested intentional behavior on their part. After ruling out other possibilities, such as the possibility that the lobster fossils were just molts (old exoskeletons that crustaceans shed as they grow), Klompmaker and Fraaije became relatively sure that the lobsters did in fact live within the ammonoid shell. Yet, the reason for such a habitation remain uncertain. The tough ammonoid shell would have served as great protection from predators for the little lobsters, and would have been a safe place to feed and to molt. Although other invertebrate fossils have been found inside other larger fossil shells (e.g., trilobites inside other cephalopod shells, fish inside inoceramid bivalves), this species of crustacean has only been found inhabiting empty ammonoid shells.
Read more at wired.com.
The original article was published in the electronic journal PLoS ONE.