My fossil fish was keeping a secret from me.

A few months ago I found a near-perfect fossil fish from the Triassic period in what is now Connecticut. However, it was hiding a secret from me: underneath the positive impressio of the fish was a think layer of rock. It broke off while I was moving the specimen to reveal even more fossil scales. How could this happen? Let’s consider the facts.

A fish, after death, experienced decomposition which led to a buildup of internal gases causing it to float. Once floating, the gases reach a critical point, and the fish's body bursts, scattering its scales. These scales then settle to the bottom of the aquatic environment and become buried, eventually fossilizing. Later, another fish dies and is buried in a layer above this "explosion" layer, also becoming fossilized.

Here's how this might be explained step-by-step in the context of the Triassic:

Fish Death & Decomposition: Like modern fish, when Triassic fish died, they likely went through a similar decomposition process. Decomposing bacteria produce gases (such as methane and hydrogen sulfide) inside the fish's body, which can cause the fish to float.

Fish "Explosion": If the internal pressure from the gases built up sufficiently before being released naturally or by scavengers, it's plausible that the fish's body could rupture, scattering parts like scales.

Sedimentation: The scattered scales fall to the lake or sea floor. Over time, sediment accumulates on top of these scales, preserving them. This sediment can come from various sources, including runoff from the land, decaying organic matter, or even volcanic ash.

Another Fish Fossilization: Later on, another fish dies, sinks to the bottom (perhaps it doesn't undergo the "explosion" event or it's rapidly buried), and gets covered by sediments. This fish eventually becomes the fossilized specimen you found in the layer above the scattered scales.

Lithification: Over millions of years, the accumulated sediments are compressed and undergo processes that turn them into rock, preserving both the scattered scales and the fish fossil in distinct layers.

So long story short, a specimen I treasure just became even better and tells a more complete and compelling story of the cycles of life and death. Hope you enjoy!