The field guides below are a part of the Guidebook to the Geology of Eastern Idaho :
Introduction to Fossils
Paleontology is the study of plant and animal remains. Paleontologists trace the development of life from its forms more than 600 million years ago through its evolution today. Fossils are the remains or evidence of ancient plants or animals that have been preserved in the earth's crust.
Plants and animals have undergone great change through geologic time. The general trend is toward more complex and advanced forms of life. However, some life forms have not changed and others have become extinct. The succession of life indicates that older rocks generally contain the remains of more primitive life forms and the remains of more advanced life forms are confined to the younger rocks.
Most fossils are found in marine sedimentary rocks. Only a very small fraction of prehistoric plants and animals have left a record of their existence.
Three requirements must be satisfied for ancient
life to be preserved as fossils:
1 . the organism generally must have hard parts such as shell, bone, teeth or wood tissue;
2 . the remains must escape destruction after death; and
3. the remains must be buried rapidly to stop decomposition.
Very fine-grained sediments are much more proficient in preserving fossils than coarse-grained sediments. Ash-fall tuffs from nearby volcanoes have covered forests near Challis, Idaho. These fossil forests were formed while the trees were still standing.
Fossils are preserved in four basic ways: (1) original soft parts of organisms; (2) original hard parts of organisms; (3) altered hard parts of organisms; and (4) traces of organisms.Original Soft Parts of Organisms
Parts of Organisms
Most plants and animals have hard parts capable of becoming fossilized. These include shells, teeth, bones and woody tissue of plants. These hard parts are composed of substances such as calcite, calcium phosphate, silica and chitin which are capable of resisting weathering and chemical action.
Parts of Organisms
The alteration process occurs during and after burial and the results are determined by the composition of hard parts. The following methods are common:
1.Carbonization - As the organic material decays after burial, gases and liquids are lost leaving only a thin film of carbonaceous material. Coal is formed in this way. Also fish, graptolites and reptiles are individually preserved in this manner.
2.Petrifaction - Fossils are commonly preserved by mineral-bearing ground waters infiltrating porous bone, shell or plant material and converting the material to stone. Calcite, silica and compounds of iron are normally the minerals deposited.
3.Replacement - The original hard parts are dissolved and removed by underground water. Simultaneously the original structure may be replaced by substances such as calcite, dolomite, silica and iron compounds.
4.Traces of Organisms - Shells, bones, leaves, tracks, burrows and trails are commonly preserved as molds or casts. If a shell or track is pressed down on the ocean bottom while the sediment is still soft, an impression called a mold is left. If this impression is later filled with another material, a cast is produced.
Fossils Indicate Environment of
Fossils are used to trace the development of plants and animals through geologic time. We have learned that fossils become progressively complex and more advanced in younger rocks. Fossils are valuable for indicating the environment of deposition of the surrounding sediments. For example, reef corals indicate deposition in warm, shallow salt water. Fossils also indicate the depth, temperature, bottom conditions and salinity of ancient seas.
Correlation of Rocks
One of the most important uses of fossils is to correlate or match rock layers separated by many miles. If a similar assemblage of fossils is found in both layers, it may indicate the two layers are related to each other. To be useful for correlation, a fossil should have a very limited vertical range (period of living) and a wide horizontal range (geographic distribution). This means that a fossil lived in a short time in geologic history but was widely distributed during its short life. This type of fossil is called an index fossil or guide fossil.
FOSSILS OF IDAHO
This information was taken from "Exploring Idaho Geology" by Terry Maley (1987). New dating and estimates of duration of geologic periods (i.e. Cambrian) in the last 15 years has revised some of the ages listed here.
Paleontology is the search for knowledge about past life through the study of the evidence (fossils) preserved in the geologic formations of the earth. It is the basis of the geologic time scale and of the correlation of formations on a worldwide basis. New methods of dating formations have refined the time scale but have not changed the correlation's based on the fossil evidence.
This evidence of life covers all of the five kingdoms presently defined in the study of life. The five kingdom system (monera, protista, fungi, plantae, and animalia) was developed by R. H. Whittaker of Cornell University. This system is generally accepted by biologists today, but is still not perfect. Nature seems to have an aversion to pigeonholes.
The present system, as well as all previous systems, leaves viruses out in the cold even though viruses are definitely organic and contain complex molecules. The new system is still an improvement over the previously used two kingdom system (plants and animals), the three kingdom system (protista, plants and animals, or the four kingdom system (protista, fungi, plants, and animals).
The newest system adds the kingdom Monera. This kingdom includes bacteria and cyanobacteria (blue-green algae). These life forms are biologically unique and did not fit well into the old classification systems. This uniqueness includes the lack of a nuclear envelope and membrane-bound organelles.
Monera are also paleontologically unique as they represent the oldest fossils ever found on the earth and are responsible for our oxygen enriched atmosphere. Evidence of the existence of this simple form of life can be traced back 3.5 billion years. About 10,000 species have been described but some question this and believe that less than 3,000 distinct species actually exist.
