Taphonomy—Death & Decay

Most of these fossil fish in Fossil Butte National Monument are partially disarticulated (e.g., not in the position that they were during life) because gases that formed during decomposition caused the dead fishes to explode, scattering the bones.

Introduction

Taphonomy is the study of what happens to the remains of an organism between the time that it dies and when it becomes fossilized. The term comes from the Greek words for burial or grave.

Many different things may occur to a plant or animal after it has died. The soft tissues may decay and decompose. Remains may be transported by wind or water currents from the place where the organism died, or be buried rapidly. Animal carcasses can be scavenged and bones can dry out and become brittle if exposed to the elements for any period of time. Shells may break apart due to the action of waves or currents.

Taphonomic processes do not stop once a dead organism is buried. Organic material may undergo physical or chemical changes such as the ones involved in making compressions and plant material may become coal. Minerals may replace organic material or infill small pores in bones or wood, both important processes in the preservation of fossil wood and bones. Other chemical changes may occur, such as the original minerals in bones or shells recrystallizing, or even dissolving away so that only a mold or impression of the original material is left. Preservation of unaltered remains and soft tissues is rare, usually occurring in unique circumstances like being frozen in permafrost or in environments such as within dry caves where soft tissues may be desiccated.

Taphonomy also pertains to what may happen to animal tracks, burrows, and coprolites after they are formed. These traces may become degraded by weathering or exposed to additional bioturbation.

Taphonomy greatly impacts the level of preservation of fossils. For example, scavenging, decomposition, and mechanical abrasion by waves and water currents can destroy parts of an organism, even its hard parts. Geochemical changes like dissolution and replacement may also either destroy fossils or remove their fine details.

Badlands National Park

Paleontologists working on  fossil remains at the Big Pig Dig. Badlands National Park.

NPS photo.

Badlands National Park is one of the richest fossil mammal localities on Earth. Based on taphonomic studies, most of these sites were formed when animal remains were rapidly buried on floodplains adjacent to rivers. Bones that became fossilized in these environments are somewhat weathered and sometimes disarticulated and are found in sediments that have undergone soil formation. Additionally, these bones sometimes are aligned by fluvial currents.

The fossils at the Big Pig Dig, a site that the NPS excavated for 15 field seasons, ending in 2008, after park visitors discovered fossil vertebra near a picnic area. The bones at the Big Pig Dig are not weathered and may be found articulated (e.g., with bones in their proper order) or alternatively appear to have been trampled, perhaps by scavengers. Overall, the evidence at the Big Pig Dig indicates that it was a watering hole where animals gathered during times of drought. The bones of Archaeotherium, a large pig-like scavenger, have been recovered from the site.

Learn More

• Badlands—The Big Pig Dig

Dinosaur National Monument

Isolated Allosaurus tooth exposed in the bone bed in the Quarry Exhibit Hall. The tooth may have come loose while the animal was eating, or after the dinosaur had died, it may have been transported by stream currents to this location. Dinosaur toy for scale.

Quarry Exhibit Hall in Dinosaur National Monument contains an exposure of a bonebed that contains more than 1,500 dinosaur bones. Taphonomic studies have shown that the great concentration of bones in this layer of the Morrison Formation results from them being transported from where the animals died to a bend or sandbar along an ancient river bed where the bones and other debris accumulated. Many of the bones are disarticulated. Isolated teeth also occur in the deposit. Some of the bones also have tooth marks on them, which is evidence of scavenging.

Learn More

• Dinosaur N.M.—Quarry Exhibit Hall

Florissant Fossil Beds National Monument

A fossil of a true fly preserving many fine details. Florissant Fossil Beds National Monument.

The preservation quality of fossil insects in Florissant Formation is related to the taphonomic processes that the insects were subjected to after death. Only a small percentage of fossil insects have excellent preservation; most are poorly preserved or consist of only a part of an insect, like a wing.

The Florissant Formation was deposited in a lake (lacustrine) environment and insects became fossilized after drying and sinking to the lake floor where they were entrapped in fine-grained sediments. Studies of different depositional environments (e.g., nearshore and from locations closer to the center of the lake) and fossils collected from different rock types (shale, mudstone, and siltstone) show that fossil flies tend to have a larger size in the deeper water deposits than the nearshore ones. This difference may result from differences in the amount of time it takes for large and small dead flies to sink to the bottom of the lake. Fossil beetles were more intact (e.g., less disarticulated) in nearshore deposits (siltstones) and more likely to be preserved laying on their sides than in offshore (shale) deposits.

