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Was the ancestor of the giant sauropods a predator?

How cool would it be to go back in time and see how dinosaurs behaved in real life?? I think most people who’ve seen Jurassic Park (the original one…) would agree this would be pretty awesome. However, at the moment, the science behind both time travel and genetic manipulation of frog DNA is lacking (we’re looking at you, research funding bodies), so we’re a little stuck.

That is, unless you’re a master detective of the fossil record. By combining scientific research, the latest technologies, and the fossil record with a bit of imagination, researchers now are able to breathe a dimension of realistic life into even the most ancient dinosaurs.

The early sauropodomorph Saturnalia tupiniquim. Skeletal reconstruction (A). Virtual preparation of cranial bones as preserved inside the matrix (B), with braincase highlighted in right lateral (C) view. Reconstruction of the soft tissues associated with the braincase: right inner ear in lateral (D) and dorsal (E) views, and endocast in lateral (F), dorsal (G), and, ventral (H) views. Abbreviations: asc – anterior semicircular canal; co – cochleae; fl – Floccular Fossae Lobe; ie – inner ear; lsc – lateral semicircular canal; psc – posterior semicircular canal; V – trigeminal nerve; VI – abducens nerve; VII – facial nerve; XII hypoglossal nerve. Scale bars = 1 cm. (Bronzati et al., 2017)

CT, or Computed Tomography, is a digital scanning method borrowed from medical research. If you’ve ever had your brain scanned, chances are it was by a CT machine. Mario Bronzati, a grad student studying at the Ludwig-Maximilians-Universität in Munich, along with colleagues from Brazil, used CT scanning to create a high-resolution and detailed image of the skull and braincase of a dinosaur called Saturnalia.

Paleoneurology – interdisciplinary research at its finest!

Just to reiterate – they are studying actual dinosaur brains here, based on the structure of their braincases! That’s pretty awesome, seeing as brains don’t really preserve well over millions of years in the fossil record. Using digital reconstructions is the only way that we can really look at their brains in any sort of detail. Without breaking them, importantly.

Saturnalia is one of the earliest known dinosaurs, coming from Brazil during a time known as the Late Triassic, around 230 million years ago. It belongs to a group of dinosaurs called sauropodomorphs – including famously known species such as Diplodocus and Dreadnoughtus. These animals were true giants of the Mesozoic, with species weighing up to 90 tonnes, and growing up to 40 metres in length!

But not Saturnalia. This little dinosaur was the early precursor to its behemoth descendants, and only grew to around 1.5 metres in length, weighing only up to 10 kilograms.

During this period, dinosaurs weren’t quite the dominant animals that we know often think of them as, and lived alongside and competed with a whole range of other strange reptilian groups.

Why dinosaurs?

This Triassic diversity begs the question of why did dinosaurs go on to become the sole winners for so long? They reigned supreme on land for around 160 million years, going on to even give rise to modern birds – as such, dinosaurs are still in some ways the one of the dominant vertebrate groups on this planet!

This new study is the first time that the braincase of one of the earliest dinosaurs has ever been able to be reconstructed in such a way, and reveals exciting possibilities for what we can learn about their behaviour.

Brains > brawn

With dinosaurs, scientists can usually figure out roughly what they ate based on their teeth. If they’re sharp and pointy, usually this means they liked to chow down on other animals. If they were more flattened or peg-like, they usually preferred a diet of plants – veggiesaurs. This includes the sauropodomorphs, and also their ornithischian cousins. Or at least, that’s what scientists broadly understand based on their teeth.

Simplified Archosauriformes phylogeny highlighting character acquisition in Sauropodomorpha (A). Endocasts of Saturnalia tupiniquim (MCP-3845-PV), Plateosaurus (MB.R.5586-1), and a sauropod specimen tentatively reffered to Cetiosaurus (OUMNH J13596) in dorsal (B,C,D) and anterolateral (E,F,G) views showing the morphology of the Floccular Fossae Lobe in sauropodomorph dinosaurs. Abbreviations: fl – Floccular Fossae Lobe, ie – inner ear, 1 – Archosauriformes, 2 – Archosauria, 3 – Dinosauromorpha, 4 –Dinosauriformes, 5 – Dinosauria, 6 – Saurischia, 7 – Sauropodomorpha, 8 – Sauropoda. (Bronzati et al., 2017).

By looking at the brain of Saturnalia, Bronzati found that the earliest sauropodomorphs most likely actually had a diet of meat – they were predators! This is because two regions of the brain – the flocculus and the paraflocculus lobes – were both found to be surprisingly large compared to other herbivorous sauropods; what Bronzati calls an “enlarged protuberance”. Reduction of these brain sections is usually associated with the adoption of a four-legged, quadrupedual, stance in later sauropodomorphs. Which works nicely, as Saturnalia most likely frolicked around on just two legs, unlike its giant descendants.

Both of these brain sections are part of the cerebellum, and are responsible for moving the head and neck, as well as in stabilizing the gaze of an animal. The large size suggests that Saturnalia was quite smart in the way it co-ordinated its head and neck, much like we see in modern predators when hunting their prey. For example, think of a wolf chasing a rabbit – small, rapid movements enable a predator to respond fast to an elusively darting prey.

Previous research based on their anatomy suggested at most an omnivorous diet, with their teeth being curved backwards and with small serrations on the tips. Bronzati’s study shows us that by looking at old animals in new ways, we can unlock a whole new understanding of dinosaurs and their evolution. In the paper, it is stated “making inferences on the lifestyle of extinct taxa using a single criterion can be misleading. Form/function correlations should be very carefully made, and other parameters (historical and ahistorical) should be taken into account when inferring the ecology of extinct taxa.”

For example, Saturnalia, like other sauropods, had a small head and a long neck. Typically, these features have been associated with adaptations for herbivory and grazing – swinging your head from side to side like a rake to pull in foliage. But what if actually these features were originally triggered by adaptations to predation? This would flip our understanding of their evolutionary history around, as well as change our interpretation of the evolution of the feature in itself.

Bronzati is already on the lookout for more dinosaur skulls to scan, hoping that he can build up a more complete picture of their brain evolution through time.

Reference

Bronzati, M., Rauhut, O. W., Bittencourt, J. S., & Langer, M. C. (2017). Endocast of the Late Triassic (Carnian) dinosaur Saturnalia tupiniquim: implications for the evolution of brain tissue in Sauropodomorpha. Scientific Reports7, doi10.1038/s41598-017-11737-5

Featured image: Saturnalia, by Nobu Tamnura, CC BY-SA 4.0

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