Although crocodilians are without a doubt some of the deadliest carnivores alive today, they
also occasionally consume fruit. The pond apple is even sometimes called the "alligator apple"
due to the preference alligators have for it. Of course, fruit doesn’t make up a large enough
portion of the diets of modern crocodilians for them to be classified as omnivores,
but their prehistoric relative Iharkutosuchus was a true, specialized herbivore. Indeed, it was
able to process its food more efficiently than any modern herbivorous reptile. Iharkutosuchus
was not the only extinct relative of crocodilians who became a plant-eater. Herbivory and omnivory
evolved multiple times within the larger clade Crocodilia belongs to: Crocodylomorpha. However,
most of the others were terrestrial species only distantly related to true crocodilians.
What sets Iharkutosuchus apart from them is that it was part of the branch of Crocodylomorpha which
ancestrally already looked and acted like the crocodilians alive today: Neosuchia.
Even though it did not belong to Crocodilia proper, Iharkutosuchus was a herbivorous
crocodilian in all but name. Iharkutosuchus belonged to the neosuchian clade Hylaeochampsidae.
Like it, the other hylaeochampsids were small and had short, round snouts.
The hylaeochampsid Acynodon is also thought to have been a herbivore, although its teeth were
not as complex as those of Iharkutosuchus. Iharkutosuchus’s fossils are found in the
Hungarian Csehbánya Formation, which is part of the greater Iharkút locality. It lived eighty-five
million years ago, during the Santonian Age of the Late Cretaceous. Late Cretaceous Europe was less
of a continent and more of a collection of islands connected by a shallow sea, and due to the limited
habitat available, many of the local dinosaurs were smaller than their mainland counterparts.
All definitive Iharkutosuchus fossils are skulls. Other neosuchian fossils have been
found in the Csehbánya Formation, some of which probably belong to Iharkutosuchus,
but since they are disarticulated, their identity cannot be confirmed.
Still, even without post-cranial remains, analysis of the skull’s oxygen isotope composition has been
able to confirm Iharkutosuchus spent most of its time in swamps, ponds, and lakes. It therefore
seems that despite how much it had changed from crocodilians, Iharkutosuchus retained
its ancestors’ semi-aquatic lifestyle. The largest Iharkutosuchus skull measures a mere
eleven centimeters long, and its total body length is estimated to have been just 0.8
meters long, smaller than any modern species of crocodilian and half the length of Acynodon.
Its diminutive size doesn’t appear to have been due to island dwarfism. The other hylaeochampsids
were never very big, nor were the terrestrial plant-eating crocodylomorphs. Meanwhile, the size
of the contemporary, carnivorous neosuchians was comparable to that of modern species.
As a consequence of its herbivorous diet, Iharkutosuchus’s jaw muscles were dramatically
rearranged from those of its carnivorous ancestors, and as a result it had fewer openings
in its skull. Unlike crocodilians and most other reptiles, Iharkutosuchus’s teeth were heterodont,
meaning they came in multiple, distinct shapes. The first five rows were spatulate, with large
crowns. Like the incisors of mammals, they were used to bite off foliage. The six rows behind them
deviated even more from those of crocodilians, with three cusps on their crowns, but it was the
larger teeth at the back of the jaws which were truly special. They were wide, flat, multicupsed,
and fit together precisely. A few terrestrial land crocs, like Chimaerasuchus, had similar,
molar-like teeth, but the only living animals with such complex teeth are mammalian herbivores.
Something Iharkutosuchus shared with both groups was the ability to efficiently chew its food,
something crocodilians and most other modern reptiles are incapable of.
The tuatara of New Zealand is an exception, but even its food processing capabilities pale
in comparison to Iharkutosuchus, whose teeth and jaws rivaled the sophistication of many mammals.
Chewing was divided into two phases. First, the front teeth were used to crush the food into
smaller pieces. The plant matter was then grinded by the back teeth with a side-to-side motion.
This created extensive wear. Fortunately, unlike mammalian herbivores, which have a permanent set
of adult teeth, Iharkutosuchus continuously replaced them, much as crocodilians do.
