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MOSASAUR FOSSILS FOR SALE
What Did Mosasaurs Look Like?
Mosasaurs probably evolved from semi-aquatic scaled reptiles that were similar in appearance to modern-day monitor lizards. These reptiles look like an amalgamation of a child’s favorite animals: a whale’s body with the head of a Komodo dragon and the tail of a shark. Their long, lithe bodies may have been countershaded in shades of gray. Countershading is a camouflage method in which the top half of the animal is a darker color than the underside. This coloration creates uniform darkness when viewed from above. Many sharks exhibit this type of countershading. A study done in 2014 on fossilized mosasaur skin shows that the skin was extremely rich in pigment, suggesting that it was at least partially very dark, supporting the countershading claims. Dark pigment was beneficial for mosasaurs living close to the surface because it increased UV protection and helped with thermoregulation.
Reconstruction of Mosasaurus beaugei, whose fossils are found in the Late Cretaceous phosphate deposits of Morocco. By Dmitry Bogdanov
There are numerous similarities between mosasaurs and snakes, including the presence of a second row of teeth in the upper jaw of both reptiles. This second upper set of conical teeth goes a long way when capturing quick prey with a lightning-like strike. Another similarity between snakes and mosasaurs are flexible skulls with double-hinged jaws, which enabled them to gulp down their prey whole or almost whole. These adaptations set a precedent for a near limitless threshold on prey size. Considering that most mosasaurs were the largest creature in their environment, it's safe to assume that they ate nearly everything else that was smaller than them.
Bruce, the giant mosasaur at the Canadian Fossil Discovery Centre. Photo credit: Robyn Hanson
Unlike snakes, mosasaurs most likely propelled themselves through tail movements closer to that of a shark than a sea snake or eel. This beguiled early scientists, who firmly believed that they must have moved like snakes. However, evidence of a tail fluke similar to a shark points to a drag-reducing rigid body posture while the tail provided powerful thrust. This would be a more efficient method of locomotion for mosasaurs' large body plans, making ambush hunting more plausible.
How Big Were Mosasaurs?
Larger mosasaurs were the true leviathans of their time, extending an average of 10–15 meters (33–49 feet) long. Two species compete for the record of longest mosasaur at a seemingly impossible 56 feet; Hainosaurus bernardi and Mosasaurus hoffmannii. The smaller genera also attained impressive lengths of 10–20 feet long, which is nothing to sniff at! These figures are truly massive, though fall short of the length of the Mosasaurus that was depicted in the film Jurassic World. The movie mosasaur was over double the length of the largest recorded mosasaur remains and is completely unsupported by fossil evidence, though it makes for a titanic on-screen visual piece.
What Did Mosasaurs Eat?
Mosasaurs would gulp down partially chewed prey, which is quite beneficial for scientists interested in the mosasaur diet. The gruesome unchewed contents of fossilized mosasaur guts reveal a varied diet of sea birds, ammonites, smaller marine lizards, pterosaurs, turtles, sharks (potentially), dinosaurs carcasses that drifted offshore, and even other mosasaurs. Ammonites were especially crunchy mosasaur treats: some genera even evolved specialized teeth for crushing cephalopod shells (Igdamanosaurus).
A large fossil ammonite from Alberta preserved in brilliant ammolite showing circular teeth marks of a bite from a mosasaur.
Most larger mosasaur species were generalists, snagging any creature that crossed their path and making a quick snack of them. This is perhaps why these creatures attained such colossal sizes: to eat anything they wanted! Feeding preferences also contributed to body plans and special characteristics of other species. For example, the quicker, smaller, and greater habitat depth of the food source, the sleeker, lighter, and more efficient a predator’s body and teeth need to be. This logic is evident in members of the Plioplatecarpinae subfamily of mosasaurs, like Platecarpus tympaniticus found in modern-day Kansas.
How Did Mosasaurs Hunt?
In addition to the wide diversity of species and prey types, hunting strategies may have varied widely as well. Smaller species may have pursued their prey, though it is commonly agreed that mosasaurs, lurked in ambush, especially larger species. Marine animals lacking gills need to surface for oxygen, and it is this need that mosasaurs preyed upon. Through a combination of camouflage and thrust power, large mosasaurs lurked near the surface and would lunge out to snatch surfacing marine animals or flying animals hunting on the surface. In a quick burst of speed and a snap of jaws it would all be over for the unsuspecting victim. This is supported by the idea that they used their powerful tail flukes for extra thrust to dart out and swallow unsuspecting prey.
