Name:
Mosasaurus
(Meuse lizard - after the Meuse River).
Phonetic: Moe-za-sore-us.
Named By: William Daniel Conybeare - 1822
(Gideon Mantell added the species name in - 1829).
Synonyms: Amphekepubis?, Baseodon,
Batrachiosaurus, Batrachotherium, Capelliniosuchus, Drepanodon,
Lesticodus, Nectoportheus, Mosasaurus fulciatus, Mosasaurus
oarthrus, Mosasaurus, maximus, Mosasaurus princeps, Pterycollosaurus.
Classification: Chordata, Reptilia,
Mosasauridae, Mosasaurini.
Species: M. hoffmannii (type),
M.
beaugei, M. conodon, M. lemonnieri, M. missouriensis.
Diet: Carnivore.
Size: Largest individuals from 15 to potentially up
to 18 meters long.
Known locations: Western Europe and North America,
quite probably even further afield with fossils also attributed from
Antarctica.
Time period: Maastrichtian of the Cretaceous.
Fossil representation: Many specimens.
Discovery, classification and
naming
Like
with the dinosaur Megalosaurus,
the official naming date for
Mosasaurus actually belies its history of study.
The first
fragmentary skull material was found in the Netherlands in 1764,
with subsequent study by Martinus van Marum concluding that the
remains were those of a fish (To be fair to him no one at the time
knew of the prior existence of giant marine reptiles). In the
early 1770‘s a canon named Theodorus Joannes Godding found a second
incomplete skull.
It
was a retired army physician named Johann Leonard Hoffmann however that
would raise the profile of the creature with his discovery of further
remains and correspondence with scientists about them. The true
nature of the creature still remained elusive however as Hoffman
thought he had the remains of a crocodile, and even the Dutch
professor Petrus Camper also misidentified them as an ancient sperm
whale in 1786. Still it is quite easy to understand where Camper
was coming from as even today these remains can be taken as bearing a
superficial resemblance to toothed whales like Acrophyseter.
The
fossils also form a part of French revolutionary history in that French
forces seized them from the Fortress of Maastricht in the Netherlands
where they were then transported to France. An additional bit of
trivia: the Maastrichtian age of the Cretaceous (which Mosasaurus
is known from) is named after the Maastricht region. The story of
how the remains were captured and the resulting legal challenges in the
later years of the eighteenth century is often mentioned but exact
details are hard to verify, and the story seems to have developed
through a combination of ideas about what happened coming together to
form a sequence of events that may not have happened exactly as told.
When
the fossils were in France they were studied by Barth�lemy Faujas de
Saint-Fond, who also thought the earlier crocodile identification was
the correct one. Study of them continued elsewhere however when
Petrus Camper’s son, Adriaan Gilles Camper reviewed his father’s
original notes. Adriaan Camper disagreed with both the crocodile and
whale hypothesis and thought the remains were those of a giant monitor
lizard. Although not quite on the mark, he was still pretty close
as monitor lizards are members of the diapsid group of reptiles, the
earliest members of which are thought to be the ancestors of the marine
reptiles that included the later mosasaurs. Other later finds such as
the 2005 discovery of Dallasaurus
lend further weight to the idea
that mosasaurs evolved from monitor lizards.
Confirmation
for this idea came in 1808 when Georges Cuvier, a leading
naturalist who used comparative anatomy to identify unknown bones also
agreed with the analysis. William Daniel Conybeare formerly named the
creature Mosasaurus in 1822 with the second
skull used for the
holotype. However Conybeare only came up with the genus name,
something that happened surprisingly often in the early years of
palaeontology. Mosasaurus did not get a specific
type species name
until 1829 when Gideon Mantell provided one (something that he
also had to do for the first known dinosaur Megalosaurus).
Despite
the advancement in its identification, the suggestion that
Mosasaurus was an aquatic creature did not happen
until 1854 when
Hermann Schlegel proposed that the limbs of Mosasaurus
where flippers,
not feet.
1 - Halisaurus, 2 - Pannoniasaurus, 3 - Plioplatecarpus, 4 - Carinodens, 5 - Globidens, 6 - Platecarpus, 7 - Plesioplatecarpus, 8 - Plesiotylosaurus, 9 - Yaguarasaurus, 10 - Clidastes, 11 - Hainosaurus, 12 - Liodon, 13 - Prognathodon, 14 - Plotosaurus, 15 - Tylosaurus, 16 - Mosasaurus, 17 - Taniwhasaurus, 18 - Moanasaurus. |
Mosasaurus the
marine reptile
Although
probably not quite as long as some of the larger mosasaurs,
Mosasaurus seems to have been one of the more
heavily built. In fact
Mosasaurus was so robust that a skull discovered in
1998 was
mistakenly classed as belonging to Prognathodon,
a mosasaur that
specialised in eating armoured prey. Being such a large creature with
a heavy build suggests that Mosasaurus had a
preference for larger
slower prey, quite probably other marine reptiles. Further support
for this specialisation and behaviour comes from the side wards facing
eyes that meant Mosasaurus had poor stereoscopic
vision. A lack of
this ability strongly suggests that Mosasaurus did
not rely heavily
upon gauging distances between itself and prey and as such probably did
not rely upon speed to chase down prey over distance.
While
some would envision Mosasaurus as a scavenger the
fossil evidence also
contradicts this as the olfactory bulb (the part that processes
smells) is one of the most poorly developed areas. While many
oceanic predators use smell to detect injured prey for an easy meal,
Mosasaurus would have been at a disadvantage to
most of these.
