When Charles Darwin stepped onto the Royal Navy’s HMS Beagle on December 27, 1831, as a naturalist invited to accompany the crew on its mission to map the coastal waters of southern South America and then circumnavigate the globe with a famous five-week stopover on the Galapagos Islands, common wisdom agreed that the oldest fossils on earth dated to the Cambrian Period, 541 million years ago. The Ediacaran biota, tiny organisms 1 centimeter to 2 centimeters long (0.39–0.78 inches) thought to be the forefathers of invertebrates such as jellyfish and worms, may change that. The fossils are named for Australia’s Ediacara Hills, where they were first uncovered in the late 1940s. Retellack says they may date back another hundred million years and are “more similar in appearance and preservation to lichens and other microbial colonies of biological soil crusts … than marine animals, or protists,” the last being land-based organisms such as yeasts that live together in bunches and don’t build body tissues.3
It’s a minority view, but not a minority of one. Although most paleontologists do consider the Ediacaran biota to be water babies, an adventurous few think Retallack may just be onto something. “It’s kind of a radical idea, but the fact is we don’t know,” says Paul Knauth of the School of Earth and Space Exploration at Arizona State University, adding “that means that the Earth was not a barren land surface until about 500 million years ago, as a lot of people have speculated.” On the other hand, some, like Virginia Tech geobiolgist Shuhai Xiaom, say that accepting Retallack’s theory means accepting the idea that a species could have adapted to living both on dry land and in and under a very salty sea, at best an “unlikely prospect.”4
Time will tell who’s right, but for now let’s agree that regardless of the starting point, eventually more complex life did arise in and climb out of the ocean. Most had teeth, but even some of those who remained in the sea did, too. Fish, for example, may not get cavities, but some, such as piranha, tiger fish, and of course Jaws the shark, have impressive and efficient choppers. Other sea dwellers have other dentition, sometimes multiple, like the 25,000 teeth on a snail’s tongue; sometimes really powerful, like the spotted eagle ray’s, which can crush shellfish; sometimes nightmare strange, like the eel’s pharyngeal teeth that swing forward from inside its throat to grab and drag in prey for dinner.5 And exceptions being what proves the rule, you may take a moment to consider the blue whale (Balaenoptera musculus), up to 98 feet long and weighing up to 191 tons (more than 380,000 pounds), the largest animal living on earth (perhaps the largest-ever denizen of the planet) which has no teeth at all and thus dines exclusively on tiny shrimp-like krill that it takes in with seawater and then filters through dental plates that look something like an open lady’s fan with no silk or paper between the spokes.
So, around 400 million years ago, when the ancestors of all vertebrates climbed, slithered, or walked up onto dry land—or, in Retallack’s view, climbed, slithered, or walked back onto dry land6, many came with a full set of teeth or the prospect of developing them. True, some dinosaurs were toothless and mashed up their food with their gums. But many weren’t and didn’t. The impressive T. Rex had about fifty teeth, some twelve inches long and all strong enough to crush bone. Over the next hundreds of million years, even as the dinosaurs with and without teeth died, other animals survived and held onto their ivories.
With one obvious exception, some important descendants of this one: Archaeopteryx.
In 1861, archeologists in Southern Germany came upon the fossil of a bird-like dinosaur that they named Archaeopteryx from the Greek words arkhaios- meaning ancient and pteryx meaning wing. The idea was that this creature might be a transition point between dinosaurs with feathers and modern birds. And that possibility pointed paleontologists to the idea that modern birds and crocodilians are the descendants of archosaurs, a group of flesh-eating really big lizards that hung around for a while after other dinosaurs went extinct 66 million years ago.7 As usual, the archosaurs’ name itself tells you what they were. Arkhos is Greek for ruler; sauros is Greek for lizard, so archosaurians are beasts who survived to become the ruling lizards. With teeth.
At first, the archosaurians’ descendants, both birds and crocodiles, also had teeth. Today, except for the “egg tooth” (more a bone than a tooth) that enables baby birds, snakes, turtles, and crocodiles to break out of the shell and into the world, the only thing that remains of a bird’s teeth is an effectively evolved biting and crushing instrument: the beak.
