11 December 2015

11. Caribbean Amber

Ichneumonid wasp in Dominican amber
George Poinar, Jr., Wikimedia
Location: Dominican Republic &Haiti
Formation: Numerous
Age: Oligocene (25 Ma)

Many of the fossils presented here this month are figurative gems, but a few sites literally preserve fossils within gemstones.  As any fan of trivia will tell you, there are two gems created by organisms: pearls and amber.  As hardened tree resin, amber is itself a fossil, but the fossils most often associated with amber are the remains of organisms entombed within.  These can range in size and taxonomy from pollen grains to vertebrates, but most famously includes insects, which are preserved in resin relatively frequently.  Two region of the world are especially well-known for their amber lagerstätten: the Baltic Sea (representing the European jungles of the Eocene discussed at the beginning of this series) and the island of Hispaniola (which dates to the Oligocene).  Then as now, the Greater Antilles were in the tropics, meaning that the region has not been subjected to the same degree of cooling as much of the rest of the world.  This is confirmed by the fossils themselves; most of the amber on the island is formed from the resin of a relative of the modern algarrobo tree, a tropical legume.  Preserved organisms include organisms such as palms, ants, and lizards, all of which indicate a tropical climate.  Like the Oligocene-Early Miocene sites from Riversleigh, then, the environmental story told by Caribbean amber is not one of organisms and ecosystems adapting to colder climatic conditions.  Rather, amber provides a window on the evolution of one particular ecosystem through time: tropical rain forests.  Rainforests are cradles of biodiversity today and, presumably, through much of Earth's history, but despite their huge importance, they are among the worst-represented biomes in the fossil record.  Decomposition occurs at high rates in jungles and soil conditions are generally unfavorable for preserving many types of fossil (most of the rainforest ecosystems discussed so far this month are actually preserved in lake or marine sediments, which are much better preservational environments).  The rare in situ snapshot of an Oligocene rainforest provided by Caribbean amber allows the study of a forest ecosystem that persists in the area to this day.  To the north, though, formerly forested land was beginning to give way to an entirely new biome dominated by a particularly hearty group of plants and populated by animals forced to play by an entirely new set of rules.

Visit: Caribbean amber is mined commercially, and based on what I can glean from the Dominican Republic's tourism site, none of these mines are open to the public.
Fossils: Two Dominican museums focus on local amber: the Museo Mundo del Ambar in Santo Domingo and the Museo del Ambar in Puerto Plata.  Also in Santo Domingo, the Museo Nacional de Historia Natural has an amber exhibit.
Is there a relevant book full of gorgeous fossil photos that I can gift to a paleontologically-minded friend?: Not as such, but there is a well-written survey of Dominican amber available.

This post is part of my 2015 Paleontology Advent Calendar, a series of vignettes on lagerstätten - sites of exceptional fossil preservation - that document changes in climate and environments through the Cenozoic.  You can see the other posts here.

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