The oxygen produced as a waste product by the monera did not become immediately available for use of other types of organisms or for the development of an oxygen enriched atmosphere. The Archean (3.8 to 2.5 bybp) and proterophytic (2.5 to 2.0 bybp) oceans were rich in free iron (bybp means billion years before present). Precipitation of this iron in banded iron formations had to occur before free oxygen could become readily available for other uses. It was not until well into the Proterozoic (2.0 to 0.57 bybp) that changes in the environment allowed the next important advance in life to occur.
The fossil record for the Late Precambrian is very poor. Evidence that is available indicates that the kingdom protista and the kingdom animalia developed during this time period. All of the representatives of the animal kingdom during the Late Precambrian were soft bodied.
The discussion of the various formations in Idaho and their associated fossils comes from a review of many geologic and paleontologic references dealing with Idaho. Those sources reviewed during the preparation of this discussion represent only a small portion of the existing literature.
Many fossil genera and species are not mentioned because the scope of this discussion is not appropriate to a complete listing of all genera and species known from Idaho.
The Late Proterozoic time period lasted for 330 million years (1000 to 540 mybp). Multicellular animals such as protomedusae, hydrozoa, anthozoa, octocoralla, and annelida developed in a shallow-water environment. Cyanobacteria continued to be an important life form.
The fossil evidence of monera in Idaho exists in the form of stromatolites. Stromatolites are laminated masses of calcareous rock formed by mat-like communities of cyanobacteria and other monera. Being the only level of the food chain allowed for a tremendous population to develop during the Proterozoic. Unfortunately, there are no published articles dealing specifically with Proterozoic or later monera in Idaho. Those articles that do happen to mention the presence of monera represent passing references to stromatolite structures or beds and their utility or lack of utility in geologic correlations and the study of pateoecology.
Late Proterozoic formations are the oldest fossil bearing formations in Idaho. The Belt Supergroup of northern Idaho and the Brigham Quartzite of Southern Idaho are the remnants of Precambrian rocks that probably covered the entire state.
Possible worm tracks and worm tubes have been noted in the Brigham Quartzite. Stromatolites, both conical and flat-lying, have been reported in the Gospel Peak area of Northern Idaho. The Lower Wilbert Formation in the Lemhi Range may be Precambrian- however, no fossils have been found.
The Cambrian time period lasted for 65 million years. The moderate to shallow marine waters of the Cambrian System were an excellent environment for a tremendous explosion of life forms. The first sponges, jellyfish, tabulate corals, brachlopods, chitons, gastropods, cephalopods, nautiloids, bivalves, hyolithids, trilobites, crustaceans, ostracods, crinoids, echinoderms, conodonts, graptolites and other marine life forms come from Cambrian deposits.
The Cambrian System in Idaho is represented by formations extending from southeastern Idaho to the Pend Oreille area of northern Idaho. The sediments and the fossils indicate that a broad oceanic shelf existed along the western margin of the existing continent. Idaho was completely underwater during this period.
The northern Idaho Cambrian sediments are metamorphosed and rarely produce good fossils. The Rennie Shale and the Lakeview Limestone have produced identifiable Middle Cambrian fossils. Hyolithids, the crustacean Agnostus bonnerensis, various genera and species of trilobites and some brachiopods have been identified. The Lakeview Shale is the main fossil producing formation. Trilobites are the most abundant fossil found.
The southern Cambrian Formations such as the upper Brigham Quartzite, Spence Shale, and the upper Wilbert Formation have produced many identifiable fossils. The Malad, Bear River and Lemhi Ranges yield such fossils as the monera genus Girvanella, worm tubes such as Arenicolites and Monocreterion, trilobite trace fossils Cruziana and Rusophycus, and trilobites including species of Albertella, Elrathina, Glossopleura, Idahoia, Pagetia and many more. Brachiopods may also be found, particularly in the St. Charles Limestone.
The Ordovician time period lasted for 67 million years. Moderate to shallow water marine environments continued to produce an explosion of new life forms. The greatest diversification was in the invertebrate animal kingdom at the genera and species levels. The first rugose corals, bryozoa, Strophomenide brachiopods, Spiriferide brachiopods, Rhynchenellidae-type brachiopods, starfish and vertebrates show up in the Ordovician along with new cephalapod subclasses, bivalve subclasses and others.
The first vertebrates are placed in the Ordovician because fossil fish of the class agnatha have been found in Ordovician deposits. There is the possibility that conodonts represent the first vertebrates or chordates. Small tooth-like and plate-like calcium phosphate remains are all the evidence we have of the conodonts. Such evidence is inconclusive.
The Ordovician System in Idaho is well represented in the central and southern part of the state. A continuation of the marine shelf environment is indicated. Quartzites, slates, shales, limestones and dolomites have produced identifiable fossils. The quartzites are the least productive. Calcareous algae and fucoid markings have been reported from the Kinnikinic Quartzite. The Swan Peak Quartzite has produced brachiopods and ostracods in the Montpelier region. The Ramshorn Slate has produced crustaceans of the genus Caryocarls, graptolites and sponge spicules. The Fish Haven Dolomite has produced corals, brachiopods, gastropods and crinolds in Fish Haven Canyon.
