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Trace Fossils

• A trace fossil is indirect evidence of ancient life(exclusive of body parts) that reflects some sort ofbehavior by the organism. Examples of tracefossils are tracks, trails, burrows, borings,gnawings, eggs, nests, gizzard stones, and dung.

• In contrast, a body fossil is direct evidence ofancient life that involves some body part of theorganism.

paleoichnology

• Dinosaurs left trace fossils represented by tracks,tooth marks, eggs, nests, gastroliths (stones in thestomach for grinding), and coprolites (fossilizedpoop).

• Body fossils of dinosaurs include bones and skinimpressions. As an example of the distinctionbetween dinosaur body fossils and trace fossils,skin impressions are not trace fossils unless theywere made while the dinosaur was still alive, suchas the skin impressions that might be associatedwith a footprint.

Types of Dinosaur Trace Fossils

• Tracks and Trackways

• Eggs and Nests

• Tooth Marks

• Gastroliths

• Coprolites

Tracks• A track is the impression left by a foot in a

sediment or other substrate, although some two-legged dinosaurs also made "hand" (forelimb)impressions, which are also considered as tracks.Tracks are preserved in two main ways:

(1) as impressions (negative relief), which are moldsof the original foot; and

(2) as casts (positive relief) made by overlyingsediments into the original impressions.

Cast

Impression or Mold

• Some dinosaurs were also heavy enough todeform layers of sediment below the surface;such impressions (and their overlying casts)are called undertracks because they wereunder the original track surface.

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This track, in the Entrada Formation (Jurassic) ofeastern Utah, shows only a partial impression andis probably an undertrack.

However, a deep claw impression is visible on thefar left toe, probably indicating a shift of thetheropod's weight to the left.

• A trackway is two or more consecutive tracksmade by the same animal. Many mammals andbirds leave a walking trackway that shows anangle between the footprints from a midline oftravel; some trackers refer to this progression asdiagonal walking. All dinosaurs seemingly werediagonal walkers.

• Dinosaur trackways show no evidence of eithertail or belly dragging, meaning that dinosaurswalked erect with their limbs underneath theirbodies, rather than sprawled to the sides of thebody.

• Dinosaurs either traveled on two rear feet (bipedal)or four feet (quadrupedal).

• If a dinosaur was obligated to walk on two feet(such as humans) for most of its life, then it wasan obligate biped; an obligate quadruped spentmost of its life on four feet.

• If a dinosaur could walk on two feet (similar tomodern bears) but spent most of its time on fourfeet, it was a facultative biped but an obligatequadruped. Accordingly, a normally bipedaldinosaur that could have gone onto all four limbswas a facultative quadruped.

• Because actual body remains are only very rarelyassociated with trackways - tracks have their ownunique taxonomy that is not associated with thetaxonomy of the dinosaur body fossils.

• Different types of dinosaurs left distinctive tracksthat can be attributed to general classifications(ceratopsians, theropods, ornithopods, sauropods)but tracks rarely give enough detail to identify thegenus or species of the trackmaker (e.g.,Tyrannosaurus, Apatosaurus, Triceratops).

Bipedal Trackways

• The first dinosaurs are thought to have beenbipedal descendants of archosaurs that evolvedduring the Triassic Period. Dinosaur tracks fromthe Late Triassic, which show bipedalism, supportthis hypothesis. These tracks have a three-toedshape (with narrow-width toes) that ischaracteristic of theropods from the Late Triassicthrough the Late Cretaceous Periods.

• All theropods were obligate bipeds,although some rare examples of trackwaysshow that they went down onto all fours,meaning some of them were facultativequadrupeds. Some tracks show clawimpressions at the ends of toes. Theropodstrackways show little deviation from themidline of travel, as if they were walking ona tightrope.

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• This foot belongs to Allosaurus, a large Jurassictheropod. Notice the three toes with a relativelynarrow width. The skeleton is mounted atDinosaur National Monument, northeastern Utah,USA.

• This foot belongs to Tyrannosaurus, a largeCretaceous theropod. Although separated bymillions of years, both Allosaurus andTyrannosaurus would have left similar footprintsthat were attributable to large theropods. Foot isfrom a replica mounted in Western Colorado'sDinosaur Valley, Grand Junction, Colorado.

• This theropod track is in the Morrison Formation(Jurassic) of eastern Utah. Notice the greater depthof the track in the toe region, which suggests ahorizontal posture for the dinosaur while it waswalking.

theropod trackway

• Ornithopods were also capable of leavingbipedal trackways but were mostlyfacultative bipeds. Their tracks are similarto those of theropods in that they frequentlyshow a three-toed pattern;

• they differ from theropod tracks in thewidth of the individual toe prints, which aregreater than those of theropods.

• Theropod tracks also show distincitive clawimpressions and lack the “heel” impressionsfeatured in ornithopod trackways.

