In today’s blog post we look at the dwarf nodosaurid Patagopelta (P. cristata), which was formally named and described earlier this month.

A new, very small, armoured dinosaur has been named and described from fossils found in Argentina. The dinosaur which measured around 2 to 2.3 metres in length (based on the dimensions of the femur), suggests that some members of the Nodosauridae in Gondwana became smaller in the Late Cretaceous, perhaps as armoured dinosaurs in South America were under evolutionary pressure from other ornithischians and titanosaurs.

Dwarf Nodosaurid Patagopelta

Fragmentary remains of Late Cretaceous armoured dinosaurs are known from Chile and Argentina, but little work had been undertaken to assess these specimens and to review their phylogeny and taxonomic relationship with other members of the Ankylosauria clade from North America and elsewhere in the world.

Writing in the ” Journal of Systematic Palaeontology”, the researchers led by Facundo Riguetti, a CONICET doctoral fellow, reassessed the known ankylosaur material in conjunction with some other recently found fossils and, as a result, they were able to establish a new nodosaurid species from bones and a single tooth found in sediments of the Allen Formation (Campanian–Maastrichtian) in Salitral Moreno, Río Negro Province (northern Patagonia).

Patagopelta cristata

The dinosaur’s genus name translates as “Patagonian shield” whilst the trivial name derives from the Latin for crest – a reference to the diagnostic crests on both the anterior surface of the femur and the lateral osteoderms of the cervical rings.

Dr Riguetti commented:

“The importance of the study lies in the fact that Patagopelta is the first species of Ankylosauria described for the continental territory of Argentina, which fills the existing gap for this group and adds a new thyreophoran to the very few incomplete and indeterminate remains known for our country from this type of ornithischian dinosaur.”

The Right Femur

The best-preserved fossil element is the right femur, which is complete and shows typical anatomical characteristics associated with the Nodosauridae. This bone along with the distinctive cervical osteoderms led to the erection of this new species. As the femur is only 25 cm in length and bone histology suggests an adult animal, the researchers conclude that Patagopelta was a dwarf form of armoured dinosaur.

Co-author Sebastián Apesteguía, a CONICET researcher, explained:

“For an armoured dinosaur, Patagopelta is extremely small. Due to the size of the femur, only 25 centimetres in length, we estimate that the animal must have been between two and three meters long, while, in general, ankylosaurs are medium-sized or large animals, with an average length of between four and five metres.”

A Faunal Exchange Across the Americas

Although it is thought that the Nodosauridae evolved in the Northern Hemisphere, towards the end of the Cretaceous (Campanian – Maastrichtian), a land bridge existed between North America and South America that permitted a faunal exchange. Titanosaurs migrated north, which explains why fossils of titanosaurs such as Alamosaurus occur in the USA. Ornithischian dinosaurs such as hadrosaurs and nodosaurids moved south.

The image above shows a typical Late Cretaceous titanosaur, for models of Late Cretaceous dinosaurs including titanosaurs and armoured dinosaurs: CollectA Prehistoric Life Models.

Sebastián Apesteguía added:

“That is why in South America we only expect to find animals like Patagopelta in rocks from the Late Cretaceous, just before the global extinction of the dinosaurs took place.”

Dwarfism in Late Cretaceous South American Thyreophora

The size of Patagopelta along with the recently described Stegouros (Soto-Acuña et al, 2021)*, from southernmost Chile, suggests that armoured dinosaurs in South America may have gradually become smaller. This trait is not known in members of the Thyreophora described from other parts of the world. Palaeontologists have speculated that perhaps competition from titanosaurs and the migration of hadrosaurs into South America might have led to armoured dinosaurs adapting to different ecological niches to avoid competition. By being smaller these animals needed fewer resources than larger, contemporaneous herbivorous dinosaurs.

It has also been suggested that the geology of Patagonia where the fossils of Patagopelta were found might provide a clue to the dwarfism. Geologists are aware of several Late Cretaceous marine transgressions in the region. This might have led to the establishment of an island archipelago with dinosaurs living on these small islands gradually become smaller due to a scarcity of resources (the “island rule”).

Tracks of Dwarf Ankylosaurs

Members of the Patagopelta research team had previously described tracks of dwarf ankylosaurs, possibly affected by similar circumstances, preserved in Upper Cretaceous deposits in Bolivia.

*To read Everything Dinosaur’s 2021 article about the discovery of Stegouros: New Armoured Dinosaur from Chile.

Everything Dinosaur acknowledges the assistance of a media release from Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) in the compilation of this article.