Shale units and limestones are by far the best-producing units for well preserved fossils. The Garden City Limestone has yielded many fossils. Many brachiopods, including Dalmanella and Strophomena species, have been found in the Montpelier area. Gastropods including Maclurea, Lophospira, and Hormotama are common. The sponge-like fossil Receptaculites, trilobites and the Nautiloid Cephalopod Endoceras are also present. Shale, dolomite and limestone units within the Phi Kappa Formation and Saturday Mountain Formation also contain good identifiable fossils. The Saturday Mountain Formation has produced the coral Columnaria stokesi and others, graptolites, crinoids, brachiopods, gastropods and the nautiloid cephalopod Endoceras. Look near the south side of the Salmon River near Sullivan Hot Springs for these fossils.
The Phi Kappa Formation needs to be especially noted for its fossils. Graptolites first reported by Blackwelder in 1913 are well preserved in this formation. There is a tremendous variety of genera and species many of which can be identified in the field. The Trail Creek area in Custer and Blaine Counties is an exceptional graptolite locality that has been extensively studied. The crustacean Caryocarz's, sponges and brachiopods are also present. The sequence deposited in this area represents sedimentation from the Ordocician period through the middle of the Silurian period.
The Genera and species of graptolites are too numerous to list completely. Some of the more important Ordovician genera include Didymograptus, Isograptus, Glossograptus, Climacograptus, Pleurograptus and Dicellograptus.
The Silurian time period lasted for 30 million years. Where life forms expanded into deeper water during the Ordovician as compared to the Cambrian, they began to colonize the land in the Silurian. Most of the major invertebrate life forms are already present. The protista Dinoflagellata and the Pteridophyta and Psilophyte types of vascular plants show up in the Silurian. Hippuritoida mollusca, arachnids, barnacles and terrestrial arthropods also first show up in Silurian deposits along with a great variety of fish.
The Silurian system in Idaho is represented by formations cropping out in the central and southeastern part of the state. The sediments and associated fossils indicate the presence of continued nearshore shelf sedimentation and coral reef building.
The fossiliferous silurian formations include the Roberts Mountain Formation, the Laketown Dolomite and the Trail Creek Formation. Unfortunately none of the new forms of life discussed above have been found in the Idaho formations.
The Roberts Mountain Formation has produced many brachiopods, some gastropods and both tabulate and rugose-type corals in the Challis area.
The Trail Creek Formation produces excellent graptolites in both the Trail Creek area and Malm Gulch. Many species of Monograptus and Crytograptus have been collected. The type locality in the vicinity of Trail Creek is a continuation of environmental conditions that existed locally for some 60 million years.
The Laketown Dolomite has produced the greatest variety of fossils of the three above-mentioned formations. The corals Halysites and Cyathophyllum and some brachiopods have been identified from the Montpelier area. The tabulate corals Heliolites, Favosites, and Halysites have been found in the typical Silurian coral reef-type deposits within the Bayhorse Quadrangle. Brachiopods such as conchldium and plectatrypa are known as are large crinoid columns.
The Devonian time period lasted for 48 million years. The shelf sea continues to produce a great variety of stromatoporoids, brachiopods, corals, cephalopods and ostracods. The monograptids die out in this period as do most of the trilobites. The first mosses, liverworts, lycopods, ferns and gymnosperms show up in the Devonian. The first terebratulid-type brachiopods, scap4opods, ammoinoids, coleoids (belemnites), mytiloids (mussels), unionoids (fresh water bivalves), brachiopods, hexapods, placoderms, chondrichthyes, and amphibia show up in the Devonian.
Idaho was still under water during the Devonian. We therefore have none of the land forms mentioned above represented in Idaho formations. The Devonian system in Idaho is represented by formations cropping out in the central and southeastern part of the state. Erosion has removed all other traces of this system in Idaho. The sediments that remain indicate moderate to shallow water marine deposition.
There are only six formations in Idaho representing the Devonian. They are the Jefferson, the Grandview, the Three Forks, the Water Canyon, Darby and the lower part of the Milligen. The Three Forks and the Jefferson are the most productive.
The Darby Formation has only produced unidentifiable gastropods whereas the Water Canyon Formation in Bear Lake County has produced a few fish scales and plates as well as Lingula brachiopods, pelecypods, gastropods and ostracods. Psephaspis williamsi, Uranolophus sp. Dipterus sp. and other Lung fish have been identified. The lower part of the Milligen has produced brachiopods including Cyrtospirifer monticola, Clelothyridina Devonica and others. The Grandview dolomite has produced a few poorly-preserved corals, brachiopods and gastropods.
The Jefferson in the aspen range has produced corals and brachiopods. In the Mackay area, the coelenterate Stromatopora has been collected. A few disarticulated fish scales and fragments from the Lemhi Range have been identified. The Lungfish Psephaspis idahoensis, Holonema haiti and others have been studied. The coral Favosites, crinoids, sponges and the coelenterate Stromatopora have also been found in the Jefferson.
The three Forks Formation is the most fossiliferous. The Lost River Range between Mackay and Dickey has been highly productive for Devonian fossils. Brachiopods including Schizophoria striatula, Athyris parvula, Cyrtospirifer whitneyi, Spirifer utahensis and others have been identified. The gastropod Euomphalus eurekensis, bryozoans, pelecypods, crinoids, tabulate corals, rugose corals, cephalopods, conodonts and large fish bones have been found. Worm tracks and algal filaments have also been noted in Devonian formations.
