Unravelling the mystery of “Madagascar copal”: Age, origin and preservation of a Recent resin

Abstract

The loss of biodiversity during the Anthropocene is a constant topic of discussion, especially in the top biodiversity hotspots, such as Madagascar. In this regard, the study of preserved organisms through time, like those included in "Madagascar copal", is of relevance. "Madagascar copal" originated from the leguminous tree Hymenaea verrucosa, which produced and produces resin abundantly. In the last 20 years, interest has focused on the scientific study of its biological inclusions, mainly arthropods, described in dozens of publications. The age and origin of the deposits of "Madagascar copal" have not yet been resolved. Our objectives are to determine its age and geographical origin, and thus increase its scientific value as a source of biological/palaeobiological information. Although Hymenaea was established in Madagascar during the Miocene, we did not find geological deposits of copal or amber in the island. It is plausible that the evolution of those deposits was negatively conditioned by the type of soil, by the climate, and by the development of soil/litter microorganisms, which inhibit preservation of the resin pieces in the litter and subsoil over 300 years. Our results indicate that "Madagascar copal" is a Recent resin, up to a few hundred years old, that originated from Hymenaea trees growing in the lowland coastal forests, one of the most endangered ecosystems in the world. The included and preserved biota is representative of that ecosystem today and during historical times. Inclusions in this Recent resin do not have the palaeontological significance that has been mistakenly attributed to them, but they do have relevant implications for studies regarding Anthropocene biodiversity loss in this hottest hotspot.

A review of amber and copal occurrences in Africa and their paleontological significance

“…1). All African copals derive from legume trees in the family Fabaceae, mostly Hymenaea or Guibourtia in the Caesalpinioideae group, but also Colophospermum, Copaifera, Daniellia or Tessmannia in the Detarioideae group (Howes, 1949;Langenheim, 2003;McCoy et al, 2017;Delclòs et al, 2020). V. Bouju and V. Perrichot: BSGF 2020, 191, 17…”

“…1). Copal was traded into Indian Ocean networks, including India, by Swahili communities as soon as in the eighth century AD, but a rise in the trade came with the arrival of European and American ships in Zanzibar between the sixteenth and nineteenth centuries (Hedley Barry, 1932;Howes, 1949;Sunseri, 2007;Delclòs et al, 2020). Most of the copal traded on the Zanzibar market, however, originated from the coastal forests of mainland Tanzania.…”

“…Here we use Tanzanian copal in its broad sense including deposits from coastal hinterlands of Tanzania as well as the Zanzibar archipelago. The trade of East African copal, particularly that of Madagascar, has been recently reviewed by Delclòs et al (2020).…”

“…Amber is a fully polymerized, cross-linked resin that can at most softened using organic solvents. A resin that is incompletely cross-linked and not fully polymerized can dissolve in various solvents and is sometime called copal, although the use of this term is ambiguous (Anderson and Crelling, 1995;Langenheim, 2003;Vávra, 2009;Lambert et al, 2012;Penney, 2016;Delclòs et al, 2020). The time needed for full polymerization greatly varies depending on the resin composition and the burial conditions, so that there is no temporal feature to characterize copal and amber.…”

“…The time needed for full polymerization greatly varies depending on the resin composition and the burial conditions, so that there is no temporal feature to characterize copal and amber. Commonly, however, copals are considered as young, semifossilized resins ranging from Recent up to the Pliocene age (5.3 Ma) (Poinar, 1992;Grimaldi, 1996;Delclòs et al, 2020). But there are older resins that are only partially polymerized and can readily dissolve, or that remain sticky and aromatic when cut or polished, and should therefore be copals.…”