As this is a perpetually-recurring newsgroup question, here's a stab at a FAQ-style answer.

Q: If intelligent dinosaurs had created a civilization prior to the end-of-Cretaceous mass extinction (+/- 65 million years before the present) [note 1], what sort of artifacts might survive (if any) and how might we recognize them?

A: The fossil (or archaeological) record is a numbers game -- it depends on:

1. an item (corpse, feces, tool, footprint, whatever) has to be buried
2. under conditions that preserve it
3. in some recognizable form, and
4. it has to be found and identified as a fossil (or artifact).

Think of this as a geologic Drake equation: if any term is zero, no fossil (or artifact) will be found or recognized.

So, the most common fossils will be common critters, sturdy enough to be easily-preserved, and easy to recognize when found. Consider sea shells: ubiquitous marine life, shells are sturdy, and if they fall into limy mud (eg in a coral-reef environment), they are well-preserved (often silicified as the mud is lithified). They look like shells when found. They live in shallow water on continental margins, where (relative) sea levels rise and fall. Thus, once buried, the rocks they are entombed in are likely to be uplifted some time later. Once eroded, the fossils will be exposed to view once again. So, one might suppose that shallow-water marine critters with hard shells would be the most common fossils, and in fact limestone composed mainly of identifiable fossils (eg coquina) is not uncommon. Indeed, limestones are largely biogenic, though much of the rock is no longer recognizable as fossils.

Compare this to, say, Tyrannosaurus rex: an uncommon animal that lived (and died) on dry land. Only rarely would a T. rex corpse be preserved: for example, if it got mired in a swamp or buried in a flood. Indeed, intact T. rex skeletons are very rare, and worth millions (in sales price and legal fees). But they certainly exist.

As geologists have gotten more skilled at identifying fossils, as fossils bring better prices, and as more mines and quarries expose buried rock to view, more tiny, fragile, old and ephemeral biologic artifacts are found each year -- such as dinosaur eggs, some with embryos inside, and even imprints of the skin of feather-covered dinos -- both of which are now common (if pricy) at major fossil trade shows. A decent-quality egg-clutch will go for US$10,000 and up. Common, fully-articulated (but small) dino skeletons start at around $500 wholesale -- ranging up into the millions for rare, beautifully-preserved and prepared, museum-quality specimens.

So, if a dinosaur civilization had existed and reached even a modest level -- say, if dinos had once made stone tools in, let's say, present-day Argentina -- it seems almost certain that some tools would have been found along with their skeletons (as have been their gastroliths or gizzard-stones, not to mention footprints and fossil dung (coprolites), all of which are fairly common). This assumes that the tools would have been recognized, but there's no reason to suppose that a stone axe or spearhead for a dino would be shaped much differently than for a human. Bigger, maybe....

One might argue that, if stone tools were found in a dino-dig, they would be rejected as contamination or a practical joke. There were similar arguments about whether Paleo-Indians had actually hunted mammoths. Doubts were dispelled by finding spear-points imbedded in mammoth fossils, as well as by identifying unambiguous tool marks (from butchering) on mammoth bones. Vertebrate paleontology is a very small field: if there were Cretaceous bones with butchering-marks, someone would have noticed.

My conclusion is that it's barely possible that relics of a small stone-age dino civilization could remain undiscovered in some poorly- known part of the world. A larger or more-advanced civilization would have been discovered by now, at least to the extent of rumors over the campfire or at geologic watering-holes. If such rumors exist, I haven't heard them, and I talk with fossil-hunters regularly.

Similar arguments would apply to hypothetical earlier (Eurypterid? Edocarian?) civilizations, though it would be easier to hide a small older culture -- the quality of the fossil record does get poorer as it gets older. But we do have identifiable fossils back to something like 4 bybp, or some 500 million years after the planet cooled down enough to reset the geochronometers. And there really aren't any land animals before the dinosaurs that look at all likely as candidates for sapience.

An extinct sapient but non-toolmaking culture, such as has been hypothesized for present-day dolphins or whales, would leave few if any traces. Biologists no longer think that marine mammals have near-human level intelligence, but there's no doubt that dolphins are very bright animals, with a well-developed social structure (or culture) that parents teach to young dolphins. But this is true for all higher animals, which is why captive-bred animals seldom survive in the wild -- they haven't been taught their culture. Even snails have to be taught how to survive in the wild. A marine biologist recently started a conch survival school: he puts a sacrificial conch into a cage with a lobster, with his class of juvenile conchs surrounding the cage.

"The poor conch was eaten while his buddies watched. They heard the screams and smelled the blood," the researcher said. After about a week of that, the young conchs learn to bury themselves in the sand. [note 2]

So culture and intelligence, like most animal traits, come on a sliding scale: even conchs have some. But I think it's fair to say that no widespread nonhuman culture on Earth has ever reached Paleolithic levels of tool-making -- even though found tool-use is not uncommon (as when monkeys use grass-stalks to catch termites).

A brief visit or a small, failed colony by hypothetical alien visitors can't be ruled out, but a larger settlement would have been found by now, I think. Geologists read science fiction too, and a weird find would get talked about even if it never got published. For that matter, think what an Arcturan thu'up bowl or bhirr bottle would bring at auction at Christies!

Footnotes

1) Perhaps blasted into extinction with (iridium-bearing) asteroids by paranoid Arcturans. Or maybe they did themselves in with BIG nukes and iridium powerguns. [back to main text]

2) From Raphael Carter's always-interesting Honeyguide. [back to main text]

© Peter D Tillman.
Pete Tillman is a Consulting Geologist, based in Arizona, USA.

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