Most of the evidence of human evolution comes from the study of the dead. To obtain as much information as possible from the remains of once-living creatures, one must understand the processes that occur after death. This is where taphonomy comes in (Figure 7.2.1). Taphonomy can be defined as the study of what happens to an organism after death (Komar and Buikstra 2008, 189; Stodder 2008). It includes the study of how an organism becomes a fossil. However, as you’ll see throughout this book, the majority of organisms never make it through the full fossilization process.
Definition: taphonomy
The study of what happens to an organism after death.
Taphonomy is extremely important in biological anthropology, especially in subdisciplines like bioarchaeology (study of human remains in the archaeological record) and zooarchaeology (the study of faunal remains from archaeological sites). It is so important that many scientists have recreated a variety of burial and decay experiments to track taphonomic change in modern contexts. These contexts can then be used to understand the taphonomic patterns seen in the fossil record (uniformitarianism at work; see Reitz and Wing 1999, 122–141).
Figure \(\PageIndex{1}\): Taphonomy focuses on what happens to the remains of an organism, like this coyote, after death.
An example of taphonomic study in action comes from Iron Age England (circa 750 B.C.E. to 43 C.E.). The Iron Age in southern England has a rich and diverse burial record. Since there is no universal or “normative” burial rite, taphonomic study is crucial to figuring out what cultural and ritual processes were operating at this time. Suddern Farm, an Iron Age site in Hampshire, England, includes a cemetery as well as isolated burials outside the cemetery and burials in ritual pits accompanied by the remains of feasting (King 2014, 187).
One of these pit burials, identified as P78, presents an interesting taphonomic case. He was a young adult male approximately 18–25 years old at the time of his death. His remains showed multiple sharp-force and penetrating wounds acquired around the time of his death. There were also carnivore tooth marks on the head of his right femur. These tooth marks provide an important taphonomic clue about how this individual was treated after death. P78 not only met a violent end, but his body was also allowed to lie exposed to the elements and animal scavengers before burial. If an individual is buried immediately, or protected prior to burial, animals do not have the opportunity to gnaw on the bones and flesh (Komar and Buikstra 2008, 196–200). Most Iron Age burials from this site were buried without exposure to scavengers, so P78 stood out as different. He was also buried in a pit when the majority of individuals at Suddern Farm were buried in the cemetery. He was not treated in the same way as the other dead in his community (King 2010, 136–139), and it is useful for us to consider why. P78 may represent a special ritual burial associated with violence or punishment. By better understanding the processes that occur in and to the body after death, we can reconstruct the cultural, biological, and geologic processes that affect remains.
Taphonomic analysis can also give us important insights into the development of complex thought and ritual in human evolution. In Chapter 11, you will see the first evidence of recognized burial practices in hominins. Taphonomy helped to establish whether these burials were simply the result of natural processes or intentionally constructed by humans (Klein 1999, 395; Straus 1989). Deliberate burials often include the body placed in a specific position, such as supine (on the back) with arms crossed over the chest or in a flexed position (think fetal position) facing a particular direction. If bones have evidence of a carnivore or rodent gnawing on them, it can be inferred that the remains were exposed to scavengers after death (as with P78 above). Going back further in time, taphonomic evidence may tell us how our ancestors died. For instance, several australopithecine fossils show evidence of carnivore tooth marks and even punctures from saber-toothed cats, indicating that we weren’t always the top of the food chain. The Bodo cranium, a Homo erectus cranium from Middle Awash Valley, Ethiopia, shows cut marks made by stone tools, indicating an early example of possible defleshing activity in our human ancestors (White 1986).
Preservation of Biological Remains
As we can only study the evidence that gets left behind in the fossil and archaeological record, preservation is a key topic in anthropological research. This chapter is concerned with the fossil record; however, there are other forms of preserved remains that provide anthropologists with information about the past. You’ve undoubtedly heard of mummification, likely in the context of Egyptian or South American mummies. However, bog bodies and ice mummies are further examples of how remains can be preserved in special circumstances. It is important to note that fossilization is a process that takes much longer than the preservation of bog bodies or mummies.
