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A collection of original photos taken by GRI scientists, illustrating a variety of specimens and features of paleontological interest.
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“Image copyright © Geoscience Research Institute, www.grisda.org. Used with permission."
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This relatively complete skull of an amphibian was excavated from Mid-Triassic layers of the Transantarctic Mountains, in Antarctica. It's fascinating to see that this large landmass mostly covered in ice contains a fossil record indicative of very different conditions than the present glacial environment. Specimen, about half meter in size, on display at The Chicago Field Museum of Natural History.
Bats are an example of abrupt appearance in the fossils record, without much subsequent modification of their body plan. This exquisitely preserved and articulated specimen (about 15 cm in size) is on display at the Field Museum of Natural History, Chicago, and comes from Eocene strata of Fossil Lake Basin, Wyoming.
A variety of invertebrate organisms live and feed within the soft sediment accumulating under water. The activity of these organisms, known as bioturbation, can leave traces in the sediments of the substrate. These traces can become fossilized, as is the case for this Cretaceous sandstone from the coast of Chile. The meniscate patterns in the sand are indicative of bioturbation. Surface view of bed, pencil for scale.
Birds have very delicate bones and are hard to find as articulated fossils. Here is a spectacular specimen from the Eocene of Fossil Lake Basin, Wyoming, on display at the Field Museum of Natural History, Chicago.
Three specimens of a Devonian armored fish, fossilized together. What is preserved are the armored head and the fins of the fish, still articulated. The fish must have died together, are found in close proximity, and are exceptionally well preserved. Slab (about 20 cm in size) on display at the Field Museum of Natural History, Chicago.
This is a specimen (several cm in size) of a fossil jawless fish, from the Devonian of Wyoming, on display at the Field Museum of Natural History, Chicago. Several groups of fish (like the ostracoderms, to which this fish belongs) appear suddenly in the rock record, without many intermediates.
Entire groups of fish found as fossils in Devonian rock layers disappear from higher strata. Among them are osteostracans, like Cephalaspis, a jawless armored fish. Human fingernail for scale. Specimen on display at the Colorado Museum of Nature and Science.
The fossils in this picture comprise the skull, pelvic bones, a few vertebrae, and hind limb bones of two organisms that have been presented as a part of an evolutionary sequence leading from terrestrial mammals to whales. Number 1 in the foreground is Rhodocetus, number 2 in the background is Basilosaurus. The specimens, on display at the Chicago Field Museum of Natural History, are meant to convey to the observer the concept of progressive adaptation to a fully aquatic behavior. However, inferences about the relation of past life forms should be introduced with awareness of the fragmentary nature of the fossil record.
A fossilized example of predation. This Cretaceous fish from the Crato Formation of the Araripe Basin, Brazil, died while ingesting another fish. Specimen on display at the Paleontological Museum in Santana do Cariri, few cm in size.
Dickinsonia is one of the macroscopic fossils found in the geologic layers just below the Cambrian. It is part of the so called "Ediacaran biota." There is no modern animal that has a similar body plan, so its mode of life remains a bit of a mystery. Specimen (several cm in size) on display at the Field Museum of Natural History, Chicago.
Exceptional preservation of organisms without hard skeletal parts, like this spider, requires special conditions for fossilization. Spiders appear abruptly in the fossil record. This is a Cretaceous specimen (few cm in size) of Dinodiplura ambulacra from the Crato Formation of Brazil, on display at the Paleontological Museum in Santana do Cariri.
It's not easy to become a fossil... and it's even more difficult if you don't have hard skeletal parts. That is why explaining the exceptional preservation of a dragonfly like this one, on display at the Chicago Field Museum of Natural History, is not a trivial matter. This specimen, from the Eocene of the Fossil Basin, Wyoming, is a few cm in size.
Edaphosaurs were large herbivores that had a peculiar "sail" on their back, supported by long neural spines with projecting tubercles. It is not clear what the function of this structure was, although a popular suggestion is thermoregulation. Specimen on display at the Field Museum of Natural History, Chicago.
