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Sauropod Enamel: Sign of Evacuation or Migration?

by Dr. Elizabeth Mitchell on November 5, 2011

Nature: “Tooth chemistry reveals sauropod sojourns:
First hard evidence of seasonal dinosaur migration found in dental enamel
Sauropod sojourns or enamel of evacuation?

Dinosaur migration, like other dinosaur behavior, can only be guessed at. Geochemist Henry Fricke’s group at Colorado College has been scraping up some clues. They have scraped the enamel from sauropod teeth and analyzed the oxygen isotopes in it. Oxygen isotope ratios matching those of drinking water are typically incorporated into vertebrate tooth enamel. Their findings, published in Nature, are believed to be the first proof that sauropods were migratory.

“The common occurrence of sauropods in this basin [Morrison Basin in Wyoming and Utah] has remained a paradox.”

“The common occurrence of sauropods in this basin [Morrison Basin in Wyoming and Utah] has remained a paradox,” the researchers write, because “in the Late Jurassic-aged Morrison depositional basin . . . these animals occupied lowland river-floodplain settings characterized by a seasonally dry climate.”1

Fricke’s team measured oxygen isotope ratios in enamel scraped from 32 Camarasaurus teeth. These fossils are dated from the late Jurassic period (160 to 145 million years ago) by evolutionary reckoning. The team also measured isotope ratios in the basin’s sedimentary rock. Some enamel had ratios matching local rocks, and some did not.

If isotope ratios don’t match those in the local rocks, scientists assume the animal traveled elsewhere for a time. There is typically less oxygen-18 in water at higher elevations, so animals with tooth enamel low in oxygen-18 are believed to have spent time at higher elevations. Currently, the nearest higher elevations are about 300 kilometers from the Morrison Basin. Therefore, the finding of enamel low in oxygen-18 in some of the enamel is interpreted as evidence the dinosaurs migrated to those highlands.

Fricke’s team also compared isotope ratios from the recently formed enamel on the base of one animal’s tooth with the older enamel at the tip. Because tooth enamel incorporates oxygen from an animal’s drinking water, the enamel provides a record of the animal’s travels while that tooth formed. Internal tooth characteristics suggest these teeth reflect 4-5 months of growth.2 In this case, the older enamel’s isotope ratio was consistent with life in the basin, and the enamel formed later was suggestive of a highland location. The team therefore concludes this animal lived in the basin, migrated to the highlands, and returned to the basin shortly before death, probably in a seasonal migration.

Fricke says, “[These sauropods] are huge — they would probably have eaten themselves out of house and home if they stayed in one place. Now we have evidence that demonstrates that, and a method to move forward and study other dinosaurs.”

It is quite impossible to observe the behavior of an extinct fossilized animal, so clues must be interpreted to draw inferences about ancient behavior. The interpretation of this enamel evidence illustrates the extent to which worldview-based assumptions can influence scientific conclusions.

In this case, the scientists are assuming that the sauropods lived in a basin habitat with geography, seasonal climate, and topography similar to today’s—even though they believe million years have elapsed since those animals became extinct. Therefore, they not only assume these sauropods died and were fossilized in their native habitat but also that the basin habitat was subject to seasonal droughts. Thus, assuming the sauropods had a reason to migrate, they interpret the enamel variations as conclusive evidence that they did. They’re even confident that the place to which they migrated was the same highlands seen on today’s map, again assuming the topography remained unchanged for millions of years.

But stripped of assumptions, what Fricke’s group has demonstrated is that the sauropods fossilized in Morrison Basin probably spent time in different habitats, probably at different elevations.

But stripped of assumptions, what Fricke’s group has demonstrated is that the sauropods fossilized in Morrison Basin probably spent time in different habitats, probably at different elevations. While it is possible that ordinary seasonal migration produced the isotopic variations, it is equally possible that the sauropods, faced with rising floodwaters in the time of Noah, migrated to higher elevations. The Flood did not instantaneously engulf the earth but according to Genesis 7:17–18 rose for quite some time before all the land was covered.

Eventually, sauropods and other dinosaurs that moved to higher ground were engulfed in the Flood, possibly got swept to different locations, and were rapidly buried. The sediment in which the dinosaurs were buried may or may not have been related to their original habitats. The ability of animals like dinosaurs to flee to higher ground during the earlier part of the Flood year explains their higher position in the geologic column. The rock layers represent the order of Flood-related burial, not an evolutionary timeline.

We cannot be certain oxygen isotopes were distributed in the pre-Flood world just as they are today. And biblically there is absolutely no reason to doubt that animals, including dinosaurs, could be migratory in the pre-Flood world. But, if the lower amount of oxygen-18 at higher elevations was the condition early in the Flood year, the tooth enamel may be not a record of seasonal sojourning, but a dinosaurian attempt at flood evacuation. Fricke’s findings are entirely consistent with the biblical model.

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  2. Fricke, H. 2011. et al. Lowland-upland migration of sauropod dinosaurs during the Late Jurassic epoch. Nature, doi: 10.1038/nature10570.


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