The most important element in the preservation of remains is a stable environment. This means that the organism should not be exposed to significant fluctuations in temperature, humidity, and weather patterns. Changes to moisture and temperature cause the organic tissues to expand and contract repeatedly, which will eventually cause microfractures and break down (Stodder 2008). Wetlands are a particularly good area for preservation because they allow for rapid permanent burial and a stable moisture environment. That is why many fossils are found in and around ancient lakes and river systems.
Bog bodies are good examples of wetland preservation. Peat bogs are formed by the slow accumulation of vegetation and silts in ponds and lakes. The conditions are naturally anaerobic (without oxygen). Much of the bacteria that causes decay is already present in our gut and can begin the decomposition process shortly after death during putrefaction (Booth et al. 2015). Since oxygen is necessary for the body’s bacteria to break down organic material, the decay process is significantly slowed or halted in anaerobic conditions. Throughout western Europe in the Bronze and Iron Ages, individuals were buried in these bogs. When they were found thousands of years later, they resembled recent burials. The hair, skin, clothing, and organs were exceptionally well preserved in addition to the bones and teeth (Eisenbeiss 2016; Ravn 2010). Preservation was so good in fact that archaeologists could identify the individuals’ last meals and re-create tattoos found on their skin.
Definition: bog bodies
Bodies preserved in the peaty, waterlogged bogs, typically in northern Europe.
Definition: anaerobic
An oxygen-free environment.
Extreme cold can also halt the natural decay process. A well-known ice mummy is Otzi, a Copper Age man found in the Alps (Vidale et al. 2016). As with the bog bodies, his hair, skin, clothing, and organs were all well preserved. Recently, archaeologists were able to identify his last meal (Maixner et al. 2018). It was high in fat, a necessity when trying to survive in the extreme cold.
Definition: ice mummy
A specimen of human remains that is naturally mummified by extreme low temperatures.
In the Andes, ancient peoples would bury human sacrifices throughout the high peaks in a sacred ritual called Capacocha (Wilson et al. 2007). The best-preserved mummy to date is called the “Maiden” or “Sarita” because she was found at the summit of Sara Sara Volcano. Her remains are over 500 years old, but she still looks like the 15-year-old girl she was at the time of her death, as if she had slept for 500 years. A Ripina Van Winkle, if you will (Reinhard 2006).
Finally, arid environments can also contribute to the preservation of organic remains. As discussed with waterlogged sites, much of the bacteria that is active in breaking down bodies is already present in our gut and begins the putrefaction process shortly after death. Arid environments deplete organic material of the moisture that putrefactive bacteria need to function (Booth et al. 2015). When that occurs, the soft tissue like skin, hair, and organs can be preserved. It is similar to the way a food dehydrator works to preserve meat, fruit, and vegetables for longterm storage. There are several examples of arid environments spontaneously preserving human remains, including catacomb burials in Austria and Italy (Aufderheide 2003, 170 and 192–205).
Fossilization
Though much of our knowledge about human evolution relies on evidence derived from fossils, it is important to realize that fossils only represent a tiny fraction of creatures that existed in the past. It would be impossible to calculate the exact amount, but the vast majority of animals that once lived do not make it into the fossil record. The reason for such a small number is that it is extremely difficult for an organism to become a fossil. There are many stages involved and if the process is disturbed at any of the stages, the organism will fail to become a fossil. After all, organisms are set up to deteriorate after we die. Bacteria, insects, scavengers, weather, and environment all aid in the process that breaks down organisms so their nutrients, molecules, and elements can be returned to Earth to maintain ecosystems (Stodder 2008). Fossilization, therefore, is the preservation of an organism against these natural decay processes (Figure 7.2.2).
Definition: fossilization
The process by which an organism becomes a fossil.
Figure \(\PageIndex{2}\): A simplified illustration of the fossilization process from the organism’s death to its eventual discovery by paleoanthropologists.
