New Origin of Thalassinoides Burrows (Gastropod Dwelling Structures) in the Qamchuqa Formation (Lower Cretaceous), Kurdistan Region, Northeastern Iraq

Abstract

Imad Mahmood Ghafor, Zryan Sardar Tahir, Javadova A* and Kamal Haji Karim

This study documents the first significant occurrence of Thalassinoides ichnofossils in the Lower Cretaceous Qamchuqa Formation of northeastern Iraq. Preserved in coarse detrital limestones, terrigenous carbonates, and mixed sediments, these burrows are associated with coastal to shallow-marine ichnofacies, particularly Skolithos and Cruziana. Extensive burrow networks—horizontal tubes with vertical or inclined shafts—show features like eccentric swellings at branch points and smooth walls, ranging from 5 to 20 mm in diameter. The burrows exhibit backfill structures, indicating active construction by tracemakers. Decapod crustaceans, possibly crayfish like Hoploparia, are the likely producers. Notable findings include crab trackways and gastropod trails up to 0.5 m long, among the longest invertebrate cursorial traces known. The presence of lateral movement features suggests the emergence of crab-like sideways locomotion during the Cretaceous. This discovery marks the first recorded presence of Thalassinoides in Iraq and adds new insight into Cretaceous trace fossil assemblages in the region.

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