The scientific paper: “A new small-bodied ankylosaurian dinosaur from the Upper Cretaceous of North Patagonia (Río Negro Province, Argentina)” by Facundo Riguetti, Xabier Pereda-Suberbiola, Denis Ponce, Leonardo Salgado, Sebastián Apesteguía, Sebastián Rozadilla and Victoria Arbour published in the Journal of Systematic Palaeontology.

The first, definitive proof of a dinosaur eating a mammal has been found. A foot of a tiny, mouse-sized mammal has been discovered inside the body cavity of the feathered theropod Microraptor (M. zhaoianus). Previously, other Microraptor specimens from Lower Cretaceous rocks of northern China had revealed the fossilised remains of a fish, a primitive bird and a lizard associated with the body cavity. Palaeontologists now know that this crow-sized predator also ate mammals. This is the first record of a dinosaur consuming a mammal.

Mammal Foot Found Inside Ribcage

A new study led by Dr David Hone (Queen Mary University of London), published in the academic “Journal of Vertebrate Paleontology”, documents the first known incident of a dinosaur having eaten a mammal.

Microraptor is a genus of small, dromaeosaurid which lived in the forests of northern China around 120 million years ago (Early Cretaceous). The remarkable fossils found in Liaoning Province have enabled palaeontologists to build up a detailed picture of life in these ancient, dinosaur-dominated forests.

Researchers have also identified a wide variety of mammals and mammaliamorphs that co-existed with the dinosaurs and pterosaurs. Together these creatures make up a diverse ecosystem known as the Jehol biota

To read Everything Dinosaur’s blog post from 2021 describing the remarkable diversity of vertebrates associated with the Jehol biota: The Jehol Biota.

Microraptor had long feathers on its arms and legs and was, very probably arboreal, gliding from tree to tree, hunting out small animals to eat.

Spotting the Fossilised Foot

The Microraptor specimen was first described twenty-two years ago, but the preserved remains of the tiny foot had been overlooked. Professor Hans Larsson of McGill University in Montreal spotted what others had missed – the remains of another animal inside the Microraptor’s rib cage. In collaboration with Dr Hone, and colleagues from Canada, China and the USA, a paper describing this remarkable discovery has now been published.

Dinosaur Eating a Mammal

The mammal foot is almost complete and belonged to a very small animal, approximately the size of a modern house mouse. Examination of the bones suggest that it was one that predominantly lived on the ground and was not well adapted for climbing trees, making it an interesting prey choice for the mainly arboreal Microraptor.

Previous studies have revealed other Microraptor specimens containing the remains of a bird, a lizard and a fish. This specimen of the species Microraptor zhaoianus demonstrates that Microraptor also consumed small mammals. This little feathered dinosaur was a generalist, consuming a wide variety of prey.

It is not certain if the dromaeosaurids in question had directly preyed upon and eaten these animals or found them already dead and had scavenged them (or a mixture of both) but the mammal at least falls into the range of typical prey size predicated for a predator the size of Microraptor.

Dr Hone’s co-authors on the paper include Dr Alex Dececchi, Mount Marty College (USA), Dr Corwin Sullivan at the Department of Biological Sciences, University of Alberta, and Professor Xu Xing at the Institute of Vertebrate Palaeontology and Palaeoanthropology, Beijing.

A Significant Fossil Discovery

Commenting on the significance of this fossil discovery, Dr David Hone stated:

“It’s so rare to find examples of food inside dinosaurs so every example is really important as it gives direct evidence of what they were eating.“

Dr Hone from the University’s School of Biological and Behavioural Sciences added:

“While this mammal would absolutely not have been a human ancestor, we can look back at some of our ancient relatives being a meal for hungry dinosaurs. This study paints a picture of a fascinating moment in time – the first record of a dinosaur eating a mammal – even if it isn’t quite as frightening as anything in Jurassic Park.”

Co-author of the study, Dr Alex Dececchi, from Mount Marty College, commented:

“The great thing is that, like your housecat which was about the same size, Microraptor would have been an easy animal to live with but a terror if it got out as it would hunt everything from the birds at your feeder to the mice in your hedge or the fish in your pond.”

Everything Dinosaur acknowledges the assistance of a media release supplied by Dr David Hone in the compilation of this article.

The scientific paper: “Generalist diet of Microraptor zhaoianus included mammals” by Hone, D.W.E., Dececchi, T.A., Sullivan, C., Xu, X. and Larsson, H.C.E. published in the Journal of Vertebrate Paleontology.

