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.Keywords: Brachyura, Dialucidae, Diaulax, ammonites, Valanginian, Colombia. (Lisson, 1907), Acantholissonia gerthi (Weaver, 1931 Resumen El registro más antiguo del género Diaulax Bell, 1863 se basa en la descripción de Diaulax rosablanca n. sp. de la parte media de la Formación Rosablanca (Cretácico Temprano, Valanginiano temprano, Departamento de Santander, Colombia). El reporte representa también el registro más antiguo de crustáceos fósiles para Colombia. La nueva especie está representada por numerosos especímenes que muestran variación ontogénica en tamaño y forma, con adultos que presentan un caparazón más grande y ancho en la porción anterior. Las diferencias con las otras cinco especies del género son sutiles pero suficientes para proponer una nueva especie. Los ammonites asociados Lissonia riveroi

A new species of the brachyuran Ophthalmoplax is documented based upon two specimens collected from shales of the Lodolitas de Aguacaliente Formation, Guadalupe Group, (Cordillera Oriental, Colombian Andes), which represents a regional transgressive event. The small crustaceans were found in the uppermost parasequences with retrogradational stacking pattern, near to the maximum flooding surface (MFS), at the end of the late Campanian Transgressive Systems Tract (TST). This is the oldest record for Ophthalmoplax in America. Morphological affinities with other species of the genus are discussed, including size reduction related with anoxia events and paleotemperature.Keywords: Crustacea, Portunoidea, Ophthalmoplax andina n. sp., Campanian, anoxia, Colombia. Resumen Se documenta la presencia de una nueva especie del braquiuro Ophthalmoplax con base en dos especimenes recolectados en lutitas de la Formación Lodolitas de

No abstract