While the Triassic period was filled with a menagerie of strange creatures, among the
strangest were the rhynchosaurs. Part of Archosauromorpha, making them distant relations of dinosaurs
and crocodilians, the rhynchosaurs were small to medium sized herbivores with hooked, beak-like
snouts. One of the most prolific rhynchosaurs was Hyperodapedon. Not only is Hyperodapedon
important in understanding its own time, the Carnian stage, but its extinction was critical
in the rise of the dinosaurs. Hyperodapedon was named in 1859 by the famous naturalist
Thomas Henry Huxley. Like the names of most prehistoric animals people are familiar with,
Hyperodapedon is not a single species but a genus. While many genera only contain a
single species, the species contained in Hyperodapedon are numerous. The basic features of these
species were fairly similar. Hyperodapedon’s pig-like body was barrel shaped, likely to
hold a large gut to digest plant matter. It was one of the larger rhynchosaurs, ranging
from 1.3 meters long to 2 meters long, depending on the species. While short, it would have
been easy for Hyperodapedon to hide under foliage to avoid detection from predators.
While the limbs of more derived archosauromorphs were held directly beneath their bodies, the
forelimbs of Hyperodapedon were only semi-erect. Examination of their bone historiology has
revealed that they were ectothermic, or cold blooded, like other early archosauromorphs.
However, the rhynchosaurs were closely related to the first endothermic archosauromorphs,
who gave rise to dinosaurs, crocodilians, and many of the contemporary top predators,
such as Saurosuchus. While they may have not have had fully erect limbs, Hyperodapedon’s
hindlimbs were powerfully built with large claws. While too blunt to be effective weapons,
they are thought to have been used for digging. While Hyperodapedon’s body was unassuming,
its wide, short skull made up for it. Its shape was triangular, starting extremely wide
and narrowing until it formed the beak-like structure. This structure was formed from
the premaxilla, which forms the end of the upper snout in most other animals. Two smaller
prongs were present at the end of the lower jaw, with space between them to accommodate
the larger premaxilla. It has been reconstructed in a variety of ways, with earlier reconstructions
leaving it exposed in a manner like that of a reptilian naked mole rat. It may have also
covered by lips, much like how overbite of the modern tuatara is not apparent in life.
Another idea is that it was covered in keratin, making it a true beak. The beak hypothesis
is probably the most likely, as examination of the skull of the rhynchosaur Fodonyx indicates
support the keratin of such a beak. Either way, Hyperodapedon’s odd premaxilla is thought
to have been used shear off tough vegetation or to dig in search of roots like its hindlimbs.
This was far from its only strange feature. While the lower jaw held one row of teeth,
the upper jaw held multiple rows. Unlike most other reptiles, Hyperodapedon’s small, numerous
teeth were not constantly shed and replaced throughout adulthood. While incapable of chewing
its food, Hyperodapedon’s jaws fit together precisely to create a powerful shearing action.
The strong jaw muscles needed to create this bite were part of the reason it had such a
wide head, as muscles filled the large openings on both sides. The primary purpose of such
a powerful bite would have been to consume tough vegetation. Given its short height,
Hyperodapedon was limited to low lying plants, with taller plants being the domain of larger
herbivores such as dicynodonts and Sillosuchus. Hyperodapedon lived near the beginning of
the Late Triassic, specifically during the latter half of the Carnian stage, between
231 to 227 million years ago. During this time Hyperodapedon was extremely widespread.
When it was alive, all of the world’s major landmasses formed a single mega-continent
called Pangea. While most genera were limited to particular regions, fossils of Hyperodapedon
are found on every continent besides Australia and Antarctica. With the limited Triassic
fossils from these two continents, Hyperodapedon may have inhabited them as well. Given its
large range, Hyperodapedon coexisted with a variety of species. The most dangerous contemporary
predators were not dinosaurs but pseudosuchians, including Saurosuchus and Ornithosuchus. Though
dinosaurs were not yet apex predators, species such as Buriolestes and especially Herrerasaurus
were still large enough to be a threat. Hyperodapedon was not only widespread, but extremely abundant.
In some localities it made up 70–80% of fossil tetrapods excavated, showing it was
a very important component of the ecosystem. This makes Hyperodapedon essentially the reptilian
equivalent of the synapsid Lystrosaurus, who was extremely abundant across Pangea during
the Early Triassic. Hyperodapedon’s global abundance within a short time span also makes
it a good index fossil for the Carnian stage, much as Lystrosaurus is an index fossil for
the earliest Triassic. While prolific, Hyperodapedon became extinct at the a very important time.
The Carnian stage saw several other major changes happen in the biosphere, such as the
extinction of several other prolific taxa and other groups such as conifers and dinosaurs
becoming a lot more common. The extinction of Hyperodapedon and these other events is
hypothesized to be connected to a period of climate change called the Carnian pluvial
event. While not one of the big five (or six) mass extinctions, the Carnian pluvial event
was the largest extinction event within the Triassic period. This extinction event is
thought to have been caused by the release of greenhouse gases from increased volcanism,
which resulted in global warming, greater humidity, and acid rain for a period of roughly
two million years. Notably, Hyperodapedon was prolific during this period. Therefore,
like Lystrosaurus, Hyperodapedon’s abundance may have been a result of it filling in the
void from extinctions connected to the Carnian pluvial event. This may have helped stabilize
the ecosystem, reducing the severity of the extinctions. More precise dating is needed
to know whether the end of the Carnian pluvial event and the return to arid conditions resulted
in Hyperodapedon’s sudden extinction or if it suffered a slower decline. Either way,
this was critical in the rise of the dinosaurs. Before Hyperodapedon’s extinction, dinosaurs
made up less than 5% of the fauna in the regions where they were even present. Afterwards,
they became much more common and diverse. While they were previously carnivores and
small omnivores, some sauropodomorphs soon became major herbivores in the southern continents,
helping to fill the ecological hole Hyperodapedon left behind. These new herbivores, the plateosaurian
grade sauropodomorphs, would grow to become some of the largest herbivores in the Triassic
period. Additionally, they would later give rise to the famous sauropods in the following
Jurassic period. From this foothold, dinosaurs were able slowly to increase their diversity
throughout the rest of the Triassic period, though it wouldn’t be until the Jurassic
period that they were in their more familiar role as the dominant large animals. While
Hyperodapedon was not the last of the rhynchosaurs, after the Carnian stage, rhynchosaurs were
bit players in a world increasingly dominated by archosaurs, archosauromorphs more closely
related to dinosaurs and crocodilians than the rhynchosaurs. It doesn’t seem that the
rhynchosaurs even made it to the end of the Triassic period. Though just as dinosaurs
were more than simply a prelude to mammals, Hyperodapedon was more than a footnote in
the story of the dinosaurs. It was part of a successful linage of beaked reptiles, helped
to stabilize global ecosystems during a major catastrophe, and defined an important time
in Earth’s history. Thank you for watching. And a thank you to everyone who has helped
this channel grow to over 1000 subscribers. Many more videos about prehistory are on the
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