The Mississippian or Early Carboniferous time period lasted for 40 million years. The marine environment continues to produce a great variety of life during this period. The increase in the diversity of life occurs to the greatest extent at the genera and species levels. Conifers, Heterocorallia-type corals, Myoida-type bivalves and reptiles first show up in Carboniferous rocks.
Idaho has mostly marine deposits with coral reef faunas well represented. Coarse-grained, distinctive, continentally-derived sediments with associated plant fossils show up in Idaho for the first time during the Mississippian period as a result of the Antler Orogeny. Parts of Idaho were probably not very high above sea level nor were they above sea level for very Iong.
The Mississippian system in Idaho is represented by formations cropping out in the central and southern parts of the state. Many formations have been named and renamed. The earlier named Brazer Limestone now includes the Lodgepole, Little Flat, and Monroe Canyon Formations in the Chesterfield Range where the Madison includes the Lodgepole and Mission Canyon in the Garns Mountain area. The White Knob Limestone has been raised to a group status and includes the Middle Canyon, Scott Peak, South Creek and Surrett Canyon Formations. The Milligen, Arco Hills, Bluebird Mountain, Snakey Canyon, Big Snowy, McGowan Creek, Humbug, Copper Canyon and Railroad Canyon Formations have been considered part or wholly Mississippian.
For invertebrate fossils, the Mississippian Formations of Idaho have the greatest diversity and quantity. All of the formations seem to have forams, brachiopods and conodonts. Trace fossils, algae, corals, crinoids, blastoids, bryozoans, gastropods, pelecypods, ostrocods, trilobites, cephalopods, fish fossils and plant remains have also been reported.
The Milligen Formation is the only Mississippian formation with plant remains. The material is poorly preserved and rare. Sbhenophyllum, fern and possible Lepidodendron fragments have been tentatively identified.
If conodonts are excluded, then fish fossils have only been reported from the White Knob Limestone, the Humbug, The Surrett Canyon Formation and the Scott Peak Formation. The Surrett Canyon and Scott Peak Formations have produced shark teeth.
Many well-preserved fossils can be found in the Lost River Range. The Mackay region is highly fosiIiferous. Corals are especially common and diagnostic. Colonial types and horn corals are present and well preserved-, however, the honeycomb coral Favoyltes is no longer found.
The Pennsylvanian or Late Carboniferous lasted for 34 million years. Large shallow seas and fresh water swamps created an excellent environment for a great abundance of life. The great swamp forests are todays major coal fields. The plant life was quite diverse and very large when compared to present plant life.
Insects, amphibians and reptiles increased in diversity during this period. Brachiopods, bryozoa and crinoids were abundant. Corals were few and mostly of the solitary type. The blastoids became extinct during this period. An exceptionally large type of foram known as the fussilinid is characteristic of the Pennsylvanian. Trilobites are still around but rare.
The Pennsylvanian system in Idaho is represented by formations in the central and southeastern parts of the state. Tectonic activity during the Pennsylvanian caused uplift and many interruptions of sedimentation. Fossils representing the quality, quantity and diversity of life that existed in the Mississippian were never again repeated in the marine deposits of Idaho. Erosion and metamorphism since the Pennsylvanian has added to the problem of finding good Pennsylvanian fossils.
The lower Wells, lower Snaky Canyon, lower Oquirrh (Manning Canyon), Wood River, upper Amsden, Bluebird Mountain, and Quadrant are the Pennsylvanian formations of Idaho. All have been identified as Pennsylvanian based on fossil evidence, especially the fusilinid-type foraiiis.
The Wells Formation has in some areas produced a good variety of fossils, Forams including Fusilina and Fusulinelia are well preserved. Bryozoans such as Fenestella, Rhombopora, and Batostomella, and Brachlopods including Lingula, Schizophoria, Chonetes, and Productus are also found in the Wells Formation. Corals such as Syringopora and Lophophyllum and the gastropods Euconospiria and Platyceras are also known. Less common are the scaphopod Dentalium, the pectin Aviculopectin and the pelecypod Mucula. Crinoids are also known as are algae and ostracod fossils.
The Snaky Canyon has produced stromatolites, fusilinid and nonfusilinid-type forams, crinoids, bryozoans, brachiopods, corals and gastropods. The Oquirrh has produced conodonts from the Manning Canyon Shale.Fusilinids include Wedekindellina, Fusulina, Fusulinella and others. These are also found in the Wood River Formation near Hailey. The Oquirrh has also produced the colonial rugose corals Paraheritschloides grandis and Paraheritschioides complexa from the Deep Creek Mountains. Brachiopods, bryozoans, other corals and gastropods are found in the Oquirrh.
The Wood River has produced algae, fusilinid and non-fusilinid type forams, crinolds, bryozoans, brachiopods and corals. The upper Amsden has produced forams, echinoderms, bryozoans, mollusks, conodonts and hydrozoans whereas the Bluebird Mountain has only had conodonts cited. The Quadrant has stromatolites, bryozoans, brachiopods, corals, crinoids and fusilinids.
