MOSASAUR PATHOLOGY "Even the big guys got no respect"     Copyright © 2001-2008 by Mike Everhart Last revised 01/22/2008

Mosasaurs were the largest predators in the shallow sea that covered Kansas during the Late Cretaceous. Even being the top predator was no guarantee for survival, especially since they were living with giant sharks like Cretoxyrhina mantelli that were competing for the same prey, and always looking for a chance to feed on a sick or injured mosasaur. It was a dangerous place to live, especially for the younger, smaller mosasaurs. Mosasaurs lived for 20 or more years, and non-fatal injuries sometimes occurred during their lifetime. Records of these injuries are occasionally preserved in preserved in the fossil record.

Professor Benjamin F. Mudge (1878) was one of the first paleontologists to discuss mosasaur pathology. He had been collecting mosasaurs in western Kansas since the late 1860s and at the time had probably seen more mosasaur remains than anyone else.

Writing about the geology of Kansas in the U.S. Geological and Geographical Survey of the Territories (Hayden, 1878), Mudge described several of the injuries he had seen in mosasaur bones.  He noted (page 287) that "...it was no uncommon thing to find Saurian [mosasaur] ribs that had been broken and again united while the animal lived." LEFT: Mosasaur rib (VP-3366) in the Sternberg collection with healed fracture. RIGHT: Mosasaur rib(VP-4516) in the Sternberg collection with healed fractures.

Mudge continued, "In one case a more serious injury occurred. In a fine specimen, one of the most perfect collected by us, we discovered that the animal had received a very serious injury to his back, which he outlived. Five of the vertebrae had been fractured so seriously as to loose many of the spinous processes, after which it had healed, but the whole had grown together (anchylosed) so as to lose the natural form of the separate bones and become a confused, firm mass. The enemy that could have thus injured a monster 35 or 40 feet in length, and whose jaws of defense were 33 inches long, must have made a fierce contest."

LEFT: Three fused vertebrae near the end of the tail of a small mosasaur. It appears that the bone was severely infected, possibly as the result of a bite.  A similar but much larger fragment was discussed by Martin and Rothschild (1989) who noted that the fused vertebrae contained the fragment of a shark tooth. See additional examples below. (

Mudge's student and co-worker, S. W. Williston (1898, p. 214) noted, "That they [mosasaurs] were pugnacious in the extreme is very evident from the many scars and mutilations which they suffered during life. I have observed exostosial growth in their lower jaws, the vertebrae, especially those of the tail, and the paddles, especially the digits. In some the mutilations have been extensive. One tail of a Platecarpus has the spines of the distal half of the tail broken off and false joints produced. Never have I known a case where there has been evidence of ante-mortem loss of the tail, or any part of it. A paddle of another specimen, figured in part in plate LVI, has the bones of the forearm, carpus and metacarpals all united by exostosis." Williston was probably the first to photograph and publish an image of a pathology in mosasaur remains. 

LEFT: In 1992, my wife found a similar specimen in the chalk (early Santonian) of Trego County, Kansas. In this example, upper limb bone (humerus) was crushed, probably by the bite of a larger mosasaur, and had begun to heal crookedly. The humerus, radius and ulna appeared to have been involved in an infection related to the original bite. The specimen was found by itself and may have been torn from the mosasaur by scavengers.

Later (1914, p. 161), Williston enlarged somewhat on his previous statement. "That the mosasaurs were pugnacious in life is conclusively proved by the many mutilations of their bones that have been observed, mutilations received during life and partly or wholly healed at the time of death. Bones of all vertebrates are repaired after injury by the growth of more or less spongy osseous material about the injured part, forming sort of a natural splint. This material is more or less entirely removed by absorption when it is no longer required for the support of the broken ends. Many such injured bones of the mosasaurs have been found; sometimes the bones of the hands and feet have grown together, and not infrequently  the vertebrae have been found united by these osseous splints; occasionally even the skull itself, especially the jaws, attest extensive ante-mortem injuries. In a single instance the writer has observed the loss of a part of the tail, where it probably had been bitten off.  It may be mentioned, however, that the bones of the tail had no such "breaking points" in the mosasaurs as have those of many land lizards, whereby a part or all may be lost as a result of even a trivial injury."

More evidence of healed injuries preserved on the remains of a mosasaur

LEFT: One of the more complete Platecarpus tympaniticus specimens (FHSM VP-322) in the Sternberg Museum collection shows an unusual accumulation of damaged and healed bones near the end of the tail, as well as a front limb and the skull.  The mosasaur is about 6 m (20 ft.) long. The end of the tail of FHSM VP-322 has two vertebrae that are fused together, and two other places where the chevron bones below the vertebrae are also fused or misshapen. The skull and left front paddle show healed puncture wounds that may have resulted from the bite of another mosasaur.  The specimen was collected by G. F. Sternberg from the Smoky Hill Chalk of Gove County in 1949, and was exhibited for many years in the original Sternberg Museum on the campus of Fort Hays State University.

	LEFT:  The two damaged vertebrae (right circle) are probably evidence of a bite to the mosasaur's tail that became infected, and resulted in bone growth that fused them together. This wound is curious because neither the dorsal processes above the vertebrae or the chevrons below them appear to have been damaged by the bite or the resulting infection. The left circle shows two chevron bones that were fused together.  RIGHT: A close-up of the damaged vertebrae showing how the damaged vertebrae have grown together.
	LEFT: Slightly forward of the healed injuries shown above, there is evidence of another injury to the chevron bones that resulted in pathological bone growth. Reconstruction in this area by Sternberg may have modified the actual damage. RIGHT: The anteriormost ribs on the left side of the rib cage are expanded and do not appear to be normal. This may also be the result of preservation or preparation.
	LEFT: A healed puncture wound to the first finger of the left paddle has fused the joint between two of the paddle bones. RIGHT: A healed puncture wound is visible on the top of the right surangular (back of the lower jaw).

