What’s your favorite dinosaur? Mississippi fossil findings helping to understand what varieties lived here

Published 11:33 pm Friday, September 29, 2023

Fossils are incredibly important tools for geologists. They are essential for unlocking the details of deposits and in determining both environment and time. This is especially true in parts of the geologic section that seem largely barren of fossils. In those cases, every detail can offer scientists valuable world clues.

A good case study for this is the geology of south Mississippi. Here the Grand Gulf Group outcrops from the southern edge of capital city in Jackson to the Gulf of Mexico. Sedimentary deposits of Grand Gulf Group span the time from the late Oligocene to Pliocene in age and reach a maximum thickness of three to 5,000 feet of section.

Determining and constraining the age and stratigraphic boundaries of the individual formations that make up these deposits has been a major challenge for geologists for a very long time. This is because this part of the geologic section is almost completely terrestrial and contains very few fossils.

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Plant fossil sites are the most common occurrence in south Mississippi. They are important environmental indicators, but they lack the necessary information that fossils of marine organisms can tell us about their age. The occasional find of the rare occurrences of terrestrial vertebrates in south Mississippi has recently been able to give us this great insight.

A happen-chance finding of a fossil bone at a hunting camp near Meadville, Mississippi in Franklin completely changed our understanding of the geology of the area. It was brought to the attention of the camp by one of the members and was dismissed as a cow bone. Not satisfied with that answer, he brought it to the attention of the Mississippi Museum of Natural Science in Jackson, who immediately contacted MDEQ’s Mississippi Office of Geology for a joint investigation of the find.

The find turned out to be the fossil leg bone of a type of ancient rhinoceros. Rhinoceros are part of a group of mammals called perissodactyls that evolved right here in North America about 55 million years before spreading to other parts of the globe. Rhinoceros became extinct in North America about five million years ago. So how does this find help us to better understand the geology of south Mississippi?

Being able to identify the fossil rhinoceros down to a specific species answers many questions. This fossil find was carefully studied and shared with other researchers to help narrow it down. The fossil bone was specifically from a stout legged rhinoceros named Teleoceras that lived from the Miocene to early Pliocene. These animals were semi-aquatic and lived along coastal swamps and freshwater river deltas similar to modern hippopotamuses.

Because this fossil bone was so well-preserved it could be narrowed down to a specific species, Teleoceras medicornutum. This animal lived during a narrower time frame in the middle part of the Miocene epoch called the Barstovian, which is the North American Land Mammal Age that lasted from 16.3 to 13.6 million years ago. From this one rare fossil we were able to reconstruct the geologic age, depositional environment, and reconstruct an ancient habitat for this part of the geologic section where before this discovery we knew so little about.

Pelletal Jaspers From Mississippi Gravel

Pelletal Jaspers are a chert-replacement of iron-rich pelletal carbonate mudstones derived from Paleozoic bedrock that once formed in ancient tropical, near-shore marine environments. Today’s example comes from the Pre-loess Terrace gravel photographed by MDEQ, Office of Geology staff in the field this week in Yazoo County, Mississippi. Most geologists that study petrology and how sediment forms think that pellets are an accumulation of many tiny fossils, called coprolites.  They are thought to be the fecal products of invertebrate organisms because of their consistent size, shape, and very high iron content. Pelletal jasper forms from chert replacement of Pelletal limestones and were carried here from Paleozoic bedrock sources up in the mid-continent by ancient rivers. Two types of pelletal jasper, red and green, are both available in the Pre-loess Terrace gravels along the bluffline and are also a constituent of the Mississippi River gravels.  The differences in color of pelletal jaspers are derive from the state of their iron impurities.  Red, the most found variety, like the example in today’s Fossil Friday. It gets its color from iron in an oxidized state.  The less common color, green, is also due to iron, but iron in a reduced state. These high-quality jaspers were culturally utilized for a few implements and ornaments in Mississippi’s rich prehistoric archaeological record.  Most notably, in the ancient Native American lapidary industry that began in the Middle Archaic cultural period and saw its height in the lower Mississippi Valley during the Late Archaic cultural period. Due to the texture and color variety of pelletal jaspers, they often can be mis-identified in describing artifacts from our ancient archaeological record. The gravel clast-size pelletal jasper can range widely, from small pebbles to large cobble size specimens.   Other types of local jaspers found naturally here (and similarly utilized from our gravels) are banded-iron formation jaspers (originating from bedrock much further up the watershed of the Mississippi River) and chert jaspers (which are basically just red chert, either natural or from heat-treatment).

