EVIDENCE FROM CORE OF OLDER EUSOCIAL INSECTS AND A WETTER PALEOCLIMATE: MIDDLE TRIASSIC SKAGERRAK FORMATION (LADINIAN-CARNIAN), CENTRAL NORTH SEA

Five cores through the Joanne and Judy Sandstone members of the Ladinian–Carnian Skagerrak Formation in the Central North Sea contain moderately to well-developed paleosols and associated continental ichnofossil assemblages. Usually considered to represent a classic dryland fluvial depositional setting, abundant rhizocretions, rhizohaloes, Naktodemasis, and complex burrow networks resembling extant and fossil eusocial termite nests and galleries, indicate pedogenesis, well-established vegetation, and humid climatic settings. The complex burrow networks are very distinct and include alteration haloes around the main bodies of networks with galleries, chambers, ramps, and tunnels. They are very similar in appearance to nests of the extant termites Trinervitermes sp. (a harvester in the Termitidae) and Macrotermes carbonarius (also in the Termitidae), possibly indicating fungal-farming behavior. Primitive species of termites (e.g., the harvester Hodotermes mossambicus in the Hodotermitidae) construct nests at depths of 6 m or more while some dryland species burrow up to 40 m deep. Termites require high humidity (89–99%) due to their extremely thin, soft skin and need to soften sediment for excavation and construction. Molecular genetic data have recently pushed back termite divergence from roaches to 170 Ma, extending their range by 100 million years relative to body fossils and demonstrating increased congruence with the ichnofossil record, suggesting a Triassic or older origin. The burrow complexes from the Skagerrak Formation raise the possibility that: 1) eusocial insects (termites, or something very similar to them) evolved prior to the Middle Triassic as previously demonstrated by ichnofossils in the Upper Triassic Chinle Formation of the western U.S.; 2) paleoclimate during deposition of the Skagerrak Formation was more monsoonal than arid; and 3) some of the burrows appear to be similar to fungus-farming termites (or termite-like insects) which evolved more recently according to molecular genetic data, suggesting that simple to advanced nest construction in eusocial termites was present early in their evolution and has persisted to the present day.