Fossil Roulette

Between 7 million and 125 thousand years ago, waves of species moved between the South and North America. Raccoons, cats, and camels went south. Porcupines, armadillos and giant ground sloths went north. Some of these new arrivals likely caused upheaval in native habitats. Others, like the capybara, integrated into native communities with no harm to native species yet detected. Capybara added to Floridian diversity, ate the native plants, and became prey for native predators.

Capybara arrived in Florida in the time of terror birds and mastodons. The earliest Floridian record of Hydrochoerus is 2.2 million years old. Capybara lived in Florida and the southeastern United States for over 2 million years before being extirpated, or driven locally extinct, in Florida about 10,000 years ago. They were not seen again until reports from northern Florida around 1990 after a handful of animals escaped from human settlements. They have only been sighted eleven more times since then.

Specimen Number: UF VP 11337 References: Benson, A.J. "Hydrochoerus hydrochaeris (Linnaeus, 1766)": U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=2587, Revision Date: 6/3/2013, Access Date: 2/10/2018. Hulbert, Richard C. "Blancan North American Land Mammal Age": Encyclopedia of Florida Vertebrate Paleontology Land Mammal Ages. Florida Museum of Natural History, Gainesville, FL, https://www.floridamuseum.ufl.edu/florida-vertebrate-fossils/land-mammal-ages/blancan/, Revision Date: 2/8/2016 Access Date:2/10/2018 Hulbert, Richard C. "Coleman 2A": Fossil Sites of Florida. Florida Museum of Natural History, Gainesville, FL, https://www.floridamuseum.ufl.edu/florida-vertebrate-fossils/sites/coleman-2a/, Revision Date: 6/16/2015 Access Date:2/10/2018 Woodburne, Michael O. "The Great American Biotic Interchange: dispersals, tectonics, climate, sea level and holding pens." Journal of Mammalian Evolution 17(2010):245-264.

Where are similar fossils found?

If they do, then fossils of raccoons from particular places should be a predictable size. To test those predictions, a single fossil like this one is measured a dozen different ways. Researchers measure the length and width of each gray tooth in this partial jaw. They also measure the height of the jawbone underneath each tooth. Then, they compare the measurements to a database of tooth sizes of modern raccoons.

In that database, the smallest modern raccoons are found in the Florida Keys. The largest are found in and around Idaho. Between the two extremes is a gradient in sizes, with some exceptions. For example, raccoons in central Florida are, on average, a little larger than nearby raccoons from southern Florida and the rest of the southeastern United States.

This fossil from central Florida matches that pattern. Fossils of raccoons from Melbourne, another Floridian site, are similarly in size to raccoons living in the region today. Fossils like these, and their measurements, support ideas that regional differences have been in place for at least 10,000 years, over thousands of generations of raccoons.

Specimen Number: UF/TRO 29379 References: References: Hulbert, Richard C. "Ichetucknee River": Fossil Sites of Florida. Florida Museum of Natural History, Gainesville, FL, https://www.floridamuseum.ufl.edu/florida-vertebrate-fossils/sites/ichetucknee-river/, Revision Date: 6/10/2015 Access Date:2/13/2018 Ritke, Mark E., and Michael L. Kennedy. 1988. “Intraspecific Morphologic Variation in the Raccoon (Procyon lotor) and Its Relationship to Selected Environmental Variables.” The Southwestern Naturalist 33(3): 295–314. https://doi.org/10.2307/3671758. Wright, Thomas, and Ernest Lundelius. 1963. Post-Pleistocene raccoons from central Texas and their zoogeographic significance. The Pearce-Sellards Series 2. Texas Memorial Museum, University of Texas.

Where are similar fossils found?

On one hand, rivers do a great job of exposing fossils. They cut down into long-buried rocks and ancient soils. They carry away smaller, lighter grains of sand and clay. They leave fossils behind in the river bed or along the river bank where they are more likely to be discovered.

On the other hand, by carrying away surrounding rock, the river also carries away information about which layer a fossil comes from. The sediment layer, not the fossil itself, often carries the evidence of how old a fossil is.

