Cretaceous Jaws by Robert Nicholls. Copyright © 2003 by Robert Nicholls; used with permission of Robert Nicholls. The large shark at the top is Cretoxyrhina mantelli, while the two smaller sharks at lower right waiting their turn are Squalicorax falcatus. (Click picture for larger version)
June 12, 2003 - Translated into French by Jean-Michel Benoit (Click on flag)
* Author's note: Over the past several years, we have found a number of instances where the fossilized parts and pieces of mosasaurs are all that remained of some sort of feeding activity. In some cases, these fossils have been partially digested by something large enough to swallow a large piece of a mosasaur. In others, there are embedded pieces of teeth from the large lamnid shark, Cretoxyrhina mantelli. In one well documented specimen (FHSM VP-13283), there were embedded Cretoxyrhina teeth, two vertebrae that had been bitten completely through, and the evidence of partial digestion (Shimada, 1997; Everhart, 1999). We were left with the conclusion that it was this large and apparently very powerful shark that was feeding on mosasaurs. Since the shark had no common name in the literature, and since it fed by slicing up its victim into bite-size pieces, we decided that the title Ginsu Shark, was an appropriate, descriptive (and somewhat humorous) name for this awesome creature.
The specimens (FHSM VP-13746 mosasaur vertebrae; and FHSM VP-13937 embedded Cretoxyrhina tooth) described on this web page have been published as (see abstract below):
Everhart, M. J. 2004. Late Cretaceous interaction between predators and prey. Evidence of feeding by two species of shark on a mosasaur. PalArch, vertebrate palaeontology series 1(1):1-7.
An overhead view of the remains of a shark scavenged mosasaur. A single, dislocated cervical vertebra is at the right side of the picture, near a series of fourteen dorsal vertebrae with attached ribs. The last dorsal vertebra (left side of picture) was fractured prior to burial. Seven additional dorsal vertebrae were removed earlier and are not shown.
On our first field trip of the season in February, 1992, Pam found two mosasaur vertebrae that had eroded from the side of a steep gully on the west side of our favorite site. The two vertebrae were about three inches long and appeared to be from the lower back of a medium sized mosasaur. They had been on the surface long enough for their color to bleach from a reddish brown to a light gray but were otherwise in good condition.
When we looked closely at the chalk slope, we found the end of another vertebra emerging from the matrix. One of the first things we noted (and were pleased with) was that it was the rounded end (posterior) of the vertebra that was exposed. This meant that we would be digging toward the head of the mosasaur, not the tail. When you are looking at the prospect of removing several tons of rock, its much easier to be enthusiastic about the possibility of also finding the skull of the mosasaur.
It was already late in the day, but I still had time to do some exploratory digging. Since the slope of the gully wall was so steep, I had to remove about 18 inches of chalk overburden in order to go back about 15 inches into the side of the gully. The chalk was fairly easy to dig (a good sign) and within 30 minutes, I was down to the level of the bone. Working carefully with an ice pick and brush, I was soon able to uncover five chalk covered lumps that were barely recognizable as articulated vertebrae. I was disappointed (briefly) to see that there was empty chalk behind the fifth vertebra, but soon discovered the rounded end of the next, but unattached, vertebra that was still buried under 18 inches of chalk. Satisfied that the specimen continued further into the side of the gully, I continued to excavate around the first five vertebrae.
As I dug downward around them, I found that the specimen was laying on/in a thin layer of volcanic bentonite. We refer to this as a release layer since it usually allows the fossil to be lifted easily from the chalk. We are not sure whether or not there is a connection between this periodic volcanic activity and the death of marine life in the Western Interior Sea, but we do find many fossils in association with these thin bentonites.
Minutes later, I was able to remove the remaining five vertebrae from the chalk and put it into a box for transport. By then, the sun had dropped below the hill and it was time to leave. I covered up the site with loose chalk and began thinking about how I was going to uncover the rest of the mosasaur. I realized that the vertebrae that I was carrying were from the middle of a mosasaur that was probably about 15-16 feet long. I would have to open an excavation about 8 feet long by 5 feet wide though three feet of chalk to get down to the level of the mosasaur remains. That is roughly 4 cubic yards of chalk......all I could hope for was that the chalk over the rest of the specimen was as easy to remove as the chalk at the edge of the gully.
The preparation of the seven vertebrae was uneventful. They appeared to be typical of most mosasaur material found in the chalk....well preserved but flattened from side to side during preservation. Examination confirmed my field observation that they were lower abdominal vertebrae. The back half of the mosasaur, if it had been complete, was already gone down the gully. It would be several months before we were able to return to the site to see what was left.
