Geology 103 Slide Set 3-Ichnology
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College of the Canyons**We aren't endorsed by this school
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GEOLOGY 103
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Biology
Date
Jan 14, 2025
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25
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Trace Fossils and Ichnology
Ichnology Overview: Learning OutcomesDefine and describe ichnologyCover history of the study & key playersDescribe types of ichnofossils & how they formDiscuss the utility of trace fossils for telling a story of the life that left itimage source: National Geographic
Ichnology defined:Ichnology is the branch of geology and biology that deals with traces of organismal behavior, such as footprints and burrows.Widely considered a topic within paleontology; although not all subtopics concentarte on ancient samples.paleoichnology studies ancient traces and neoichnology studies new/modern traces
Common dinosaur ichnofossilsIchnofossils, or trace fossils, can tell us where and how an animal lived. In that way, they can be considered more interesting or useful than finding a bone.Common dinosaur ichnofossils include tracks (footprint), trackways (series of footprints), burrows, bite marks, gastroliths (aka gizzard stones), coprolites (feces), nests and empty egg shells.Oryctodromeus Burrow in IdahoImage source: Idaho State University and KCBY Newshttps://kcby.com/outdoors/isu-researcher-discovers-first-dinosaur-burrow-in-idaho-second-in-north-america
Keep in Mind- Slide Set 3, 1Ichnofossils can also be called “trace fossils”Coprolites, Nests, Footprints, Gizzardstones, Eggs, Trackways, Toothmarks, and Burrows are all types of Ichnofossils
Preservation bias based on substrateJust as you are more likely to leave footprints in mud than on a leaf-littered forest floor, the presence of fine grains and wet deposition makes the lithification of an imprint far more likely. We call this preservation bias. We know not every dinosaur footprint was preserved, only a small percentage in just the right conditions.Immediate cover with a cementing agent such as snow, ash followed by rain, or sediment fill to allow filled in spaces to create casts or molds.Sauropod Trackway.image by Roland Bird, Copyright: © 2014 Falkingham et al. CC BY-SA 3.0
Track, a single step’s imprintA track is a footprint or “handprint” preserved in some kind of substrate, usually sediment. Smaller grain sizes such as mud, clay, silt, or sand are more likely to be associated with a well preserved impression.Tracks can be preserved in one of two ways. An impression, or a negative relief, is a mold of the original imprint. A cast or positive relief is formed by sediment in-filling the imprint.Photo of dinosaur footprintGreg Willis 2009, CC BY-SA 2.0
Different prints from front and back feetBecause all quadrupedal dinosaurs, or those that walk on four limb, descend from bipedal common ancestors that walked on two limbs, their front feet are generally smaller and create different imprints as compared to the imprints left by back feet.A front feet is referred to as a manus while the back foot is a pes.image source: Wikimedia Commons. Joaquin Eng Ponce. 2021. CC BY-SA 4.0
TrackwaysTwo or more consecutive tracks made by the same animal is called a trackway.Examination of trackways facilitates modeling of biomechanics of dinosaurs.Dinosaur track site in the Cretaceous of Colorado, USA. (geologist James St. John for scale)source: Wikimedia, James St. John. 2021. CC BY-2.0
What can trackways teach us?Trackways indicate quadrupedal or bipedal stance. One can also identify the ability to alternate stance for a different purpose such as when a dog rears up to access something beyond typical head height.Track spacing indicates speed, direction and sometimes predator and prey relations.Groups of trackways can indicate herding behavior and social habits.
Keep in Mind- Slide Set 3, 2We can decipher many dinosaur details from studying trackways/footprints. This includes speed, gait (how it walked), weight, leg length (and therefore infer height), stance and morphology (body shape).
Burrowing was rare among dinosaursOryctodromeus is known to have burrowed. Examples have been discovered in Idaho and Montana.Artist’s imagining of an Oryctodromeus cubicularisin a burrow.image creator: Michael B.H. 2009, CC BY-SA 3.0
Keep in Mind- Slide Set 3, 3Based on evidence found in Montana and Idaho, the Oryctodromeus created and inhabited burrows.
Oviparous vs Viviparous OrganismsOviparous refers to egg-laying reproduction. Examples include some mammals, most fish, some sharks, most reptiles and all birds.Viviparous refers to live birth. Examples include most mammals, some fish, some sharks and some reptiles.Ovo-viviparous is when a parent carries eggs until maturity (but without an umbilical connection during development) Mantas are an example of this type of reproduction.
Were dinos oviparous or vivaparous? How do we know?1859: 1stdocumented dinosaur egg discovery by Jean-Jacques Poech. Intially thought to be large bird eggs. Later recognized as dinosaur eggs in 1923. Most modern birds and reptiles are oviparous but just as there are outliers among the typically viviparous mammals there are atypical reptiles .There are no viviparous birds and no ovo-viviparous birds. As a group, birds are unique in being a clade with no known variation in reproductive strategy.
NestsA nest that contains eggs close together is called a clutch. This is the same term for a group of reptile eggs. Dino nests have only been found on the ground, not in trees like many modern Aves (birds).Eggs in nest are often arranged in circular shapes to keep weight off eggs.image source: Wikimedia. Natural History Museum of Vienna. CC BY-2.0
Keep in Mind- Slide Set 3, 4A nest containing dinosaur eggs is called a “clutch”.
Eggs can be true fossils or trace fossilsWhat delineates a trace fossil from a true fossil is that true fossils are the preserved remains of the organism that once lived. A trace fossil is a trace of the organism and was never part of the original organism.An empty egg shell is a trace fossil while an egg with the embryo is a true fossil because it contains the organism.Studying eggs teaches us what size babies were and how many offspring shared a nest.Intact egg from a museum in Hunan ChinaPhoto by Gary Lee Todd, Public Domain
Keep in Mind- Slide Set 3, 5An egg is only a trace fossil if it is hatched.
Piecing together food websIn this image we can see 2 trace fossils and 2 true fossils, but there are only 3 artifacts. How can this be?Here we see a coprolite (fossilized feces), a tooth and a jaw bone. The tooth and jaw bone were once part of organisms and are thus true fossils.The coprolite is a trace fossil. Where is the 2nd?Looking closely at the jaw, you can see teeth marks. These are impressions from another organism and thus a trace fossil.This image is of a case in the Dinosaur Hall of the LA NHM. Photo taken and shared by COC instructor Jenni Pavia, 2015
Keep in Mind- Slide Set 3, 6Bite marks on a bone would count as trace fossils. In this case it, would be a trace fossil left on a fossil.
GastrolithsGastroliths refers to stones found in the ribcages of animals. They would have tumbled around the gut, breaking down fibrous plant material.Also known as “gizzard stones” were swallowed by the dinosaur to add in digestion. Beware of imposters because pretty much any rounded stone could be labeled as one in a gift shop. Gastroliths from Jurassic strata near Starr Springs, Utah.Image source Wikimedia Commons, User Wilson44691, 2012 CC BY-SA 3.0
Keep in Mind- Slide Set 3, 7Gastroliths are rounded rocks found in the ribcages of animals known to eat plants.
CoprolitesFossilized feces can indicate dietary patterns. (e.g. Plant material or bones in coprolites)image source: Wikimedia Commons from User Philipp66, 2008, Public Domain
Keep in Mind- Slide Set 3, 8Coprolites are fossilized feces.Gastroliths are stones swallowed to breakdown plant-matterCoprolites provide info on the diets of dinosaurs.