Under normal circumstances, this tooth replacement would have threatened the precise occlusion which
made Iharkutosuchus’s teeth so efficient. However, the dental wear on the molar-like teeth is fairly
uniform, so it is thought they were replaced simultaneously. Iharkutosuchus’s rate of tooth
replacement was also much faster than in other reptiles, so the replacements were almost fully
grown by the time their worn predecessors finally fell out. All of this came together to ensure
that its ability to efficiently chew its food remained uncompromised. Based on the microwear
patterns found on its teeth, it appears that Iharkutosuchus consumed a wide variety of plants.
The teeth belonging to a juvenile Iharkutosuchus bear the marks of consuming predominantly softer
materials, while those of adult possess wear from both soft and hard food.
Additionally, the environment preserved in the Csehbánya Formation had distinct wet and
dry seasons, so Iharkutosuchus likely consumed different types of plants throughout the year.
It has also been proposed that Iharkutosuchus may not have been a strict vegetarian, supplementing
its plant-based diet with invertebrates much like how crocodilians supplement their meat-heavy diets
with fruit. Invertebrates form most of the diet of crocodilian hatchlings, but Iharkutosuchus’s
potential success in such ventures was far more limited, as the muscles responsible for rapidly
closing its jaws were greatly reduced from those of its predatory ancestors.
Although the fauna of the Csehbánya Formation remains obscure, a great deal of research has been
done trying to understand Iharkutosuchus’s home. Among the dangers Iharkutosuchus coexisted with
was a larger neosuchian similar to Allodaposuchus. Notably, its bite marks have been found on an
Iharkutosuchus skull roof. This was likely the result of predation rather than mere scavenging,
since predators rarely leave traces like this on the skull when feeding.
However, the deadliest predator in the water was not a fellow crocodylomorph, but Pannoniasaurus,
a species of freshwater mosasaur. Other neosuchian bones found in the Csehbánya Formation belong to a
more terrestrial form similar to Theriosuchus. Crocodylomorphs such as these were long gone
elsewhere in the world, but the islands of Europe served as a refugium for a number of lineages that
had perished elsewhere. Since Iharkutosuchus and Acynodon are the only known hylaeochampsids from
the Late Cretaceous, they themselves may have been example of this phenomenon. That is not to
say that Iharkutosuchus only lived alongside “evolutionary relics”. Another contemporary
terrestrial crocodylomorph, the small notosuchian Doratodon, might be the oldest known sebecid.
Although Doratodon itself wasn’t very big, Sebecidae survived into the Cenozoic Era and
included the largest terrestrial carnivores after the demise of the non-avian dinosaurs.
Another unusual neighbor of Iharkutosuchus was the pterosaur Bakonydraco, who was one of the last of
the tapejarids. Besides serving as a haven for relict taxa, Late Cretaceous Europe was also a
crossroads between the otherwise distinct faunas of the two hemispheres, and Santonian Hungary was
no exception. Among the northern, Laurasian fauna native to the Csehbánya Formation was the small
ceratopsian dinosaur Ajkaceratops. Additionally, fossils have also been found belonging to an
abelisaurid, a type of large theropod otherwise restricted to the southern, Gondwanan continents.
A sauropod tooth has also been found at the site. Even if it belonged to a dwarf
like the later Magyarosaurus, the sauropod it belonged to was still likely the largest
herbivore which coexisted with Iharkutosuchus. Other contemporary dinosaurs, such as the early
diverging iguanodontian Mochlodon, were relict taxa like Iharkutosuchus. Other examples are
the armored nodosaurid ankylosaurs Struthiosaurus and Hungarosaurus, the latter of which is notable
for its proportionality long forelimbs. They were last members of Struthiosaurini,
a nodosaurid clade which, despite its obscurity, had been common during the Early Cretaceous.
Even though Iharkutosuchus lived alongside many so-called “living fossils”, it is also
an example of why the term is misleading. It may have been one of the last hylaeochampsids,
but it became incredibly specialized compared to its ancestors. It also shows just how adaptable
crocodilians and their relatives, who themselves are often called “living fossils”, were.
While crocodilians are carnivores who indulge in occasional fruity snacks, Iharkutosuchus
built upon the same template until it ended up surpassing all modern herbivorous reptiles.
Thank you for watching, and a thank you to the themattalorian for narrating this video.
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