Teeth reveal a vast amount of information about the creatures that once used them. The strong and hard composition of teeth resists the ravages of time, making them especially valuable to archaeologists and paleontologists. From information about who was eating whom among dinosaurs, to the diets of our ancestors, to possible speaking ability in Neanderthals, teeth reveal valuable information. I’ll share some of those stories in this post.
What Were They Eating?
Giant Tyrannosaurus rex, or T-rex, had formidable teeth and could exert an extremely strong, bone-crushing bite force. Clearly a carnivore, this dinosaur was likely both an active predator and a scavenger. Characteristic T-rex puncture bite marks, and even embedded T-rex teeth, have been found in the bones of many dinosaurs that lived alongside these giants. Paleontologists have also found T-rex tooth marks on the lower legs and foot bones of other T-rex specimens – not the choicest meat morsels — suggesting that opportunistic scavenging, as well as cannibalism, was practiced.
The patterns of pits and scratches on the teeth of our extinct ancestors provide useful information in “dental microwear” analyses when they are compared to the diets of living species. Studies of early hominins in South Africa, Australopithecus sp., indicate that around 4 to 2 million years ago, some species predominantly ate fruits and leaves, whereas other species included grasses and seeds in their diets. Tooth enamel thickened over time, possibly as a response to eating more foods found on the ground, such as cereal grains with grit that could wear away enamel. Fossil animal bones with butchery marks dating to 2.6 million years old provide evidence that hominins were also eating meat.
Material that builds up on teeth, called dental calculus, can also provide information about diet. This residue can preserve the microscopic silica structures found in some plant tissues, called phytoliths. The chemistry of phytoliths means that they don’t decay with the rest of the plant, and this toughness makes them valuable to archaeologists. In the Andes Mountains, identification of phytoliths collected from the teeth of ancient mummies provides evidence of timing of domestication of certain plant foods.
Did Neanderthals Speak?
Neanderthals ruled Eurasia from around 400,000 to 40,000 years ago. In the past few decades, opinions of Neanderthals have moved from dull brutes to a recognition that they were quite similar to us, with fiber technology, symbolic behavior, and a varied diet. (Highly recommended: the book “Kindred – Neanderthal Life, Love, Death and Art” by Rebecca Wragg Sykes). One of many puzzling questions: could Neanderthals speak? In a recent article titled “Neanderthals Like Us”, evidence related to teeth and speaking ability is described (Frayer and Radovčić, 2022).
Researchers set out to determine whether Neanderthals used a dominant hand in their daily tasks by examining scratches on their teeth. Right-handedness is common in humans, with right-handers dominating over left-handers in every living human population. This trait reflects the two cerebral hemispheres of the brain, with each side specialized for different tasks, known as lateralization. The function or activity that occurs on one side of the body in preference to the other side is associated with language capacity. Although other primates have varying degrees of lateralization, only humans show the high frequency of a dominant right hand.
Striations that appear exclusively on the lip side of incisor and canine teeth are produced when a stone tool scrapes a tooth, or when something like an animal hide is held in the teeth while a tool is scraped across the object. By studying the angles of the scratch marks with optical and scanning electron microscopes, researchers can determine if the individual is right-handed or left-handed. Researchers studied Neanderthal fossils from many sites in Europe and discovered that right-handedness dominates. It also turns out that the typical pattern found in living humans — with a ratio of right- to left-handedness of 9:1– is also found in Neanderthals. This information is a solid piece of evidence suggesting that these ancient relatives could speak. Fascinating!
Looking Back into a Dim Past
The appearance of jaws was a major evolutionary development in the history of vertebrates. Jawless fish were the earliest vertebrates. The gill arches of the fish eventually evolved into upper and lower jaws, and when these were lined with teeth, many adaptations could develop for types and processing of food. Teeth probably evolved from modified fish scales. The earliest teeth were simple, single-rooted pegs or blades. These types of teeth worked splendidly for tens of millions of years, including for the dinosaurs. Some dinosaur species had as many as five hundred pegs or leaf-like teeth in the mouth – highly efficient for processing the amount of food needed to fuel their enormous bodies.
When placental mammals arrived on the world scene (i.e., those with young that are born at a relatively advanced stage of development), a new basic formula had evolved for teeth. Many mammals have three incisors, a canine, four premolars, and three molars on each side in both upper and lower jaws. The incisors (front teeth) have single roots and are adapted for nipping; canines are also usually single-rooted. Premolars and molars show complex structures, including deep roots, and extensive adaptations of these teeth provided a foundation for the expansion and impressive success of mammals through history.
Hominin fossils dating back to 7 million years ago share with humans a pattern of two pairs of incisors, one pair of canines, two pairs of premolars, and three pairs of molars on each side of the jaw. Over time there were many changes in teeth that reflected diet and food processing. These included transitions from thin to very thick enamel, and from very large canines to the mild ones found in Homo sapiens today.
Our knowledge of the evolution of mammals through time is based on the details displayed in molars. Fossil fragments of jaws containing teeth make it possible to reach conclusions about mammal relationships and place in evolutionary history. I have heard that if all mammals except humans were extinct, and represented only by fossil teeth, their basic classification would probably be essentially the same as the classification we know now, which is based on knowledge of the complete anatomy of these mammals. There other good reasons to study mammal teeth. As a vertebrate paleontologist once told me: the paleo-types who study mammals have a big advantage because the teeth they study can be carried around easily in a shoe box. MUCH simpler than studying the enormous bones of dinosaurs in a laboratory!
One more tale to address an intriguing question. Why do so many people have crowded, crooked teeth and need to have their 3rd molars (wisdom teeth) pulled? Looking back in time, it turns out the jaws of Homo sapiens have evolved faster than the teeth. Once our ancient relatives started to eat softer, less gritty foods and to cook meat, the need for big, powerful jaws was no longer necessary. Mutations popped up that weakened the jaw, and the bones began to shrink. The genes that control teeth, however, didn’t get the same message. Now, our modern sets of teeth are crowded into smaller jaws. Interesting stuff! And there are many more tales that teeth can tell!
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Frayer, D. W. and D. Radovčić, 2022, Neanderthals Like Us, Scientific American, February, 5 -55.
Photo of complete Tyrannosaurus rex skull, American Museum of Natural History. https://commons.wikimedia.org/wiki/File:Tyrannoskull.jpg
Photo of comparison of modern and Neanderthal from the Cleveland Museum of Natural History, 2008. https://commons.wikimedia.org/wiki/File:Sapiens_neanderthal_comparison.jpg
Photo of right side of jaw with 2nd and 3rd molars of American Mastodon Mammut americanum, on display at the State Museum of Pennsylvania. Late Pleistocene in age (Wikipedia) https://commons.wikimedia.org/wiki/File:Mastodon_teeth.jpg