For Charles Robert Darwin, the beak was all-important.
In the Galapagos, Darwin did not simply wake up one morning shouting, “Eureka! Evolution!” No, he went about his business, first in South America and then in the islands, collecting birds he called finches (most weren’t) which he killed and carted back to England, where he brought them to ornithologists, who agreed that the Galapagos birds’ beaks were different from those of similar birds from South America. “Seeing this gradation and diversity of structure in one small, intimately related group of birds,” Darwin wrote in the second edition of The Voyage of the Beagle (1845), “one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.”8 In other words, over time, while the birds were isolated on the islands, their beaks had adapted naturally from the graceful long and pointy ones South American birds stuck into trees to extract fluid and insects to the short and sturdy ones required to crack nuts and prosper on the Galapagos.
And that was the Eureka! moment: natural selection.9
Of course, important as it was, that moment was not the last chance for discovery. More than 150 years after Darwin’s visit, the Galapagos Islands remain a place where strange and wonderful creatures flourish, waiting to teach lessons about our world. In the spring of 2016, Aaron Pomerantz, the entomologist/biologist creator of The Next Gen Scientist blog, made the trip and met one fascinating lizard: “On my recent trip to the Galápagos, I could hardly contain my joy at seeing some of the animals that, until then, I had only seen on TV. The marine iguanas were one of my favorites, blending in with the lava rocks, not giving a care in the world about the human activity around them. But I noticed them doing something interesting — every few minutes, an iguana would let out a big old sneeze, spraying out water up to several feet. But why are these lava-looking reptiles firing out snot rockets? To start, it’s interesting to note that the marine iguanas, Amblyrhynchus cristatus, are the only lizards in the world to adapt to a marine lifestyle, as they swim out into the ocean to forage on algae. Due to this feeding behavior at sea, understandably the iguanas ingest not only algae, but also a lot of extra salt (mainly sodium chloride along with some potassium). In order to deal with this excess amount of salt, the marine iguanas have a unique solution. A book on iguana biology summed it up pretty nicely: To cope with this high-salt diet, the marine iguana uses large cranial salt glands that excrete most of the sodium, potassium, and chloride ingested; forceful expulsion of the secreted fluid is the cause of the dramatic snorting and sneezing observed in these animals. So it turns out that violent sneezing is actually a pretty clever evolutionary adaptation to dealing with what would otherwise be a fatal salt overload! Not only did we get to see the world’s only marine lizards, but I got to learn something new by getting iguana snot sprayed on me.”10
Today the Pacific Ocean still has more than one treasure-filled island waiting for new Darwins to study and preserve, such as the four-island Palymyra archipelago west of the Galapagos. In 2016, the Nature Conservancy called for naturalists to exercise what may be the “last chance to truly protect [this] intact Pacific atoll ecosystem.” Field biologists call it an environmental treasure of wildlife, plants, and fish that are gone or disappearing elsewhere. You might call it paradise: an uninhabited tropical island, where great swarms of rare, colorful birds gather to nest, where tall palms, drop coconuts on sandy beaches, and where schools of large fish laze through warm lagoons. Palmyra is a privately owned American island in the central Pac
ific, 1,000 miles south of Hawaii. Except during World War II, when the US Navy maintained a base there, it’s never really been occupied. Species that have been hunted to local extinction elsewhere flourish on Palmyra—frigate birds, enormous land crabs, rare trees, marine corals, and fish. The atoll has been mostly in the possession of one family for almost a century; now, the Nature Conservancy is trying to buy Palmyra to keep it and its biological riches protected forever. The environmental group plans to raise $37 million dollars to pay for the atoll and establish a fund to maintain it for conservation and research, as well as a small scale ecotourism site. In 2000, National Geographic Radio Expedition NPR’s Alex Chadwick reported on his charter flight to paradise, where he discovered that “even here there are many challenges, including the dubious experience of landing a small plane in a tropical storm on an old, unpaved Navy runway. The island is flourishing indeed, thanks in large measure to the heavy rainfall. The expedition finds biologists from the U.S. Fish and Wildlife Service recording extraordinary bird colonies, coral beds that are far richer than those found in Hawaii or the Caribbean, and schools of large, rare fish that may be impossible to still find elsewhere.” Chadwick concludes his two-part series on Palmyra with further reports on the rainy island’s birds, wildlife, and schools of large tropical fish. He also talks about the efforts to preserve the atoll. Alterations to the atoll made by the Navy present real problems for the health of the atoll’s central lagoons, and weather and infrastructure will make difficulties for ecotourism, but if the Nature Conservancy can push ahead with its ambitious plans, it may yet preserve a last tropical atoll in something like a state of Eden.11
HOW OLD IS YOUR EON?12
Geologists measure the age of the earth in Eons, which are subdivided into Eras, which are subdivided into Periods and then Epochs and finally Ages. The names of these time spans come from the Greek, as you can tell as soon as you see -zoic from the Greek word zoion meaning animal tacked on to the end. For example, add -zoic to the Greek phaneros meaning visible and you get the Phanerozoic Eon, the “time of visible animals,” which is to say, the time of us. And so on.
