Persistent biotic interactions of a Gondwanan conifer from Cretaceous Patagonia to modern Malesia

Michael P Donovan,Peter Wilf,Conrad C Labandeira,N Rubén Cúneo,Ari Iglesias

doi:10.1038/s42003-020-01428-9

Abstract

Many plant genera in the tropical West Pacific are survivors from the paleo-rainforests of Gondwana. For example, the oldest fossils of the Malesian and Australasian conifer Agathis (Araucariaceae) come from the early Paleocene and possibly latest Cretaceous of Patagonia, Argentina (West Gondwana). However, it is unknown whether dependent ecological guilds or lineages of associated insects and fungi persisted on Gondwanan host plants like Agathis through time and space. We report insect-feeding and fungal damage on Patagonian Agathis fossils from four latest Cretaceous to middle Eocene floras spanning ca. 18 Myr and compare it with damage on extant Agathis. Very similar damage was found on fossil and modern Agathis, including blotch mines representing the first known Cretaceous–Paleogene boundary crossing leaf-mine association, external foliage feeding, galls, possible armored scale insect (Diaspididae) covers, and a rust fungus (Pucciniales). The similar suite of damage, unique to fossil and extant Agathis, suggests persistence of ecological guilds and possibly the component communities associated with Agathis since the late Mesozoic, implying host tracking of the genus across major plate movements that led to survival at great distances. The living associations, mostly made by still-unknown culprits, point to previously unrecognized biodiversity and evolutionary history in threatened rainforest ecosystems.

Highlights

Many plant genera in the tropical West Pacific are survivors from the paleo-rainforests of Gondwana
These biogeographic connections derive from the former presence of mesic austral rainforests toward the end of Gondwana, which were nearly exterminated following the final separation of South America, Antarctica, and Australia starting from the middle Eocene
The first South American members of the Old World broadleaved conifer genus Agathis, including its oldest known representatives, were recognized from multiple vegetative and reproductive organs found in early Paleocene[7], early and middle Eocene[22], and probably in terminal Cretaceous[7] floras of central Patagonia, Argentina

Summary

Introduction

Many plant genera in the tropical West Pacific are survivors from the paleo-rainforests of Gondwana. The oldest fossils of the Malesian and Australasian conifer Agathis (Araucariaceae) come from the early Paleocene and possibly latest Cretaceous of Patagonia, Argentina (West Gondwana). It is unknown whether dependent ecological guilds or lineages of associated insects and fungi persisted on Gondwanan host plants like Agathis through time and space. Terminal Cretaceous to Eocene floras from Patagonia, Argentina show affinities with fossil floras from Australia and other southern land masses, as well as living subtropical and tropical montane rainforest floras from Australasia to Southeast Asia[1,2,3,4,5,6,7,8]. The genus faces immense logging pressure through much of its modern range[38]

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