• Ornithopod tracks are present in depositsfrom the Jurassic through the LateCretaceous but are particularly common inLate Cretaceous deposits. Hadrosaurs areprobably the best known ornithopods thatleft tracks attributable to the trackmaker.

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• This is a typical ornithopod foot (a hadrosaur),showing the widely splayed three-toed anatomy.Skeleton is in the Museum of Western Colorado'sDinosaur Valley, Grand Junction, Colorado.

• This ornithopod track was cast in the bottom of asandstone bed, hence you are looking at thebottom of the footprint in positive relief. Track isin the Museum of Western Colorado's DinosaurValley, Grand Junction, Colorado.

• The large size attained by some ornithopods late inthe Mesozoic Era is shown by this LateCretaceous ornithopod print, with my sandaledfoot (size 9, men's) for scale. This track is alsopreserved as a sandstone cast, so you are lookingat the bottom of the footprint.

Quadrupedal Trackways

• Most dinosaurs were obligate quadrupeds; well-known groups of dinosaurs that normally walked onall four legs include prosauropods, sauropods,ceratopsians, ankylosaurs, and stegosaurs. Althoughsauropods have been shown in some books, theJurassic Park movies, and museum displays ascapable of standing on their hind limbs (thusbecoming facultative bipeds), no trackwayevidence exists to corroborate such an assertion.

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• The front foot of a quadrupedal animal iscalled the manus, whereas the back foot iscalled the pes.

• Quadrupedal dinosaurs seemingly walkedlike most diagonal walkers do nowadays, bymoving the right manus and left pes atabout the same time, alternating with theleft manus and right pes. Trackways showthe manus print slightly in front of the pesprint on each side of the trackway.

• Prosauropods, ceratopsians, ankylosaurs,and possibly stegosaurs left four-toedimpressions in their tracks, both for themanus and pes.

• Sauropods have five-toed tracks for theirpes impressions but do not show toes inmanus impressions.

• Some quadrupedal ornithopods have three-toed tracks for their pes impressions butmanus prints do not show obvious toes,either.

• The large padded footprint left by the hind foot ofa sauropod dinosaur. The print shows the curvedclaw marks typical of this type of dinosaur. Theprint which is on a fallen block is on the base of asandstone unit.

• This sauropod print is of a right pes and is one track in atrackway. The tip of a field boot is the scale in the lowerlefthand corner. The mud "push-ups" in the front of thetrack (toward the top of the image) and to the rightindicate the shifting of the sauropod's weight forward andto the right. Locality is in eastern Utah, MorrisonFormation (Jurassic).

• The following trackway, to which the previouslydepicted sauropod print belongs, registers a rarelyrecorded event; a sauropod that changed itsdirection of travel abruptly to the right. Theprogression of the sauropod was from the lowerlefthand corner to the upper righthand corner ofthe picture. Both manus and pes prints are visiblein the image. (If you look closely to the lowerright, a theropod track is pointed in a directionperpendicular to the sauropod trackway.)

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• Trackways may indicate specific behavioursor social interactions. Any interpretationsmust, of course, be made with caution.

• A site with many trackways may notnecessarily indicate herding or other socialgroupings, especially if the hiatus betweendeposition was particularly lengthy.

• However, there is evidence that, for at leastsome of the time, brontosaurs traveled inherds. At Davenport Ranch, Texas "thelimestone records the passage of two dozenbrontosaurs in a compact mass, the verylargest prints at the front periphery, the verysmallest in the middle of the group. Sobrontosaur bulls or maybe senior cows musthave guarded their young." (Bakker, 1986).

• This interpretation has been modified byMartin Lockley (1986), who inferred fromthis and other Colorado tracks that largersauropods ranged in front of smallermembers of the herd and "were probablywalking in some type of staggered orspearhead formation" (Lockley et al.,1986).

• "There is evidence of predation, of solitaryhunters stalking their prey, and ofopportunists and scavengers roaming inpacks“ (Thulborn, 1990).

• Trackways can also indicate swimming,stampeding or even limping dinosaurs(Thulborn & Wade, 1984 in Thulborn,1990).

• Any inferences about dinosaur behavior willalways be limited. We can never know thereal complexities of dinosaur behavior.

• The previously shown set of trackwaysfrom Colorado shows two things aboutsauropods and helps in our understanding ofa third. Firstly it shows that these largeanimals did move in herds. Secondly itproves that these dinosaurs (and indeed,probably all others) did not drag their tailsalong the ground. And thirdly is suggeststhat eggs were abandoned and juvenileswere not nurtured. It generally appears to bethe case that tracks such as these were allmade by well-grown individuals togetherand are not accompanied by young.

