The 'classic stromatolite' Cryptozoön is a keratose sponge-microbial consortium

Area of Science:

• Paleontology
• Microbiology
• Evolutionary Biology

Background:

• Animal evolution significantly impacted microbial mat development, with grazing, disturbance, and competition for space being commonly inferred negative effects.
• Ancient examples of cooperation between microbial mats and invertebrates are rare in scientific literature.
• The Late Cambrian (approx. 485 million years ago) Cryptozoön is recognized as the first stromatolite to be taxonomically named.

Purpose of the Study:

• To investigate the composition and formation of Cryptozoön, challenging the traditional view of animal-microbe interactions in stromatolite development.
• To re-evaluate the ecological role of Cryptozoön in the context of early animal-microbial cooperation.
• To explore the potential for misidentification of ancient keratosan-microbial consortia as stromatolites.

Main Methods:

• Microscopic and geochemical analysis of Cryptozoön specimens.
• Comparative study with modern microbial mat and invertebrate interactions.
• Reconstruction of Cryptozoön's growth patterns and environmental context.

Main Results:

• Cryptozoön is identified as a layered consortium of keratose sponges and microbial carbonate in nearly equal proportions.
• The distinct layering indicates repeated alternation between sponge and microbial mat activity.
• Cryptozoön's lateral growth is attributed to the ability of sponges to colonize challenging surfaces.

Conclusions:

• Cryptozoön demonstrates a mutualistic relationship where sponges and microbial mats cooperated for support, stability, and resource sharing.
• This finding contrasts with the prevailing view of Phanerozoic stromatolites as merely surviving in a eukaryotic world.
• Keratosan-microbial consortia may have been misidentified as stromatolites throughout the fossil record for over 500 million years.