The famous Sarcosuchus and Deinosuchus were gigantic relatives of today’s crocodilians
capable of killing large dinosaurs.
However, during the Jurassic period, before either of these species evolved, there lived
another large, semi-aquatic relative of crocodilians.
Named Machimosaurus, it hunted along the coasts of what is now Europe and Africa from the
Late Jurassic to Early Cretaceous.
Machimosaurus was found in Switzerland during 1837.
It is named after the machimoi; a type of low-ranking Egyptian soldier of the Hellenistic
Ptolemy Dynasty.
Rather than consisting of one species, like many other prehistoric genera, Machimosaurus
included at least five.
These were Machimosaurus nowackianus, Machimosaurus mosae, Machimosaurus buffetauti, Machimosaurus
hugii, and Machimosaurus rex.
Most of these were restricted to the Late Jurassic period though Machimosaurus rex lived
during the Early Cretaceous.
The species of Machimosaurus varied in size.
The type species, Machimosaurus hugii, was about 6.9 meters long, making it perhaps the
largest known crocodylomorph from the entire Jurassic period.
The only Jurassic crocodile relative that may have been larger was the terrestrial notosuchian
Razanandrongobe, who is only known from parts of a skull.
When Machimosaurus rex was first found, it was thought to be nearly 9 meters long, though
more recent estimates place it as a little over 7 meters long.
The reason for this initial overestimate was because the calculations used were based on
crocodilians.
However, Machimosaurus had a proportionally larger head than its modern relations, inflating
the results.
Like the more famous Sarcosuchus, Machimosaurus was technically not a true a crocodilian but
a crocodylomorph, the larger clade crocodilians are a part of.
While many crocodylomorphs never evolved to become amphibious, others, the neosuchians,
were already very much like crocodilians.
These species are not classified as crocodilians only because they are not part of the crown
group formed by modern crocodilians.
However, many of Machimosaurus’s crocodilian-like attributes may be the result of convergent
evolution.
While the clade it belongs to, Thalattosuchia, has traditionally been placed in Neosuchia,
some recent research suggest they are more distant relations who took to the water independently.
Whether or not Machimosaurus’s crocodilian-like appearance was the result of common ancestry
or convergence, there were some critical differences between it and crocodilians besides skull
proportions.
Thalattosuchians like Machimosaurus were better adapted to living and hunting in the open
ocean than most other crocodylomorphs.
While some thalattosuchians, the fully aquatic metriorhynchids, took this to an extreme,
those belonging to the clade Teleosauridae, including Machimosaurus, were still able to
come ashore.
Still, with its smaller legs, Machimosaurus was not as well adapted to terrestrial locomotion
as modern crocodilians.
In the water, these legs were mostly used for steering while its tail was its main source
of propulsion.
Machimosaurus is the namesake of Machimosauridae, a smaller clade within Teleosauridae.
This clade is well named, as Machimosaurus was the apex of their evolutionary path.
Most teleosaurids, including early members of Machimosauridae, were slender, with long
snouts specialized for catching small prey such as fish.
Over time, the machimosaurids evolved to become larger, more heavily built, and possess shorter
snouts.
Of these, Machimosaurus was the largest and most deadly.
Machimosaurus’s teeth were rounded, blunt, and conical, suggesting it primarily subsisted
on prey that was large or had hard shells.
Fossils bite marks confirm such a diet.
Marine turtle fossils from the same time and place as Machimosaurus have been found with
bite marks matching those of its distinctive teeth, sometimes with the teeth even still
imbedded within them.
Its bites marks have also been found on the bones of the sauropod dinosaur Cetiosauriscus,
though whether this was the result of scavenging or hunting is unknown.
Other marine reptiles, such as smaller thalattosuchians and plesiosaurs, were also likely on the menu.
When it was first found, Machimosaurus rex was the first teleosaurid known from the entire
Cretaceous period.
This was a very significant discovery.
It was once proposed that there was a mass extinction at the end of the Jurassic period,
similar to those at the end of the Triassic and Cretaceous periods.
This hypothesis has received criticism, as many of the clades proposed to have gone extinct
at the end of the Jurassic seem to have gone extinct much more gradually that initially
proposed.
The discovery of Machimosaurus rex provided further evidence against such a large extinction
event, as it shows that the teleosaurids did not die out suddenly.
Another hypothesis is that most of the other teleosaurids died out due to a more local
event.
By the beginning of the Cretaceous period, the oceans around what would become Europe,
which is where most teleosaurids have been found, began to cool.
This wasn’t a problem for most of the large marine reptiles, who were at least partially
endothermic, or warm blooded.
On the other hand, teleosaurids like Machimosaurus were ectotherms, possessing a more crocodilian-like
metabolism that made them reliant on the external environment for thermoregulation.
A shift to cooler temperatures could have easily made this environment unsuitable for
them.
This may be why Machimosaurus rex hasn’t been found in Europe.
While not as large as more famous Sarchosuchus or Deinosuchus, Machimosaurus was a survivor,
and included the largest amphibious crocodylomorphs the world had yet seen.
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