Fossils1Paleo.pdf

8/11/2019 Fossils1Paleo.pdf

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FossilsMike Viney

Hermanophyton taylorii

Morrison Formation, Brushy Basin Member

Upper JurassicEast McElmo Creek, Cortez, Colorado

8. cm ! ". cm

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$he %ord &ossil is deri'ed &rom the (atinfossilis, %hich means )du* up). +nitially, the

term &ossil applied to any stran*e or interestin* material &ound %ithin rock %hether or not

it %as o& or*anic ori*in -rothero, //0, p. 1. Most modern de&initions include theconcept that &ossils are e'idence o& ancient or*anisms, %hich ha'e become a part o& the

Earth2s crust. $he %ord ancient is arbitrary. $o some ancient applies only to e!tinct

or*anisms %hile, to others, it implies time limits. 3rimaldi and En*el //1 point outmany %ould like to restrict the term &ossil to species that ha'e become naturally e!tinct.

$hey ar*ue that ha'in* this kno%led*e is problematic. 3rimaldi and En*el su**est the

&ollo%in* practical de&inition, )...a &ossil is the remains or %orkin*s o& any species, li'in*or e!tinct, that ha'e been naturally preser'ed &or se'eral thousand years or more p. 41.

5 more common time limit de&ines &ossils as bein* prehistoric thus6 &ossils preser'e

remains or acti'ities o& ancient or*anisms older than #/,/// years 3arcia 7 Miller,

#8, p. #06 9chop&, #", p. "1.

$he ma:ority o& &ossils are &ound in sedimentary rocks. ;r*anisms become trapped %ithin

sediment layers due to the action o& %ater, %ind or *ra'ity. Fossils can sometimes be

&ound in metamorphic rocks &ormed &rom &ossili&erous sedimentary rocks altered by heatand pressure. Fossils can e'en be &ound in i*neous rock created &rom lahars or pyroclastic

&lo%s that entomb trees or other or*anisms.

$%o ma:or types o& &ossils are reco*nized. Body &ossils re'eal the structure o& an

or*anism, %hile trace &ossils re'eal the acti'ities o& or*anisms. $here are many reasons tostudy &ossils. $he &ossil record indicates that di&&erent li&e &orms ha'e e!isted at di&&erent

times re'ealin* the e'olution o& li&e on Earth. Fossils and rock types ser'e as clues to

determinin* ancient en'ironments. Finally, &ossils are the most practical %ay o& tellin*

time in *eolo*y -rothero, //0, p. 'ii1.


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reduce decomposition &rom bacteria and &un*i. @ecomposition, erosion, deposition and

rock &ormation are processes that o&ten destroy so&t tissue, so it is the hard parts o&

or*anisms such as shells, bones and teeth, %hich are most o&ten preser'ed. ;ccasionallyconditions e!ist that allo% &or preser'ation o& or*anisms in en'ironments that rarely

produce &ossils. E!ceptional conditions may also help to preser'e so&t tissue or

impression o& so&t body parts.

Fossil deposits %ith so&t>bodied or*anisms %ell preser'ed or %ith terrestrial animals,

such as dinosaurs in the Morrison &ormation are termed (a*erstAtten. (a*erstAtten is a3erman %ord used in minin* that denotes a particularly rich seam and has been adopted

by paleontolo*ist to si*ni&y these rare &ossil deposits because they *i'e us a %indo% into

past en'ironments seldom preser'ed in the &ossil record 9elden 7 udds, //0, p. "1.

$%o types o& &ossil la*erstAtten are reco*nized. @eposits that contain 'ast numbers o&&ossils represent Concentration (a*erstAtten. $he preser'ation may not be e!ceptional,

but the *reat numbers can be 'ery in&ormati'e. Conser'ation (a*erstAtten contain &ossils

%ith so&t body preser'ation, impressions o& so&t tissue or &ossils o& %ell>articulated

skeletons %ithout so&t tissue preser'ation. Conser'ation (a*erstAtten are particularlyimportant because they pro'ide kno%led*e o& so&t>bodied or*anisms, allo%in*

paleontolo*ists to reconstruct paleoecosystems, and *i'e insi*hts into the morpholo*yand phylo*entic relationships o& or*anisms udds 7 9elden, //8, pp. 8>1.

Preservation Types

$he science o& taphonomy e!plores the en'ironmental conditions that promote

&ossilization. Both body and trace &ossils can &orm under a 'ariety o& circumstances

representin* multiple modes o& preser'ation. Compare se'eral books on &ossils o&& anylibrary or bookstore shel& and you %ill soon realize there is no standard &or cate*orizin*

types o& &ossil preser'ation. +n this paper %e %ill brie&ly describe modes o& preser'ation

that one is likely to &ind in both scienti&ic papers and popular books.

Molds & Casts

Casts 7 Molds o& $rilobites

Ellipsocephalus hoffi

;r*anisms buried in sediment may decay or dissol'e a%ay lea'in* a ca'ity or mold. +&the space is subseuently &illed %ith sediment, an e!ternal cast can be made. Molds and

casts are three>dimensional and preser'e the sur&ace contours o& the or*anism. 5 mold

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preser'es a ne*ati'e imprint o& the sur&ace, %hile a cast preser'es the e!ternal &orm o& the

or*anism $aylor, $aylor 7 rin*s, //, p. 1.

9ometimes a shell can be &illed %ith minerals and then dissol'e a%ay. $he internal cast

that remains is termed a steinkern, %hich in 3erman means )stone cast) -othero, #8,

p. "1. 9teinkerns are most o&ten represented by the internal molds o& mollusks. $he pithcast o& Calamitesis the most common plant steinkern. 5s a Calamitestree matured the

Calamites-ith Cast 9teinkern1

center o& the stem pith1 became hollo%, de'elopin* into a tube>shaped air ca'ity. $he

pith cast preser'es an impression o& the pith ca'ities outside sur&ace, %hich represents the

inside 'ascular and corte! tissue $aylor, $aylor 7 rin*, //, p. D1.