Correction

This is not the first recorded incidence of a dinosaur consuming a mammal. The press release, although provided by the appropriate authorities, had failed to recognise evidence cited in an earlier scientific paper.

Ankylosaurs battled each other using their tail clubs for social dominance in intraspecific combat. A recently published scientific paper on the ankylosaur Zuul crurivastator suggests that these armoured dinosaurs used their tail clubs to bash each other as well as to fend off tyrannosaurs.

In the study, published in “Biology Letters” the research team, examined the osteoderms of the remarkably well preserved Zuul crurivastator, an armoured dinosaur described from fossils found in the Coal Ridge Member of the Judith River Formation (Montana). Several of osteoderms along the flanks show signs of damage and healing which led the scientists to postulate that these dinosaurs battled each other with their tail clubs. These fights would have been for social or territorial dominance, perhaps even a result of a “rutting” season fighting for mates – behaviour associated with many mammals today.

Zuul crurivastator

Named and formally described in 2017, Zuul crurivastator (pronounced Zoo-ul cruh-uh-vass-tate-or) roamed the northern part of Laramidia approximately 76 million years ago (Campanian faunal stage of the Late Cretaceous).

To read Everything Dinosaur’s 2017 blog post about the fossil discovery: Zuul – The Destroyer of Shins.

Zuul’s body was covered in bony plates (osteoderms) of different shapes and sizes and the ones along its flanks were particularly large and spiky. Interestingly, the scientists which included lead author and renowned ankylosaur expert Dr Victoria Arbour (Royal British Columbia Museum, Canada), noted that dermal armour near the hips on both sides of the body showed damage that had subsequently healed. This localised, bilaterally symmetrical pathology is speculated to have been caused by ritualised combat rather than wounds inflicted by an attacking theropod dinosaur.

An Exciting Piece of the Ankylosaur Puzzle

Dr Arbour commented:

“I’ve been interested in how ankylosaurs used their tail clubs for years and this is a really exciting new
piece of the puzzle. We know that ankylosaurs could use their tail clubs to deliver very strong blows to an opponent, but most people thought they were using their tail clubs to fight predators. Instead, ankylosaurs like Zuul may have been fighting each other.”

The genus name honours a fictional monster from the 1984 film “Ghostbusters”, whilst the trivial part of the binomial name translates as “the destroyer of shins”, a nod to the idea that tail clubs were used as defensive weapons to deter attacks from predatory theropod dinosaurs. The substantial club on the end of the three-metre-long tail being used to bash into the lower legs of tyrannosaurs. This new research does not refute the idea that these tail clubs had a role in defence, but based on the pathology seen in the Zuul holotype (specimen number ROM 75860) the scientists propose that sexual selection and intraspecific combat drove their evolution. Many mammals today such as deer, antelope, cattle and sheep have horns and antlers that have evolved for use in battles between members of the same species.

It had been suggested previously that ankylosaurs may have clubbed each other, and that broken and healed ribs could provide evidence to support this idea. Unfortunately, ankylosaurid skeletons are extremely rare in the fossil record, these animals were not common, even in the Late Cretaceous of North America, where the ecosystem was dominated by other ornithischian dinosaurs such as duck-billed dinosaurs and ceratopsians.

Implications for Ankylosaur Behaviour

The remarkable Zuul fossil skeleton provides palaeontologists with an opportunity to study pathology recorded on the bones and dermal armour.

Co-author Dr David Evans (Curator of Vertebrate Palaeontology at the Royal Ontario Museum) explained:

“The fact that the skin and armour are preserved in place is like a snapshot of how Zuul looked when it
was alive. And the injuries Zuul sustained during its lifetime tell us about how it may have behaved and
interacted with other animals in its ancient environment.”

Tail Clubs for Social Dominance

The researchers conclude that the imposing tail club of Zuul could have been used in defence when needed, but the analysis suggest that sexual selection drove the evolution of this weapon. This finding has consequences for how palaeontologists perceive ankylosaurs. It suggests that these dinosaurs were capable of complex behaviours and that they likely engaged in ritualised combat over mates or for social dominance as inferred in other types of dinosaurs and observed in living mammals and birds.

To view a replica of the armoured dinosaur Zuul and other prehistoric animal models (whilst stocks last): Armoured Dinosaurs and Prehistoric Animal Figures (Wild Safari).

Everything Dinosaur acknowledges the assistance of a media release from the Royal Ontario Museum in the compilation of this article.

The scientific paper: “Palaeopathological evidence for intraspecific combat in ankylosaurid dinosaurs” by Victoria M. Arbour, Lindsay E. Zanno and David C. Evans published in Biology Letters.