Rivers also mix things together. They cut through layers of rocks and soils without discriminating one from another. Fossils from different ages and environments can all end up together on a riverbank. Fossil ages are further obscured as material gets added to riverbeds and banks year by year. Floods wash carcasses into rivers. Trash still ends up in streams. Pleistocene fossils from fifty thousand years ago can end up lying next to modern muskrat jaws and fifty-year-old fishing gear.

Specimen Number: UF 3470 References: References: Hulbert, Richard C. "Ichetucknee River": Fossil Sites of Florida. Florida Museum of Natural History, Gainesville, FL, https://www.floridamuseum.ufl.edu/florida-vertebrate-fossils/sites/ichetucknee-river/, Revision Date: 6/10/2015 Access Date:2/13/2018 Phylum: Chordata

Where are similar fossils found?

Differentiating a young individual from a new species is a challenge. Confusing the two happens occasionally. One good way for researchers to avoid that mistake is to gather dozens to hundreds of specimens from the same time and place. Replicate specimens help give a sense of which features are consistent across a species and make for good identifying features.

The fossil in the photograph and others of Archaeeocidaris featured previously all come from the same site, the Brownwood Spillway. Among the tons of rock making up the wall of the site are layers of dark, blue-gray, flaky rock. Those layers encased thousands of fossils.

Many of those specimens belonged to Archaeocidaris. In the case of that species, the key features turned out to be the dimensions and ornamentation of the spines.

Both small and large fossils had similar spines. That range of individuals with the same key features at different sizes allowed researchers to track the range of life stages in the species, from young ones slightly smaller than a dime to presumed adults a little smaller than the diameter of a soda can.

Specimen Number: TMM 1967TX16 References: Schneider, Chris L., James Sprinkle, and Dan Ryder. “Pennsylvanian (Late Carboniferous) echinoids from the Winchell Formation, North-Central Texas, USA.” Journal of Paleontology 79, (2005): 745–62.

The oceans were different back when Metengonoceras dumbli was alive. The Atlantic Ocean existed, but was smaller. Another ocean, called the Tethys, cut into Europe, Asia, and parts of Africa. At most points in history, the two oceans had different collections of species with little overlap.

In Africa, a deep trough linked the two oceans and their animals, but animals rarely crossed through the trough to span both oceans. At a few points in time, such as the formation of the Dumbli Horizon, about 100 million years ago, something changed. Metengonoceras dumbli shows up in the fossil record suddenly in what was then both oceans, in sites from Texas to Nigeria to France.

After Metengonoceras dumbli appeared, more species from one ocean appeared in the trough, then in the opposite ocean, increasing the range of the species and degree of similarity between the two oceans. The sudden, widespread appearance of the species happens at the same time that sea levels rose worldwide. It is possible that rising sea level made the trough a more suitable ocean bridge through which animals could cross, including Metengonoceras.

Specimen Number: BEG R19559=R19562 References: Courville, Philippe, Jacques Lang, and Jacques Thierry. “Ammonite Faunal Exchanges betweenSouth Tethyan Platforms and South Atlantic during the Uppermost Cenomanian-Lower most/Middle Turonian in the Benue Trough (Nigeria).” Géobios 31, no. 2 (1998): 187–214.

The central problem involves finding a standard. Researchers need to figure out what each species i>is before they can decide what belongs to it.

To solve the problem, scientists created a reference system of specimens called type specimens. The fossil in the photograph is the type specimen of Eopinnacrinus pinnulatus. If anyone finds a new fossil and wants to know if it's Eopinnacrinus pinnulatus, they check its features against the features of this fossil. Once a specimen is designated a type specimen, it becomes like a dictionary definition of a species and gains special status.

Like a dictionary definition, the type specimen doesn’t capture the entirety of the species it represents. The definition of “love” doesn’t give the full sense of what it means to love someone. The type specimen of the human species doesn’t capture the depth of humanity, and the type specimen of Eopinnacrinus pinnulatus doesn’t tell scientists everything they need to know about that group of 450 million-year-old animals.

Scientists prefer to use a suite of individuals to get a better picture of a species, but in a world of millions of words and millions of species the type system gives scientists a starting point.