Most molds and casts do not contain the actual remains o& an or*anism. 9hells, bone, and

%ood o&ten &orm as molds or casts. 9ome trace &ossils ichno&ossils1, such as tracks andburro%s can &orm as casts or molds. $racks and burro%s can pro'ide clues to the

beha'ior and biomechanics o& an or*anism %hile it %as ali'e.

Concretions o&ten encapsulate a &ossil mold and cast. $he siderite iron carbonate1nodules o& Mazon Creek, +llinois preser'e Carboni&erous a*ed animals and plants as

molds and casts udds 7 9elden, //8, p. #/1. +t should be noted that some authors

classi&y the &ossils in Mazon Creek nodules as impressions Janssen, #", p. 06 ?ich,?ich, Fenton 7 Fenton, #4 pp. 0>41. (imestone concretions in Ft. Collins, Colorado

contain the molds and casts o& Cretaceous a*ed mollusks. 5s kids, my &riends and +

collected multipleInoceramusclams &rom a D>&oot diameter concretion. $hese &ossils are&ound as molds and casts %ith the cast &illin* the mold.

+t is important to realize that many &ossil specimens represent more than one mode o&

preser'ation. For e!ample, the cast in a Mazon Creek nodule also represents &ossilization

by authi*enic mineralization, a type o& replacement. 9ubtle p< chan*es created by thedecayin* body o& the buried or*anism caused a'ailable iron carbonate to precipitate.

$hus, the or*anism became its o%n nucleation site &or the &ormation o& a siderite nodule.9ome o& the shells &ound in the limestone nodules o& Ft. Collins retain altered shell

material, %hich represents recrystallization. 5ra*onite calcium carbonate1 in the shell

recrystallized to calcite, a more stable &orm o& calcium carbonate.

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e usually think o& casts and molds as e!hibitin* ob'ious three>dimensional character.

$he thin lea'es o& plants or the %in*s o& insects can produce shallo% casts and molds.

9hallo% casts and molds may take the &orm o& imprints, or impressions, preser'in* thethree>dimensional character o& an or*anism. +mpressions o& %in*s are a common insect

&ossil. E'en some o& the relie&, like pleatin* on the %in*s can be preser'ed. $his is

important because the 'eins on a %in* can be used to key an insect to the &amily le'el3rimaldi, @. 7 En*el, M.9., //, pp 0>01.

+mprints, impressions and many trace &ossils, such as, burro%s, insect *alleries, andtracks, may represent types o& molds or casts i& they retain their three>dimensional

character. Molds and casts are important because they can &aith&ully replicate the e!ternal

&orm o& an or*anism in a three>dimensional &ashion, *i'in* paleontolo*ist in&ormation

about sur&ace anatomy.

Impressions, Compressions & Carbonization

hen or*anisms become trapped and sueezed bet%een sediments they may &ormcompressions. (ar*er or*anisms can be distorted by compression.


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5s or*anisms are sueezed into compressions they may &orm an imprint or impression.

$hus, &ossils disco'ered by splittin* beddin* planes may re'eal t%o &ossils &rom a sin*le

specimen. $he side %ith more or*anic material is called a compression. Compressionso&ten sho% the e!ternal sur&ace o& an or*anism &lattened in a t%o dimensional &ashion.

$he side %ith little or no or*anic material is called an impression $id%ell, #8, p. "6

$aylor, $aylor 7 rin*s, //, p. #6 9chop&, #", p. D"1. +mpressions o&ten represent ane*ati'e imprint o& a compression.

+mprint 7 Compression o& Fish

Knightia eocaena

+mprints are shallo% e!ternal molds or 'oids le&t by animal or plant tissue. hen the

siltstone pictured abo'e %as split into t%o slabs the or*anic matter adhered to one side.

$he top picture represents an imprint in %hich bones and scales le&t a shallo% e!ternal

mold. $he lo%er picture is a compression because it possess or*anic residue le&t &romscales, ori*inal bone, and bone rein&orced %ith calcite. Fish, lea'es and insects are o&ten

&ound as imprints and compressions.

$he compression is re&erred to as the part positi'e side1 and the impression as the

counterpart ne*ati'e side1. $he impression in this case sho%s all the sur&ace details o&

the compression and represents an imprint $aylor, $aylor 7 rin*s, //, p. #1. $hecounterparts o& 3reen ?i'er &ish that represent imprints can be used to make positi'e

layte! casts to study e!ternal sur&ace &eatures 3rande, #80, pp. ## 7 #/1. +& the layer

o& carbon is lost on the compression throu*h %eathernin* or &urther dia*enesis then it is

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also kno%n as an impression Cleal 7 $homas, //, p. 01. $hus, an impression, unlike

an imprint, can be positi'e or ne*ati'e.

For the paleontolo*ist that studies insects, impressions are like casts and molds, %hich

may preser'e some relie& like pleatin* on %in*s 3rimaldi 7 En*el, //, p. 0D1. $his is

important because %in* 'enation can be used to identi&y an insect. Many Mazon Creeknodules do not retain or*anic material and so both the part and counterpart are re&erred to

as impressions Janssen, #", p. 06 ?ich, ?ich, Fenton 7 Fenton, #4 pp. 0>41.

9ometimes parts o& a specimen are preser'ed as a compression %hile other parts are animpression. +n this case the term adpression may be used. 5dpressions &orm %hen the

matri! o& a &ossil is so&t and the phytoleim has &allen o&& in some places Cleal 7

$homas, //, p. 01.

+nsects and lea'es preser'ed in the Eocene a*ed Florissant beds o& Colorado are o&ten

carbonized. +t is belie'ed that lea'es and insects became entan*led in diatom mucus mats

&ormed by a**re*ates o& diatoms under stress1. +nsects and lea'es %ere incorporated into

layers o& sediments and 'olcanic ash at the bottom o& (ake Florissant. Many o& theseinsects and lea'es decomposed lea'in* imprints. 5s the sediments compacted and

hardened into shale the imprints became impression &ossils. 9ome or*anisms onlypartially decayed retainin* a dark colored carbon residue to become compression &ossils

carbonization1. Many insects ha'e their %in*s preser'ed as impressions and their bodies

as dark compressions. Compressions are o&ten &lattened, ha'in* a t%o>dimensionalappearance. dimensional character. 9ome insects are &ound %ith or*ans and appenda*es.