The skull in this picture belongs to an entelodont, a pig-like mammal that could reach the size of a cow. Specimen from the Oligocene of South Dakota, on display at Chicago Field Museum of Natural History.
A set of Homo erectus calvaria (skull caps) on display at the Chicago Field Museum of Natural History. The sudden appearance of Homo erectus in disparate geographic areas from Africa to east Asia contrasts with the traditional gradualistic model of human evolution.
Fossil of frogs are not particularly common, but the ones we find tend to be preserved in articulation. This is a specimen of a Cretaceous neobatrachian frog from the Crato Formation of the Araripe Basin, Brazil, on display at the Paleontological Museum in Santana do Cariri. Few cm in size.
The genus name Glossopteris comes from the shape of these leaves: it means "tongue-shaped feather." These leaves are a typical fossil of Permian strata from continents of the southern hemisphere and were important for the development of the theory of continental drift. Specimen on display at the Chicago Field Museum of Natural History.
Glyptodonts are another impressive type of mammal lost to extinction and part of the Pleistocene megafauna. Specimen on display at the Chicago Field Museum of Natural History.
The dentition of this Permian gorgonopsian from South Africa shows features, such as elongated canines, interpreted as indicative of a carnivorous mode of life. The skull (about 20 cm in size) is on display at the Field Museum of Natural History, Chicago.
Cannibalism exhibited by the fish Dastilbe crandalli, Cretaceous Crato Fm., Brazil. Specimen on display at the Paleontological Museum in Santana do Cariri. Larger fish is about 10 cm in size. Unique environmental conditions are required for such spectacular preservation of fossil fish. This form of cannibalism is also interpreted as indicative of stressful environmental conditions.
Dinosaur trackways, the main one thought to have been left by an ankylosaurid (hammer for scale). Cretaceous El Molino Fm., Torotoro, Bolivia. Well developed fossil trackways imply a special set of conditions, with sediment wet enough for footprints to remain impressed followed by prompt induration and burial.
Accumulations of skeletal fragments of marine invertebrates are common in the geologic record and are important for reconstruction of depositional processes. This is a Permian example from the Copacabana Fm. of Bolivia, dominated by brachiopods (including Neospirifer condor) and crinoids.
The distinctive linear patterns observed on the surface of this sandstone bed are trace fossils produced by crustaceans as they were moving in the originally loose sediment. The technical term for this type of biogenic structures is bioturbation. Photo taken on a sandstone slab at the Varvito Park, Ito, Brazil, with exposures of Permian strata from the Itararé Group.
Mesosaurus is an extinct, small-sized, Permian marine reptile. It is very important for the history of geology because its disjunct distribution (eastern South America and western Africa) was used to argue in favor of continental drift (an early version of plate tectonics). These impressions of a vertebral column and a few ribs were photographed at the Cruziero Quarry, where strata of the Irati Formation of the Paraná Basin of Brazil are exposed.
Walking on mudcracks. A dinosaur left this track in muddy sediment that shrank, forming polygons upon desiccation. Trackway exposed in Cretaceous layers from the Sousa Basin of Brazil, at the Vales Dos Dinossauros geosite.
On the surface of this Cretaceous mudstone bed from the Sousa Basin of Brazil, one can see both polygonal cracks (indicative of subaerial exposure) and wave ripples (indicative of a thin cover of water).
Fossil branches and leaves of an araucarian tree from the Cretaceous of the Crato Basin, Brazil. On display at the Paleontological Museum of Santana do Cariri
Fossil feather from the Crato Formation, Cretaceous, Brazil. It is possible that this feather belonged to an individual of the bird species Cratoavis cearensis. Specimen on display at the Paleontological Museum of Santana do Cariri
3D preservation of pterosaur bones, in articulation, is extremely rare and requires special conditions for fossilization. This example comes from a concretion within the Cretaceous Romualdo Formation, Brazil. On display at the Paleontological Museum in Santana Do Cariri
Fossilized hatchling of a Cretaceous pleurodiran turtle from the Araripe Basin, Brazil. Specimen on display at the Paleontological Museum in Santana do Cariri, few cm in size.