One Bad Luck Mosasaur

LEFT: At first glance, this pile of mosasaur caudal vertebrae (FHSM  VP-13750) appeared to be evidence of just another mosasaur tail bitten off by a large shark and partially digested before being regurgitated. However, the odd shaped lump of bone in the lower left turns out to be at least 3 and probably 4 caudal vertebrae that have been fused together as the result of an infection.  It appears likely that the mosasaur had the end of it's tail bitten off by an unknown predator (probably a shark). The wound became infected, fusing the vertebrae and more or less forming a bony club at the end of the tail as it healed. The mosasaur survived the initial attack but then was "sliced and diced" some time afterwards by a large shark, most likely Cretoxyrhina.

LEFT: The fused terminal vertebrae at the end of the mosasaur's tail. The number of vertebrae included in this lump of bone is uncertain because of the bone growth and the subsequent partial digestion inside the stomach of the shark. RIGHT: A series of caudal vertebrae from the same specimen, showing the effect of stomach acid on the surface of the mosasaur bone.

"OUCH!  That must have hurt!!!"

Below are photographs of the right side of the skull of a Tylosaurus proriger that I saw in an exhibit in a small museum in Hobetsu, Japan. The specimen (HMG-1288) had been discovered in the Smoky Hill Chalk of western Kansas and purchased by the museum for their exhibits. While the left side of the 1.2 m skull appears undamaged, the broken bones on the right side suggest that this mosasaur ran into something hard, like a rock.

(LEFT) A large area of damaged bone was visible on the right side of premaxilla and a fracture was evident in the suture between the premaxilla and right maxilla.   The unusual 'humped' silhouette of the skull may indicate an additional fracture of the posterior extension of the premaxillae. (CENTER)  This picture shows the extent of the damage to the suture between the right maxilla and the premaxilla, including the rearward displacement of the first tooth in the right maxilla. (RIGHT) The appearance of the bone in this picture appears to indicate that some healing had taken place before the mosasaur died. According to Gorden Bell (pers. comm., 2002), the snout of a mosasaur was very well equipped with nerve endings... and this sort of injury would have been extremely painful.

Rothschild and Martin (1987) discussed what appears to be evidence of avascular necrosis (the bends or decompression sickness)  in the vertebrae of mosasaurs.  If true, it means that mosasaurs were apparently not well adapted for deep diving.

Below are several pictures of a fragment at the back of a mosasaurs left, lower jaw (surangular and articular). The breaks on both ends are fresh, but no other pieces were found. This bone fragment is the portion colored yellow in the drawing at left.  In life, it served as the attachment (hinge) point between the left lower jaw and the quadrate at the back of the skull. There are three oblong holes in the outside surface (arrows) of this fragment that may not belong there. The two larger holes (2 x 3 mm) are connected by a larger cavity which is barely visible as a light spot in the largest blow-up. The smaller upper hole is rounder in shape and all three holes seem to angle somewhat downward rather than going straight into the bone. The edges of all three holes are smooth and there is no sign of a recent bite trauma that I can see.

This isolated bone fragment was found in the lower Smoky Hill Chalk Member (late Coniacian) of the Niobrara Chalk in Gove County, Kansas. It probably came from an adult mosasaur (Platecarpus tympaniticus) that was 16-18 feet long.  Bones preserved in the Smoky Hill Chalk Member frequently show marks from scavenging by sharks (mostly Squalicorax) but are very rarely, if ever, damaged by invertebrate borings. The openings  look very similar to the unexplained holes in the back of both of the lower jaws of Sue, the Tyrannosaurus rex, but do not penetrate completely through the bone. 

	Here is the fragment shown next to a relatively complete left surangular and articular from a Platecarpus tympaniticus for comparison.  The arrow indicates the locations of the unusual holes. (Scale = mm)
	The first close-up shows the location of the holes in the surface of the articular near the suture with the surangular.
	The second close-up gives a better view of the holes and the surface texture of the surrounding bone.  The openings appear to angle downward toward the bottom of the picture.
	The third close-up, taken with different lighting, shows that the two lower holes are interconnected (light spot in the lower opening is illumination coming in through the adjoining hole to the right).  The two larger holes are about 5-6 mm deep.  (Scale bar = 3mm)
	(Added 08/05/01) After I received a couple of replies to my initial inquiry, I decided that the broken end of the bone need further preparation. This picture is taken from different angle and shows the broken end of the articular and a cavity that projects toward the holes in the surface of the bone.  This area had originally been filled with chalk.
	(Added 08/05/01) This low angle photo shows that the large cavity is connected with the two larger holes.  A closer examination shows a small, chalk filled opening in the vicinity of where the third hole should connect to the cavity. The arrows indicate the location of the two larger holes.  Note that the cavity appears to be smooth walled and oval in shape.  Was this an injury, an infection or a parasite of some sort?  We don't know....

Now, the other side of the story.............

If you looked closely at the first close-up picture above, you might have noticed a semi-circular scratch on the left side of the fragment.  These two pictures show the lower side of the bone and give you an idea of what your bones would look like if chewed on by a modern Mako Shark ..... In this case, the shark was Cretoxyrhina mantelli. There should be no connection between the mystery holes in the bone and these post-mortem bite marks from scavenging.

LEFT: Another specimen of a Platecarpus lower jaw (FHSM VP-2116) with three holes in the angular (inset). In this case, the holes are still filled with chalk so I am unable to determine how deep they are or if they are connected. I have seen several other specimens with similar pathology.