Specimen Number: 1121TX66 Figure courtes of Paleocentral. References: Mayr, Ernst, Gorton Linsley, and Robert L. Usinger. Methods and Principles of Systematic Zoology. New York: McGraw-Hill Book Company, Inc., 1953. Sprinkle, James, ed. “Echinoderm Faunas from the Bromide Formation (middle Ordovician)of Oklahoma,” The University of Kansas Paleontological Contributions Monograph, 1 (1982): 1–369.

The star shape (in blue) is not made of petals. The five structures are sepals. Sepals are flower parts that grow outside the petals. They share a similar, but not identical, genetic basis with petals, and often work to protect or support the rest of the flower or the resulting fruit.

When scientists first discovered and described the fossil in the photograph in the 1930s, they identified the sepals, but made no comment on the blob where they met. They tentatively referred the specimen to a genus of plants still alive today, just as they had referred similar-looking fossils around the world from Switzerland to Colorado.

Seventy years later, researchers recognized the blob in the middle of some of the fossils (in green) as a fruit, and the specimen as part of a new group called Chaneya. The sepals ringing the fruit functioned as gliding wings. Like the helicopters of maple trees or the samaras of elms, the five-pointed wings on this fruit helped the wind pick up the fruit and carry it to new ground. Just as expected for wind-carried fruits, these types of fossils are often found in the remains of ancient lakes.

Photo credit: Angie Thompson

Special thanks to Sarah Allen for her help identifying the specimen

Specimen Number: OMB 1785 References: Ball, O. M. “A Contribution to the Paleobotany of the Eocene of Texas.” Bulletin of the Agricultural and Mechanical College of Texas, 4, 2, no. 5 (May 1, 1931): 1–173. Wang, Yufei, and Steven R. Manchester. “Chaneya, a New Genus of Winged Fruit from the Tertiary of North America and Eastern Asia.” International Journal of Plant Sciences 161, no. 1 (January 2000): 167–78. doi:10.1086/314227.

The log-like object on the bottom of the fossil is part of one shell of an adult rudist, an extinct, two-shelled animal related to clams and oysters. The tinier shells encrusting the top are the remains of at least two dozen baby rudists. When living relatives of rudists hatch out of microscopic eggs, they spend at least a day or two floating in the ocean as plankton before settling and cementing themselves to a permanent home. For rudists, sometimes, that home was the shell of another rudist.

Other fossils of accumulated rudists, called bouquets, are even larger than the one in the photograph. One bouquet from Croatia contained 160 individuals. A scientist shaved off such fossils millimetre by millimetre to get inside the fossil look for patterns to the accumulations.

He found that such large bouquets were mainly made up of rudists that died young. Newly-cemented rudists packed in tightly, taking up 85% of the available space, but few grew for long. Of the 160 individuals that settled on top of one another over the years, only one in four made it to an adult size.

Specimen Number: NPL 36298 References: Gotz, Stefan. "Inside rudist ecosystems: Growth, reproduction, and population dynamics" Cretaceous Rudists and Carbonate Platforms. SEPM Special Publication 87 (2007):97-113.

Oyster shells are irregular and asymmetric. Ilymatogyra is no exception. The shell in the photograph is an example. The right half of the shell is the small cap nestled into the rest of the shell on the upper right. The rest of the shell, and all of the spiral, is the left half.

Although living oysters don't form as obvious a spiral as the extinct relative in the photograph, remnants of spiral growth remain in the the early growth of today's oysters. Early in the development of baby oysters, a notch forms at a particular point in the tiny shell. As the oyster grows bigger, the notch deforms the edge of the shell and turns into a spiral growth track.

It's not clear why individuals of Ilymatogrya grew more strongly spiraling shells than other oysters. One proposal is that the kind of continuously growing spiral like the one in the photograph might prevent an oyster from sinking into soft mud on the seafloor, but the idea remains untested.

Specimen number: BEG 21161 References: Waller, Thomas R. “Functional Morphology and Development of Veliger Larvae of the European Oyster, Ostrea Edulis Linne.” Smithsonian Contributions to Zoology 328 (1981): 1–70.

Though most insect-like trilobites are known for their complex, mineralized, multi-lens eyes, at least one species lost those eyes. Instead of going extinct, the species multiplied. It split into many species that themselves split, becoming a group of animals that included Seleneceme.