Ambush hunting strategies are further supported by findings of cavities in fossilized bones that may have once held fat cells, which assisted in buoyancy, reduced weight, and increased speed. Non-reflective keeled scales may have been a great advantage to the mosasaur sneak-attack, reducing drag and improving camouflage. Additionally, there is little evidence that mosasaurs dove to significant lengths in the pursuit of prey, especially considering mosasaurs' need for accessible oxygen. All of this evidence points quite clearly to ambush hunting, and until new evidence arises that seems the most plausible.
Teeth And Tooth Specialization
Like other marine predators, specifically crocodilians and spinosaurids, most mosasaurs had conical teeth that were often hooked, or slightly curved, toward the rear of the mouth. This style of tooth is extremely useful for capturing agile prey underwater, though not all mosasaurs exhibited teeth of this variety. With widespread specialization of feeding niches and species diversity comes a need for different styles of teeth. In a similar fashion to other large reptiles, sharks, and dinosaurs, mosasaurs would shed and replace their teeth throughout their lives. Once a tooth was broken or inadequate for its size, they would drop it and eventually a new tooth would replace it. This process, while necessary, was extremely complex and completed in eight stages. It is truly a wonder it was as effective as it was!
Mosasaur teeth can be divided into three feeding categories: feeding generalist, pursuit predator, and crushing.
Many of the colossal species of mosasaurs like Mosasaurus and Tylosaurus were feeding generalists. These species were best equipped with the aforementioned thick, conical teeth. These durable teeth shaped like spearheads are excellent tools for catching and dismembering any animal that crosses their path. Teeth like this are efficient for capturing fish and birds as they were about to swim off or crush through an ammonite or turtle shell. For a predator like Prognathodon, these teeth were perfect.
Conical teeth in the jaw of Prognathodon, a giant Mosasaur from Morocco.
A secondary type of tooth exhibited by mosasaurs belonged to species that were typically pursuit or more active predators. Teeth from sleeker, more agile mosasaurs are often smaller, slightly hooked, and more numerous than larger species. Halisaurinae is a subfamily that illustrates this tooth style beautifully. However, tooth style does not always provide an accurate picture of how a mosasaur fed. Halisaurus sports a jaw full of small hooked teeth, but based upon its flipper bones paleontologists think it may have been a rather awkward swimmer. Its tooth shapes may have compensated its lack of mobility for security when grasping prey. This is a perfect example of how a lot of paleontology is based upon educated guesses until it is confirmed or denied by further research and evidence.
A partial Halisaurus jaw from the Late Cretaceous of Morocco, whose slightly hooked teeth were optimal for grabbing and holding slippery prey.
An excellent example of crushing teeth are present in the Globidens mosasaurs, such as those in the genus Igdamanosaurus. These mosasaurs primarily fed upon shelled organisms like ammonites, and their teeth were adapted to capturing and crushing those cephalopods. Teeth from a Igdamanosaurus look much like an acorn without its cap. These teeth are short and squat with a small point in the center to direct the full force of the bite into a small area. Globidens species were able to make short work of shelled prey, and many ammonites met an untimely demise between mosasaur jaws.
Upper jaws of Igdamanosaurus (Globidens) aegyptiacus with rounded teeth specialized for crushing ammonite and mollusk shells.
How Did Mosasaurs Reproduce?
This subject is of major discussion within the scientific world, though little evidence exists. Many paleontologists believe that mosasaurs gave birth to live young, or hatched their eggs internally, like many snake species today. This theory is especially plausible given mosasaurs' body size to flipper size ratio, which would make it extremely difficult for them to leave water and lay eggs like sea turtles do. This claim is now under some contention with the discovery of a massive, fossilized soft shell egg that was unearthed in Antarctica in 2020. The egg is of such an immense size that the most likely candidate is a mosasaur, though this is unsupported and is still an emerging discovery. The presence of mosasaur remains in the surrounding area have led paleontologists to temporarily assign the egg to the family until further research can be done.
Where Did Mosasaurs Live?
