Although they are experts in the water, most crocodilians are also surprisingly competent
on land. Nonetheless, even the fastest of today’s crocodilians would have been put to shame by the
prehistoric Boverisuchus. This fully terrestrial crocodilian lived during the Middle Eocene, about
48 to 41 million years ago. After the extinction of the non-avian dinosaurs at the end of the
Cretaceous Period, this land croc became one of the top predators of the newly ascendent mammals.
It is nicknamed the “hoofed crocodile” for the large, blunt claws it evolved to help it traverse
on land. Yet despite its evolutionary convergence with many of today’s mammals, Boverisuchus may
have also been capable of limited bipedalism, echoing its distant dinosaurian cousins.
Older media, including the TV series Primeval, refers to Boverisuchus as “Pristichampsus”.
Boverisuchus was first named in 1938, but was later synonymized with the previously named
Pristichampsus. In 2012 the type specimen of the Pristichampsus genus was found to be undiagnostic,
so Boverisuchus was again considered valid. There were at least two species of Boverisuchus.
The type species, Boverisuchus magnifrons, is basically the same
animal as the now invalid Pristichampsus type species, Pristichampsus rollinatii.
All definitive Boverisuchus magnifrons fossils are from Germany, although fossils which may belong
to it have been found as far as Central Asia. The second species, Boverisuchus vorax, lived
in North America, with all definitive fossils coming from Wyoming. Additional Boverisuchus
fossils have been found in Texas, Italy, and Romania, all of which may represent new species.
The Romanian fossils are notable for being from the Late Paleocene, making them roughly ten
million years older than the other Boverisuchus fossils. The hoofed crocodile grew 3 meters long.
Although it may not have been as large as many of the predatory theropods it replaced, Boverisuchus
was still large enough to compete with the Middle Eocene’s largest mammalian predators,
such as the hoofed Harpagolestes and the local species of the creodont Hyaenodon.
As a fully terrestrial animal, Boverisuchus’s limbs were straighter and longer, and its leg
muscles more robust, than those of other crocodilians. Besides their sheer mass,
the position of these muscles made Boverisuchus better suited for running at high speeds.
To put this into context, many of today’s semi-aquatic crocodilians are actually capable
of galloping, the fastest reaching speeds of over twenty miles per an hour. Boverisuchus would have
left them in the dust. Many of its terrestrial adaptations echo those of the distant ancestors
of crocodilians, who lived during the Triassic Period nearly two hundred million years before it.
Of course, when it returned to land, Boverisuchus evolved traits not present
in its Triassic predecessors, namely its famous hooves. These consisted of three large,
blunt claws on each foot, which were the only toes which made contact with the ground.
By spreading its weight across these larger claws, Boverisuchus’s feet would have been more
resistant to stress, allowing it to safely gallop at higher speeds. However, galloping may not have
been the hoofed crocodile’s only option. Between the length of its hindlegs and the orientation
of their muscles, it is possible Boverisuchus could have run on two legs. This inspired the
bipedal hoofed crocodile in Primeval. Of course, merely being possible within the confines of the
existing data is not the same thing as knowing for sure that Boverisuchus was an actual biped.
Still, as strange as a bipedal crocodilian may sound, their Triassic ancestors were facultative
bipeds, and some of their relatives like Postosuchus were obligate bipeds.
Likewise, footprints from Early Cretaceous Korea suggest Boverisuchus wasn’t the first
of these reptiles to regain the ability to run on just two legs. Named Batrachopus grandis,
the footprints seem to have been made by a bipedal crocodylomorph at least as large as Boverisuchus.
Still, although the hoofed crocodile was portrayed with an almost human-like stance in Primeval,
Boverisuchus was incapable of this. At most, it could have only assumed a two-legged stance when
running. The rest of the time it was restricted to walking on all fours like any other crocodilian.
Whether it ran on two legs or four, perhaps Boverisuchus’s greatest challenge when chasing
its food was its own metabolism. Ectotherms have limited stamina, and crocodilians can
only gallop short distances, with most tiring out after galloping a mere twenty meters.
As it switched to a terrestrial lifestyle, Boverisuchus may have evolved a higher metabolism.
Just like a crocodilian walking on two legs, the idea of a warm-blooded crocodile is not
as farfetched as it may sound. The larger clade crocodilians belong to, Pseudosuchia,
ancestrally had an intermediate, or mesothermic, metabolism. Those with the highest metabolisms
were ironically the direct ancestors of today’s cold-blooded crocodilians.
Additionally, other terrestrial ectothermic predators, like monitor lizards, have evolved
a higher metabolic rate, even if they remain within the ectothermic range.
Unfortunately, no analyses of the bone histology of hoofed crocodile fossils have been conducted to
confirm if this was true for them as well. Even if Boverisuchus’s metabolism was not the equal of its
Triassic ancestors, the wider world it lived in would have helped to compensate for this.
Ectotherms thrive in warm climates, and global temperatures were much higher during the Eocene
than today, to the extent that even parts of Antarctica were sub-tropical. Additionally,
tropical forests covered most landmasses. Such habitats would have provided Boverisuchus with
plenty of places set up an ambush before making short, swift dashes after its prey.
Once it caught them, Boverisuchus did not dispatch its victims in the same manner as
other crocodilians. The teeth of both species of hoofed crocodile are ziphodont, meaning they
were compressed, recurved, and serrated. Their semi-aquatic relatives have straighter conical
teeth, which are used to firmly hold upon to their prey as they drag them into the water.
The ziphodont teeth of Boverisuchus instead evolved to slice through flesh,
killing their victims through blood loss. Ziphodont teeth independently evolved in
a number of other lands crocs, as well as in theropods dinosaurs and monitor lizards.