For fossilization to occur, several important things must happen. First, the organism must be protected from things like bacterial activity, scavengers, and temperature and moisture fluctuations. Since soft tissue like organs, muscle, and skin are more easily broken down in the decay process, they are less likely to be preserved except in rare circumstances. Bones and teeth, however, last much longer and are more likely to be preserved in the fossil record (Williams 2004, 207).
The next important step in the fossilization process is sediment accumulation. The sediments cover and protect the organism from the environment. They, along with water, provide the minerals that will eventually become the fossil (Williams 2004, 31). Sediment accumulation also provides the pressure needed for mineralization to take place. Lithification is when the weight and pressure of the sediments squeeze out extra fluids and replace the voids, that appear in the remains as they decay, with minerals from the surrounding sediments. Finally, we have permineralization. This is when the organism is fully replaced by minerals from the sediments. A fossil is really a mineral copy of the original organism (Williams 2004, 31).
Definition: lithification
The process by which the pressure of sediments squeeze extra water out of decaying remains and replace the voids that appear with minerals from the surrounding soil and groundwater.
Definition: permineralization
When minerals from water impregnate or replace organic remains, leaving a fossilized copy of the organism.
Types of Fossils
Plants
Plants make up the majority of fossilized materials. One of the most common plants existing today, the fern, has been found in fossilized form many times. Other plants that no longer exist or the early ancestors of modern plants come in fossilized forms as well. It is through these fossils that we can discover how plants evolved and learn about the climate of Earth over different periods of time.
Another type of fossilized plant is petrified wood. This fossil is created when actual pieces of wood—such as the trunk of a tree—mineralize and turn into rock. Petrified wood is a combination of silica, calcite, and quartz, and it is both heavy and brittle. Petrified wood can be colorful and is generally aesthetically pleasing because all the features of the original tree’s composition are illuminated through mineralization (Figure 7.2.3). There are a number of places all over the world where petrified wood “forests” can be found, but there is an excellent assemblage in Arizona, at the Petrified Forest National Park. At this site, evidence relating to the environment of the area some 225 mya is on display.
Definition: petrified wood
A fossilized piece of wood in which the original organism is completely replaced by minerals through petrifaction.
Figure \(\PageIndex{3}\): An exquisite piece of petrified wood.
Human/Animal Remains
We are more familiar with the fossils of early animals because natural history museums have exhibits of dinosaurs and prehistoric mammals. However, there are a number of fossilized hominin remains that provide a picture of the fossil record over the course of our evolution from primates. The term hominins includes all human ancestors who existed after the evolutionary split from chimpanzees and bonobos, some six to seven mya. Modern humans are Homo sapiens, but hominins can include much earlier versions of humans. One such hominin is “Lucy” (AL 288-1), the 3.2 million-year-old fossil of Australopithecus afarensis that was discovered in Ethiopia in 1974 (Figure 7.2.4). Until recently, Lucy was the most complete and oldest hominin fossil, with 40% of her skeleton preserved (see Chapter 9 for more information about Lucy). In 1994, an Australopithecus fossil nicknamed “Little Foot” (Stw 573) was located in the World Heritage Site at Sterkfontein Caves (“the Cradle of Humankind”) in South Africa. Little Foot is more complete than Lucy and possibly the oldest fossil that has so far been found, dating to at least 3.6 million years (Granger et al. 2015). Through tedious excavation, the specific ankle bones of the fossil were extricated from the matrix of concrete-like rock, revealing that the bones of the ankles and feet indicate bipedalism (University of Witwatersrand 2017).
Both the Lucy and Little Foot fossils date back to the Pliocene (5.8 to 2.3 mya). Older hominin fossils from the late Miocene (7.25 to 5.5 mya) have been located, although they are much less complete. The oldest hominin fossil is a fragmentary skull named Sahelanthropus tchadensis, found in Northern Chad and dating to circa seven mya (Lebatard et al. 2008).
