Tuesday, June 30, 2015

Hawai`i old enough for fossils? Oh yeah.

A lot of folks think of fossils in terms of dinosaurs—things a couple of hundred million years old.

In the Hawaiian Islands, which emerged from the ocean far more recently, couldn’t have much of a fossil supply. Right?

Wrong. There are fossils all over the islands—fossil shells, fossil birds, even fossil plants.

Let’s start with what a fossil is. It can refer to a form of life that has been preserved in stone or converted to stone, like dinosaur bones. But a liberal definition is any evidence of a form of life from a distant time. Even the burrows of ancient animals are considered fossils.

Most of our island’s fossils are stone memorials of sealife or coastal life. 

They can be found on all the islands, but we'll focus on Kaua`i.

They are actually quite easy to find in sandstone fields, like the lithified (turned to stone) sand dunes of Maha`ulepu. There, fossil shells are common in the rock. Kaua`i geologist Chuck Blay, author of the book “Kaua`i’s Geological History,” regularly takes tours to fossils in geological formations.

Fossils of extinct Kaua`i birds have been uncovered in those same hardened dunes by Storrs Olson, curator emeritus of birds at the Smithsonian National Museum of Natural History. His work proved that long before humans, numerous species of flightless ducks and geese  waddled the island’s shores.

At the Kaua`i South Shore’s Makauahi Sinkhole, paleoecologist David Burney has found sediments dating back to long before humans arrived on the island. The fossil array, preserved in moist sediment, has been just amazing.

There were shells, and bird bones, but also a really remarkable archive of the ancient botany of the island. Burney was able to find fossil pollen, bits of wood and ancient seeds, and to identify plant species that once lived in the region. 

One of the bits of evidence he was able to uncover was that the useful and attractive tree kou, Cordia subcordata, grew on these islands long before humans arrived. That was news, since it had long been assumed kou was brought by the first Hawaiian settlers in their canoes.

He also confirmed through pollen analysis that hala, Pandanus tectorius, fell into a similar category—it had previously been assumed a Polynesian introduction, but it was in the Islands long before humans.

There is additional fossil evidence for the hala—another kind of fossil. On a North Shore cliffside, in a lava flow several hundred thousand years old, are ancient hala impressions—molds in the black rock of hala fruit and hala trunks. 
It was fossil proof that a hala forest had stood on the island’s north shore when the island was still volcanically active. Since the first humans only arrived about a millennium ago, that makes hala clearly indigenous.

Similar fossils are formed during most volcanic eruptions, as lava flows through forests and creates tree molds and basalt "casts" of the plants they engulf.
Shell collectors like Reginald Gage have found evidence of many species of native land shells—now all extinct—in the soils of the island.

In sediment, sandstone, lava rock and soil, fossils, clearly, are all over the island.

(A version of this article first appeared in ForKauai magazine.)

© Jan TenBruggencate 2015

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