Life reconstruction of the Cretaceous Period armoured dinosaur Borealopelta markmitchelli, which lived 110 million years ago in what is now Alberta. © Royal Tyrrell Museum of Palaeontology. Illustration by Julius Csotonyi.

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Dinosaur diaries: Fossilised stomach contents reveal a dinosaur's last meal

The Museum's dinosaur experts are rounding up the latest news from across the world of palaeontology.

Join them as they discover the last meal of an armoured dinosaur, find out how temperature affected body size and look inside the skull of a fish eater.

The dinosaur that ate its greens

About 110 million years ago, an armoured dinosaur ate its last meal and was promptly washed out to sea. Now, researchers have been able to uncover what it digested in its final hours.

It's a major discovery because for all that we understand about dinosaurs, we know little about their diets. We can broadly deduce whether they were carnivores or herbivores, but direct evidence of what they ate is rare.

A team led by Dr Caleb Brown of the Royal Tyrrell Museum has been able to examine the stomach contents of one dinosaur, Borealopelta markmitchelli. This was an armoured, herbivorous dinosaur known from Early Cretaceous marine deposits in Alberta, Canada.

Direct evidence of the diets of dinosaurs comes from two main sources: coprolites (fossil poo) and cololites (fossilised contents of the stomach or intestine). While freeing Borealopelta from its rocky tomb, researchers discovered a football-sized mass of rock in the ankylosaur's abdomen that looked like it could be a cololite.

A stomach block from the dinosaur, about the size of a football and containing rocks for grinding up plant material. © Royal Tyrrell Museum of Palaeontology.

 

They discovered the mass contained several gastroliths, rocks swallowed by the dinosaur that pulverised plant material in its stomach. Numerous tiny pieces of partially digested plant matter were alongside, and although one section of woody stem was nearly 35mm in length and had growth rings that could still be seen, it was the abundant smaller fragments that told the story of what this dinosaur was eating.

Microscopic analysis revealed fragments from 24 species of plant, mostly leaf material from ferns, although there was some material from clubmosses, conifers, cycads and rare flowering plants.

Charcoal fragments also found, which means Borealopelta could have been browsing in areas where wildfires had raged previously and was selectively feeding on the new plant growth that grew low to the ground.

This is the most detailed evidence yet discovered about the diet of a large herbivorous dinosaur and offers a fascinating insight into the final meal of Borealopelta, 110 million years ago.

Temperature and dinosaur metabolism

Next up is a study on temperature. Scientists often track heat transfer to understand the effects of temperature on where modern-day animals and plants live. However, unpicking the factors controlling the distributions of species that went extinct tens of millions of years ago is harder.

A new study published in PLoS ONE by David Lovelace and team at the University of Wisconsin-Madison used a series of climate models and predictions of body temperature to investigate the biology of some Late Triassic dinosaurs. They investigated the small theropod Coelophysis bauri and large prosauropod Plateosaurus engelhardti during the hot, dry global greenhouse conditions that prevailed at that time. 

An artist's reconstruction of Coelophysis, with a long body, long neck and large head.

Coelophysis lived towards the end of the Triassic Period

 

A range of different metabolic variables (for instance, body mass, body shape, scaly or feathered skin) were tested within six climate models built on the basis of geological information collected from the rocks of the Chinle Formation of the southwestern United States. The living Komodo dragon was added to these models to give a point of comparison for Coelophysis and Plateosaurus.

The researchers think that Coelophysis and Plateosaurus had a metabolism like those of modern flightless birds (emus and ostriches) and body temperatures comparable to those of primitive egg-laying mammals (platypus and echidnas).

Small theropods, weighing about 20 kilogrammes, may have needed feathers as insulation in cooler, temperate environments. Large prosauropods, weighing about 1,000 kilogrammes, would likely have become heat stressed in open, tropical environments and should have been restricted to cooler microclimates, such as dense forests or higher latitudes. 

These results are in agreement with the known distribution of dinosaurs from these groups and their size ranges as revealed by the Late Triassic fossil record. Their results might explain the previously mysterious absence of large prosauropods from areas known to be have been particularly warm and dry during the Late Triassic.

The fossil skull of Irritator challenger, (left) and a new reconstruction (right). The blue region is the brain cavity, the pink region is the inner ear and the yellow regions are cranial nerves.

The fossil skull of Irritator challenger, (left) and a new reconstruction (right). The blue region is the brain cavity, the pink region is the inner ear and the yellow regions are cranial nerves.

 

Peering inside the skull of a fish-eating theropod

For centuries, palaeontologists have been trying to understand how dinosaurs lived by looking at the fossilised clues they've left behind, whether that be in bones, footprints or nests. Digital technology has allowed us to investigate their behaviours and life habits in new and exciting ways.

In a new study, Marco Schade and colleagues reveal the virtually reconstructed brain anatomy of the meat-eating dinosaur Irritator challengeri from the Early Cretaceous of Brazil.

Irritator belongs to the group Spinosauridae, whose members are known for their long snouts and long, unserrated conical teeth. These distinctive crocodile-like features, along with other evidence including fossilised stomach contents, suggest they ate fish at least some of the time.

There has however been a long-standing debate as to whether these dinosaurs predominately lived on land or in the water. Just last month we reported on a new study which suggested that Irritator’s North African cousin Spinosaurus was probably aquatic.

Irritator presents an exciting new avenue to this discussion, as the holotype specimen includes a relatively well-preserved braincase, a delicate part of the skull that is rarely preserved without significant damage.

The braincase houses soft tissues such as the brain and inner ear, which are responsible for a wide range of cognitive, locomotory and sensory functions. These soft tissues rot quickly after death, leaving behind empty cavities in the skull. By digitally filling in these cavities from CT scans of the Irritator skull, Schade and colleagues were able to reconstruct the brain anatomy of this dinosaur. 

The results suggested that this animal had highly sensitive, fast head movements and good eye-head co-ordination, which it would have needed to execute the precise and fast striking motions required to catch fish.

The inner ear canals could suggest Irritator naturally held its head tilted downwards, possibly to avoid its elongate snout obstructing its field of vision when hunting.

Whether this Cretaceous carnivore was hunting from the river banks or the water remains to be shown, but this is surely an important piece of the puzzle.