The Permian time period lasted for 41 million years. It was a time of continental-wide tectonic disturbance and climatic changes. The first cycads show up in the Permian. The first Urochordata (sea squirts or tunicates), Archosauria (dinosaurs, crocodiles), Euryapsida (nothosaurs, plesiosaurs, pliosaurs, ichthyosaurs) and the first snyapsida (mammal-like reptiles) show up in the Permian.
The Permian also represents great extinctions. The end of trilobites, conocardiacea-type mollusks, bactritoidea-type cephalopods, rugose corals and hyolithids came during the Permian. All productid brachiopods and most other types also died out as did all of the blastoids and most crinoids.
The Permian System in Idaho is represented by formations in the west and east central areas and the southeast. The formations and fossils indicate a restricted marine environment in the east-central and southeastern parts of the state. The west-central area is characterized by volcanics.
Other major Permian formations in Idaho are the Phosphoria, Park City, Shedhorn and Wells. The Snaky Canyon, Oquirrh, Windy Ridge, Hunsaker Creek, Casto volcanics, upper Wood River and Park City Formations also contain Permian sections.
The Phosphoria is by far the most fossiliferous of the Idaho Permian formations. Sponge spicules, horn corals, bryozoans, brachiopods (including Lingula, Orbiculoidea, Cancrinella, Productus and others), pelecypods, pectins, gastropods, belemnite and ammonoid cephalopods, ostracods, conodonts and fish remains including Helicoprion.
The large spiral teeth from Helicoprion are the most impressive fish remains from the Paleozoic of Idaho. All of the fish remains reported from earlier formations are isolated teeth, scales, dermal plates and small bones. A recent discovery of a fish cranium in a nodule from the Phosphoria may prove to be an exceptional find. This specimen, found by Dave Hovland and Steve Moore of the Bureau of Land Management, is being prepared for study at the Idaho State Museum of Natural History in Pocatello.
Other Permian formations in Idaho have produced fish remains. These include the Wells which has produced sponges, bryozoans, brachiopods and fish remains; and the Park City which has produced bryozoans, brachiopods, corals, pelecypods, pectins, gastropods, ammonoids, ostracods and fish remains.
In contrast, the Shedhorn, Windy Ridge and Casto Volcanics have not produced any fossils. The Hunsakeer Creek Formation has yielded a few identifiable Permian brachiopods. The Wood River Formation has produced algae, fusulinid-type forams and other forams.
Recent work in the east-central part of the state has brought to light some fossils in the Snaky Canyon Formation that are Permain. These include the Hydrozoan Palaeoaplysina, fusulinids such as Schwagerina, the rugose corals Heintzella, spitsbergensis and Durhamina cordillerensis and a few crinoids, bryozoans, brachlopods, gastropods and other forams and corals.
The Montpelier Region, Arco Hills, Southern Lemhi Range and southern Lost River Range are the best areas for finding Permian fossils.
The Triassic time period lasted for 37 million years. It started out with many unfilled ecological niches due to the extinctions of the Permian. Bivalves, including the unionids and oysters became very diverse in the Triassc. New types of gastropods developed during this period including limpets and periwinkles. The scleratinia-type corals which are the most abundant coral today first showed up in the Triassic. The first snakes also showed up during the Triassic period.
Especiallv noteworthy is the development of the first mammals. The mammal record is poor until the Paleocene and the extinction of the dinosaurs. It is, however, evident that by the end of the Triassic, animals with distinctively mammalian oestological features had evolved on the largest single land mass to ever exist.
Very few life forms became extinct during the Triassic. The conodonts, Bellerophon gastropods and the mammal-like reptiles known as paramammals are notable exceptions to the rule.
The Triassic system in Idaho is represented in the western part of the state by the Seven Devils Group, the Martin Bridge Formation and the Hurwal Formation. The Seven Devils Group, which includes the Doyle Creek and Wild Sheep Creek Formations, is known to have ammonites, echinolds, worm-like tubes, corals, gastropods, pelecypods, sponges, bryozoans and brachiopods. The Lewiston area is the best collection localltv. The Martin Bridge Formation has produced gastropods, bivalves, corals, echinoderms, spongiomorphs and ammonites. The best collecting is, however, in Oregon. The Hurwal Formation has not produced any fossils.
In the central and eastern parts of southern Idaho, many Triassic formations are exposed. These include the Higham Grit, Ankareh Formation, Dinwoody, Woodside, Thaynes, Timothy Sandstone, Deadman Limestone and Wood Shale.
Many of the formations are fossil poor. The Higham Grit, Deadman Limestone and the Wood Shale have so far been unproductive. The Ankareh Formation has rarely produced any fossils. The Timothy sandstone has only produced minor amounts of coal and unidentifiable plant material.
The Dinwoody and Woodside Formations have been somewhat better sources of paleontologic specimens. These formations, where they are exposed in the Montpelier area, have been considered "one of the finest Triassic columns in the world" (Newell and Kummel, 1941). These formations have produced pelecypods and ammonites. The Dinwoody has produced brachiopods including Ll'ngula sp. and gastropods including the last known occurrence of the genus Bellerophon.