9ome lea'es can be &ound %ith internal structures Meyer, //D, pp. D>D"1.

Cone 7 eedle Compression o&Metasequoia

Feathers are o&ten preser'ed throu*h compression and carbonization. +t is belie'ed that

the carbon residue is the result o& &eather de*radin* bacteria. 5n analysis o& a Cretaceousa*ed &ossil &eather sho%in* a banded color pattern &rom Brazil produced interestin*

results. $he li*ht areas o& the &eather represented an impression no or*anic residue1. $he

dark areas, representin* a compression, consisted o& #> micrometer oblate carbonaceous

bodies. $hese ob:ects turned out to be carbonized melanosomes6 molecules that %ere

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responsible &or the ori*inal &eather color. $he &act that the structure o& the melanosomes

is preser'ed opens up the possibility o& determinin* the ori*inal &eather color Vinther, J.,

//8, p. 1.

FusainizedLithocarpus sp.

Most &ossils &ound in coal deposits are compressed and carbonized or coali&ied. Coal

balls are the e!ception and are discussed under permineralization. -lant and animal

remains may also be Charcoali&ied or Fusainized. Many belie'e that &usainized or*anisms

are trans&ormed to charcoal by ancient &orest &ires. 5lthou*h e'idence o& &ire is associated%ith some &usainized plant tissues there are e!ceptions. 9ome &usainized remains

preser'e cuticle and resins, %hich does not seem consistent %ith an ori*in that includes

&ire 9chop&, #", p. 01. Fusainized remains are three>dimensional and may bereplicated to the cell le'el by carbon 3rimaldi 7 En*el, //, pp. 0>/1.

Permineralization

-ermineralized ;ak

Quercus sp.

-ermineralized &ossils &orm %hen solutions rich in minerals permeate porous tissue, suchas bone or %ood. Minerals precipitate out o& solution and &ill the pores and empty spaces.

9ome o& the ori*inal or*anic material remains, but is no% embedded in a mineral matri!

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9chop&, #", p. D#1. Bone and %ood tissues act as e!cellent &rame%orks to preser'e cell

structure. 9ilicates, iron o!ides, metal sul&ides, nati'e elements, carbonates, and sul&ates

can be in'ol'ed in permineralization. -ermineralization is one o& the most &aith&ul modeso& &ossil preser'ation. +n &act, scientists ha'e tried to replicate the process in the

laboratory, but no arti&icial permineralization is eual to the best natural preser'ation by

cryptocrystalline silica or calcium carbonate 9chop&, #", p. DD1.

Formation o& the &inest petri&ied %ood in'ol'es permineralization %ith silica, usually

&rom a 'olcanic source, alon* %ith replacement and recrystallization. @urin* the initialsta*es o& permineralization amorphous silica in&ills pits connectin* cells precipitatin* on

cell %alls. 5t this early sta*e no replacement has occurred. ?eplacement o& cellulose in

cell %alls may occur as permineralization continues. Cellulose that de*rades lea'es room

&or the emplacement o& silica bet%een and %ithin cells %alls. $he more decay resistantli*nin that remains in the cell %alls continues to act as a *uidin* &rame%ork to preser'e

structure. (ater silica is deposited in cell lumina, the ca'ity enclosed by the cell %alls

and 'oids le&t by %ood de*radation.

9ilica that initially permeates the porous tissue and that %hich replaces cell %all material

is amorphous. $his amorphous silica is unstable and slo%ly crystallizes to more stable&orms o'er millions o& years. $he transition to more stable &orms o& silica in'ol'es

continued polymerization and %ater loss.


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kno%n permineralized

&ossils amon* the *eneral public. 5lthou*h not as %ell kno%n, the coal ball represents a

'ery in&ormati'e permineralized &ossil. 5 special type o& &ossil, the coal ball, can be&ound in the coal deposits o& the -ennsyl'anian and -ermian periods. Coal balls contain

s%amp 'e*etation, %hich has been permineralized %ith calcium carbonate, preser'in* D>

@ cellular structure. Coal balls are studied in serial section usin* the cellulose acetatepeel method to re'eal microscopic structure. 9erial sections can be used to reconstruct

or*ans and entire plants. $he &i'e ma:or *roups o& plants &ound in coal balls includeH

(ycophytes, sphenopsids, &erns, seed &erns, and cordaiteans ?oth%ell, //, p. 0/1. $he

in situ preser'ation o& plant materials in coal balls allo%s paleontolo*ist to study plantassociations that tell us somethin* about the palaeoecolo*y o& the coal s%amps. Coal

balls re'eal that the arborous &ernPsaroniusbecame the dominant canopy tree a&ter the

e!tinction o& (epidondendrales near the Middle -ennsyl'anian. Certain species o& small

&erns and horsetails ha'e been &ound, %hich *re% in association %ith the roots o&Psaronius?oth%ell, //, p 01.

Amber

asp in Baltic 5mber

5mber is re&erred to as petri&ied tree resin or sap. + pre&er petri&ied tree resin as the term

sap re&ers to &luids transported by !ylem or phloem tissues ?a'en, E'ert, 7 Curtis, #8#,

p. 41. Coni&ers and some deciduous trees produce resin in response to in:ury.

?esins are 'iscous liuids that contain 'olatile terpene compounds and or*anic solids.Under the ri*ht conditions resins polymerize and harden %ith a*e, turnin* into copal.

5&ter se'eral million years or more, copal matures into amber.

