The abundance of Arachnostega in trilobite molds remained unaffected by the climatic warming during the Ordovician in Baltica

Arachnostega gastrochaenae Bertling, 1992 burrow systems are found in trilobite molds preserved in carbonate rocks from the Dapingian to upper Katian of Estonia. The average diameter of Arachnostega traces found in trilobites closely resembles those observed in mollusks from the Middle and Upper Ordovician in northern Estonia. Our data suggest a weak correlation between the size of the trilobite and the diameter of Arachnostega, implying that larger tracemakers may have somewhat favored larger skeletons. The abundance of Arachnostega in trilobite molds does not exhibit a decrease as the climate warms during the Katian of Baltica, whereas such a decline is evident in traces found in gastropod steinkerns. This scenario can be attributed to two distinct tracemakers with differing physiological characteristics but similar burrowing behaviors in the Ordovician of Estonia. One group resides in mollusk shells and shows sensitivity to water temperature, preferring colder climates, while the other inhabits trilobite shields and is less affected by climatic conditions.