Excavation of a Cretaceous Mosasaur Fossil by MDEQ’s Office of Geology for the Mississippi Museum of Natural Science

The discovery of an important mosasaur fossil was made in July of last year by the Mississippi Museum of Natural Science’s paleontologist and their Special Events coordinator as they were passing through an area that the Museum had worked several years ago for studies on Pleistocene fossils.  They had stopped again to visit this old fossil research haunt to look for more Pleistocene age fossils eroding from the alluvium outcrops along a small drainage through a vast expanse of agricultural fields.  The floor of these small drainages in this part of northeast Mississippi often exposes fresh Cretaceous age bedrock underneath that once was part of a shallow tropical sea.

This vast prairie region of northeast Mississippi is important for agriculture but is also unique and very important scientifically in other respects. They are windows into two distinctly different ancient worlds that can only be viewed here.

Fossils of both extinct ice age and dinosaur age animals can be found near one other another.  But they are separated vastly by both time and environment. Fossils of ice age animals that used to live on this rich prairie land are tens of thousands of years old.  While fossils from marine environments from the days of the dinosaurs that form the limestone bedrock that underlies this area are upwards of 80 plus million years in age.  This dinosaur age bedrock weathered over many thousands of years to form the rich prairie soils that sustain the farmlands of northeast Mississippi.

The museum’s scientists must have had their attention focused on looking high up in the outcrops of the ice age stream alluvium along the walls of the drainage because they had only noticed the dinosaur age fossil bones, a giant jaw full of teeth partially exposed in the floor of the drainage, on their way back out.  The bones imbedded in the rock are not much different in color or texture than the ancient limestone they are contained in.

The Mississippi Museum of Natural Science paleontologist immediately recognized the type of fossil it was by the shape of the teeth and jaw as a mosasaur fossil, possibly of the genus Clidastes.  Mosasaurs were a diverse group of marine lizards that inhabited various ocean environments of the Late Cretaceous period. These animals lived at the same time as Tyrannosaurs rex, Velociraptor, and Triceratops. Clidastes were relatively small to medium sized mosasaurs (reaching only about 20 to 30 feet in length).  The skull of this specimen was approximately 4 feet in length.

These types of mosasaurs were fast and very agile swimmers. They were highly adapted to hunting in the late Cretaceous seas. They sported jaws full of up to 60 dagger-like sharp pointy teeth that were curved inward, with additional rows of teeth at the roof of the back of their mouths to help secure larger prey.  Mosasaur’s teeth were frequently lost and replaced while hunting fish, swimming shellfish called ammonites, other marine reptiles, and likely each other.

Mosasaurs were sea dragons both large and small and were truly the apex predators dominating the various environments of the seas of this time. Some mosasaurs, such as Tylosaurus reached over 50 feet in length. While the dinosaurs ruled the land, these Mesozoic era oceans were likely the most dangerous of any time in the entire history of our planet.

The museum immediately contacted MDEQ’s Office of Geology research staff to coordinate a paleontological recovery excavation.  The team returned the next day to carefully photograph and excavate the near perfectly preserved lower jaws that were exposed in fossil-rich marine limestone of the ravine.  The team of scientists noticed while we were there salvaging the toothy jaws, that other elements of the skeleton were also present, fossil vertebrae and ribs scattered about nearby.  They carefully removed the randomly scattered pieces of bone that were associated with the jaws because they were also at risk of further eroding out of the hard limestone ground and lost forever.