$ree resin breaks do%n %hen e!posed to dryin* and o!idation %ithin :ust a &e% thousand

years. +t is not surprisin* then that amber deposits do not represent &orest &loor

en'ironments. 5mber deposits usually represent marine en'ironments. 5mber deposits&orm %hen resins produced in &orests are transported by %ater to oceans or lakes, %here

they are deposited into the sedimentary layers. Iuick transport and deposition protects

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http://petrifiedwoodmuseum.org/PDF/Permineralization.pdfhttp://petrifiedwoodmuseum.org/PDF/Permineralization.pdfhttp://petrifiedwoodmuseum.org/PDF/Permineralization.pdf


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the resin &rom %eatherin*. ;nce deposited, the resin chemically matures into

intermediate &orms called copals and &inally into amber a&ter millions o& years. $he

amberization process is estimated to take bet%een and #/ million years. 1.

-etri&ied resins ha'e been &ound in Carboni&erous, $riassic, and Jurassic deposits, butrepresent minute amounts o& resins produced inside trees. ?esin that collects inside trees

does not act as an insect trap. $he &irst occurrence o& &ossil containin* amber is

Cretaceous in a*e. $he ma:ority o& amber deposits that contain &ossils %ere &ormed

durin* the Cenozoic eitschat 7 ichard, //, pp.>#/1.

Fossils entombed in amber are re&erred to as inclusions. 5lthou*h the or*anisms o&ten

look complete, most appear to be thinly lined hollo% spaces eitschat 7 ichard,

//, p. 1.


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so&t tissue is not preser'ed the bones retain much o& their ori*inal composition. ?apid

burial &ollo%ed by asphalt permeation accounts &or the e!cellent bone preser'ation

udds 7 9elden, //8, p 4>481. $he bones are black %ith tar and ha'e the smell o&petroleum. 9cientists ha'e e!tracted @5 &rom the bones to compare these e!tinct

or*anisms %ith their li'in* relati'es -rothero, //0, p. 1.

eplacement

-yritized 5mmonite

Minerals can replace bone, shell, %ood, and e'en so&t body parts as they dissol'e a%ay

due to the action o& %ater and decay. ?eplacement and mineralization are terms used to

describe this &ossilization process 3arcia 7 Miller, #8, p. #1. -art o& the ammoniteshell abo'e has been replaced by the mineral pyrite. $he replacement o& so&t or hard body

parts may occur %hen minerals precipitate out o& solution due to the action o& bacteria orp< chan*es. @urin* replacement coats o& bacteria uickly mineralize the decayin* tissue.+& replacement results in a &ossil that is completely articulated %ith three>dimensional

&idelity the process is re&erred to as mineral replication 3rimaldi and En*el, //, p. 01.

3rimaldi and En*el also classi&y permineralization as a type o& mineral replication that isa result o& microbial decay. ;r*anic residue on compression &ossils can be replaced by

minerals lea'in* an impression coated %ith a mineral. -yrite is a common replacement

mineral. +n pyritization sul&ur reducin* bacteria &acilitate the precipitation o& pyrite

durin* decay.

$he (a*erstAtten kno%n as BeecherKs $rilobite Bed in e% Gork is &amous &or its

pyritized trilobites. $rilobite e!oskeletons as %ell as so&t body parts, includin* antennae,le*s, muscles, and di*esti'e tract, ha'e been preser'ed %ith the mineral pyrite Etter,

//, p. #D#1.

+n the ;rsten deposits o& 9%eden the meio&auna makin* up the paleoecosystem o& a

&locculent>layer :ust abo'e the seabed is e!uisitely preser'ed by phosphatization. Eyes,

hairs, spines, muscle scars, :oints, pores, and so&t body parts ha'e been preser'ed on

miniature late Cambrian arthropods. E!oskeletal replacement and or coatin* by calcium

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phosphate occur only on specimens less than mm is size. $he ;rsten (a*erstAtten is

important because it helps to deepen our understandin* o& arthropods as many lar'al

sta*es are preser'ed $an*, //, pp. ##">##1.

E!uisite e!amples o& lea'es, stems, cones, and seeds o& Carboni&erous plants alon* %ith

animal li&e can be &ound in the (a*erstAtten kno%n as Mazon Creek, %hich is :ust #/ kmsouth%est o& Chica*o, +llinois. $he so&t and hard parts o& plants and animals are replaced

%ith the mineral siderite iron carbonate1. 9ubtle p< chan*es created by the decayin*

body o& the buried or*anism caused a'ailable iron carbonate to precipitate. $hus, theor*anism became its o%n nucleation site &or the &ormation o& a siderite nodule. hen

these nodules are split open, the &ossil appears as a D>@ e!ternal cast and mold. Mold

sur&aces may be coated %ith kaolinite, pyrite, calcite or sphalerite. -lant material is

sometimes co'ered %ith a carbonaceous &ilm udds 7 9elden, //0, p. #/1.

9iderite odule %ith 9eed Fern (ea&

-lant material preser'ed in barite sand nodules can be &ound near the to%n o& 9teinhardt3ermany in an ;li*ocene a*ed deposit. hen split open some o& these nodules re'eal

molds and casts o& plant material replaced %ith the mineral barite barium sul&ate1.

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ara*onite to calcite represents a type o& replacement. 9ome shells are made o& layers o&

calcite and ara*onite. $he small crystals o& calcite in shells may recrystallize into lar*er

calcite crystals. $he o'erall shape o& the shell may remain, but the e&&ect o&recrystallization on microscopic te!ture is e'ident -rothero, //0, p. 1.

Freezing

Mammuthus primigeniusyear>old %oolly mammoths &ound are so &resh

they can supposedly be eaten by humans and animals -rothero, //0, p. 1.

+n the sprin* o& //" Guri hudi, a enet reindeer herder, disco'ered a baby

Mammuthus primigeniuse!posed on a sandbar o& the Guribey ?i'er in 9iberia. $he

0/,/// year old &ossil mammoth %as named (yuba a&ter hudiKs %i&e.

(yuba, nicknamed the +ce Baby, represents one o& the best>preser'ed &ossils &ound to date

in the perma&rost o& 9iberia. (yuba %as one month old %hen she dro%ned in so&tsediments o& silt and clay. -aleontolo*ist @an Fisher has determined that more than :ust

the &rozen perma&rost %as essential in (yubaKs e!cellent preser'ation Miller, //, p.

