Insect and plant diversity in hot-spring ecosystems during the Jurassic-Cretaceous boundary from Spain (Aguilar Fm., Palencia)

Abstract

Hydrothermal palaeoenvironments are very uncommon in Upper Jurassic and Lower Cretaceous deposits worldwide. We present new plant and insect remains from travertines formed during the Jurassic-Cretaceous boundary in northern Spain (Aguilar Fm., Palencia province). A total of 136 plant specimens and three insect wings were collected and studied. This entomofauna consists of dragonfly (Odonata) wings including Cymatophlebiidae and an undetermined new genus and species of Aktassiidae, representing the first report of these families for the Iberian Peninsula. The fossil flora shows different morphotypes of plants, which have been tentatively assigned to three different genera. The taphocoenosis of the flora was dominated by Bennettitales (98.5%) including cf. Pterophyllum sp., Ptilophyllum cf. acutifolium, Ptilophyllum cf. pecten, Ptilophyllum cf. pectiniformis and cf. Ptilophyllum sp., and the occasional presence of ferns (1.5%) represented by the taxon Cladophlebis cf. denticulata. The presence of the Anisoptera Cymatophlebia cf. longialata suggests a higher affinity for a Tithonian age of the studied site, and the anatomy and palaeogeographical distribution of this species suggest capacity to migrate for rather long distances. The floristic composition of the site differs remarkably from other Tithonian-Berriasian floras of the Iberian Peninsula. The presence of Odonata and the distinctive flora in (semi)arid conditions could be due to the hot-spring providing an environmental niche with constant conditions of warmth and humidity forming an ‘ecological oasis’.