This list shows the geologic time scale, a scheme invented by British geologists to measure the earth’s time periods. In 1841, John Phillips published the first such chart, standardizing earth’s history based on the types of fossils found in each era.13 It begins at the top with the latest, our current moment of supremacy, and then goes backwards all the way to the Hadean Era, the chaotic flash in the universe when the earth was formed. The common Greek prefixes cen- from kainos, meso- and paleo- translate to late, middle and early; eo- means earliest, i.e., dawn, and neo- means new. As for the rest of the names here, the truly curious may wish to check out their fuller meaning and history in the wonderfully expansive Online Etymology Dictionary at http://etymonline.com/, which tells such linguistic tales as this: “Cambrian (adj.) 1650s. ‘from or of Wales or the Welsh,’ from Cambria, variant of Cumbria, Latinized derivation of Cymry, the name of the Welsh for themselves, from Old Celtic Combroges ‘compatriots.’ Geological sense (of rocks first studied in Wales and Cumberland) is from 1836.”
The Phanerozoic Eon (542 million years ago to the present)
The Cenozoic Era (63 million years ago to now), the time of “new” or “recent” animals, including us, comprises the current Quaternary Period and the preceding Neogene and Paleogene Periods, when mammals and man rose to dominate life on earth.
The Mesozoic Era (251 to 65 million years ago), the time of the “middle animals,” a name coined by Phillips in 1840, includes the Cretaceous, Jurassic, and Triassic Periods when mammals and birds appeared and then poof! the moment approximately 100 to 116 million years ago when all the birds on earth, descendants of well-toothed carnivorous dinosaurs, somehow evolved to lose the genes required for building teeth. The birds’ greatest achievement, however, was their surviving the mass extinction of all nonavian dinosaurs 65 million years ago, the catastrophic event that opened the door for the rise of the eventually-dominant mammals, most of whom would come to live on the continents just beginning to drift apart from their original configuration.
The Paleozoic Era (542 to 251 million years ago), the time of “ancient animals,” includes the Permian, Carboniferous, Devonian, Silurian, Ordovician, and Cambrian Periods when marine vertebrates—fish, seabirds, sea reptiles and sea-going mammals—were the prevailing life forms. Midway through this era, just short of 400 million years ago, the first four-limbed vertebrates, creatures who looked like lizards but were actually the ancestors of all mammals, shuffled out of the waters to live on land.14 (It is worth noting that not every marine mammal went this route. Many, if not all, such as seals, sea lions, whales, dolphins, porpoises, manatees, and walruses, traded front legs for flippers, while a careful examination of the skeleton shows both very tiny legs and remnants of hip bones way back in the animal’s body, structures that fit the modern definition of truly vestigial.)
The Precambrian Eon (4,600 to 542 million years ago)
The Proterozoic Era (2,500 to 542 million years ago), the time “before animals,” includes the Neo-, Meso-, and Paleoproterozoic Period, when the first multicell organisms, creatures still so preliminary that they lacked rigid skeletons or protective shells, appeared.15, 16
The Archean Era (4,000 to 2,500 million years ago), from the Greek arkhaios meaning “ancient” and arhhe meaning “beginning”, respectively, ancient and beginning, includes the Neo-, Meso-, Paleo-, and Eoarchean Periods, when the earth cooled and the continents were born.