Skull and foot of Hyracotherium, a small horse with 3 hooves on its hind feet. Specimens from the Paleocene of Colorado, on display at the Field Museum of Natural History, Chicago.
This iguanid lizard, on display at the Field Museum of Natural History, Chicago, is perfectly preserved in full articulation. Minimal decay after death is necessary for this type of fossilization. Specimen from the Eocene of Fossil Lake Basin, Wyoming. Note the close association with some fossil fish also perfectly preserved.
An example of exceptional preservation of a fossilized water strider (Telmatrechus parallelus). Slab, a few cm in size, on display at the Chicago Field Museum of Natural History, from the Eocene of Fossil Lake, Wyoming.
Flowering plants appear abruptly in the fossil record in Mesozoic strata. Here is an example of an exquisitely preserved sycamore-like leaf from the Cretaceous of Kansas. Specimen (several cm in size) on display at the Field Museum of Natural History, Chicago.
This incomplete but articulated skeleton is a specimen of Lystrosaurus, an extinct terrestrial vertebrate (synapsid) the remains of which are found in several distant locations in the southern hemisphere, including Antarctica. The widespread distribution of Lystrosaurus was used by early proponents of the continental drift theory to suggest the existence of a once unified supercontinent, Pangea. Hence, its iconic status in geology and paleontology. Specimen on display at the Chicago Field Museum of Natural History.
Stasis and plants: specimens of fossil maple leaves and fruit from the Miocene of Oregon. On display at the Field Museum of Natural History, Chicago
Marginocephalians are a group of herbivorous dinosaurs found in Cretaceous layers and characterized by a bony frill at the back of their skull. This photo shows specimens of 4 different species within this group, on display at the Field Museum of Natural History, Chicago.
Megatherium is one of the largest land mammals known to have existed and is part of the Pleistocene megafauna. This ground sloth was endemic to South America. Specimen on display at the Chicago Museum of Natural History
A perfectly preserved fish resting by a perfectly preserved palm frond...This slab on display at the Field Museum of Natural History, Chicago, comes from Fossil Lake Basin, Wyoming, a locality that has yielded exquisite specimens of a variety of organisms. Special conditions are required for this kind of uncommon preservation.
Pantodonts are an extinct type of large mammals, somehow reminiscent of hippos. Skull (from Paleocene of Colorado, US) on display at the Field Museum of Natural History, Chicago.
What do these two fossils share? They died together, they are spectacularly preserved, and they were buried rapidly. These specimens of a prawn (Bechleja rostrata) and a herring (Knightia eocaena) are from Eocene deposits of the Fossil Lake, Wyoming, on display at the Chicago Field Museum of Nature and History.
Trimerophytes were leafless vascular plants, with branches departing from the stem in a spiral pattern. This specimen containing multiple stems (several cm in size) is from the Devonian of Quebec, on display at the Field Museum of Natural History, Chicago.
The body plan of fossil scorpions is not much different from modern ones: an example of morphological stasis. This is a Cretaceous example from the Crato Formation of Brazil. Specimen on display at the Paleontological Museum in Santana do Cariri, few cm in size.
Two types of fossils preserved in close proximity. The herring-like fish, Dyplomystus dentatus, consists of actual bone remains. The gastropod is an internal mold made of sediment, with the original shell being dissolved. Slab is about 10 cm in size, on display at the Chicago Field Museum of Natural History. From Eocene deposits, Fossil Lake, Wyoming.
Snakes appear in the fossil record in Mesozoic layers. Here is a cast of a fully articulated specimen from the Cretaceous of Bosnia-Herzegovina, on display at the Field Museum of Natural History, Chicago.
Reconstruction of the skeleton of a dicynodont synapsid, from the Permian of South Africa, on display at the Field Museum of Natural History, Chicago. These large animals with big barrel-shaped trunks are thought to have been herbivores.
A cast of a famous specimen (about 50 cm in size) of the lobe-finned fish Tiktaalik roseae, from the Devonian of Canada, on display at the Field Museum of Natural History, Chicago. Tiktaalik is often presented as a "missing link" in tetrapod evolution. However, as it often happens, the picture of "sequential transitions" is much more complicated when looked at in detail, with mosaic distribution of characters between various forms.