0#1.

(actobacilli colonized her tissues a&ter death. $he lactic acid produced by these bacteria

acted as a preser'ati'e, picklin* (yubaKs tissues. 5s ne% sediments accumulated abo'e

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(yuba the layers in %hich she %as entombed turned to perma&rost. E'entually,

&lood%aters eroded the perma&rost that encased (yuba and transported her do%nstream.

$he lactic acid that ori*inally helped to preser'e the tissues no% protected the &ossil &rompresent day sca'en*ers as it lay e!posed on the sandbar. $hus, &or (yuba preser'ation by

both chemical means and &reezin* %ere critical &actors in the &ossilization process.

!ncaps"lation

Encapsulation occurs %hen minerals &orm around an or*anism. (ate Miocene *ypsumdeposits in the 5lba area in -iedmont, orthern +taly contain dra*on&lies mostly lar'ae1

entombed in sin*le clear *ypsum crystals. $he insects became trapped in the *ypsum as

the e'aporate deposit &ormed. $he entombed insects, like most inclusions in amber, are

thinly lined hollo% spaces 9chluter, ohrin*, 7 3re*or, //D, p. D"01.

;r*anisms may also become entombed in microcrystalline material. $he @e'onian a*ed

?hine Chert near the 5berdeenshire 'illia*e o& ?hynie in 9cotland represents an

ecosystem near a sinter terrace. $he area %as periodically &looded %ith silica richsolution &rom hot sprin*s and *eysers 9elden 7 udds, //0, p. and enrick 7

@a'is, //0, p. 01. ;r*anisms %ere permeated %ith silica and entombed be&ore anycellular decay could occur. +nsects ha'e also been &ound encapsulated in Miocene a*ed

ony! &rom 5rizona 3rimaldi 7 En*el, //, pp. 0>/1.

#esiccation

@esiccation occurs %hen an animal dies in a 'ery dry en'ironment. ater is dra%n out o&

the tissues slo%in* the process o& decay. $he dryin* process may also reduce theprobability o& sca'en*in*. $his process is similar to human mummi&ication. +n &act, some

authors use the term mummi&ication to describe this process. 3round sloths preser'ed

throu*h desiccation ha'e been &ound in 9outh 5merica 3arcia 7 Miller, #8, p. #1.Moa remains preser'ed throu*h desiccation ha'e been &ound in e% Lealand alker 7

ard, //, p. #D1. Many o& these specimens ha'e been &ound in dry ca'es. aturally

mummi&ied insects ha'e been &ound in association %ith -leistocene mammals &rozen intundra perma&rost. +nsects preser'ed throu*h desiccation ha'e also been &ound in

E*yptian mummies and the stomachs o& Eocene a*ed bats Martinez>@elclos 7

Jarzembo%ski, ///1.

hen is a preser'ed remain considered a &ossil= alker and ard //1 do not consider

or*anisms preser'ed throu*h desiccation to be &ossils because they are only temporarily

spared &rom decay p. #D1. Earlier %e discussed that some limit the de&inition o& &ossils tothe remains o& a species that ha'e become naturally e!tinct. Many de&initions ha'e time

limits, %hich are set some%hat arbitrarily. 3imaldi and En*el //1 su**est that

e'idence o& any or*anism, %hich has been naturally preser'ed &or se'eral thousand yearsor more constitutes a &ossil p.41. Under this de&inition desiccation may be considered a

&ossilization process.

#"


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5s discussed earlier, desiccation also seems to play a role in the preser'ation o& some

or*anisms encapsulated in amber. $ree resin pro'ides a microen'ironment in %hich

mummi&ication can take place. 5s the resin matures into amber the mummi&ied remainscontinue to be protected &rom decay.

$naltered emains

Mammuthus primigeniusmolar

$he concept o& unaltered remains can re&er to multiple modes o& preser'ation. Freezin*,

encapsulation in amber tree resin1, desiccation, and chemical preser'ation, such asentombment in petroleum containin* sediment, are e!amples e!plored in our museum.

$he term unaltered remains is a bit misleadin*. +t does not mean that the or*anism is

unchan*ed. ucleic acids @5 and ?51, proteins, pi*ments, and so&t tissues may be

de*raded. $issues, i& present, ha'e usually lost %ater.


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Chemical Fossils

Crude ;il

Chemical &ossils are chemicals &ound in rocks that pro'ide an or*anic si*nature &or

ancient li&e. Molecular &ossils and isotope ratios represent t%o types o& chemical &ossils.

Molecular &ossils are o&ten re&erred to as biomarkers or biosi*natures and represent

products o& cellular biosynthesis that are incorporated into sediments and e'entually into

rock. Many o& these chemicals become altered in kno%n %ays and can be stable &orbillions o& years.

ucleic acids @5 7 ?51, proteins, and carbohydrates do not sur'i'e lon* in the

*eolo*ic en'ironment. $he ma:ority o& biomarkers are hydrocarbons deri'ed &rommembrane lipids, %hich under certain conditions can be stable o'er billions o& years.

Molecules deri'ed &rom pi*ments, such as chlorophyll, can also act as biomarkers. +n

#D4 5l&red $eibs reco*nized that 'anadyl porphyrin %as a molecular &ossil o&chlorophyll. $eibs disco'ery helped support a biolo*ic ori*in &or petroleum noll,

summons, aldbauer, 7 Lumber*e, pp. #D0>#D1.

$he &ossil &uels petroleum crude oil1, coal, and natural *as are the result o& biolo*ic

acti'ity and contain chemical &ossils. Ma:or coal deposits represent plant material that

*re% primarily durin* the Carboni&erous period. Crude oil and natural *as &ormed

primarily &rom prehistoric al*ae and zooplankton that %ere deposited on the ocean &loorunder ano!ic conditions. atural *as can also &orm &rom &ossil plant material. @urin*

sedimentary rock &ormation the remains o& al*ae and zooplankton are con'erted into a

mi!ture o& or*anic hydrocarbons kno%n as kero*en. ;'er *eolo*ic time heat andpressure can con'ert kero*en into oil or natural *as. $he ma:ority o& oil deposits are

Mesozoic or Cenozoic in a*e.