Learn More

• Florissant Fossil Beds—Well preserved?

Fossil Butte National Monument

This disarticulated fossil fish from Fossil Butte National Monument has been given the affectionate nickname of “Napoleon Blown-apart.”

The layer of oxygen-poor water present near the bottom of Fossil Lake generally led to excellent fossil preservation as it prevented decay and scavenging. Fish, plant, and other types of fossils from Fossil Butte National Monument are usually articulated and sometimes exhibit carbon-film remnants of soft tissues. Fish and other animals as well as leaves became preserved when their remains sunk to the bottom of the lake. The lack of currents near the bottom of the lake is also evident from the random orientation of fish fossils who died in mass mortality events.

Some of the fish fossils are well articulated, while others are not. Gases formed by decomposition after death sometimes accumulated in the body where the increasing pressure caused the fish to explode. Sometimes these explosions blew out the stomach and other times damaged the head or impacted the entire fish.

Petrified Forest National Park

Concentrations of petrified wood were once part of an ancient log jam in a river, approximately 215 million years ago.

Petrified Forest National Park preserves a rich diversity of both plant and vertebrate fossils. The taphonomy associated with these fossils helps paleontologists understand the past environmental conditions that produced this world-renowned fossil locality.

In addition to areas in the park with great concentrations of petrified logs, such as at Giant Logs within the Rainbow Forest, the Chinle Formation contains other plant fossils such as leaves and trunks of giant horsetails, fern fronds, and leaves of cycads. Many of these fossils have been preserved in situ (e.g., where the plants lived) or have not been transported by river currents far from where they grew. They were buried in fluvial sediments in environments such as floodplain deposits and marshes.

Petrified Forest National Park also contains a variety of vertebrate fossils including phytosaurs[AM1] . These animals who had a body type similar to modern alligators and crocodiles lived in environments such as ancient rivers and lakes. Paleontologists study modern environments in South America in order to better understand how the remains of animals with similar body types (e.g., caimans, a type of alligator) get mired in sediment.

A partial phytosaur skull at Petrified Forest National Park.

Photo courtesy of Alex Apgar.

Modern caiman skull on a river floodplain in Paraguay in 2023.

Photo courtesy of Alex Apgar.

Modern caiman remains on a river floodplain in Paraguay in 2023.

Photo courtesy of Alex Apgar.

Waco Mammoth National Monument

Careful study of the sediments containing most of the mammoth fossils has shown that the nursery heard may have been buried in a single flood event.

Taphonomic studies have helped paleontologists understand the fossils of a nursery herd of adult females and juveniles found at the Waco Mammoth site. Although mammoths have been recovered from more than one stratigraphic level, 19 of the fossils are found in a single stratigraphic layer. It appears that the animals were trapped by steep banks of a tributary during a flood and drowned. Their bodies then came to rest in a slackwater deposit and then later were buried by sediments.

Learn More

• Waco Mammoth—Current Research

• Park Paleontology News—Bringing The Past Alive: Mammoth Behavior Seen Through Waco Mammoth National Monument and its Impact on Interpretation

Featured Parks

• Badlands National Park (BADL), South Dakota—[BADL Geodiversity Atlas] [BADL Park Home] [BADL npshistory.com]

• Dinosaur National Monument (DINO), Colorado and Utah—[DINO Geodiversity Atlas] [DINO Park Home] [DINO npshistory.com]

• Florissant Fossil Beds National Monument (FLFO), Colorado—[FLFO Geodiversity Atlas] [FLFO Park Home] [FLFO npshistory.com]

• Fossil Butte National Monument (FOBU), Wyoming—[FOBU Geodiversity Atlas] [FOBU Park Home] [FOBU npshistory.com]

• Petrified Forest National Park (PEFO), Arizona—[PEFO Geodiversity Atlas] [PEFO Park Home] [PEFO npshistory.com]

• Waco Mammoth National Monument (WACO), Texas—[WACO Geodiversity Atlas] [WACO Park Home] [WACO npshistory.com]