Boverisuchus’s skull is much deeper, and thus would have been less hydrodynamic, than those
of modern crocodilians. It is also the source of one of the distinctions between the two species,
as the snout of Boverisuchus vorax is notably broader than that of its European cousin.
Like other crocodilians, Boverisuchus’s body was covered by osteoderms,
bony plates within its skin. Crocodilians use osteoderms for a variety of purposes,
including armor, thermoregulation, and mechanical support when running.
The latter purpose is likely partially responsible for why the hoofed crocodile
had even more extensive osteoderms than its surviving cousins. Boverisuchus may have also
needed the extra protection since it could no longer flee to the water when it felt threatened.
Boverisuchus’s tail was very different from those of other crocodilians. Their’s are flattened on
the sides, a shape which allows them to serve as effective sources of propulsion in the water.
Without this tail, they would be more awkward in the water than they are on land.
The tail of Boverisuchus was instead round, like most other land crocs.
Furthermore, it was entirely encased in osteoderms, meaning it couldn’t make the
side-to-side movements that propel crocodilians through the water. It is therefore apparent
that the hoofed crocodiles had put their days as amphibious predators long behind
them. Boverisuchus did not belong to any of the three major clades of modern crocodilians but to
the now extinct clade Planocraniidae, previously called Pristichampsidae.
All other known planocraniids are only known from skulls. Like Boverisuchus, they had deep snouts,
but their teeth don’t seem to have been as well adapted for life on land. The most basal-known
planocraniid is the small Duerosuchus, who lived in Spain during the Middle Eocene. Its teeth are
more circular than those of Boverisuchus, lack serrations, and only its front teeth are recurved.
More closely related to Boverisuchus is Planocraniidae’s namesake, Planocrania.
It consisted of two species, both of which lived in Late Paleocene China. Planocrania teeth are
compressed and have fine serrations, whereas the serrations of most Boverisuchus teeth are
more robust. The exception is the Boverisuchus fossils from Paleocene Romania, whose teeth have
fine serrations like those of Planocrania. It is unclear where Planocraniidae fits within
Crocodilia. It is sometimes found to be closely related to crocodiles and gharials, although
since it belongs to neither group, the hoofed crocodile is technically not a crocodile at all.
Some studies have even found the planocraniids may not be true crocodilians.
Crocodilia consists of all its living species and the descendants of their last common ancestor, and
Planocraniidae may have evolved just before that common ancestor. If true, this wouldn’t change
much about our understanding of Boverisuchus, since crocodylomorphs much more distantly
related to true crocodilians were already very similar to them in both appearance and lifestyle.
What all studies agree on is that even though the oldest identifiable planocraniid fossils are from
the Cenozoic, the clade first evolved during the Late Cretaceous. Mesozoic planocraniids are
generally held to have been ecologically similar to other crocodilians, with their descendants
only becoming terrestrial predators after the demise of the large, carnivorous dinosaurs.
Boverisuchus coexisted with other, more traditional crocodilians. While the European
Boverisuchus magnifrons terrorized mammals on land, Diplocynodon gave them reason to continue
fearing the water. In North America, Boverisuchus vorax lived alongside the small, mollusk eating
Allognathosuchus and the larger Borealosuchus, a survivor of the end-Cretaceous mass extinction.
A more distantly related group of crocodylomorphs, the terrestrial notosuchians, also survived into
the Cenozoic Era. One of these land crocs, Bergisuchus, was a contemporary of Boverisuchus
magnifrons. At a meter and a half long, it would have been lower in the food chain than the hoofed
crocodile. Even though the non-avian dinosaurs had been extinct for twenty million years,
most mammals of the middle Eocene remained small, perhaps in part due to the prevalence
of dense tropical forests. Both species of hoofed crocodiles hunted the early horses of their time,
and it has become something of a paleoart meme to depict Boverisuchus chasing them.
The largest item on the menu for Boverisuchus magnifrons would have been not a mammal but
the giant flightless bird Gastornis, which despite its portrayal in Walking with Prehistoric Beasts,
was a herbivore. In North America, Boverisuchus vorax lived alongside
the iconic mammal Uintatherium, who was likely too large for it to bring down.
The leading hypothesis for the extinction of the hoofed crocodiles is that they were outcompeted
by mammalian predators. This hypothesis was formulated during a time when the same was
thought to be true of the non-avian dinosaurs, and reflects the mammal-centrism of the time.
Competition from mammals is an unlikely explanation for the disappearance of Boverisuchus
since it coexisted with large mammalian carnivores for some time, and large ectothermic predators
existed long after it. Examples include the famous monitor lizard megalania and
the notosuchian Barinasuchus, who was perhaps the largest land predator of the entire Cenozoic era.
In Boverisuchus’s case, it is not even certain whether it even was an ectotherm, or mesothermic
or outright endothermic like most mammals. Instead, like so many other amazing creatures, the
hoofed crocodile may have been a victim of climate change. Global temperatures declined during the
Late Eocene, bringing with them the end of the global tropical forests. Lower temperatures would
have been for a major problem for Boverisuchus if it was an ectotherm, but climate change brought
about other, more indirect perils. As the dense forests receded, the hoofed crocodiles would have
found fewer places to hide, while their prey would have had an easier time evading them in
the more open environments which replaced them. Additionally, as the climate changed, not all
of Boverisuchus’s prey survived the transition, and the hoofed crocodile may simply have perished
alongside them. Boverisuchus was perhaps one of the most fascinating crocodilians.
It was not the only one to return to a fully terrestrial existence, but it developed a number
of unique adaptations, ranging from hooves, to possibly even limited bipedalism. It is
also yet another example of just how adaptable crocodilians can be when given the opportunity.
Thank you for watching, and a thank you to the themattalorian for narrating this video.
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