#


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+t is interestin* to contemplate the ori*ins o& &ossil &uel ener*y. 5ncient plants and al*ae

con'erted solar ener*y into the chemical bond ener*y o& carbohydrates. Con'erted

ener*y &rom the 9un %as then passed throu*h the &ood chains o& these prehistoricecosystems. ;r*anic chemicals &rom these or*anisms %ere incorporated into sediments

and e'entually rock. 9o, the &ossil &uels %e humans ha'e come to depend upon represent

ancient sunshine stored %ithin the EarthKs crust.

Fossil &uels currently pro'ide more than 8 o& all the ener*y consumed in the United

9tates. Crude oil supplies 0/ o& our ener*y needs and accounts &or o& the &uel &orcars and trucks. Coal is the ma:or source o& ener*y &or *eneratin* electricity %orld%ide

U.9. @epartment o& Ener*y1. e depend upon &ossil &uel ener*y &or our a*riculture.

9ome studies estimate that %ithout &ossil &uels the United 9tates could only sustain t%o

thirds o& its current population -&ei&&er, @.5., //4, p. 0#1. ;ur dependence upon thesenonrene%able resources should be a %ake up call to in'est in and de'elop alternati'e

ener*y sources. 5t present, it is clear that coal, oil and natural *as, chemical &ossils in the

&orm o& &ossil &uels, are the li&eblood o& 5mericaKs economy.

For paleontolo*ists and *eobiolo*ists the in&ormation pro'ided by molecular &ossils

'aries *reatly. 9ome molecular &ossils can help to determine %hat or*anisms %erepresent, %hile others can indicate %hat biosynthetic path%ays %ere in operation6 still

others pro'ide in&ormation re*ardin* the depositional en'ironment noll, 9ummons,

aldbauer, and Lumber*e, //", p. #D1.

+sotope ratios represent another type o& chemical &ossil and result &rom metabolic

processes that pre&erentially utilize one &orm o& an isotope o'er another Co%en, ?. p.

#41. Molecular &ossils represent biomolecules or their deri'ati'es that %ere once part o& ali'in* or*anism. +n this %ay, molecular &ossils are similar in concept to con'entional

body &ossils. +sotope ratios are not preser'ed bits o& an or*anism, rather they result &rom

acti'ities durin* li&e and in this %ay are analo*ous to trace &ossils.

$he &irst chemical e'idence o& photosynthesis, in the &orm o& C># to C>#D ratios, can be

&ound in 5rchean rock o& D.8 3a &rom +sua, 3reenland enrick 7 @a'is, //0, pp #/>##6 Johnson 7 9tucky, #, p 1. $he process o& photosynthesis pre&erentially utilizes

C># o'er C>#D %hen remo'in* C;&rom the air to synthesize carbohydrates, creatin*

ratios o& these carbon isotopes that di&&er &rom normal back*round ratios. $hus, carbon

compounds processed by photosynthetic or*anisms are enriched %ith C># ?ich 7Fenton, #4, p #1. $he enrichment o& C># in rocks is a test &or the presence o& li&e.

Carbon isotope ratios consistent %ith presence o& cyanobacteria are %idespread in rock

dated at D. 3a Johnson 7 9tucky, #, p. 1. ;ne problem %ith the e'idence abo'e isthe &act that chemical path%ays in non>photosynthetic autotrophs and nonautotrophs can

produce C># enrichment Blankenship, 9adekar, 7 ?aymond, //", pp >D1.

Molecular &ossils ha'e been a key to understandin* the e'olution o& primary producers in

EarthKs oceans. Micro&ossils and molecular &ossils ha'e helped to establish that EarthKs

oceans ha'e e!perienced t%o ma:or shi&ts in the composition o& primary producers.

+nitially, cyanobacteria alon* %ith other photosynthetic bacteria %ere the primary

/


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producers durin* the -roterozoic eon. $he &irst shi&t occurred durin* the early -aleozoic

era %hen eukaryotic *reen al*ae :oined cyanobacteria in bein* ma:or primary producers.

$he second shi&t %ould occur durin* the Mesozoic era %hen dino&la*ellates andcoccolitho&ores %ould be :oined by diatoms in the Jurassic. @iatoms, dino&la*ellates, and

coccolithophores %ould assume their dominant role as the base o& many modern marine

ecosystems by Cretaceous times. noll, 9ummons, aldbauer, and Lumber*e, //", p.#1.

Trace Fossils

$rilobite $racks

Fossils do not al%ays represent a part o& the or*anism. $race &ossils record the acti'ities

o& or*anisms. $racks, burro%s, e**shells, nests, tooth marks, *astroliths *izzard stones1,and coprolites &ossil &eces1 are e!amples o& trace &ossils or ichno&ossils. $race &ossilsrepresent acti'ities that occurred %hile the animal %as ali'e. $hus, trace &ossils can

pro'ide clues to diet and beha'ior. +chnolo*y ichn )trace or track, >olo*y )the science

o&)1 is the study o& trace &ossils. $race &ossils represent multiple modes o& preser'ation

and are considered here as a cate*ory &or con'enience.

$racks represent animals *oin* about their day>to>day acti'ities and may pro'ide insi*ht

into the dynamic beha'ior o& e!tinct or*anisms. $racks are &ormed in situ, that is they are&ound in the place %ere the or*anism made them. $he rocks containin* tracks pro'ide

clues to the en'ironment in %hich the imprints %ere made.

Footprints makin* up a track can re'eal the pace steps1, stride the distance bet%een

consecuti'e steps made by the same &oot1, and track%ay %idth or straddle. 9teps and

stride can re'eal anatomical &eatures, such as, number o& toes or %hether the or*anism%as a biped or uadruped. 9traddle can be used to measure the e!tent to %hich the animal

spra%ls or %alks erect (ockley 7 Meyer, ///, ppD>01. -ace an*ulation can an*le

bet%een step line se*ments1 help to determine the body %idth o& an animal -rothero,

#8, p. 0#D1.

