Mosasaurs from the deep...

As the Cretaceous period drew inexorably to it's closing chapter, Plesiosaurs and Ichthyosaurs vanished from the fossil record, Mosasaurs (over a period of around the last 20 million years of the period), took the dominant apex predator roll in their marine environment, from the Turonian age to the Maastrichtian age some 93 to 66 million years ago, the divisions of time in the late Cretaceous. Mosasaurs eventually themselves became extinct around the Cretaceous–Paleogene (K–Pg) extinction event.

 

Mosasaur swimming under water with jaws open to viewer

 

Mosasaurs breathed air, lived in the warm shallow seas and gave birth to live young ‘viviparity’, embryo incubation occurs inside the body of the parent rather than for example, in turtles which occurs initially in the egg sack and latterly in the laid egg, incubation outside of the parent. Thus Mosasaurs didn't have to return to land to give birth where they could be vulnerable to predators.

Mosasaurs had two lungs with one trachea and were endothermic (able to regulate their body temperature) and therefore self regulating to the temperature deviations of the environment. Had webbing between their toes and evolved paddles. Broad tails with a fluke which produced the power to chase prey and evade larger Mosasaur predators, yes they were cannibalistic! Possibly even filial, At least one palaeontological report illustrates evidence of a small sized Mosasaur found in the stomach contents of a larger mature Tylosaurus proriger Mosasaur.

The Teeth of specialist Mosasaurs were very successful and were developed to many differing marine habits, some like Globidens aegypticus which exclusively fed on molluscs while others were thought to be fish and cephalopod specialists, like the first Mosasaur Dallasaurus sp.

 

Mosasaur Cretaceous monster teeth

 

Over 40 species mosasaurs have been discovered since 1780's in Maastricht, Netherlands. With at least six differing species from Morocco consisting of;

1. Leiodon anceps (described by Richard Owen 1841), firstly classified by Owen and later re-classified by Arambourg as Prognathodon, this re-classification has caused much confusion when identifying this particular Mosasaur tooth, very similar to M.beaugei with fine smooth enamel, the crowns laterally compressed, both the labial and lingual carinae (cutting edges), have fine serrations, however a much less robust tooth than M.beaugei.

2. Halisaurus (Marsh 1869), one of the smaller mosasaurs from this Moroccan fossil resource, displays a sabre curve with fine carinae serrations, slender with a pronounced round cross section at the base of the tooth.

3. Prognathodon giganteus (Dollo 1904), a much larger and more robust tooth than M.leiodon, having large robust crowns, sub circular in cross section and carinae having serrations.

4. Mosasaurus beaugei (Arambourg 1952), Mosasaurus beaugei having large rooted teeth with robust crowns, these triangular in section with two serrated carinae with a quite noticeable feature, prism shaped longitude facets.

5. Platycarpus ptychodon, evolved a much slimmer less robust tooth having numerous well pronounced longitudinal facets on the lingual side (tooth face adjacent to the tongue, away from the inner jaw).

6. Globidens aegypticus, a specialist mollusc and shell crushing tooth. The globular crown having a crenelated surface (wavy or scalloped enamel), the anterior teeth becoming peg like. This is the rarest of the Moroccan fossils at the Benguerir deposits, Ganntour basin, the northern Oulad Abdoun basin, including Sidi Daoui, M’Rizig and Sidi Hajjaj. 

The Mosasaur lineage and most recent research leans towards ancestry from early land dwelling lizards. This wasn't always the case, for a long time Mosasaurs were thought to have evolved from the Serpentes. These earliest thoughts suggested a lineage to snakes, as both have similar anatomical traits. Yes Mosasaurs could open their jaws with an extreme gape, unhinging the jaws and having a flexible skull enabling the swallowing of large chunks of food or a whole prey in one gulp. A second row of teeth growing from their palate, as do snakes, extremely useful to grip prey before swallowing. However recent research has favoured a convergent evolution rather than a direct one, latest research suggests the Monitor lizard family tree.

Mosasaur size. The smallest Mosasaur known is the Dallasaurus turneri at under one metre (3 feet), in length. The largest giant yet discovered is the Mosasaurus hoffmannii at seventeen metres (56 feet), hoffmannii had a large fluke on the tale similar in shape to that of a dolphin or a sharks dorsal fin.

What did Mosasaurs look like. A recent study by Johan Lindgren 2014, concluded that Mosasaurs scales contain melanin and were probably coloured with a dark upper body and lighter underbelly much like the modern great white shark of today. Differing Mosasaurs had specialist lifestyles from the smallest to the largest. All Mosasaurs were air breathing like modern day Cetaceans (whales). Often breaching to fill their lungs probably gave the Mosasaurs opportunity to discover prey and attack from the depths much like the Great White’s off The Cape Of Good Hope do today and as in the ‘Jurassic World’ film the Mosasaur reaching upwards to grab a large Gt.White shark. As Mosasaurs are depicted by many paleontological artists. breaching could also have made them vulnerable prey to other larger Mosasaurs.