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• In the film Jurassic Park we sawVelociraptors attacking their preysimultaneously from several directions afterhiding quietly in the bushes. Such particularbehaviors would be very hard to find orinterpret from the fossil track record.

• Furthermore if they were represented, it islikely that several, equally-plausiblebehavioral explanations could be suggested. • A = Theropod - habitually bipedal

• B = Sauropod - habitually quadrupedal• C = Iguanadont - quadrupedal• Drawings not to scale. Drawing by Myles McLeod after Paul

(1987)

• TW = Trackway Width

• SL = Stride Length

• PL = Pace Length

• FL = Footprint Length

• FW = Footprint Width

• A = Pace angulation

• L = Left print

• R = Right print

Geometric Method

Drawing by M McLeod after Avnimelech (1966) inThulborn (1989)

DINOSAUR EGGS AND NESTS

• Dinosaurs reproduced through eggs laid onland, just like most modern reptiles andbirds, rather than giving live birth (such asmost mammals). Dinosaur eggs are eitherrepresented in the geologic record asindividuals or are arranged in definitepatterns, indicating the former presence ofnests.

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• An egg is an enclosed, mineralized structurecontaining an amniote (yolk sac) that helps tonourish the developing embryo. The structure is atype of protection for the embryo that also keepsall of its nutrients in a restricted space. In contrast,amphibians require a water source for their eggs,hence times of drought (and consequent shrinkageof aquatic habitats) can be detrimental toamphibian reproduction. Amniotic eggs also havea porous and permeable structure that allows thedeveloping embryo to "breathe," thus offeringprotection but also allowing an exchange with thesurrounding environment.

• Dinosaur eggs are preserved as oblate tosemispherical structures that also show distinctiveshell microstructures. In some cases, dinosaureggs have preserved parts of embryonic dinosaurs,which can help to correlate a dinosaur egg with aspecies of dinosaur, such as Maiasaurus andOviraptor.

• However, the egg itself is the trace fossil, whereasany bodily remains of an embryo constitute a bodyfossil.

• An assemblage of eggs in close associationwith one another in the fossil record is oftenregarded as part of a clutch, meaning thatthese eggs represent one egg-laying episode.

• This dinosaur egg, attributed to the theropodOviraptor, is partially crushed but still shows theasymmetrical and oval shape associated with thisspecies' eggs. Shell fragments are to the right ofthe egg. Samples are in Western Colorado'sMuseum of Dinosaur Valley, Grand Junction,Colorado, USA.

• This pair of partially preserved dinosaur eggscome from the Late Cretaceous Nanxiong Basin ofsoutheastern China, a locality that has yieldedthousands of dinosaur eggs. The specimens are inthe Löwentor Museum, Stuttgart, Germany. Hadrosaur Egg

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Hadrosaur Eggs Sauropod Egg

Sauropod Egg Oviraptor Egg

• A nest is a biogenic structure typicallycontaining a clutch and commonlyrepresented by an arrangement of eggs in asemicircular or spiraled pattern.

• In some instances, a raised area surroundingthe eggs will denote the border of the nest.

• Dinosaur nests were on the ground, likesome modern reptiles and a few birds (i.e.,penguins), rather than in trees, like manymodern birds.

• No evidence exists indicating that anydinosaurs lived in trees, let alone built nestsin trees.

• Nests are sometimes found containing hatchlingsor other remains of juveniles, which assists in theidentification of the parental species.

• Community structures and social interactions forsome dinosaurs, such as Maiasaurus, are indicatedby multiple nests preserved on the samesedimentary horizon. The significance of thisinferred interaction is that certain dinosaursbehaved much more like birds, rather than likemost reptiles.

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• This dinosaur nest shows a spiraled arrangementof the eggs, which were probably oriented in thenest by the mother dinosaur after they were laid.Specimen is in the Fruita Paleontogical Museum,Fruita, Colorado, USA.

• One of the more spectacular dinosaur fossilfinds of recent years was of a LateCretaceous specimen of Oviraptor that wasfound in a sitting position directly over itsnest. This find, a wonderful combination oftrace fossils and a body fossil, representsone of the most compelling pieces ofevidence for brooding behavior indinosaurs.

• ALL dinosaur eggs are basketball-sized orsmaller: NO dinosaur hatched from eggs thesize of people!!

• ALL dinosaurs came from small babies!

(Differs from the mammalian condition,where baby elephants etc. are BIG animals!)

DINOSAUR TOOTHMARKS

• All animals with teeth have the capability ofleaving tooth marks on any solid substancethat they bite, whether these substances areplants, animals, or (who knows why) rocks.A tooth mark is the impression left by abiting animal with teeth, regardless of whatwas being bitten.

• Dinosaurs who fed on other dinosaurs leftdistinctive tooth marks on bones, indicatingfeeding habits for some types of dinosaurs.In some cases, these tooth marks perfectlymatch the "dental records" of teeth fromknown dinosaurs and are preserved in bonesof an identifiable species of dinosaur.

