THE FIRST RECORD OF LOWER CRETACEOUS LINGULIDAE (BRACHIOPODA) FROM THE TROPICAL AMERICA

Lingulid brachiopods were globally widespread during the Lower Cretaceous. However, few taxa are adequately described and almost nothing is known about the group in the tropical America during these times. Indeed, very few localities have been systematically studied. Reports of Cretaceous lingulids in the region are restricted to the upper Cretaceous of Colombia and Brazil (Turonian). This huge knowledge gap hinders biogeographical studies of the group, and thus their evolution. Several questions remain to be explored: How do lingulids respond to the major environmental changes during early Cretaceous times (i.e., warming)? Where did their Cenozoic relatives (i.e., Glottidia) originate? A renewed interest in this group during the last two decades is due in part to its important role as an organo-phosphatic biomineralizer during the Phanerozoic and its notoriety as an example of evolutionary stasis since the Paleozoic.

An extensive field survey in the northern South America (Western Cordillera of Colombia) uncovered multiple occurrences of lower Cretaceous lingulids. Two stratigraphic sections of the Valanginian-Hauterivian Rosablanca Formation (65 m and 140 m in thickness) were logged. A total of 45 well-preserved valves of Lingularia? sp. were collected from three stratigraphic horizons of slightly bioturbated siltstones at the base of the unit. Lingulids in at least one of these horizons could be tracked laterally for almost 1000 m. The size of the collected specimens ranged from 4.5 to 15.0 mm in shell length. No preferential orientation of those shells in relation to the bedding plane was observed. The occurrence of single valves and fragments of lingulids, and also disarticulated bivalves and crabs in those levels, suggests that the material was transported prior to deposition. This study documents the oldest occurrences of lingulid brachiopods in the region so far. The new Cretaceous material should help us to reconstruct the biogeographic history of the group more accurately. Although lingulids are considered to have been rare in Cretaceous near-shore marine communities the results reported here suggest that they may have been common locally.