Ambilobeia is an extinct genus of prawn from the Isalo II Formation in Ambilobé, Madagascar, dating to the Olenekian stage of the Early Triassic period (approximately 251–247 million years ago). It contains a single described species, Ambilobeia karojoi.
Discovery and naming The genus and species were named and described in 2002 by Alessandro Garassino and Giovanni Pasini. The holotype specimen (MSNM 125459) was discovered by an unknown French palaeontologist in a deforested outcrop of the Isalo II Formation near Bobasatrana, Madagascar, during the 1990s. It was donated to the Museo Civico di Storia Naturale di Milano before 2002 by Mr. Karojo, a local Malagasy prospector, after whom the species is named. Most specimens described in the original 2002 study were collected during the 1980s and 1990s following local surveys of decapod fossils.
Description Ambilobeia is one of the earliest known prawn species from the Southern Hemisphere after the Permian–Triassic extinction event. It grew to approximately 8 centimetres (3.1 in) in length. Morphologically, it is characterized by a slender carapace, an elongate rostrum lacking supra- or subrostral teeth, and the first three pereiopods bearing short, thin chelae (claws). These features differentiate it from the related genus Ifasya.
Classification Ambilobeia belongs to the infraorder Penaeidea (family Penaeidae Rafinesque, 1815), placing it within the group of dendrobranchiate crustaceans that includes modern penaeid shrimps and prawns.
Significance As a Lower Triassic (Olenekian) fossil, Ambilobeia provides insight into the recovery and diversification of decapod crustaceans in the aftermath of the Permian–Triassic extinction event, the most severe mass extinction in Earth's history.