The Thaynes Formation, in contrast to all of the above formations, has been very productive and includes a wide variety of fossils. Many ammonoids have been found in the Thaynes outcrops in the Wasatch Mountains. In the Caribou Range, the Thaynes has produced forams, conodonts, sponge spicules and shark teeth. Near Hot Springs, Idaho, the decapod crustacean Litogaster turnbullensi's has been found. Cephalopods, including ammonoid and nautiloid types, pelecypods, gastropods, conodonts, and fish remains such as shark teeth and dermal denticles have been found in the Bear River Range. Pelecypods, worm borings and fucoids have been reported in the Garns Mountain area. Crinoids and brachiopods are also known from Thaynes Formation outcrops in Idaho.
The only published record of a genus and species of a Triassic fish from Idaho rocks was recorded in 1904. Herbert Evans described a new species of cestraciontidae (Cosmacanthus elegans). He named the fish from a spine found in Paris Canyon.
The Jurassic time period lasted for 64 million years. It was a time of great evolutionary growth in terrestrial life and a time of expansion for shelf seas. World-wide temperatures were moderate.
Pulmonate mollusks (gill breathers) and coccolithophorida developed during this period. Bivalves, gastropods and crustaceans (ammonites) were the major marine organisms inhabiting the continental shelves. Ammonites became widespread and have proven useful in accurate correlation on a world-wide basis. There are 64 zones used in the study of the Jurassic. One for each million years on average.
Reptiles and land plants became quite diverse and widespread. Mammals continued to develop but remained small. The mammal-like reptiles (paramammals) became extinct during the Jurassic. The flying reptiles reached their peak during this period and the first birds developed.
The Jurassic system in Idaho is represented by formations in the western and eastern parts of the state. Erosion has removed all other traces of Jurassic sedimentation in Idaho.
Jurassic formations in the eastern part of the state include an unnamed formation near mineral, Idaho, the Coon Hollow Formation and the Idorwa Formation. It is possible that they are isolated remnants of a previously continuous sedimentary unit. Fossils are rare in these formations,
Near Mineral, excellent specimens of ammonites, including kepplerites snugharborensis and coiled bivalve oysters, including Gryphaea culebra have been collected. The Idorwa Formation near the Idaho-Oregon-Washington border has produced a total of 3 ammonites and 1 belemnite fossil. The Coon Hollow Formation has produced 5 specimens of ammonites belonging to the genus Cardioceras (scarburgiceras) . No other fossils have been reported from the Coon Hollow Formation.
The eastern side of the state has proved more fruitful. The formations here include the Nugget Sandstone, Twin Creek Limestone, the lower part of the Beckwith (now known as the Preuss Sandstone and Stump Sandstone Formations), and the lower Ephraim Formation of the Gannet Group. No fossils have been reported from the Nugget Formation in Idaho except for one bivalve specimen of the genus Trigonta. The Nugget Formation is the oldest Jurassic Formation in the Eastern part of the state.
The next younger formation is the Twin Creek Limestone which is the most fossiliferous Jurassic formation in Idaho. Fossils are generally fairly abundant but rarely well preserved.
Crinoids including Pentacrinus asteriscus and oysters including Gryphaea planoconvexa and Ostrea strigilecula have been identified. Bivalves, other than the oysters, include pectins and pelecypods. Brachlopods, ostracods, cephalopods, belemnites, worm burrows, gastropods and a probable hydrozoan have also been reported. The area around Bear Lake seems to be the most productive of identifiable material.
The Pruess Formation is the next younger formation. No fossils have been found in it. The overlying Stump Formation on the otherhand has produced Upper Jurassic fossils including oysters, crinoids, belemnites, corals and sea urchin spines. The lower Ephraim has yielded oysters and belemnites.
The Cretaceous time period lasted for 79 million years. It was a time of great change for the dinosaurs which reached both their peak and their demise during this time period.
In the protista kingdom at the other end of the scale, life was also changing. Silicoflagellata and Diatomacea began to appear. Diatoms have proven to be very useful for dating later formations. The first angiosperms also appear in Cretaceous times. These flowering plants produce leaves, seeds and pollen. Petrified wood and leaves are the most commonly collected fossil. Fossil seeds are relatively rare. Pollen may be preserved in excellent condition.
The Neogastropoda also developed in the Cretaceous while the Ammonoids which were so widespread and useful during the Jurassic died out. The bivalve order Hippuritoida which developed during the Silurian also passed away by the end of the Cretaceous.
The Cretaceous system in Idaho is only known from the southeastern part of the state. The rest of Idaho was undergoing uplift and erosion during this period.
The Gannet group, which represents the upper part of the previously named Beckwith Formation, is well exposed in Idaho. The formations involved include the Upper Ephraim, Peterson, Bechler, Draney and Tygee (Smoot). The Wayan Formation follows. The Smiths Formation, Thomas Fork, Sage junction, Cokeville and Quealy have also been described in the Caribou Range. These formations intertongue with the Bear River Formation and the Aspen Formation. The Frontier Formation lies above them and is the youngest Cretaceous formation in Idaho.
