Internal anatomy of a brachyuran crab from a Late Cretaceous methane seep and an overview of internal soft tissues in fossil decapod crustaceans

Abstract

Cretaceous-aged methane seep carbonates in the Western Interior Seaway, USA, have yielded a relatively high diversity and concentration of fossils, including decapod crustaceans, compared to their surrounding, contemporaneous sediments. With technological advances in non-destructive imaging techniques, the internal anatomy of decapods can be studied in remarkable detail. Here, we present a brachyuran crab specimen from an upper Campanian methane seep carbonate in South Dakota, USA. While the external morphology of the crab is insufficient for species identification (Secretanella sp.), remarkable details of the internal morphology are preserved including soft tissues. Four phyllobranchiate gills are visible due to a broken cuticle. A µCTscan revealed parts of the digestive tract including the esophagus and the cardiac stomach (foregut), and possible anterior gastric muscles. An esophagus has not been reported previously in a fossil decapod. We also found mandibles and their apodemes. Because of soft tissue preservation, the South Dakotan locality may be a candidate Konservat-Lagerstätte. To our knowledge, the studied crab contains the first preserved animal soft tissue reported from an ancient methane seep. Our new overview of internal soft tissues preserved in fossil decapod crustaceans shows that, besides muscles reported previously, gills and remains of the digestive tract are most often reported (8 and 13 occurrences, respectively). Reproductive organs, nerve chords, and the heart are only known from one or two occurrences. Although reports of soft internal anatomy preservation remain relatively rare, continued application of µCT-scans to fossil decapods has the potential to illuminate our knowledge of the evolution of internal decapod anatomy.

Exploring the preservation of a parasitic trace in decapod crustaceans using finite elements analysis

“…As high-quality specimens of fossil decapods are rare and scientifically valuable, particularly those bearing additional abnormalities such as traces of parasitism, destructive sampling techniques and intrusive attempts to reveal fossils from the matrix are inadvisable. CT scanning has seen a dramatic increase in widespread use for paleontological study over the last 20 years, as the technology has become more accessible, and CT data has become easier to analyze and manipulate [24][25][26][27][28][29][30].…”