Perhaps the most likely scenario for Mosasaurus
hunting behaviour is
one that saw it hanging around the upper ocean and waiting for other
marine reptiles to surface for air. At this time they would be at
their most vulnerable as they would be in the most lit portion of the
water (and silhouetted against the light if Mosasaurus
was looking up
from below), and unable to dive back down as they would drown
without a fresh supply of air in their body. Using its tail to
provide a quick burst of speed Mosasaurus could
launch a sudden attack
that if it did not kill the prey, would at least injure it so that
Mosasaurus could follow and hound it until it tired.
By
being a predator of the upper ocean Mosasaurus
probably did not have
much cause to dive deep. However the optimum angle of approach for an
ocean predator is from below as not only does this make prey easier to
spot against the surface light, the murk of the deeper water can
conceal some if not all of the body of the hunter until it is ready to
strike. This does not mean descending into the abyssal zone (the
part of the ocean so deep sunlight can’t penetrate) as the effect of
an animal beginning to disappear into the depths can be seen after just
a few meters down. Mosasaurus probably never had
to go further than
the maximum depth that its prey commonly frequented which realistically
was probably near the surface as well as this provides the greatest
abundance of large scale prey species like fish. It also should be
remembered that Mosasaurus is best associated with
Europe, much of
which was submerged under a shallow sea during the Cretaceous. Such a
marine environment would have made permanent deep water living
physically impossible as the depth was just not there.
Mosasaurus
has suffered from the wastebasket taxon effect which is where any
remains that remotely resemble it automatically get included into the
genus. Over the years a long list of species names has grown as a
result, although modern analysis of the remains only recognises the
four species above. Other long held species names are now considered
dubious and probably synonymous with other older species.
Further reading
- Notes on remains of fossil reptiles discovered by Prof Henry Rogers
of Pennsylvania, US, in Greensand Formations of New Jersey. - Quarterly
Journal of the Geological Society of London 5(1):380-383. - Richard
Owen - 1849.
- On the reptilian orders Pythonomorpha and Streptosauria. -
Proceedings of the Boston Society of Natural History 12:250-266. -
Edward Drinker Cope - 1869.
- A new Clidastes from New Jersey. - American Naturalist 15:587-588. -
E. D. Cope - 1881.
- Late Cretaceous marine reptiles of New Zealand. - Records of the
Canterbury Museum 9(1):1-111. - S. P. Welles & D. R. Gregg -
1971.
- Mosasaurus hoffmanni, le ‘Grand Animal fossile
des Carri�res de
Maestricht’: deux si�cles d’histoire. - Bulletin du Mus�um national
d’Histoire naturelle Paris (4) 18 (C4): 569–593. - N. Bardet &
J. W. M. Jagt - 1996.
- Transatlantic latest Cretaceous mosasaurs (Reptilia, Lacertilia) from
the Maastrichtian type area and New Jersey. - Geologie en Mijnbouw 78:
281–300 - Eric W. A. Mulder - 1999.
- Danish mosasaurs. - Netherlands Journal of Geosciences — Geologie en
Mijnbouw 84(3): 315-320. - J. Lindgren & J. W. M. Jagt - 2005.
- Reassessment of Turonian mosasaur material from the 'Middle Chalk'
(England, U.K.), and the status of Mosasaurus gracilis
Owen, 1849. -
Journal of Vertebrate Paleontology 34 (5): 1072–1079. - Hallie P.
Street & Michael J. Caldwell - 2014.
- Osteology and taxonomy of Mosasaurus conodon Cope
1881 from the Late
Cretaceous of North America. - Netherlands Journal of Geosciences. 94
(1): 39–54. - T. Ikejiri & S. G. Lucas - 2014.
- A mosasaur from the Maastrichtian Fox Hills Formation of the northern
Western Interior Seaway of the United States and the synonymy of
Mosasaurus maximus with Mosasaurus hoffmanni
(Reptilia: Mosasauridae).
- Netherlands Journal of Geosciences. 94 (1): 23–37. - T. L. Harrell
Jr. & J. E. Martin - 2014.
- A small, exquisitely preserved specimen of Mosasaurus
missouriensis
(Squamata, Mosasauridae) from the upper Campanian of the Bearpaw
Formation, western Canada, and the first stomach contents for the
genus. - Journal of Vertebrate Paleontology. 34 (4): 802–819. - Takuya
Konishi, Michael Newbrey & Michael Caldwell - 2014.
- Rediagnosis and redescription of Mosasaurus hoffmannii
(Squamata:
Mosasauridae) and an assessment of species assigned to the genus
Mosasaurus. - Geological Magazine. 154 (3): 521–557. - Halle P. Street
& Michael W. Caldwell - 2017.
- Dental variability and distinguishability in Mosasaurus
lemonnieri
(Mosasauridae) from the Campanian and Maastrichtian of Belgium, and
implications for taxonomic assessments of mosasaurid dentitions. -
Historical Biology. 32 (10): 1–15. - Daniel Madzia - 2019.
- A new Plotosaurini mosasaur skull from the upper Maastrichtian of
Antarctica. Plotosaurini paleogeographic occurrences". Cretaceous
Research. 103 (2019): 104166. - PabloGonz�lez Ruiz, Marta S.Fern�ndez,
MarianellaTalevi, Juan M.Leardi & Marcelo A.Reguero - 2019.