First report of diverse vertebrate coprofaunas from the Lower Cretaceous of Tunisia

Abstract

The Aïn El Guettar Formation in southeastern Tunisia contains one of the most diverse Lower Cretaceous vertebrate assemblages in North Africa. Although the body fossils have been extensively studied over the past years, the associated coprolites are still poorly known. Here new coprolites are comprehensively described from the Chenini and Oum Ed Dhiab members of this formation respectively and ascribed to supposed producers based on a multiproxy analysis. The phosphatic composition, bone inclusions, and internal and external morphologies suggest that these coprolites were produced by a wide range of carnivorous vertebrates. Spiral coprolites from the lower level are mostly amphipolar, suggesting that they were produced by bony fishes, whereas those collected from the upper level are dominated by heteropolar, spirally-coiled coprolites that may have been produced by elasmobranchs. The largest cylindrical coprolites with longitudinal striations, constriction marks, and concentric layers wrapped around a massive core are consistent with those produced by crocodylomorphs. Many specimens from the Chenini Member display different types of desiccation cracks suggesting that the feces were subaerially exposed in a dry environment before burial, however the coprolites from the upper member are devoid of all signs of pre-fossilization abrasion and show smooth surfaces. The highest abundance of coprolites appears to be associated with the lower assemblage, which is congruent with the body fossil record. This study provides tangible evidence about a late Early Cretaceous climatic change in the northern margin of Gondwana and supports previous sedimentology-based assumptions about a dry-to-wet climate transition before the Cenomanian flooding event.