do not always represent a part of the organism. Trace
fossils record the activities of organisms. Tracks, burrows,
nests, tooth marks, gastroliths (gizzard stones),
and coprolites (fossil feces) are examples of trace
fossils or ichnofossils.
Trace fossils represent activities that occurred
while the animal was alive. Thus, trace fossils can
provide clues to diet and behavior. Ichnology (ichn "trace
or track, -ology "the science of") is the study
of trace fossils. Trace fossils represent multiple modes
of preservation but are considered here as a category for
Tracks represent animals going about their day-to-day
activities and may provide insight into the dynamic
behavior of extinct organisms. Tracks are formed in
that is they are found in the place were the organism
made them. The rocks containing tracks provide clues
to the environment in which the imprints were made.
Footprints making up a track can reveal the pace (steps), stride
(the distance between consecutive steps made by the same foot),
and trackway width or straddle. Steps and stride can reveal anatomical
features, such as, number of toes or whether the organism
Straddle can be used to measure the extent to which
the animal sprawls or walks erect (Lockley
& Meyer, 2000, pp3-4). Pace angulation (angle between
step line segments) helps to determine the body width of an animal
(Prothero, 1998, p. 413).
Mathematical relationships between
stride length and hip height (measured by footprint length) of
some vertebrates can help us to establish
1976 R. McNeil Alexander, a British zoologist, proposed
the most widely used formula for
estimating the speed of animals from their trackways where
g is the acceleration due to gravity, SL the stride length,
and h hip height (footprint length x 4). Relative stride
length is a ratio of stride length divided by hip height. A ratio
of greater than 2.0 for most terrestrial tetrapods marks the
point at which an animal changes from walking to trotting. A
of greater than 2.9 marks the point at which an animal is running
(Prothero, 1998, p. 412). Paleontologists have also attempted
to use tracks as an indicator of
metabolism; was the organism endothermic ("warm
blooded") or ectothermic ("cold blooded")?
can provide clues to the social nature of the
animal, was it gregarious (social), and did the
animal travel in herds? Trace fossils can be combined
multiple lines of evidence. Dinosaur nesting sites
support the idea that some herbivorous dinosaurs
were gregarious. This same evidence may also point
of multiple organisms (footprint assemblage or
combined with an analysis of rock formation can
help to build
ancient environments. Trackways at Davenport Ranch
in Texas record a herd of 23 sauropods apparently being
tracked by 5 theropod dinosaurs (Prothero, 1998, p.
The system for naming footprints
(ichnotaxonomy) runs somewhat parallel to the taxonomy
for body fossils. A track made by Tyrannosaurus would
be given the formal name Tyrannosauripus.
Footprint names end in -pus ("a foot"), -podus
or -ichnus ("track or trace")
(Borror, 1988, pp 47, 78, & 82). Determining
who made tracks is a prime objective of tracking.
at body fossils from the same time period to compare
foot anatomy to the track is the key. For example, Pterosaur feet
(body fossils) are an excellent match for Pteraichnus (footprints).
very rare instances the tracks are found with the maker.
A specimen of Kouphichnium walchi (a horseshoe
crab), found in the Solnhofen strata, is
preserved at the end of its track (Boucot, 1990, p.
314). Bivalves with escape trails have been found
in siderite nodules from Mazon Creek (Nudds & Selden,
2008, p. 123).
Patterns of tracks through time, known as palichnostratigraphy
corresponds well with biostratigraphic zones (time
intervals defined by fossils). The longevity of the
average dinosaur species, defined by appearance and
disappearance from the geologic record, is 7 to 8 million
years. Ichnologists find essentially the same span
of time, 7 to 8 million years for changes in the footprint
record (Lockley & Meyer, 2000, p. 10).
Reverend William Buckland (1784-1856), an English geologist/paleontologist,
was the first scientist to recognize the true nature
of fossilized feces. Buckland coined the term coprolite
to describe these trace fossils. The oldest known vertebrate
coprolites come from Silurian deposits and represent
(Eschberger, 2000, Coprolite Article). Coprolites attributed
to arthropods are known from the Ordovician (Taylor,
Taylor & Krings, 2009, p. 1007).
Dr. Karen Chin, curator of paleontology
at the University of Colorado Museum in Boulder identifies
several criteria for coprolite identification. Coprolites
often have a high calcium phosphate content (Williams,
2008, p. 47). Phosphate helps mineralize feces. This
may help to explain why there
is a preservation bias for carnivore coprolites over
those of herbivores. Carnivore's coprolites contain their
source of phosphate in the bones and teeth of the consumed
prey. Herbivorous coprolites contain the cellulose and
of plants and
require an outside source of phosphate, usually in the
form of marine sediments. The need for phosphate does
not apply to all coprolite preservation unlike vertebrates,
of terrestrial arthropods, have
balls and fossil wood (Taylor, Taylor, & Krings, 2009,
Shape can also be an important
clue. Sharks and many primitive fish produce spiral-shaped
coprolites. The shape of coprolites from larger organisms
such as dinosaurs may be affected by splatting issues,
trampling, weather and dung consumers. Shape can also
be misleading. Salmon
Creek in the state of Washington produces beautifully
shaped siderite (iron carbonate) deposits, which resemble
These structures are sold as turtle or even ground sloth
Miocene-aged coprolites. There is some debate about the
nature of these deposits. Adolf Seilacher of Yale University
suggests they may represent intestinal casts or cololites
(Seilacher, 2001, p. 1). George Mustoe of Western Washington
University points out
is a real lack of evidence as to an animal origin for
these deposits. First, they lack calcium phosphate. Second,
lack internal clues such as pollen, scales, seeds, bones
or plant fibers. Third, the deposit in which they are
found lacks fossils. These siderite deposits most likely
represent coprolites. The real value in coprolites is
what they contain.
research is carried out primarily with thin sections.