It may be that blindness isn't advantageous, but is instead not a hindrance. Not having eyes doesn't necessarily make an animal more likely to die in a dark environment like the ocean floor, especially if that animal has other features that make it competitive. Support for that idea comes from the pattern of accumulated mutations in modern animals that live in caves and underground.

Another idea is that if an animal is born without eyes, it is actually lucky because it doesn't have to spend the energy required to grow those eyes. That chance energy savings may make it more fit than seeing animals in the right context. Others pointed out that both ideas could contribute to the survival of blind animals at the same time. Researchers continue to study what pressures, if any, drive eyelessness like that in Seleneceme.

Specimen Number: BEG 36640 References: Clarkson, Euan, Riccardo Levi-Setti, and Gabor Horváth. “The Eyes of Trilobites: The Oldest Preserved Visual System.” Arthropod Structure & Development 35(2006): 247–59. Moran, D., R. Softley, and E. J. Warrant. “The Energetic Cost of Vision and the Evolution of Eyeless Mexican Cavefish.” Science Advances 1(2015):e1500363–e1500363. Rétaux, Sylvie, and Didier Casane. “Evolution of Eye Development in the Darkness of Caves: Adaptation, Drift, or Both.” EvoDevo 4(2013):26. Turner, F.E. "Alsataspis bakeri, a new lower Ordovician trilobite." Journal of Paleontology 14(1940):516-518.

At that time, about nine million years after the extinction of T. rex and Triceratops, the world was already warmer than it is now. No ice stood on the poles. The continents themselves were also different: because of movement that proceeds every year at paces slower than glaciers, what is today France was at tropical latitudes. Those French former tropics are where people find the earliest known Volutilithes.

Then, global climate got even warmer. More and more seafloor became suitable for Volutilithes. New avenues and currents by which to cross the deep ocean also opened up. The species moved in to new habitats.

The group's range expanded from shallow, tropical seas around what is now Europe to the then-coastlines in Texas, where the fossil in the photograph lived. When earth was at its warmest during that period of 56-49 million years ago, the species lived in places as far away from each other as California and Pakistan.

Specimen Number: UT 18668 References: Givens, Charles R. "First record of the Tethyan genus Volutilithes (Gastropoda: Volutidae) in the Paleogene of the Gulf Coastal Plain, with a discussion of Tethyan molluscan assemblages in the Gulf Coastal Plain and Florida." Journal of Paleontology 63(1989):852-856.

The soft body of a brachiopod is protected by two shells that meet at a hinge, reminiscent of clams and other bivalves. However, brachiopods are more closely related to colonial, microscopic moss animals, than they are to clams.

Unlike clams, the two shells of brachiopods are never mirror images of each other. They always at least slightly different. Often, one shell is deeper, like a cup, and the other is flatter, like a cap.

Shells of Leptodus are an extreme variation on that asymmetry. One shell has dozens of vanes branching out from a sinouous center line, more like a fern than a clamshell. The other has internal ridges like rowing benches on a long boat, and pinches together to half-cover itself at one end.

The upper, flatter valve is so small that researchers debated whether it protected the animal at all or if it had become surrounded by the animal’s soft parts like an internal skeleton. A study of the muscle scars and notches on excellently preserved shells supported the more likely explanation that the flatter valve still functioned like an unusually shaped cap that fit an unusually shaped cup.

Specimen Number: NPL 62496 References: Stehli, Francis G. “Notes on oldhaminid brachiopods.” Journal of Paleontology 30(1956):305-313. Williams, Alwyn. “The morphology and classification of the oldhaminid brachiopods.” Journal of the Washington Academy of Sciences 43(1953):279-287.

Where are similar fossils found?

Some ancestors, some contemporary relatives, and possibly some descendents of Otoscaphites were tightly coiled ammonoids from origin to extinction. The animals built circular shells from a tight spiral of chambers. Some other relatives and potential descendents had radical, uncoiled shells. Some formed strange tangles and others looked like coathooks. Otoscaphites was neither a perfect spiral nor radically uncoiled. Instead, it was mostly coiled with one straightened chamber.

How did the uncoiling happen? All ammonoids were extinct at least 65 million years ago. No living descendents are around to carry genes or growth patterns that researchers can study.