Later that Spring, we finally got back to begin the dig for the rest of the mosasaur. Arriving at the site about 9 AM, I took a quick look to make sure that I had really seen another vertebra emerging from the chalk in the February twilight. I was pleased to see that the bone was really there and began the sweat work of removing the three feet of overburden that was between me and the remaining bones.
The site where the two mosasaur vertebrae were found eroding from the side of a gully (arrow). There was approximately 3 feet of chalk over the rest of the specimen.
The chalk broke up easily into thin layers and small pieces. After breaking up the surface with a large pick, I was able to do most of the work with a flat bladed shovel, literally peeling off the chalk several thin layers at a time. By noon, there were piles of chalk all around the excavation and I was down to the layer just above the specimen. Sweat work turned into slow, cautious, down on your knees work. Starting from the exposed vertebra, I began uncovering a series of lumps that led in a gentle curve toward the back edge of the excavation. Whatever was there appeared to be laid out in a more or less straight line. After about 5 more vertebrae were located, I started finding ribs that appeared to be still attached to the vertebrae. While interesting, ribs are generally pretty featureless and do not help much in identifying a specimen. However, in this case, I believed that they were a good sign that the remains had a better chance of being complete.
This photo shows what remained of the left side of the mosasaurs rib cage after being scavenging by sharks. Although not as badly damaged as the right side, many of the ribs showed bite marks from Cretoxyrhina and/or Squalicorax.
The string of vertebra continued until I had fourteen in a row. I was getting a little nervous with anticipation at this point, knowing that I was getting close to the skull. If it was there, I was going to have to remove a lot more chalk, but there would be enough adrenaline pumping at that point that it would be relatively easy to move a small mountain. My hopes were dashed shortly after that when I discovered there was nothing attached to vertebrae number fourteen! I started digging further into the chalk and was briefly rewarded by the finding of another vertebra. It was shaped differently and I soon realized that it had been preserved bottom side down instead of left side down like the others. It also appeared to be a cervical vertebra, so I knew I was only six more cervical vertebrae away from the skull. However, there was nothing attached to this vertebra and I had to keep digging. After removing more chalk, I gave up when I found nothing more within two feet of the last vertebra. Disappointed and tired, I settled down to the task of documenting, numbering and removing the four foot long series of vertebrae and ribs that I had found..........
To make a long story a little shorter, 1992 was a very good year for fossils and specimen 1992-11 went into storage for several years. It was briefly examined by Gordon Bell and Bruce Schumacher, two mosasaur experts from the South Dakota School of Mines in 1993 and 1994, and they both indicated that the vertebrae may have been from a rare mosasaur called Ectenosaurus. If so, it would have been the earliest record of this species, but without further diagnostic evidence, it was not important enough for me to pursue further identification.
A nearly complete specimen of the rare Cretaceous mosasaur, Ectenosaurus on the wall in the old Sternberg Museum, Fort Hays State University. The photo shows the unusually long and narrow skull of this species.
In 1996, I began experimenting with using sodium bicarbonate as a soft blast media to remove chalk from bones without damaging the bones. I pulled out some of the vertebrae from this specimen to use as practice material and found that the technique worked well. My equipment, however, needed major fine tuning and it was put away until it was needed to clean up the big Tylosaurus proriger skull in the Spring of 1997.
As I was cleaning the large Tylosaurus skull, I also took the opportunity to work some more on the string of vertebrae. While preparing the anterior dorsal vertebrae, I discovered evidence of bites on the vertebrae by a large Cretoxyrhina mantelli shark, including the embedded tip of one tooth.
LEFT: Although not a good picture, this photo does illustrate the location (left arrow) of an embedded Cretoxyrhina tooth on dorsal vertebra number four (D4). The right arrow shows the location of another tooth mark on the same vertebra.
