MICRO-CT INVESTIGATION OF A NEW GENUS AND SPECIES OF AMPHIPODA (CRUSTACEA: MALACOSTRACA: TALITRIDAE) PRESERVED IN AMBER FROM THE LOWER MIOCENE OF CHIAPAS, MEXICO

Crustaceans are rarely preserved in amber and their discovery warrants special attention. Several new specimens of amphipod are reported from the Lower Miocene amber of Chiapas, Mexico. A combination of standard light microscopy and photography, together with micro-CT (microcomputed tomography) scanning, allows the animals to be documented in exquisite detail. Although conventional microscopy often provides finer resolution than micro-CT scanning, scanning can resolve hidden features (e.g., obscured by inclusions or superimposition of limbs) and internal morphology that cannot be imaged using other nondestructive methods.

The specimens (one male and several females) represent a new genus and species of sexually dimorphic amphipod. The most notable feature of the new species is that it is blind (suggestive of a cavernicolous ecology). It differs significantly from the other amphipod known from the Chiapas amber, Transitroides morsei, and more closely resembles the extant genus Cerrorhestia, which today is known only from the cloud and rain forests of Costa Rica and Panama.

The scans revealed internal features that appear to correspond to parts of the digestive tract and other internal structures. Animals in amber are not pristine: internal features are the result of a complex interplay of resin infiltration, dehydration, and decay driven by the gut flora – agents that are poorly understood. Micro-CT scans and traditional microscopy can be used in concert to reveal the morphology, taphonomy, and even internal anatomy of fossil amphipods in greater detail than ever before.