The oldest Cretaceous formation in Idaho is the upper Ephraim. Fossil charophyta have been reported from this formation. The Peterson Formation has produced a typical Cretaceous fresh water assemblage. The preservation is not very good and identifications are tentative. They include the pelecyopod Unio.?,the gastropods Viviparus?, Planorbis?, Goniobasis?, and two species of physa. Ostracods and charophytes from the Peterson Formation have been possitively identified to the species level.
Charophytes are remains of a fresh water algae. The remains represent casts of the plant nucules (female reproductive structure). They are sometimes commonly referred to as stoneworts.
The next younger formation in the Ganett group is the Bechler. The Bechler has been unproductive but may in the future be found to have some fossil content. The overlying Dranev Limestone has a fossil content similar to the Peterson Limestone. This includes unfortunately the same poor preservation of charophytes, ostracods, Unio? and Goniobasis?.
The sandstone unit above the Draney has been called the Tygee or the Smoot. It is not at this time known to have any fossils preserved in it.
The Wayan Formation is the most fossiliferous Cretaceous formation in Idaho. The only known dinosaur fossils from Idaho occur in the Wayan. The fossil evidence is, sad to say, very sparse and poor. The material collected represents at least two types of crocodile, an iguanodontid dinosaur (Tenontosaurus sp.), indeterminate. Ankylosaurian dinosaur material, indeterminate ornithischian dinosaur material, possible gastroliths and egg shells. (Jnzo sp. pelecyopod; gastropods, including Vivlparus, Limnaea? and Goniobasis?; turtle shell; and plant remains including pollen, coal, leaves and petrified wood are also known from the Wayan Formation.
Pollen samples have shown that the tree ferns Taurocusporites spackmani and cf. Verricosisporites obscurilaesuratus grew in Idaho during the Cretaceous. The coal deposits have not produced identifiable material. Some indeterminate dicotyledonous leaves have been noted. Nicely preserved silicified wood has been known from the Wayan Formation for over half a century. These remains are sections of the trunk of the tree fern Tempskya. Tempskya minor and Tempskya knowltoni have been identified. These tree ferns were columnar, unbranched, and stood up to 20 feet high with diameters up to 16 inches. Most of them were less than 15 feet high with a diameter of 8 to 10 inches.
Almost all of the Tempskya material from Idaho has come from the Wayan Formation in the Ammon and Wayan areas. The Aspen Shale Formation is the only other known Idaho source.
The remaining Cretaceous formations of Idaho have so far been poor sources of fossils. The lower Bear River or its equivalent has produced ostracods and charophytes. The Thomas Fork Formation has been reported to contain some dinosaur eggshell fragments.
Eocene and Oligocene)
The Paleogene time period includes the Palcocene, Eocene and Oligocene epochs. It lasted for 43 million years. Many important changes in life occurred during the Paleogene, especially in terrestrial life.
The great Cretaceous extinctions made room for a great expansion of the survivors. This expansion generally started out slowly in the Paleocene but by the Oligocene had gained a good momentum. The complexity of this radiation, the voluminous literature associated with it, and the lack of evidence in the Idaho fossil record precludes much of a discussion of it here.
Idaho has been a land mass since at least the Early Cretaceous. Except for fresh water and volcanic deposition, Idaho has been eroding throughout the Cenozoic.
The earliest record of fossil remains from the Paleogene of Idaho, which I have been able to find, is a plant record. Angiosperms which include Monocots and Dicots possibly began in the Jurassic. They are definitely known from the Cretaceous and by the end of it are undergoing a significant expansion. Much of the work by early paleobotanists identified fossil leaves using the well-known geologic principle of "the present is the key to past." Early angiosperms, however, may not have modern keys. Identification made on the gross characteristics of specimens that do not have the fine venation patterns preserved are open to question. Most of the work published before the 1970's suffers from this problem.
Paleogene formations in Idaho include the Eocene Challis volcanics which have fossil plant remains at Salmon, Germer, Thunder Mountain, Democrat Creek and Bullion Gulch reported by Axelrod in 1968. The Middle Eocene Salmon flora is located along the Salmon River near the city dump. It represents a cool-temperature climate. Acer (maple), Alnus (alder), Amelanchier (service berry), Betula (birch), Glyptostrobus (water pine), Metasequoia (dawn redwood), Salix (willow), sequoia (redwood), Typha (cattail), and other plant remains have been identified. There is no other fossil-bearing Paleogene formation known in Idaho.
The Neogene time period includes the Miocene and Pliocene Epochs. It has lasted for 18.4 million years. Life through this period became increasingly similar to presently Iiving species. Most of the genera still exist today as do many of the species.
Modern carnivores, rodents and ungulates have gone through a period of expansion during the Neogene of North America. The primitive mammalian forms were increasingly headed towards extinction.
Angiosperms were still expanding out into new genera and species. Grasses developed and spread out into savannah lands during this period. Conifer forests, however, have declined in diversity and areal extent.
The Neogene of Idaho is represented in the northcentral and southern parts of the state. There are more published acounts of fossils from the Neogene of Idaho than there are for any other time period. A complete listing of all the general and species identified has not been made but would contain representatives of all the kingdoms of life. The record is especially good for Miocene plants, Pliocene gastropods and Pliocene vertebrates.
