Abstract
BackgroundAmber has been reported from the Early Cretaceous Crato Formation, as isolated clasts or within plant tissues. Undescribed cones of uncertain gymnosperm affinity have also been recovered with amber preserved in situ. Here, we provide multiple lines of evidence to determine the botanical affinity of this enigmatic, conspicuous cone type, and to better understand the diversity of amber-source plants present in the Crato Formation and beyond.ResultsA new taxon of amber-bearing pollen cone Araripestrobus resinosus gen. nov. et sp. nov. is described here from complete cones and characteristic disarticulated portions. The best-preserved cone portion has both in situ amber infilling the resin canals inside the preserved microsporophyll tissues and pollen of the Eucommiidites-type. This places this genus within the Erdtmanithecales, an incompletely known gymnosperm group from the Mesozoic.FTIR analysis of the in situ amber indicates a potential araucariacean conifer affinity, although affinity with cupressacean conifers cannot be definitely ruled out. Pyr-GC-MS analysis of the Araripestrobus resinosus gen. nov. et sp. nov. in situ fossil resin shows that it is a mature class Ib amber, thought to indicate affinities with araucariacean and cupressacean, but not pinaceous, conifers. This is the first confirmed occurrence of this class of amber in the Crato Formation flora and in South America, except for an archaeological sample from Laguna Guatavita, Colombia.ConclusionsThe combined results of the cones’ novel gross morphology and the analyses of the in situ amber and pollen clearly indicate that the new taxon of resinous gymnosperm pollen cones from the Crato Formation is affiliated with Erdtmanithecales. The cone morphology is very distinct from all known pollen cone types of this extinct plant group. We therefore assume that the plant group that produced Eucommiidites-type pollen is much more diverse in habits than previously thought. Moreover, the diversity of potential amber source plants from the Crato Formation is now expanded beyond the Araucariaceae and the Cheirolepidiaceae to include this member of the Erdtmanithecales. Despite dispersed Eucommiidites pollen being noted from the Crato Formation, this is the first time macrofossils of Erdtmanithecales have been recognized from the Early Cretaceous of South America.
Highlights
Amber has been reported from the Early Cretaceous Crato Formation, as isolated clasts or within plant tissues
We show that the amber can be classified as belonging to the most common type in the geosphere using pyr-GC-MS, highlighting that there were more source plants for this amber type than previously recognized
We used multiple lines of evidence to uncover the botanical affinity of cones and detached cone portions with in situ amber and in situ pollen, and to understand the potential amber sources of the Crato Formation flora, beyond the araucariacean source plants already known
Summary
Amber has been reported from the Early Cretaceous Crato Formation, as isolated clasts or within plant tissues. We provide multiple lines of evidence to determine the botanical affinity of this enigmatic, conspicuous cone type, and to better understand the diversity of amber-source plants present in the Crato Formation and beyond. The only significant fossiliferous deposit that has been described is from the middle Miocene Pebas Formation of Peru and is thought to be angiosperm in origin [1]. This amber contains inclusions of diverse arthropods, pollen and spores [1]. Amber is present inside fossil conifer (Agathis) tissues recovered from the early Eocene Laguna del Hunco flora and the early middle Eocene Río Pichileufú flora, both in northwestern Patagonia, Argentina [5]
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