Mosasaurs had a truly massive range: fossilized remains appear on almost every continent! These sea beasts inhabited almost the entirety of what is now the Atlantic Ocean, regardless of the current climate zone. They were well adapted to living in the warm, shallow, epicontinental seas of the period. Most of the well-preserved mosasaur material that circulates today is from the area of the American midwest that once was the Western Interior Seaway, much of western Europe, and the phosphate mines of Morocco. Remains in Hungary have even been attributed to a possible freshwater mosasaur species, further evidence of mosasaur's widespread diversity and adaptability.
Like other reptiles, mosasaurs breathed air. This makes a fully aquatic lifestyle quite challenging. For this reason, many paleontologists emphasize that they were scourges of shallow seas, signifying the reptiles' need for easy air availability. Mosasaurs had some distinct physiological adaptations for aquatic life besides reduced, fin-replaced limbs. The bronchi leading to the lungs ran parallel to each other instead of splitting apart from one another, as is observed in monitor lizards and other terrestrial reptiles.
These marine reptiles adapted to many different ecological niches and feeding strategies. This was a major factor in their wide distribution during the Cretaceous. Wherever water-dwelling prey could be found, mosasaurs were sure to be there as well, topping off the food chain.
How Did Mosasaurs Go Extinct?
Although mosasaurs diversified and proliferated at a spectacular rate, their specialization is considered the source of their demise when marine systems collapsed at the end of the Cretaceous. Just as specialization is a distinct evolutionary advantage, it has also been the downfall of many organisms. Overspecialization is extremely detrimentimental when multiple species are reliant on one another. As species are removed from the food chain, those above and below them are also extremely susceptible to extinction.
The food chain collapse that ultimately led to the downfall of the mosasaurs is thought to have ties to an extraterrestrial impact in the Cretaceous oceans. This may or may not be the same event, or tied to the events of the K-Pg extinction when life on Earth, specifically dinosaurs, was wiped out. As stated before, lack of lower-level food sources collapse higher trophic levels, especially apex and high-level predators.
Mosasaur Variety
Within the family Mosasauridae are four subfamilies. These subfamilies are Mosasaurinae, Halisaurinae, Tylosaurinae, and Plioplatecarpinae. Mosasaurinae is the most robust and diverse of the mosasaur subfamilies, though in some aspects this subfamily is considered a wastebasket taxon where unknown or questionable relationships are allocated. This subfamily contains upwards of 15 species, including some highly specialized genera like Globidens and the most popular genuses, Mosasaurus and Prognathodon. Halisaurinae are similar to Mosasaurinae in skeletal structure, though generally smaller, sleeker, and with slender jaws and more teeth than most other mosasaurs. These adaptations suggest that this subfamily most likely fed on smaller, faster fish, fulfilling a different niche than larger species.
Plioplatecarpinae is often defined by short skulls and squatter bodies than other medium-sized mosasaurs. Many paleontologists believe that this subfamily was extremely agile, similar to modern seals and sea lions. Many species in this subfamily exhibit crushing teeth and may have favored belemnites as prey. Tylosaurinae is the subfamily that is jam-packed with absolute leviathans. Genera within Tylosaurinae are typically found in North America and while they are the longest, they may be the lightest proportionally! This is evinced by cavities in bone that were probably filled with fat to assist with buoyancy. Their teeth and body shapes led scientists to believe that Tylosaurines were probably feeding generalists and at the tops of their respective food chains.
The History Of A Sea Monster
The first mosasaur to be discovered and recorded was in 1776, in a chalk quarry in Holland. However, mosasaur remains had been discovered throughout history by indigenous peoples of the United States and other areas. To these people, the fossilized teeth and bones were thought to belong to mythological beings like storm giants or sea monsters. As it turns out, they were half right! The specimen originally found in Holland, which we now know to be the type species Mosasaurus hoffmannii, was initially identified as an ancient whale and set aside. It wasn’t until around 1808 when a French anatomist and Dutch researcher correctly deduced that the skull belonged to a giant lizard. They also posited that this creature was proof of an extinct species and, perhaps, the victim of a major catastrophic event. From that point forward, the scientific community had a baseline to further classify and rearrange mosasaurs as more fossils were exhumed. Since then, many more fossils relating to mosasaurs were exhumed and aggressively studied. Today, mosasaur fossils are relatively readily available, and it's easier than ever to behold the glory of one of history’s most terrifying leviathans.