Since I had already reported on a Cretoxyrhina attack on a mosasaur at the Kansas Academy of Sciences in 1995, and had filmed part of a Paleoworld episode on the specimen in early 1997, one more set of shark bitten vertebrae was not big news. It was not until I had some time to finish the clean up of the specimen in early 1998 that I realized that I had clear evidence of not only an attack and/or feeding on a mosasaur by Cretoxyrhina mantelli but also what appeared to be the subsequent scavenging of the carcass by Squalicorax falcatus, another, much smaller but voracious Late Cretaceous shark. Before I get too far ahead of myself, I need to describe the remains of the mosasaur.
|As shown at left, the remains were laid out in gentle curve, and roughly along a north south line. A total of 22 vertebrae were found, and it is likely that these formed a continuous series when the mosasaur was alive. The most anterior vertebra found was a cervical. Most mosasaurs have seven cervical vertebrae that make up the neck and this appeared to be the seventh one. It had been separated from the others prior to burial and was the only one preserved in an upright position. There are two deep cuts along the upper left side that appear to be tooth marks. It is possible that this vertebra was dislocated when the head and/or neck of the mosasaur was twisted off by a large shark.|
All of the remaining vertebrae are dorsal vertebrae, starting with the first dorsal (D1) and ending just before the pygal vertebrae located at the hips of the mosasaur (D19). The string of vertebrae was continuous from vertebrae D1 through D14, then again continuous from D15 through D19. Vertebrae D20 and D21 were the ones found initially and may have been articulated with D19 prior to eroding out. Vertebrae D15 through D21 were the first to be removed in February, 1992. Vertebrae D15 was fractured prior to burial. This damage may have the result of whatever feeding activity removed the mosasaurs tail and lower limbs.
|This photo shows the right side of dorsal vertebrae D1 (right) through D4 (left) after preparation. The white arrows mark the location of several Cretoxyrhina bite marks, including the location of the embedded tooth in vertebra D4.|
|A closer view of the bitten area of the same vertebrae shown above. The spacing of the bite marks (about 3 cm) is interpreted as the spacing of the tips of the shark's teeth from a single bite, and indicates that a very large shark made this bite.|
As found, the remains of the mosasaur were laying on its left side. Most of the ribs from the left side had only minor damage and were still attached to the vertebra as shown on the right hand side of the first picture.
|The right half of the rib cage, however, had been essentially shredded by shark bites, including a major bite to vertebrae D2 through D6 that resulted in gashes to these vertebrae and a broken sharks tooth left in vertebrae D4. Since this bite was to the right shoulder area, it may have also removed the right front paddle. No limb elements were found with the remains.|
Remains of ribs from the right side of the mosasaur's rib cage, showing that most had been bitten completely through.
A close up of one of the ribs from the right side, showing a deep scar from a Cretoxyrhina tooth near the head of the rib, and another mark near the notch at the right side of the picture.
An extreme close up of the reverse side of the same rib, showing a series of Squalicorax bites (curved cuts) across the lower end of the what remained of the rib. This is interpreted as scavenging by the smaller shark after the Cretoxyrhina had fed on the carcass.
Many of the ribs had been bitten through by a large shark. Since there were no serrations on the bitten ends of the ribs, this damage was more than likely done by the Cretoxyrhina. On some ribs, the outer layers of bone had been scraped off by a sharp tooth sliding over the bone. Smaller Squalicorax sharks had gotten in on the action, however, and serrated scrapes and slices from their teeth are visible on several ribs.
In summary, it appears that an adult mosasaur was violently dismembered and fed upon by one or more Cretoxyrhina sharks. The head, neck, forelimbs and about half the ribs were removed at that time. There is no evidence to indicate whether this was predation by the shark or simple scavenging of a dead mosasaur carcass. The open ribcage suggests that the carcass had been totally gutted. A further indication of the violence of the feeding activity is that the back was broken just above the hips. It is likely that the hind limbs and tail were also detached from the body by the larger shark(s). Following the initial feeding activity, the remains were scavenged by smaller Squalicorax sharks before sinking to the sea floor. The vertebrae and ribs were exposed long enough for oysters (Pseudoperna congesta) to briefly colonize the bones.
While it is reasonable to presume that a giant shark equipped with sharp, blade-like teeth is going to feed on whatever it wants, the evidence of such behavior has been limited. Some shark bitten fossils may have been overlooked by earlier workers, but it appears that these sharks were able to swallow and digest most of what they ate, and there were few leftovers. Cretoxyrhina mantelli, the Ginsu Shark, was a very awesome and very thorough meat eater.
Note: In November, 1999, these specimens were donated to the Sternberg Museum of Natural History, Hays, KS as: FHSM VP-13746 mosasaur vertebrae; and FHSM VP-13937 embedded Cretoxyrhina tooth.
The Rest of the Story-- Additional evidence of the Ginsu Shark, Cretoxyrhina mantelli, feeding on mosasaurs. The fossil remains of the "Parts and Pieces" that were left over.
Cretoxyrhina mantelli and Squalicorax falcatus - Here are some pictures of the teeth of these sharks.