The fossils of animals can be simple or complex, from worms to mammals. The fossils of primates provide information regarding the backstory of humankind. It is through the discovery, dating, and study of primate and early hominin fossils that we find physical evidence of the evolutionary timeline of humans. Without a complete cranium (or other fossilized remains), it is difficult to tell exactly what was going on in the fossil record. Only a small number of living things will ever become fossilized. Furthermore, it is reasonable to assume that of the existing fossilized remains, many remain hidden in glaciated rock, in caves, or in the ground. (See “Special Topic: Cold Case Naia” for a particularly interesting cave discovery.)
Amber
Amber is the fossilized sap of coniferous trees. Sometimes pieces of amber contain inclusions such as air bubbles or insects that become trapped in the sap (Figure 7.2.5a). This beautiful fossil comes in a variety of colors from light gold to orange red to even green. For this reason, amber is frequently polished to a high luster and used in jewelry (Figure 7.2.5b). Raw Baltic amber is also known as succinite and can be over 40 million years old. It comes from the cold Baltic region of northern Europe. Baltic amber is often worn for pain relief by teething infants or individuals with arthritis because succinic acid is released when warmed by body heat. The notoriety of amber increased significantly when it was featured in the highly fictionalized Jurassic Park film franchise. In the film, they were able to extract dinosaur DNA from the blood inside a fossilized mosquito. Rest assured, at the time of this writing, amber is not being used as the genetic basis for the regeneration of extinct dinosaurs, although the recent discovery of a tick that fed off of dinosaur blood that is trapped in amber has renewed interest in the idea (Pickrell 2017).
Figure \(\PageIndex{5}\): a) A piece of Baltic amber with an ant trapped inside.; b) A few amber pieces that have been turned into beautiful pendants.
Asphalt
Asphalt, a form of crude oil, can also yield fossilized remains. Asphalt is commonly referred to in error as tar because of its viscous nature and dark color. A famous fossil site from California is La Brea Tar Pits in downtown Los Angeles (Figure 7.2.6a). In the middle of the busy city on Wilshire Boulevard, asphalt (not tar) bubbles up through seeps (cracks) in the sidewalk. The La Brea Tar Pits Museum provides an incredible look at the both extinct and extant animals that lived in the Los Angeles Basin 40,000–11,000 years ago. These animals became entrapped in the asphalt during the Pleistocene and perished in place. Even today, in several directions from the museum, small invertebrates such as worms and insects are still being entrapped as the asphalt seeps up from the ground. Ongoing excavations have yielded millions of fossils, including megafauna such as American mastodons and incomplete skeletons of extinct species of dire wolves, Canis dirus, and the saber-toothed cat, Smilodon fatalis (Figures 7.2.6b and 7.2.6c). Fossilized remains of plants have also been found in the asphalt. Between the fossils of animals and those of plants, paleontologists have a good idea of the way the Los Angeles Basin looked and the climate in the area many thousands of years ago.
Definition: megafauna
Large prehistoric animals, such as mammoths and mastodons, that may have been hunted to extinction by people around the world.
Figure \(\PageIndex{6}\): a) This is a recreation of how animals tragically came to be trapped in the asphalt lake at the La Brea Tar Pits; b) A dire wolf (C. dirus) found at the La Brea Tar Pits; c) The fearsome jaws of the saber-toothed tiger (Smilodon fatalis) found at the La Brea Tar Pits.
Igneous Rock
Most fossils are found in sedimentary rock. This type of rock that has been formed from deposits of minerals over millions of years in bodies of water on Earth’s surface. Some examples include shale, limestone, and siltstone. Sedimentary rock typically has a layered appearance. However, fossils have been found in igneous rock as well. Igneous rock is volcanic rock that is created from cooled molten lava. It is rare for fossils to survive molten lava, and it is estimated that only 2% of all fossils have been found in igneous rock (Ingber 2012). Part of a giant rhinocerotid skull dating back 9.2 mya to the Miocene was discovered in Cappadocia, Turkey, in 2010. The fossil was a remarkable find because the eruption of the Çardak caldera was so sudden that it simply dehydrated and “baked” the animal (Antoine et al. 2012).
