First occurrence of Ibacinae (Eucrustacea: Decapoda: Scyllaridae) from the Eocene of Pakistan
The fossil record of slipper lobsters (Scyllaridae) is very poor, even though the earliest species of the modern slipper lobsters (Neoscyllaridae) are known from the Early Cretaceous. Among the clades (‘subfamilies’) of slipper lobsters, perhaps the most remarkable is Ibacinae (currently monogeneric), which contains species with a very wide carapace (cephalothoracic shield) and very deep incisions. Fossil species assigned to Ibacinae were reported from the Oligocene and Pleistocene. However, a recent reappraisal of Scyllaridae phylogeny revealed that the genus to which these two fossil occurrences belong is not closely allied to Ibacinae. Therefore, Ibacinae was left with no known fossil record until the present study. The present study describes a new species, which can be confidently assigned to Ibacinae (closely allied to Ibacus), from the Ypresian (early Eocene) of the Ghazij Formation in Shaisuro, Dera Ghazi Khan District, Pakistan. This new species, Ibacus? mazariorum sp. nov., corresponds to the oldest recorded occurrence of Ibacinae. The Ghazij Formation was deposited on the north-western margin of the India-Pakistan plate during a critical period, shortly before the collision between the India-Pakistan plate and Asia. Consequently, it is possible that Ibacus and closely allied species may have remained in the same biogeographical area since the Eocene. Considering the extant and fossil distribution of Ibacinae, additional fossil discoveries may be found in existing collections and fossiliferous outcrops from the Neotethys, Indian and Pacific oceans.