Fossilized stomach reveals long-necked dino dining secrets

By Stephen Beech

Long-necked dinosaurs didn't bother chewing, suggests new research.

The stomach contents of a fossilized sauropod found in Australia show evidence of having been severed but not chewed, say scientists.

The first discovery of its kind supports the long-standing theory that sauropods were vegetarian, according to the study published in the journal Current Biology.

Scientists say the Aussie dinosaur, which was alive around 94 to 101 million years ago, ate a variety of plants and relied almost entirely on its gut microbes for digestion.

Study lead author Dr. Stephen Poropat, of Curtin University in Perth, Australia, said: “No genuine sauropod gut contents had ever been found anywhere before, despite sauropods being known from fossils found on every continent and despite the group being known to span at least 130 million years of time.

“This finding confirms several hypotheses about the sauropod diet that had been made based on studies of their anatomy and comparisons with modern-day animals.”

He says knowledge of the diet of dinosaurs is "critical" for understanding their biology and the role they played in ancient ecosystems.

But very few dinosaur fossils have been found with cololites, or preserved gut contents.

The researchers explained that sauropod cololites have remained particularly elusive, even though the species may have been the most ecologically impactful terrestrial herbivores worldwide throughout much of the Jurassic and Cretaceous periods, given their gigantic sizes.

Due to the lack of direct evidence when it comes to diet, the specifics of sauropods' eating habits - including the plants they ate - have been largely inferred based on anatomical features such as tooth wear, jaw shape and neck length.

In 2017, staff and volunteers from the Australian Age of Dinosaurs Museum of Natural History were excavating a relatively complete subadult skeleton of the sauropod Diamantinasaurus matildae from the mid-Cretaceous period, which was found in the Winton Formation of Queensland.

During the process, they noticed an unusual, fractured rock layer that appeared to contain the sauropod’s cololite, which consisted of many well-preserved plant fossils.

Dr. Poropat said analysis of the plant specimens within the cololite showed that sauropods likely only engaged in minimal oral processing of their food, relying instead on fermentation and their gut microbiota for digestion.

He says the cololite consisted of a range of plants, including foliage from conifers, seed-fern fruiting bodies, and leaves from flowering plants, indicating that Diamantinasaurus was an "indiscriminate, bulk feeder".

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Dr. Poropat said: “The plants within show evidence of having been severed, possibly bitten, but have not been chewed, supporting the hypothesis of bulk feeding in sauropods."

The research team also found chemical biomarkers of both flowering plants and gymnosperms - a group of woody, seed-producing plants that include conifers.

Dr. Poropat said: “This implies that at least some sauropods were not selective feeders, instead eating whatever plants they could reach and safely process.

“These findings largely corroborate past ideas regarding the enormous influence that sauropods must have had on ecosystems worldwide during the Mesozoic Era.”

Although it was not unexpected that the gut contents provided support for sauropods being herbivores and bulk feeders, Dr. Poropat was surprised to find flowering plants - or angiosperms - in the dinosaur’s gut.

He said: “Angiosperms became approximately as diverse as conifers in Australia around 100 to 95 million years ago, when this sauropod was alive.

“This suggests that sauropods had successfully adapted to eat flowering plants within 40 million years of the first evidence of the presence of these plants in the fossil record.”

Based on their findings, the team suggests that Diamantinasaurus likely fed on both low- and high-growing plants, at least before adulthood.

As hatchlings, sauropods could only access plants found close to the ground, but as they grew, so did their viable dietary options.

The researchers said that the prevalence of small shoots, bracts, and seed pods in the cololite also implies that subadult Diamantinasaurus targeted new growth portions of conifers and seed ferns, which are easier to digest.

They say the strategy of indiscriminate bulk feeding seems to have served sauropods well for 130 million years and might have enabled their success and longevity.

Dr. Poropat said, “The primary limitation of this study is that the sauropod gut contents we describe constitute a single data point.

“These gut contents only tell us about the last meal or several meals of a single subadult sauropod individual."

He added: “We don't know if the plants preserved in our sauropod represent its typical diet or the diet of a stressed animal.

"We also don't know how indicative the plants in the gut contents are of juvenile or adult sauropods, since ours is a subadult, and we don't know how seasonality might have affected this sauropod's diet.”