The scientists realized that that there was likely much more to the fossil specimen buried just below the surface. Excavating any further would certainly have put at risk damaging any remaining bones of the underlying mosasaur fossil that they could not readily see embedded in the limestone just below the surface.  They all agreed that the best thing would be to continue to monitor the site over time as erosion of the bedrock naturally took place and quite possibly naturally and more delicately exposed many more bones of the mosasaur fossil.

Based on our earlier studies of the geology of the area by the State Survey program and knowledge of the other invertebrate fossils contained in the limestone, we know that this mosasaur was alive in a part of the late Cretaceous known as the Campanian age. After death, this mosasaur came to rest on top of the shells of an oyster bed where it was quickly buried by muddy lime deposits off the bottom of a warm tropical shallow sea.  Over the next tens of millions of years, the seas dried up and left this area and retreated to what is now the Gulf of Mexico.  The limestone lithified and encased the skeleton of this mosasaur in what geologists call the Mooreville Formation. This geologic formation has been precisely dated to about 82 million years old.

Seashells fossil are commonly found by our geologists in these marine outcrops and are also encountered in wells drilled by our scientists through these rock layers.  It is because of detailed studies of these fossils that our scientists studying the paleontology of these rock units know where they are in geologic time.  These geologic formations are divided by our mapping geologists by studying the ancient ecosystems of fossils that each formation contains.  They also conduct detailed studies of the types of environments the deposits were formed in, which are the sediments that the fossils are found in.

Isolated bones and teeth of mosasaurs, other ferocious marine lizards, and various sharks and fish that ruled this terrifying sea in the Late Cretaceous period are relatively common fossil finds along these limestone outcrops in the prairie region of northeast Mississippi. Even isolated finds of dinosaur bones have been found in this area from carcasses that once got swept out to sea by ancient storms and floods and then scavenged by sharks. But associated bones from a single individual animal are very rare and partial or even more complete skeletons are extremely rare from any period of the fossil record and therefore are exciting finds for scientists.  Mosasaurs just like the dinosaurs, went extinct at the end of the Cretaceous period.

In late July of this year. A return trip to the fossil site was made by our MDEQ survey geologists.  A brief stop was made to the fossil site.  This was done between giving an educational program to kids on rocks and fossils at a 4-H Summer Earth Camp in Starkville and a professional visit to the Union County Heritage Museum in New Albany, Mississippi for a new exhibit of our newly adopted Official State Gemstone on display.  On this brief return visit to the fossil site, we noticed that now much of the skull of Mosasaur was now visible and plans needed to be quickly made to properly excavate it.

A return trip to further excavate the mosasaur fossil remains was made the first week of August.  The scientists began the laborious process of excavating the skull from the bedrock in a single block of limestone instead of trying to remove the delicate bones individually in the field.  This would be more properly done delicately in a controlled environment than in the field.  A six-inch-high earthen dam was constructed around the large 5-foot by 3-foot block to be carved from the bedrock. The dam was constructed from loose sediment in the ravine to try and keep the trickle of water out of the excavation that was running through the narrow ravine.  Water was bailed by from the excavation by hand to keep the block as dry as possible.  This was just marginally successful as water kept finding its way back in through the loose soil dam as the team worked in the summer heat.

They had made it through most of the first day and successfully prepared part of the block just before a violent thunderstorm erupted and trapped, trapping the team in the narrow ravine to ride it out. Straight line winds from the squall line were more than 70 miles an hour battered the team for what seemed like 10 minutes and scattered all their field equipment about.

They had no choice but to abandon the excavation when the rain slacked up, because more heavy storms were visible on the radar and were heading their way. The next morning, they spent gathering up our equipment and securing the site to try again to regroup sometime later.  They hated to leave it but it was starting to thunder again as they left the site again and the weather pattern was forecasted to be more unstable in the coming days.