Trace Fossils
Depending on the specific circumstances of weather and time, even footprints can become fossilized. Footprints fall into the category of trace fossils, which includes other evidence of biological activity such as nests, burrows, tooth marks, shells. When you consider how quickly our footprints on the ground or in sand disappear, you must also realize how rare it is that footprints can become fossilized. A well-known example of trace fossils are the Laetoli footprints in Tanzania (Figure 7.2.7). (You can read more about the Laetoli footprints in the Special Topics box at the end of this section.)
Definition: trace fossils
Fossilized remains of activity such as footprints.
Figure \(\PageIndex{7}\): Just a few of the early hominin footprints that fossilized at Laetoli.
Other fossilized footprints have been discovered around the world. At Pech Merle cave in the Dordogne region of France, archaeologists discovered two fossilized footprints. They then brought in indigenous trackers from Namibia to look for other footprints. The approach worked as many other footprints belonging to as many as five individuals were discovered with the expert eyes of the trackers (Pastoors et al. 2017). These footprints date back 12,000 years (Granger Historical Picture Archive 2018).
Some of the more unappealing but fascinating trace fossils are bezoars and coprolite. Mary Anning found bezoars, or hard, concrete-like substances in the intestines of fossilized creatures. Bezoars start off like the hairballs that cats and rabbits accumulate from grooming but become hard, concrete-like substances in the intestines. If an animal with a hairball dies before expelling the hairball mass and the organism becomes fossilized, that mass becomes a bezoar.
Definition: bezoars
Hard, concrete-like substances found in the intestines of fossil creatures.
Figure \(\PageIndex{8}\): An extremely large (and yet somehow endearing) coprolite named “Precious”.
Anning also found coprolite, or fossilized dung. The Dean of Westminster, geologist and paleontologist William Buckland (1784–1856), first recognized the value of coprolite, but it was Anning who provided him with specimens. One of the best collections of coprolites is affectionately known as the “Poozeum.” The collection includes a huge coprolite named “Precious” (Figure 7.2.8). Coprolite, like all fossilized materials, can be in matrix—meaning that the fossil is embedded in secondary rock. As unpleasant as it may seem to work with coprolites, remember that the organic material in dung has mineralized or has started to mineralize; therefore, it is no longer soft and is generally not smelly. Also, just as a doctor can tell a lot about health and diet from a stool sample, anthropologists can glean a great deal of information from coprolite about the diets of ancient animals and the environment in which the food sources existed. For instance, 65 million-year-old grass phytoliths (microscopic silica in plants) found in dinosaur coprolite in India revealed that grasses had been in existence much earlier than scientists initially believed (Taylor and O’Dea 2014, 133).
Definition: coprolite
Fossilized dung.
Definition: in-matrix
When a fossil is embedded in a substance, such as igneous rock.
Pseudofossils
Figure \(\PageIndex{9}\): A beautiful example of dendrites, a type of pseudofossil. It’s easy to see how the black crystals look like plant growth.
Pseudofossils are not to be mistaken for fake fossils, which have vexed scientists from time to time. A fake fossil is an item that is deliberately manipulated or manufactured to mislead scientists and the general public. In contrast, pseudofossils are not misrepresentations but rather misinterpretations of rocks that look like true fossilized remains (S. Brubaker, personal communication, March 9, 2018). Pseudofossils are the result of impressions or markings on rock, or even the way other inorganic materials react with the rock. A common example is dendrites, the crystallized deposits of black minerals that resemble plant growth (Figure 7.2.9). Other examples of pseudofossils are unusual or odd-shaped rocks that include various concretions and nodules. An expert can examine a potential fossil to see if there is the requisite internal structure of organic material such as bone or wood that would qualify the item as a fossil.
Definition: pseudofossils
Natural rocks or mineral formations that can be mistaken for fossils.
