Possible shell disease in 100 million-year-old crabs

Area of Science:

• Paleontology
• Paleopathology
• Evolutionary Biology

Background:

• Recognizing disease evidence in fossils is challenging, hindering the study of disease evolution.
• Decapod crustaceans, including crabs, are susceptible to various diseases affecting their exoskeletons.

Purpose of the Study:

• To investigate the cause of unusual damage observed on fossilized crab carapaces.
• To determine if the observed damage represents evidence of ancient diseases in crustaceans.

Main Methods:

• Examined two molts of mid-Cretaceous goniodromitid crabs (Distefania incerta and Goniodromites laevis) from Spain.
• Compared the morphology and size of lesions on fossil specimens to known damage patterns from modern decapods, including bacterial infections.

Main Results:

• Observed subcircular to quadratical holes on the dorsal carapace of both fossil crab species.
• Lesion characteristics closely resemble damage caused by bacterial infections on modern decapod cuticles.
• Alternative explanations like abiotic damage or predation were considered less likely.

Conclusions:

• The fossil lesions are hypothesized to be primarily caused by bacterial disease, potentially initiated before molting.
• This finding represents the earliest known evidence of bacterial shell disease in fossil decapod crustaceans.
• The evolutionary history of this type of shell disease in crustaceans is extended by approximately 100 million years.