Every major paleontological excavation poses a unique set of conditions and challenges for scientists in the field. It is essential for the success of the projects to be able to adapt to those challenges. Over the next two weeks that followed more detailed plans were made for the return to the dig site to finish the removal of the massive limestone block containing the mosasaur skull fossil.  Geology staff gathered some additional tools, rigged up a small submersible pump and battery to keep the water out the excavation, bentonite clay to help seal the soil dam around the excavation, a long steel cable to use as a makeshift two-man rock saw to help separate the massive block from the bedrock, and designed a sled system from an old metal road sign and a wooden pallet to move the massive block once extracted from the bedrock.

Their return trip was on August 22 and the forecast was clear with no possibility of rain but was also projected to be one of the hottest weeks ever on record in Mississippi.

The team returned to the site and they found theirs earthen dam had washed across much of the excavation block which helped protect the exposed fossil bones from the elements. But the earthen dam had to be re-built and the mud and sand around block re-excavated to the state of the previous progress.  The 50lb bag of bentonite clay they brought sealed the dam just as planned and the submersible pump and car battery worked exquisitely to drain the excavation.

Quick work was then made the first day with rock hammers, pickaxes, sledgehammers, and a rotating bucket brigade to finishing excavating a trench in the limestone around the large block and properly pedestal it. The work went on tirelessly throughout the day in temperatures reaching above 103 degrees. That evening, before the removal of the block could begin the following morning, a burlap and plaster jacket was placed over the pedestaled block to protect it for later transport and was left to dry overnight.

The next morning efforts began to undercut the pedestaled and plaster-jacked block containing the delicate bones of the mosasaur skull. This was done by going around the bottom edge of the pedestal using the steel cable like a two man saw.  After a few grueling hours sawing around the rock, the pedestal was successfully undercut by about 6 inches all the way around the pedestal block.

Stakes were then driven with a sledgehammer into the rock all around the base of the pedestal and into undercut part of the block to break it free from the bedrock beneath in one massive piece.  Once it was broken free from the bedrock, the 1,000+ pound block containing the intact fossil skull was lifted by hand onto the makeshift sled.

The sled was strapped to a wooden pallet for stability.  The 1,000+lbs sled and block were dragged together by all 6 scientists for approximately 75 yards downstream to an opening along the edge of the ravine. By this time of the day temperatures had surpassed 105 degrees.  The enormous, jacketed block was now successfully moved with minimal damage into position where it could be winched up with the sled 20 feet along a nearly vertical bluff with the aid of a powerful truck winch mounted on the front a heavy-duty pickup truck.

Once out of the ravine the important Mosasaur fossil had to dead lifted by hand into the back of the truck by all 6 scientists, where it rode for about 3 hours back to the Mississippi Museum of Natural Science in Jackson. Once it arrived, it was greeted with much excitement by the museum’s staff.  It was forklifted from the truck and placed indoors. The top of the plaster jacket was removed to see what condition the block with the mosasaur skull fossil inside was in after the long haul. Elation was felt all around that it appeared to be in nearly perfect condition, still embedded in the solid rock, just as it was when it was first discovered.

The removal of a block of rock this size containing an intact vertebrate specimen is a monumental task in paleontology.  Though it took time, it was widely successful because of the collective expertise of the scientists involved.  It now can be properly excavated and studied in a temperature and climate controlled scientific environment using laboratory techniques and tools not practical for field studies.

Enormous amounts of data and measurements will be collected on the mosasaur fossil. It will be used to compare with others that have been described from around the world.  These findings and comparisons will be published as research in the scientific community.  Being able to carefully study the marine sediments and other fossils around this mosasaur fossil in a laboratory setting can additionally help to tell a deeper story. These important details include clues about the sea the animal lived in, what type of animals could have been feeding on its carcass, and details surrounding the circumstances of the environment that it was buried in and ultimately was preserved in.

The value of the preservation of this extremely rare specimen to the international scientific community and for Mississippi’s natural history is immeasurable.  It will only be realized through future careful multidisciplinary studies on this amazingly well-preserved fossil.

The rest of the fossil is likely buried beneath several feet of limestone and may never be completely recovered, but the site will be continually monitored over time as more bones from this mosasaur specimen might be further revealed by natural erosion.

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