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• An example of this direct correlationbetween "dinner" and "diner" isTyrannosaurus tooth marks in Triceratopsbones. However, such tooth marks do notnecessarily mean that Tyrannosaurus preyedupon and killed Triceratops, because thespecimen of Triceratops may have beenalready dead when munched byTyrannosaurus (thus leaving open thepossibility of scavenging behavior, ratherthan predation).

• This tail vertebra from Apatosaurus shows a fewtooth marks on the left transverse process,indicating that some carnivorous dinosaur(probably Allosaurus) fed on Apatosaurus.Specimen is in the Museum of Western Colorado'sDinosaur Valley,Grand Junction, Colorado.

• The end of this limb bone (looks like a tibia) fromApatosaurus has parallel toothmarks on it. Thespacing of the tooth marks, as well as theindividual marks themselves, help to identify whatdinosaur was feeding on this apatosaur.

• Bite marks that show healing have beendiscovered in some dinosaurs, and in one a veryfew instances (Tyrannosaurus again and aSinraptor from China) can be attributed tointraspecific competition. In other words, a healedtooth mark on a specimen of Tyrannosaurus wasinflicted by another individual Tyrannosaurus,indicating that two individuals of the same specieswere fighting with one another. Thus, dinosaurtoothmarks can indicate feeding habits and otherinteractions between or within species.

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DINOSAUR GASTROLITHS

• Some modern birds will swallow stones,which then reside in their gizzards and aidin digestion of food by helping to grindtough food material. Because birds do nothave teeth, they need their gizzards to grindtheir food, which helps to increase thesurface area of the food for easierdigestibility.

• Stones used to help in the mechanical breakdownof food within a digestive tract are calledgastroliths ("gastro" = "stomach" and "lith" ="stone") and a colloquial term for gastroliths is"gizzard stones."

• Apparently dinosaurs also swallowed stones forthe same reason as birds; numerous polishedstones are associated with some dinosaur remainsand are especially convincing when found withinthe thoracic regions of a skeleton. These stones aretypically smooth, polished, and oblate tosemispherical.

DINOSAUR COPROLITES• One of the byproducts of digestion is waste

material, which is conveniently excreted from thebody at an end of the body opposite from themouth region in most animals. This waste materialcan be in the form of a gas, liquid, or solid, butwhen preserved as a solid is politely called feces.A socially acceptable colloquial synonym for fecalmaterial used by modern trackers is "scat," andthese same people will refer to the study of scat as"scatology."

• Coprolites are fossilized feces, anddinosaurs were no different from otheranimals in leaving such deposits afterdigesting their meals.

• Dinosaur coprolites are valuable tracefossils for figuring out the paleodiets (orfeeding behavior) of dinosaurs. Coprolitescan show either body fossils of plantmaterial (indicating an herbivorous diet) orbones (indicating a carnivorous diet).

• Modern grizzly bears of North America(Ursus horribilis) will leave scat containingboth plant and animal matter (indicating anomnivorous diet), but no dinosaurcoprolites have demonstrated anomnivorous diet by choice for dinosaurs(as far as I know).

• Herbivorous dinosaurs almost certainlywould have ingested plant-dwelling insectsand other arthropods while feeding, thusmaking them "accidental“ insectivores.

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• Coprolites also provide information about habitatsand the presence of dinosaurs in areas otherwiselacking dinosaur body fossils or other trace fossils(such as tracks). Preservation of coprolites isdependent on their original organic content, watercontent, where they were deposited, and methodof burial. For example, coprolites made bycarnivorous dinosaurs (theropods) were morelikely to be preserved than those made byherbivores because of the high mineral contentprovided by bone material of the consumed preyanimals.

• An good preservational environment wouldhave been a floodplain associated withrivers, where the feces deposited on a drypart of the floodplain dehydrated slightlybefore rapid burial by a river flood. Otherenvironments where coprolites were likelyto have been preserved include "wateringholes" (ponds), swamps, streams, andmuddy areas associated with estuaries orlakes.

• This coprolite is most likely from a sauropod,owing mainly to its large size (about 40 cmdiameter), and age (Jurassic); it is from theMorrison Formation in eastern Utah and thespecimen was in the Löwentor Museum ofStuttgart, Germany.

• A coprolite this large probably does not representone single pellet but an amalgamation of severalpellets that merged together (indicating anoriginally high fluid content to the pellets).Individual dinosaur coprolites actually can bequite small (< 10 cm length) compared to the bodysize of the tracemakers. An example of thisseemingly anomalous correlation can be observedin modern mule deer (Odocoileus hemionus) andelks (Cervus canadensis) of North America,animals that can weigh more than 100 kg but leavemany individual pellets less than 1 cm in diameter.