 

Mosasaur skeleton diagram

 

Mosasaur deadly underwater adversaries and paleobiology. Reviewing the evolution of how the Mosasaur moved had to be re-thought. Once it was believed Mosasaurs swam through the water with the undulating swimming actions like the serpents, from side to side. However imagining the monstrous heavyweight using its whole body to push itself through the seas created issues with dynamics, bulk-weight ratios and speed. Modern theorists concluded only the tail must have moved from side to side. A fin at the extremity of the tail aided speed, creating a bigger surface area, much like an oar through the water. The evolving anatomy of the Mosasaurs was all about speed. Front paddles or flippers (once phalanx), gave the Mosasaur direction, uplight or a dive mode, these mostly held against its body while hunting at speed, could be flipped out to enable high speed turns. As palaeontologists discover more and more, it has been observed in a fossil Mosasaur (discovered in Jordan, in the Middle East), the fossilised remains of diamond shaped scales similar to that of snakes, of differing size over the whole body. Some upper body scales evolved a keel reducing drag and effecting a streamlining, while scales on the lower or underbelly were smoother, again aiding the streamlining effect.

More recently discoveries of the impressions of soft body parts in the fossil record of Mosasaurs has revealed tantalising facts. An amazing breakthrough came when the fossilised skin along with internal organ placements were unearthed. The trachea of Platecarpus tympaniticus being fossilised and preserved, shows us that as in Cetaceans the bronchi run in parallel sequence to the lungs, unlike modern day monitor lizards, where the bronchi splits apart, this similarity to Cetaceans may show a complete transition to a marine life of the once land dwelling lizards. Even collagen protein material has been recovered from Mosasaurus Prognathodon sp. A remarkable turn of the page in the search for Mosasaur facts.

What did Mosasaurs eat, Mosasaurs were very successful and developed many differing marine habits, some like Globidens aegypticus exclusively fed on molluscs. Globidens evolved specialised teeth for crushing hard shell. These fossilised teeth are robust domed and slightly flattened, having a heavy dentin enamel crown. Platecarpus sp. and the early evolving Mosasaur Dallasaurus sp. at around a metre in length were mainly fish eaters. Larger Mosasaurus sp. along with Tylosaurus sp. at the top of the food chain preyed on other smaller Mosasaurs, giant ammonites, large fish and marine reptiles. Mosasaurs may have had a varied diet from surface skimming birds to dinosaurs. Like many top predators a meal scavenged is energy saved in any pursuit. Although the Mosasaurs were extremely ferocious predators, hunting down Plesiosaurs, marine crocodiles, sharks and even other smaller Mosasaurs, if a dinosaur carcass came its way, or a dinosaur ventured to close to the shoreline or even as some scientists believe swam across open water to islands or other land they could become prey for the largest Mosasaur. In the stomach contents of some fossilised Mosasaurs large bird bones have been found. Large fish, even sharks and smaller Mosasaurs! Many ammonoids bite marks have been discovered, originally these assumed to be crustacean bore holes, on closer inspection revealed the triangular shaped holes were in perfect alignment to the jaws of some Mosasaurs.

Extinction of the Mosasaurs. The Mosasaurs became extinct at the end of the Cretaceous period when much of vertebrate life on the planet including the dinosaurs, pterosaurs and other marine reptiles plesiosaurs and ichthyosaurs were becoming or were already extinct. This is the infamous K-T boundary a extinction event which typically can be seen as a blackened ash layer in the geological record. Many scientists and palaeontologists credit a massive asteroid strike. A geological depression in the Yucatan peninsula, the Chicxulub impactor coincides with the Cretaceous and Paleogene boundary (K–Pg boundary), around 66 million years ago when a crater more than 180 kilometres (110 miles) in diameter and 20 kilometres (12 miles) wide formed well into the continental crust, to a depth of about 30 kilometres (18 miles). As more is discovered, especially in recent years other less dramatic factors have also gained merit in contributing to the demise of many lineages around this KT boundary event. Much terrestrial volcanic activity, the climate changes due to the vulcanism, other environmental changes over long periods of time, the depletion of oxygen levels leading to a changing pattern in the food chain can all be considered as drastically changing the balance of the Cretaceous world.

The many volcanic eruptions on land and asteroid impacts from space coupled with diminishing sunlight as the stratosphere became heavily affected with clouds of ash cutting down photosynthesis processes, could have irreparably restricted the growth of algae and planktonic food in the oceans, reduced the numbers of small crustaceans that feed on plankton and a domino effect was created, fishes, pliosaurs and Mosasaurs would have all been ultimately effected if the balanced ecology failed. Also the reduction in sunlight reaching to the water surface of the planet could have critically affected the marine reptiles in there behaviour and ultimately reproduction. Reptiles as we know today are extremely sensitive to temperature change in their mating cycle. Theoretically all these factors could have brought the Mosasaurs to a point of no return and created a slide into extinction which became irretrievable for the species.

 

Chinese Mosasaur set in modern framed display

 

Around this time the great Cetaceans, took to the seas from the land, like Basilosaurus sp. (mistaken for a Mosasaur when its fossil remains were first discovered), as Cetaceans followed the evolutionary path and grew larger, hunters like the C.megalodon, the largest sharks to have evolved, mirrored the Cetaceans rise becoming top predators of the Eocene and Miocene seas taking the place of the Mosasaurs.