A panel on display at the Chicago Field Museum of Natural History, meant to illustrate how the appearance of more complex tool kits signals the emergence of more sophisticated tool-making abilities. However, this general stratigraphic order of appearance is not as clear cut, and tools representing different lithic industries can be found in correlative layers or even in inverted order.
Compare the foot of this big land vertebrate with the hand of a human... Pretty massive animal, right? Can you guess the species? Well, a T. rex dinosaur, of course! This specimen welcomes you in the foyer of the Denver Museum of Nature and Science, CO, US.
5 different organisms (a soft-shelled turtle, 3 species of fish, and an insect) are preserved in close proximity on this slab from the Eocene Fossil Lake Basin, Wyoming (on display at the Field Museum of Natural History, Chicago).
Replica of the skeleton of a Cretaceous large marine reptile, Taniwhasaurus antarcticus, on display at the Chicago Field Museum of Natural History. Remains of this reptile are found in locations both within the southern and northern hemisphere, illustrating an example of widespread distribution of a fossil type.
This large-sized extinct bear was a representative of the so-called Pleistocene megafauna. Specimen mounted and on display at the Chicago Field Museum of Natural History.
This specimen of a fossil wasp comes from Eocene strata of the Fossil Lake (Wyoming) and its body plan is quite similar to modern representatives of this type of organism. On display at the Field Museum of Natural History, Chicago.
Dinosaurs are not the only group of organisms to disappear above Cretaceous strata. Inoceramids, a family of large bivalves, are also extinct and not found in Cenozoic layers. Remains of fish have been found preserved within some specimens of this giant clam, leading to the suggestion of possible commensalism or symbiosis. Specimen on display at the Colorado Museum of Nature and Science.
“Brontosaur bulges." Mid-way through the picture we can observe four bulges in a sandstone layer, depressing downward the underlying layers. These have been interpreted as a dinosaur trackway viewed in cross-section. A large sauropod left these “underprints" by deforming soft sediment while walking. Very specific conditions (e.g, sediment cohesiveness, rate of sedimentation, exposure vs submergence) are necessary for the preservation of footprints in the rock record. Scale bar is 40 cm long. Photo taken at Dinosaur Ridge, Golden, Colorado.
The Dinosaur Ridge Tracksite, in Golden, CO, preserves two main types of dinosaur footprints. Both are tridactyl (with three toes). They have been colored in with charcoal to enhance their visibility. The tracks with a wider aspect and thick toes were made by ornithopod dinosaurs. They were left by animals of different sizes (possibly adults and juveniles). The narrow-toed tracks were made by theropods. See if you can recognize the different tracks. This outcrop exposes the surface of a sandstone bed in the Lower Cretaceous South Platte Formation of the Dakota Group.
Fossil impressions of palm fronds exposed on a verticalized bedding surface of fine sandstone in the Maastrichtian Laramie Formation, near Golden CO. The integrity of individual fronds implies that minimal decomposition took place prior to burial. Scale bar is 40 cm long.
Calcareous nannofossils (coccoliths) are among the tiniest fossils preserved in the sedimentary record, measuring around 5 to 10 microns. The image (plate) shows petrographic microscope photos of some of the most characteristic coccoliths of the Cretaceous/Paleogene (K/Pg) boundary. This boundary is associated with one of the most studied mass extinctions in the geological record, which has been correlated to a major catastrophic event. Photos 1 to 4 show nannofossils of the Upper Cretaceous (Maastrichtian) that are thought to have gone extinct at the K-Pg catastrophic event. Photos 5 to 7 are of Cretaceous survivors that show continuous distribution into the Paleogene (Danian). These last species are considered adapted to cold water and eutrophic environments (r-selected taxa). Photos 8 and 9 show Paleogene taxa, not present below the boundary. (Photos by E. Belia)
Large fossilized redwood stump preserved in Eocene deposits at Florissant Fossil Beds National Monument (CO). Volcanic activity was essential for rapid burial and petrification of this stump. Vertical side of notebook (for scale) is 19 cm long.