Important outcrops in the northern part of the state include various Latah flora localities and the Clarkia localities of Miocene age. The Latah flora localities have been known since the 1920's. The Clarkia fossil area of northern Idaho was not discovered until 1972. The Clarkia is especially noteworthy for the excellent preservation of leaves. Fossil evidence of all the kingdoms of life including bacteria, algae, fungi, leaves, insects, mollusks and fish has been collected from Clarkia localities.
The east-central section of Idaho north of the Lemhi River and Leadore has been studied for many years by Ralph Nichols. Mr. Nichols has reported a diverse Miocene vertebrate fauna from this area.
The Salt Lake Group of southeastern Idaho is in part Miocene. This is based on a Merychippus horse skull found in 1932. Merychippus material has been collected in the Lemhi area and in the Coal Mine Basin area of southwestern Idaho. Probuscldian, camel, rhino, horse, beaver and rodent material has been found. The closest vertebrate fossil localities are in the younger Miocene sediments of the Poison Creek and Chalk Hills Formations which crop out to the north and cast of Reynolds Basin.
Most of the Miocene localities of Idaho are known from fossil leaf localities. These include the Payette Formation flora, Trapper Creek flora, Thorn Creek flora, Succor Creek flora and those mentioned above.
The Pliocene of Idaho is not specifically known for its flora although it does contain fossil wood localities, fossil cones, pollen and some leaf impressions. Vertebrate fossils by the thousands have come from the Pliocene of Idaho. The Glenns Ferry Formation of southwestern Idaho has been the major source. New important finds continue to be made. Mastodont, equus sp., camel, cervid, canis sp., beaver and possibly felid material has been found.
I can not emphasize how important it is to insure that vertebrate fossils are properly handled. The information associated with a vertebrate fossil can be easily lost if it is not properly collected. Locality data can be a significant part of the information. A specimen that is picked up and removed from a site needs to have accurate locality information written down so that a professional paleontologist can gain information on the stratigraphic position of the specimen. Taphonomic information is also lost unless it is written down.
The specimen itself can be very fragile and so be easily destroyed. I therefore strongly urge those that find vertebrate fossils to contact professionals about any discovery that is made. Any professional geologist or paleontologist in the state should be able to help you or put you in contact with someone that can.
The Hagerman fauna sites have proven to be the richest and most important Pliocene locality in the world. The years following the original discovery have continued to be fruitful. The area has been set aside as the Hagerman Fauna Sites National Natural Landmark. Vertebrate studies, mollusk studies and recently plant (pollen) studies have created a Pliocene species list unmatched by any other Pliocene Blacan locality in the world. The area has a tremendous potential for continued research and inter retation.
The Quaternary time period includes the Pleistocene and Holocene Epochs. It represents 1.6 million years of geologic time from the beginning of the Glacial Epoch to the present. We have made a distinction between the last ten thousand vears and the Pleistocene. This distinction may not be justified. The accuracy of dating earlier periods has not allowed us to define them to so fine a distinction. We may be in an interglacial period of minor importance in terms of geologic time. Life is still adjusting to the last ice advance and retreat. It may have to adjust to a new one.
Life in the Pleistocene was very similar to the life of the present. Some species have either died out completely or have moved out of North America and continued to evolve. We no longer have any native proboscidians, rhinoceroses, camels, llamas, horses or sloths in North America. The mammoths, wooley rhinoceroses and ground sloths have passed on forever.
Pleistocene fossils have been found throughout the state. Not all areas are very productive. The only Pleistocene fossil record that I have found for northern Idaho refers to a single horse tooth found at Moscow in the "Palouse" Formation. I would be happy to hear from anyone who may have Pleistocene fossils from northern Idaho. Almost all of the Idaho Pleistocene localities are either related to the Snake River Plain or are found in Late Pleistocene cave and archeological sites.
Because archeological materials and vertebrate fossils are important to science, they are not open to collecting without a permit. This insures that collection and curation are performed professionally.
The best known Pleistocene locality in the state is American Falls Reservoir. The best collection in the world of the giant horned Bison latifrons comes from sites at the reservoir. The major part of the collection at the Idaho State Museum of Natural Historv in Pocatello, Idaho comes from American Falls.
Jaguar Cave in upper Birch Creek valley has had an extensive Pleistocene fauna found in it. Other caves that have been open since the Pleistocene have also been natural animal traps. This kind of fossil preservation is quite unique as caves commonly contain complete fossilized skeletons. Such discoveries are not common as any animal that dies and is not immediately buried is torn apart by carnivores, attacked by bacteria and subjected to the stresses of heating and cooling.
Thanks to fast burial by the Bonneville Flood, a series of articulated vertebra with the spinal processes intact, a tusk and a humerous of a proboscidian was preserved northeast of Glenns Ferry near Sugar Bowl Hill.
In a gravel deposit near Grandview, Idaho, mammoth and bison bones were found some 20 years ago by workers on site
The Holocene or Recent time in Idaho covers the last 10,000 years. Deposits containing preserved evidence of past life include swamps, caves, archeological sites and lake bottoms. A rare occurrence of preservation of bones in a talus deposit has been found near Challis, Idaho. A very good collection of rodent bones has been recovered from this site.