A Moment in Time - Another example of Cretoxyrhina mantelli feeding on a mosasaur.
One Day in the Western Interior Sea..... Life could be very short for the unwary.
The Discovery of a Giant Ginsu Shark... Seven meters of Cretaceous JAWS! April 2002
You can now download a copy of this early article on Kansas Sharks by Williston - Provided by the Kansas Geological Survey.
Williston, S. W. 1900. Cretaceous fishes: Selachians and Pycnodonts. University Geological Survey Kansas VI pp. 237-256, with pls.
Abstract of paper presented at the 1999 Society of Vertebrate Paleontology meeting in Denver, Colorado:
Everhart, M. J., 1999. Evidence of feeding on mosasaurs by the late Cretaceous
lamniform shark, Cretoxyrhina mantelli. Jour. Vert. Paleon.
17(Supplement to 3):43A-44A.
Incomplete skeletal remains of marine lizards (Mosasauridae) with feeding traces attributed to the extinct lamniform shark, Cretoxyrhina mantelli, are known from the Late Cretaceous Niobrara Chalk of western Kansas. These specimens were collected from the lower one-fourth of the Smoky Hill Member (Late Coniacian) in the biostratigraphic zone of Protosphyraena perniciosa. The most common mosasaurs in the Western Interior Seaway at that time were Tylosaurus nepaeolicus, Tylosaurus nov. sp., Platecarpus tympaniticus and Clidastes liodontus, with the larger tylosaurs reaching lengths of 10 m. Cretoxyrhina mantelli was a large shark with a world wide distribution. The fossil record suggests the species reached a length of about 6 m at this biostratigraphic horizon.
Evidence of feeding on mosasaurs by C. mantelli includes; 1) mosasaur bones with bite marks and/or embedded Cretoxyrhina teeth; 2) partially
digested bones; 3) severed bones; and 4) combinations of the above. Mosasaur vertebrae have also been found as preserved stomach contents in C.
mantelli remains. On the basis of this evidence, no other known marine predator, including other mosasaurs, could have been responsible for these
feeding traces. Most of these specimens can either represent a fatal attack or scavenging on a dead mosasaur by C. mantelli. There are specimens,
however, that show not all such bites were fatal. For example, the caudal vertebrae in some remains show fusion due to an apparent infection following a shark bite.
During the period from which evidence of this feeding behavior was observed, mosasaurs were becoming more diverse and widespread. By the early
Campanian, Cretoxyrhina mantelli had apparently become extinct and mosasaurs were the dominant large marine predators in the Earth's oceans.
Everhart, M. J. 2004. Late Cretaceous interaction between predators and prey. Evidence of feeding by two species of shark on a mosasaur. PalArch, vertebrate palaeontology series 1(1):1-7.
The fragmentary remains of a mosasaur discovered in the Smoky Hill Chalk Member (Late Coniacian) of the Niobrara Chalk of Gove County, Kansas, U.S.A., preserve a number of injuries consistent with scavenging by two species of lamnid shark. The mosasaur (FHSM VP-13746) remains were identified as cf. Ectenosaurus clidastoides and consisted of a continuous series of 21 dorsal vertebrae. No evidence was found of the anterior neck and skull, limbs or caudal vertebrae. A single cervical vertebra was located in front of the first dorsal, and one posterior dorsal vertebra had been fractured prior to burial. Although still associated with the vertebral column, most of the ribs were severed or otherwise damaged. No residual of the cartilaginous sternum was found. Deep bite marks on several of the vertebrae, severed ribs and the tip of a large, embedded tooth are interpreted as evidence that the lamniform shark, Cretoxyrhina mantelli, had fed on the mosasaur remains. The spacing of the individual tooth marks (3 cm) indicate the bites were from a very large (est. 5 m) shark. Lesser damage, including serrated bite marks and scrapes indicated that another shark species, Squalicorax falcatus, had also been involved. This specimen is important paleoecologically because it documents a predator-prey relationship between these two species of sharks and mosasaurs, and because it provides further evidence that Cretoxyrhina and Squalicorax fed on large vertebrates in the Late Cretaceous seas of North America.
Shimada, K., 1997. Paleoecological relationships of the late Cretaceous lamniform shark, Cretoxyrhina mantelli (Agassiz). Journal of Paleontology 71(5):926-933.Shimada, K. 2008. Ontogenetic parameters and life history strategies of the Late Cretaceous lamniform shark, Cretoxyrhina mantelli, based on vertebral growth increments. Journal of Vertebrate Paleontology 28(1):21-33.