Does trace fossil size correspond with burrower population density? An example from the modern counterpart of the trace fossil Bichordites

The trace fossil Bichordites appears as an intrastratal burrow and occurs in shallow-marine deposits. Its modern counterpart is the burrow produced by the spatangoid echinoid Echinocardium cordatum, found in shallow-marine regions. The relationship between burrow size and tracemaker population density was studied in the modern, subtidal, sandy deposits of a ria coast in the northeastern Japan. Burrow size decreases with increasing population density in the modern counterpart, suggesting that trace fossil size in Bichordites can be used as a proxy to quantify tracemaker population density at the time of trace formation. However, the factors that control burrow size are unclear and warrant further investigation.