The Hadean Era (4,600 to 4,000 million years ago), named for Hades, the Greek god of the underworld whose name is synonymous with Hell, which geologists suggest is as good a description as you are ever likely to find for the immediate post-Big Bang earth.
MISSING BONE & SURPLUS MOLARS
Your average modern hummingbird, the smallest living avian on earth, weighs about 4 grams (0.1428571 ounces). Our largest living bird, the ostrich, clocks in at nearly 350 pounds. Despite the difference in size, this pair has two important things in common. No, not wings and a backbone: a beak and innards that crush food as teeth might have done in earlier times.
In 1821, the French naturalist Geoffrey Saint-Hilaire set out to discover what happens as chicken embryos develop in the egg. Cracking shell after shell at different stages of the process, he found that some of the embryos had what looked like the beginnings of teeth. Saint-Hilaire published his findings, which were roundly dismissed by his contemporaries, but he turned out to be onto something important. In 2014, to find out why modern birds don’t have the teeth they should have inherited from the meat-eating archosaurs, a mystery that has defied science until now, University of California-Riverside biologist Mark Springer compared DNA from ancient bird fossils with that from today’s birds, looking for changes in the six genes that would have affected how birds form the outer layers of a tooth, the hard dental enamel and softer dentin underneath. What he found and reported in the journal Science was that “several inactivating mutations that are shared by all 48 bird species suggest[ing] that the outer enamel covering of teeth was lost around 116 million years ago.” In short, a bird’s toothless state is due to the inactivation of genes that once were vital but now appear to lie dormant in modern avian DNA.17 Whether his is true for other toothless archosaurian descendants such as turtles, armadillos, and sloths remains to be seen, but clearly the tooth-making genes are still alive and firing for the birds’ other living relatives, the closest being, as Springer notes, the American alligator.
Aha, you say, but we are not birds. We can’t fly, we don’t have feathers, and we didn’t lose our teeth. As a species, we have all the ones we started with. Our third molars—our wisdom teeth—are still with us and would be useful if we could accommodate them. The problem is that like the muscles around our ears that only some of us can wiggle, possibly as few as 10 percent of us have a jaw that’s large enough, one reason why the American Academy of General Dentistry has
decided to classify impacted wisdom teeth as the most common medical developmental disorder.18
Like the beaks on Darwin’s Galapagos finches, our jaws have adapted to our evolving life styles, this time by shrinking in size. Why? There are three possible explanations: 1.Diet. 2. Muscles. 3. Genes. The evidence suggests that #1 plus #2 equals a variety of #3.
As Darwin saw, over time our diet shifted from hard raw foods to softer beef, fish, poultry, cooked veggies, and grains. We chewed less vigorously. Exercising muscles doesn’t just make bigger muscles; it also helps to make stronger bones. So as human beings everywhere around the globe chewed less, they ended up with smaller jawbones. That explains why when Noreen von Cramon-Taubadel of the University of Kent (England) compared three hundred human jawbones from eleven different parts of the globe, she found this consistent pattern: people in agrarian societies whose diets were mainly plant foods had shorter but broader jaws than people who lived among meat-eaters. “Presumably the children growing up in these different situations have different chewing behavior,” she said. She concluded that the different shapes of the jaw were due not to group genetics but to how the children, one at a time, worked—or didn’t work—their jaw muscles while chewing their way through early life.19
Peter Brown of the University of New England (Maine) agrees. The proof, he notes, is pretty much right in front of our eyes in data from a 1950 study at Adelaide University (Australia) showing that “[w]hen Australian Aborigines were first encountered [by Europeans] they were famous for having very large teeth, large chewing muscles, and projecting faces.” But by mid-20th century, after adopting a Western diet, the Aborigines began to develop dental crowding. Then people with smaller jaws married or mated with other people with smaller jaws and produced children with smaller jaws whose third molars were still in place but now stuck in those smaller jaws. It’s a continuing problem for which Brown has a very practical remedy. “I am an anthropologist,” he says. “I tell my children to chew their food.”20
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