Herbivorous dinosaur coprolites studied by Chin have
relationship between plant eating dinosaurs and tunneling
to dung beetles (Eschberger,
2000, Coprolite Article). Dr. Chin has also established
that T-rex pulverized its victims from studying microscopic
bone fragments found in a coprolite. Indian and Swedish
scientists have found grass phytoliths in dinosaur coprolites.
This helps to establish that dinosaurs and grasses coexisted
(Williams, 2008, p. 51). Coprolites of arthropods recovered
from rock material, such as the Rhynie chert, are composed
of spores as well as plant and fungal remains (Taylor,
Taylor & Krings, 2009, p. 1007). These Devonian-aged
arthropods were probably detritus feeders. Coprolites
insight into diet, physiology as well
distribution of plants and animals.
ichnofossils (trace fossils) can be helpful in determining
what types of insects were present at a particular time
and provide information about the nature and persistence
of past plant-insect associations.
for herbivory in insects appears in the Carboniferous.
Like vertebrates, the first insects were carnivores and
detritivores. Herbivory requires hosting cellulose-digesting
bacteria through a symbiotic relationship within the
gut. The oldest examples of marginal and surface feeding
are on Carboniferous seed fern leaves of Neuropteris and Glosspteris (Grimaldi & Engel,
2005, p. 52). It is estimated that only 4% of the leaves
in Carboniferous deposits exhibit damage from feeding.
Herbivores do not make a significant impact on plant
life until the Permian (Kenrick & Davis, 2004, pp.
are excessive growths on stems, leaves, cones, and flowers
caused by insect feeding or egg laying. The earliest
fossil galls are found on the petioles of Psaronius tree
ferns of the Late Carboniferous. Insect gall fossil diversity
and abundance takes off with the advent of flowering
plant evolution in the Cretaceous (Grimaldi & Engel,
2005, p. 53).
produce tunnels in wood known as borings or galleries.
Some insects eat the cambial layer while others eat fungus
that grows within the galleries, still others eat the
wood itself. The oldest borings and galleries in wood,
attributed to mites, are known from the Carboniferous.
The first definitive beetle borings are from the Triassic.
There are some borings in permineralized Triassic-aged
wood from Arizona that are attributed to termites or
bees; however, they may be beetle borings (Grimaldi & Engel,
2005, p. 54 & 55).
mines are meandering tunnels produced by the feeding
larvae of some beetle, fly, and sawfly species. The first
definitive leaf mines first appear in the leaves of Triassic
and pteridosperms. Interestingly, the abundance and diversity
of fossil leaf mines coincides with the radiation of
flowering plants (Angiosperms) during the Cretaceous.
Leaf mines have been used to establish the persistence
of insect and plant associations. For example, the larvae
of certain moth families have been eating the leaves
of Quercus (oak) and Populus (poplars) for
20 million years and hispine beetles have been eating
the leaves of Heliconia for 70 million years
(Grimaldi & Engel, 2005, p. 52).
larvae live in lakes, ponds, and rivers. Many build
distinctive protective cases from bits of sand, shells
and vegetation. Fossil caddisfly cases can often be
identified to the family or even genus level. The oldest
larval caddisfly cases (Trichoptera) are found in the
Jurassic (Grimaldi & Engel, 2005, p. 51).
a fossil bee nest (in the form of subterranean excavations)
that is first found in Late Cretaceous deposits. Celliforma is
found from the Cretaceous to the Pliocene (Grimaldi & Engel,
2005, p. 51). Termite borings appear in the Cretaceous
and represent the oldest undisputed fossil nest for social
insects (Grimaldi & Engel, 2005, p. 54). Coprinisphaera is
the fossil burrow of a scarabaerine dung beetle, which
makes its first appearance during the Paleocene. Coprinisphaera lived
from the Paleocene to the Pleistocene and had a wide
geographic range being found in South America, Antarctica,
Africa and Asia. Coprinisphaera coincide with
the evolution of the first ecosystems to have abundant
mammalian herbivores. Evidence for the first scarab tunnels
are found in the coprolites of herbivorous dinosaurs
from the Late Cretaceous of Montana (Grimaldi & Engel,
2005, p. 50).
Trace fossils are often classified into behavioral categories.
Does the trace fossil represent resting, dwelling, crawling,
grazing or some other type of feeding behavior (see Prothero,
1998, p 406 for more details)? Perhaps the most practical
way to classify trace fossils is by their associations
with a particular sedimentary environment or ichnofacies.
In marine environments different ichnofacies are associated
with different water depths, physical energies (wave & current
conditions), or even type of substrate. Ichnofacies have
become a standard tool for sedimentary geologists as
well as paleontologists (Prothero, 1998, p. 406).
fossils can also help to establish evolutionary trends.
Deep burrows in marine sediments first appear in the
fossil record during the late Precambrian and indicate
the presence of soft-bodied coelomates (Prothero, 1998,
p. 227). The earliest evidence for herbivory in insects
appears in the Carboniferous. Specimens of Neuropteris and Glossopteris seed
fern leaves have been found that show signs of marginal
and surface feeding. Definitive leaf mines, which are
produced only by insects with complete metamorphosis,
first appear in the Triassic. The first undisputed bee
nests and termite borings appear in Cretaceous
evidence to body fossils that social insects had evolved
by this time (Grimaldi & Engel, 2005, pp 50-55).
are important tools that help geologists interpret sedimentary
environments, paleobathymetry, and provide clues to the
diagenetic history of some sedimentary rocks. For the
paleontologist and fossil collector ichnofossils represent
fossilized behavior and provide important clues to paleoecology
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