#


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Mathematical relationships bet%een stride len*th and hip hei*ht measured by &ootprint

len*th1 o& some 'ertebrates can help us to establish relati'e 'elocity.

Velocity V1 ms N /.* /.19( #.4"1h >#.#"1

+n #"4 ?. Mceil 5le!ander, a British zoolo*ist, proposed the most %idely used

&ormula &or estimatin* the speed o& animals &rom their track%ays %here * is the

acceleration due to *ra'ity, 9( the stride len*th, and h hip hei*ht &ootprint len*th ! 01.?elati'e stride len*th is a ratio o& stride len*th di'ided by hip hei*ht. 5 ratio o& *reater

than ./ &or most terrestrial tetrapods marks the point at %hich an animal chan*es &rom

%alkin* to trottin*. 5 ratio o& *reater than . marks the point at %hich an animal is

runnin* -rothero, #8, p. 0#1. -aleontolo*ists ha'e also attempted to use tracks as anindicator o& metabolism6 %as the or*anism endothermic )%arm blooded)1 or ectothermic

)cold blooded)1= $rack%ays can pro'ide clues to the social nature o& the animal, %as it

*re*arious social1, and did the animal tra'el in herds= $race &ossils can be combined to

pro'ide multiple lines o& e'idence. @inosaur nestin* sites and track%ays support the ideathat some herbi'orous dinosaurs %ere *re*arious. $his same e'idence may also point to

mi*ratin* beha'ior. $racks o& multiple or*anisms &ootprint assembla*e orichnocoenosis1 combined %ith an analysis o& rock &ormation can help to build an

ecolo*ical picture o& ancient en'ironments. $rack%ays at @a'enport ?anch in $e!as

record a herd o& D sauropods apparently bein* tracked by theropod dinosaurs-rothero, #8, p. 0#01

$he system &or namin* &ootprints ichnota!onomy1 runs some%hat parallel to the

ta!onomy &or body &ossils. 5 track made by "yrannosaurus%ould be *i'en the &ormalname "yrannosauripus. Footprint names end in >pus )a &oot)1, >podus )&oot)1, or

>ichnus )track or trace)1 Borror, #88, pp 0", "8, 7 81. @eterminin* %ho made tracks

is a prime ob:ecti'e o& trackin*. (ookin* at body &ossils &rom the same time period tocompare &oot anatomy to the track is the key. For e!ample, -terosaur &eet body &ossils1

are an e!cellent match &orPteraichnus&ootprints1.

+n 'ery rare instances the tracks are &ound %ith the maker. 5 specimen o& Kouphichnium

#alchia horseshoe crab1, &ound in the 9olnho&en strata, is preser'ed at the end o& its

track Boucot, #/, p. D#01. Bi'al'es %ith escape trails ha'e been &ound in siderite

nodules &rom Mazon Creek udds 7 9elden, //8, p. #D1.

-atterns o& tracks throu*h time, kno%n as palichnostrati*raphy corresponds %ell %ith

biostrati*raphic zones time inter'als de&ined by &ossils1. $he lon*e'ity o& the a'era*edinosaur species, de&ined by appearance and disappearance &rom the *eolo*ic record, is "

to 8 million years. +chnolo*ists &ind essentially the same span o& time, " to 8 million years

&or chan*es in the &ootprint record (ockley 7 Meyer, ///, p. #/1.

$he ?e'erend illiam Buckland #"80>#841, an En*lish *eolo*istpaleontolo*ist, %as

the &irst scientist to reco*nize the true nature o& &ossilized &eces. Buckland coined the

term coprolite or )dun*>stone) to describe these trace &ossils. $he oldest kno%n


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'ertebrate coprolites come &rom 9ilurian deposits and represent &ish &eces Eschber*er,

///, Coprolite 5rticle1. Coprolites attributed to arthropods are kno%n &rom the

;rdo'ician $aylor, $aylor 7 rin*s, //, p. #//"1.

Crocodile Coprolite

@r. aren Chin, curator o& paleontolo*y at the Uni'ersity o& Colorado Museum in

Boulder identi&ies se'eral criteria &or coprolite identi&ication. Coprolites o&ten ha'e hi*hcalcium phosphate content illiams, //8, p. 0"1. -hosphate helps mineralize &eces.

$his may help to e!plain %hy there is a preser'ation bias &or carni'ore coprolites o'er

those o& herbi'ores. Carni'oreKs coprolites contain their o%n source o& phosphate in thebones and teeth o& the consumed prey.


24/30

9almon Creek -seudocoprolite=

Coprolite research is carried out primarily %ith thin sections.


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termites or bees6 ho%e'er, they may be beetle borin*s 3rimaldi 7 En*el, //, p. 0 7

1.

-ermineralized $ermite Coprolites inPalmoxylon

(ea& mines are meanderin* tunnels produced by the &eedin* lar'ae o& some beetle, &ly,

and sa%&ly species. $he &irst de&initi'e lea& mines &irst appear in the lea'es o& $riassicconi&ers and pteridosperms. +nterestin*ly, the abundance and di'ersity o& &ossil lea& mines

coincides %ith the radiation o& &lo%erin* plants 5n*iosperms1 durin* the Cretaceous.

(ea& mines ha'e been used to establish the persistence o& insect and plant associations.For e!ample, the lar'ae o& certain moth &amilies ha'e been eatin* the lea'es o& Quercus

oak1 andPopuluspoplars1 &or / million years and hispine beetles ha'e been eatin* the

lea'es o&Heliconia&or "/ million years 3rimaldi 7 En*el, //, p. 1.

Carbonized -oplar (ea& E!hibitin* Mar*inal Feedin*

Caddis&ly lar'ae li'e in lakes, ponds, and ri'ers. Many build distincti'e protecti'e cases

&rom bits o& sand, shells and 'e*etation. Fossil caddis&ly cases can o&ten be identi&ied to

the &amily or e'en *enus le'el. $he oldest lar'al caddis&ly cases $richoptera1 are &ound

in the Jurassic 3rimaldi 7 En*el, //, p. #1.