Special Topic: Laetoli Footprints
In 1974, British anthropologist Mary Leakey discovered fossilized animal tracks at Laetoli (Figure 7.2.10), not far from the important paleoanthropological site at Olduvai Gorge in Tanzania. A few years later, a 27 meter trail of hominin footprints were discovered at the same site. These 70 footprints, now referred to as the Laetoli Footprints, were created when early humans walked in wet volcanic ash. Before the impressions were obscured, more volcanic ash and rain fell, sealing the footprints. These series of environmental events were truly extraordinary, but they fortunately resulted in some of the most famous and revealing trace fossils ever found. Dating of the footprints indicate that they were made 3.6 mya (Smithsonian National Museum of Natural History 2018).
Just as forensic scientists can use footprints to identify the approximate build of a potential suspect in a crime, archaeologists have read the Laetoli Footprints for clues to this early human. The footprints clearly indicate a bipedal hominin who had a foot similar to that of modern humans. Analysis of the gait through computer simulation revealed that the hominins at Laetoli walked similarly to the way we walk today (Crompton 2012). More recent analyses confirm the similarity to modern humans but also indicate that their gait involved more of a flexed limb than that of modern humans (Hatala et al. 2016; Raichlen and Gordon 2017). The relatively short stride implies that the hominin had short legs—unlike the longer legs of later early humans who migrated out of Africa (Smithsonian National Museum of History 2018; see Figure 7.2.11). In the context of Olduvai Gorge, where fossils of Australopithecus afarensis have been located and dated to the same timeframe as the footprints, it is likely that these newly discovered impressions were left by this same hominin.
The footprints at Laetoli were made by a small group of as many as three Australopithecus afarensis, walking in close proximity, not unlike what we would see on a modern street or sidewalk. Two trails of footprints have been positively identified with one set of the prints indicating that the individual was carrying something on one side. The third set of prints are much smaller and seem to appear in the tracks left by one of the larger individuals. While scientific methods have given us the ability to date the footprints and understand the body mechanics of the hominin, additional consideration of the footprints can lead to other implications. For instance, the close proximity of the individuals implies a close relationship existed between them, not unlike that of a family. Due to the size variation and the depth of impression, the footprints seem to have been made by two larger adults and possibly one child. Scientists theorize that the weight being carried by one of the larger individuals is a young child or a baby (Masao et al. 2016). Excavation continues at Laetoli today, resulting in the discovery of two more footprints in 2015, also believed to have been made by Au. afarensis (Masao et al. 2016).
Figure \(\PageIndex{10}\):Location of Laetoli site in Tanzania, Africa, with Olduvai Gorge nearby.Figure \(\PageIndex{11}\): A visit with Lucy at the Natural History Museum in Washington, D.C.
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Figure 7.2.2 Fossilization process original to Explorations: An Open Invitation to Biological Anthropology by Mary Nelson is under aCC BY-NC 4.0 License.
Figure 7.2.3 PetrifiedWood at the Petrified Forest National Park by Jon Sullivan has been designated to thepublic domain (CC0).
Figure 7.1.11 Woman with bronze cast of Au. afarensis at the Natural History Museum in Washington, D.C., by Lee Anne Zajicek is under aCC BY-NC 4.0 License.
Figure \(\PageIndex{2}\): A simplified illustration of the fossilization process from the organism’s death to its eventual discovery by paleoanthropologists.
Figure \(\PageIndex{3}\): An exquisite piece of petrified wood.
Figure \(\PageIndex{4}\): “Lucy” (AL 288-1), Australopithecus afarensis.
Figure \(\PageIndex{7}\): Just a few of the early hominin footprints that fossilized at Laetoli.
Figure \(\PageIndex{8}\): An extremely large (and yet somehow endearing) coprolite named “Precious”.
Figure \(\PageIndex{9}\): A beautiful example of dendrites, a type of pseudofossil. It’s easy to see how the black crystals look like plant growth.
