Long before the evolution of horned dinosaurs like the famous Triceratops, there was Shringasaurus
indicus. This unusual reptile looked vaguely like a large, muscular, long-necked lizard
with two horns upon its head. While not a dinosaur itself, it is the closet evolution has come to the
low-budget “slurpasaurs” in old dinosaur movies. Shringasaurus is a relatively new discovery.
First described in 2017, all known Shringasaurus fossils come from a single bonebed in the Indian
Denwa Formation. It contains the fossils of at least seven different Shringasaurus individuals.
Given how many skeletons of various ages were found together, along with the lack of fossils of
other species, it seems likely that Shringasaurus lived in herds. While it has not yet been dated,
the fauna present elsewhere in the Denwa Formation correlates with the Anisian age of the Middle
Triassic, between roughly 247 to 242 million years ago. By this point, life had still not
fully recovered from the Permian Mass Extinction. Not all of the gaps left by the catastrophe had
been filled and the initial diversification of the dinosaurs was still 10 to 15 million years away.
Even though Shringasaurus wasn’t a dinosaur, it was part the same group of reptiles as them:
Archosauromorpha. This is the same clade that includes the flying pterosaurs,
modern crocodilians, and a number of other extinct species that were widespread during
the Triassic Period. Shringasaurus was an early member of Archosauromorpha, and lacked many of the
traits of the more advanced archosaurs, like their fully erect limbs. Instead, it belonged to a clade
within Archosauromorpha called Allokotosauria. Like Shringasaurus, most allokotosaurs also looked
superficially like lizards. The closest relative of Shringasaurus was Azendohsaurus. While similar
to Shringasaurus in appearance, Azendohsaurus was slightly smaller, not as powerfully built,
and lacked Shringasaurus’s iconic horns. Earlier Shringasaurus reconstructions, including some used
in this video, were based on Azendohsaurus’s skeleton. It is now known that Shringasaurus
had much stockier build and thicker neck than Azendohsaurus. With this heavily built body and
a length of 3-4 meters, Shringasaurus was a larger than any other allokotosaur. Since its teeth were
leaf shaped, there is little doubt Shringasaurus was a herbivore. No other herbivorous
archosauromorphs are known to have attained such large size until the Late Triassic, with the only
comparably sized Middle Triassic herbivores being distant relatives of mammals called dicynodonts.
As the Triassic Period progressed, dicynodonts became rarer and archosauromorphs took their
place as the dominate large herbivores. However, Shringasaurus’s success seems to have come from
it finding a way to simply avoid competing with the contemporary dicynodonts. The key was
Shringasaurus’s neck, which was long enough for it to access foliage in tree branches unavailable to
them. Indeed, Shringasaurus may have been one of the first high browsers, specializing in foraging
from the tops of trees. Therefore, while its horns may make it more reminiscent of ceratopsians,
early sauropodomorphs, nicknamed prosauropods, may be better analogues for how Shringasaurus lived.
This means that despite looking more like a fat, oversized lizard, Shringasaurus convergently
evolved features similar to two very different groups of dinosaurs. Of course, Shringasaurus’s
horns were its most striking feature, which is why its name means “Indian Horned Lizard”. Attached
to the top of the head, they pointed upward and curved forward over most of its short skull. These
horns resembled those of the theropod Carnotaurus more than the brow horns of Triceratops.
However, they more closely resemble the horns of some other ceratopsians like Ojoceratops and
some members of an obscure branch of Ceratopsia called Nasutoceratopsini. Shringasaurus’s horns
have a rough texture, which usually indicates of the presence of a keratinous covering. Therefore,
like the of ceratopsians, Shringasaurus’s horns were probably longer in life. Intriguingly,
the horns are not present in two of the specimens, despite the part of the skull which would have
held them being undamaged. This means that not all Shringasaurus individuals had their namesake
feature. Additionally, the horns of younger individuals are proportionally smaller than those
of the adults. The shape of the horns is also variable among the larger horned individuals. All
of these traits are typical of traits under sexual selection, suggesting that Shringasaurus’s horns
were probably restricted to one sex, most likely males. Although such sexual dimorphism isn’t
unusual among modern horned mammals, both sexes of ceratopsians had their iconic horns and frills.
While the fact that only two of the seven Shringasaurus skeletons didn’t have horns
may suggest males were unusually common, this is likely the result of preservation basis.
The skulls with horns are more robust, and would have been more likely to survive the elements
long enough to have been fossilized. However, the presence of multiple males at the site suggests
Shringasaurus lived in mixed sex herds as opposed to the harems seen in some mammalian species.
Comparisons with modern animals found Shringasaurus’s horns were less like
those used for just display and more like those also used in active combat.
This means that male Shringasaurus likely engaged in ritualistic duels with each other to impress
potential mates. While the horns could have also been used in defense against predators,
since females apparently didn’t have them, this implies defense was at best a secondary function.
Another group of Triassic archosauromorphs, the poorly known protopyknosians, also seems to have
engaged in similar behavior. The difference is they used pachycephalosaur-like domes instead of
horns. This would have been very energy intensive behavior, which is why it is rare among cold
blooded reptiles. Evidence for an elevated metabolism has been found in Shringasaurus’s
close relative Azendohsaurus. Although such early archosauromorphs only showed the first
signs of a high metabolism, this eventually culminated in the fully endothermic dinosaurs.
Regular intraspecies combat may explain some of the other differences between Shringasaurus
and Azendohsaurus, such as its greater size and more robust build. Larger and more muscular males
would have had better chances in their duels, leading to those traits being selected for.
In the short term, this selection for greater body size may have helped Shringasaurus become
a better high browser by increasing it body size, and therefore its reach. However,
it also may be why it was later replaced by later archosaurs. Shringasaurus’s neck was shorter than
those of Azendohsaurus and other closely related allokotosaurs, apparently to support its horns
and greater muscles mass. Therefore, it couldn’t easily evolve a longer neck to reach more leaves.
The very same evolutionary pressure that may have enabled Shringasaurus to become a successful high
browser may have restricted its ability to evolve further in that direction. This was not a problem
for the archosaurs who replaced Shringasaurus. These were the sauropodomorph dinosaurs and the
shuvosaurids, who despite their dinosaur-like appearance were actually more closely related
to crocodilians. These later archosaurs also had a height advantage due to their fully erect limbs,
whereas Shringasaurus’s legs were held in a semi-sprawling stance.
This was a common story during the Triassic Period. The Permian mass extinction just a few
million years earlier had created numerous vacant niches, meaning animals that were merely “good
enough” at a role like Shringasaurus were able to evolve and last a long time before their eventual
replacement by species with less evolutionary constraints. Still, while it may not have been an
optimal high browser, Shringasaurus was certainly an impressive addition to the Tree of Life.
Thank you for watching, and a thank you to themattalorian for narrating this video. If
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