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Celliformais a &ossil bee nest in the &orm o& subterranean e!ca'ations1 that is &irst &ound

in (ate Cretaceous deposits. Celliformais &ound &rom the Cretaceous to the -liocene

3rimaldi 7 En*el, //, p. #1. $ermite borin*s appear in the Cretaceous and representthe oldest undisputed &ossil nest &or social insects 3rimaldi 7 En*el, //, p. 01.

Coprinisphaerais the &ossil burro% o& a scarabaerine dun* beetle, %hich makes its &irst

apperance durin* the -aleocene. Coprinisphaerali'ed &rom the -aleocene to the-leistocene and had a %ide *eo*raphic ran*e bein* &ound in 9outh 5merica, 5ntarctica,

5&rica and 5sia. Coprinisphaera coincide %ith the e'olution o& the &irst ecosystems to

ha'e abundant mammalian herbi'ores. E'idence &or the &irst scarab tunnels are &ound inthe coprolites o& herbi'orous dinosaurs &rom the (ate Cretaceous o& Montana 3rimaldi

7 En*el, //, p. /1.

$race &ossils can also help to establish e'olutionary trends. @eep burro%s in marinesediments &irst appear in the &ossil record durin* the late -recambrian and indicate the

presence o& so&t>bodied coelomates -rothero, #8, p. "1. $he earliest e'idence &or

herbi'ory in insects appears in the Carboni&erous. 9pecimens o&%europterisand

!lossopterisseed &ern lea'es ha'e been &ound that sho% si*ns o& mar*inal and sur&ace&eedin*. @e&initi'e lea& mines, %hich are produced only by insects %ith complete

metamorphosis, &irst appear in the $riassic. $he &irst undisputed bee nests and termiteborin*s appear in Cretaceous deposits addin* e'idence to body &ossils that social insects

had e'ol'ed by this time 3rimaldi 7 En*el, //, pp />1.

$race &ossils representin* marine en'ironments are used to determine animal beha'ior as

%ell as establishin* the type o& sedimentary en'ironment in %hich the rock &ormed. +n

&act, marine trace &ossils are o&ten classi&ied into beha'ioral cate*ories6 does the trace

&ossil represent restin*, d%ellin*, cra%lin*, *razin* or some other type o& &eedin*beha'ior see -rothero, #8, p 0/4 &or more details1= -erhaps the most practical %ay to

classi&y marine trace &ossils is by their associations %ith a particular sedimentary

en'ironment or ichno&acies. +n marine en'ironments di&&erent ichno&acies are associated%ith di&&erent %ater depths, physical ener*ies %a'e 7 current conditions1, or e'en type

o& substrate. +chno&acies ha'e become a standard tool &or sedimentary *eolo*ists as %ell

as paleontolo*ists -rothero, #8, p. 0/41.

&phiomorpha9hrimp>(ike ;r*anism1 Burro%

+chno&ossils are important tools that help *eolo*ists interpret sedimentary en'ironments,

paleobathymetry, and pro'ide clues to the dia*enetic history o& some sedimentary rocks.For the paleontolo*ist and &ossil collector ichno&ossils represent &ossilized beha'ior and

pro'ide important clues to paleoecolo*y and paleoen'ironments.

4


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Pse"do%ossils

Man*anese @endrites on 9andstone

-seudo&ossils are ob:ects that do not ha'e a biolo*ic ori*in, but may be mistaken as a

&ossil. Mineral and rock patterns o& inor*anic ori*in &ormed purely by natural *eolo*ical

processes may be mistaken &or &ossils. @endrites deposited by mineral rich %ater

percolatin* throu*h rock layers may ha'e the appearance o& a %ell>preser'ed plant.Concretions may look like e**s or other ob:ects that ha'e a biolo*ic ori*in +'ano',

D1. ChinaH Else'ier 5cademic -ress.

Borror, @.J. #881.(ictionary of )ord *oots and Com+ining ,orms. Cali&orniaH

May&ield -ublishin* Company.

Boucot, 5.J. #/1.E'olutionary Paleo+iology of -eha'ior and Coe'olution. e%

GorkH Else'ier

Cleal C.J. 7 $homas, B.5. //1.Introduction to Plant ,ossils. United in*domHCambrid*e Uni'ersity -ress.

Co%nen, ?. //1.History of LifeO0th EditionP. Malden, MainH Black%ell -ublishin*.

Eschber*er, B. ///1. Coprolites. 9uite #/#.com

"


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Etter, .. //1. BeecherKs $rilobite BedH ;rdo'ician -yritization &or the ;ther @elclos, Q., 7 Jarzembo%ski, E. ///1. Fossil insects in rocks.Meganeura

)e+site. httpH%%%.ub.edudpepme*aneurainrocks.htm

noll, 9ummons, aldbauer, and Lumber*e. //"1. $he 3eolo*ical 9uccession o&

-rimary -roducers in the ;ceans. +n Falko%ski, -.3. noll, 5.D".

8
http://www.ub.edu/dpep/meganeura/52inrocks.htmhttp://www.ub.edu/dpep/meganeura/52inrocks.htm


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Mustoe, 3.E. //81. Mineralo*y and *eochemistry o& late Eocene silici&ied %ood &rom

Florissant Fossil Beds ational Monument, Colorado, in Meyer, Fossil +nsects1, pp. D"D>D".

9chop&, J.M. #"1. Modes o& Fossil -reser'ation.*e'ie# of Palaeo+otany and

Palynology, 'ol /H pp. ">D.

9eilacher, 5., Marshall, C., 9kinner,


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9tein, C.(. #81. 9ilica ?ecrystallization in -etri&ied ood.5ournal of edimentary

Petrology, 'ol , no 0. pp. #"">#8.

$an*, C.M. //1. ;rsten @eposits &rom 9%edenH Miniature (ate Cambrian 5rthropods.

+n Bott:er, @.J., Etter, .,

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