Instead, researchers compared many specimens of Otoscaphites at different sizes and life stages. Smaller, younger specimens have an entirely coiled shell. Specimens at larger sizes have more sections to their shell added at its wide opening.

At a certain point the signals directing growth must have changed, because once individuals reach a certain size the final body chamber doesn't follow the spiral pattern. Instead, it's straight. Such changes to a body plan are very small, involving only one chamber at one stage of life.

Specimen Number: NPL 13328 References: Landman, Neil H., William A. Cobban, and Neal L. Larson. "Mode of life and habit of scaphitid ammonites." Geobios 45(2012):87-98.

Brachiopods are more closely related to tiny, colonial moss animals, called bryozoans, than they are to clams they might be confused for. When they first hatch they are tiny ocean plankton, floating and growing a special part of their shell called the protegulum.

Some grow the protegulum part of the shell only when they are in their egg, some grow it while they are floating plankton, and some do both. Some spend weeks in their floating larval stage and some float only days before they settle and metamorphose into adults. At metamorphosis, the protegulum stops growing.

In each scenario, the protegulum grows for different lengths of time and ends up a different size. In the specimens in the photograph, the protegulum is about 1/3-½ mm wide, or just barely visible as a speck to the naked eye. It has no special marks that come from growing in-egg. From that information researchers think that the young of Paucicrura started growing their shell as larvae after hatching and then spent weeks floating before settling into adulthood on the ocean floor.

Photo credit: Angie Thompson

Specimen Number: UT 0613 References: Freeman, Gary, and Judy W. Lundelius. “The transition from planktotrophy to lecithotrophy in larvae of the Lower Paleozoic Rhynchonelliform brachiopods.” Lethaia 38(2005):219-254.

Researchers studying modern-day low oxygen zones off the coast of California found several characteristics of the animal community living there. They tended to be smaller than members of closely related species, many ate trash or dead animals, a few were carnivores, and many also died young.

At some fossil sites, such as the one in Texas where these fossils were found, the fossilized collection of animals had similar characteristics to those above. Scientists concluded that they'd found the fossils in what was once a low-oxygen environment.

Some of those environments span large sections of rocks and millions of years. Scientists sampled the rocks from different levels of the preserved sequence, looking at the same environment at different points in time. When they checked the locality where the fossils in the photograph come from, they found that few groups of animals moved in or out of the community. While other ocean communities turned over more quickly, this community was stable for at least four million years.

Specimen Number: NPL 39288 References: Forcino, Frank L., Emily S. Stafford, Jared J. Warner, Amelinda E. Webb, Lindsey R. Leighton, Chris L. Schneider, Tova S. Michlin, Lauren M. Palazzolo, Jared R. Morrow, and Stephen A. Schellenberg. "Effects of data categorization on paleocommunity analysis: a case study from the Pennsylvanian Finish Shale of Texas." PALAIOS 25(2010):144-157. Kammer, Thomas W., Carlton E. Brett, Darwin R. Boardman, II, and Royal H. Mapes. "Ecologic stability of the dysaerobic biofacies during the Paleozoic." Lethaia 19(1986):109-121.

Some species have highly regular shapes and the same number of ridges on every shell. Other, like Cubitostrea perplicata, are irregular. Different shells have different number of ridges with different shapes. Each shell is disorganized with ridges starting and ending randomly throughout each shell.

When scientists investigated how such patterns were formed, they found an answer in the animals' soft parts. Shells of oysters and other related animals are laid down layer by layer. An organ called the mantle sits where each new layer will be. It lays down the biominerals that become the shell.

Researchers linked the irregular growth of oysters like Cubitostrea to the shape of the mantle. In an oyster like the one in the photograph, the mantle stretched much longer than the edge of the shell it grew on, making the surface ripple and fold like loose cloth. When the mantle started each new layer, it stretched over the old layer of shell. Researchers realized that instead of being purposefully organized, the ridges are just the results of layers after layers of oversized mantle.

References: Checa, Antonio G., and Antonio P. Jimenez-Jimenez. "Rib fabrication in Ostreoidea and Plicatuloidea (Bivalvia, Pteriomorpha) and its evolutionary significant." Zoomorphology 122(2003):145-159.