A new species of Diaulax Bell, 1863 (Brachyura: Dialucidae) in the Early Cretaceous of the Rosablanca Formation, Colombia

Resumen

The oldest record of
the brachyuran Diaulax Bell, 1863 is based on the description of
Diaulax rosablanca n. sp. from the middle part of the Rosablanca
Formation (Early Cretaceous, early Valanginian, Department of
Santander, Colombia). This is also the oldest record for fossil
crustaceans from Colombia. The new species is represented by
numerous specimens showing ontogenic variation in size and shape,
with adults becoming larger and wider at the anterior portion of
carapace. Differences with the other five species of the genus are
subtle but sufficient to erect a new species. The associated
ammonites Lissonia riveroi (Lisson, 1907), Acantholissonia gerthi
(Weaver, 1931) and Raimondiceras sp. confirm an age corresponding to
the middle part of the early Valanginian. The paleoenvironment is
interpreted as a shallow, restricted low-energy carbonate platform
or lagoon within well-oxygenated warm waters. The outcrop includes
other decapod remains, too incomplete to offer a preliminary
identification.