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A new fossil has shown what early dinosaurs may have looked like, while another has revealed once and for all what it was that killed them off 150 million years later.
Discover more with the Museum's team of dinosaur experts.
From gigantic sauropods trampling through Jurassic forest and lumbering tank-sized stegosaurs, to enormous pterosaurs that ruled the skies, these two ancient groups of animals contained some of the largest animals ever to evolve.
But dinosaurs and pterosaurs didn't begin their evolutionary journeys at such huge sizes.
A new paper by Christian Kammerer and his team from the North Carolina Museum of Natural Sciences and the American Museum of Natural History shows that their early ancestors may have been much smaller than previously thought.
The team describes a new animal from the Late Triassic of Madagascar which is close to the ancestry of both dinosaurs and pterosaurs. It has been named Kongonaphon kely, meaning 'tiny bug slayer'.
Fossils of this age and type of animal are very rare and so any that are found are extremely important. Being only around 10 cm in height, Kongonaphon shows that during this time, around 200 million years ago, these early animals were very small indeed. This could be related to the end-Permian mass extinction event.
Occurring some 252 million years ago, this was the largest extinction event in the Earth's history, seeing almost 96% of marine species and 70% of land animals wiped from the planet. But it was in this aftermath that the ancestors of dinosaurs and pterosaurs arose.
The casualties of this extinction event are thought to have included many small-bodied insect-eating reptiles. Kongonaphon and several other archosaurs might have evolved to be a smaller size to eat insects, therefore taking advantage of this now vacant ecological role previously filled by the reptiles. This suggestion is backed up by the shape of their teeth.
The paper also suggests that the reduced size may have led to these animals developing primitive feather-like structures, which could have helped the smaller animals stay warm during a time of extreme climate fluctuations, a feature that they might have passed on to their pterosaur and dinosaur descendants.
The dinosaur Dilophosaurus is perhaps best known for its staring role in the original Jurassic Park film, with its distinctive hiss, rattling neck frill and venom-spitting antics.
But while there may not be any fossil evidence for these features, a new paper is revealing how the true dinosaur did possess an impressive double-crested skull and would have reached an intimidating seven metres in length, much bigger than its more famous movie depiction.
Adam Marsh and Timothy Rowe, based at the University of Texas and Petrified Forest National Park, have published a new and extremely detailed paper on the anatomy of Dilophosaurus, based on the original and more recent specimens that had not been described before.
The authors found that Dilophosaurus was far more 'advanced' than the older and smaller theropods from the Triassic. They show that the species is already starting to display some of the anatomical features that are usually only seen in later dinosaurs like Allosaurus, Ceratosaurus and even present-day birds.
The first remains of Dilophosaurus were discovered in 1940 by a Navajo man called Jesse Williams, in Arizona, USA. He showed these fossils to Samuel P. Welles, a palaeontologist at the University of California doing fieldwork in the same area, who then dug it up the rest of the animal and named the new dinosaur.
These original descriptions of Dilophosaurus, which is one of the earliest large predatory dinosaurs, have played a significant role in how future researchers deciphered the relationship and evolution of theropods and early dinosaurs. But as new fossils have been found, and new knowledge gathered, Marsh and Rowe wanted to revisit these first descriptions to see how they fit in with our modern understandings.
They suggest that the distinctive double-crest on the skull was probably used to help animals recognise other members of their own species and potentially had a role during mating season. The authors also discovered that Dilophosaurus had much more powerful jaws than initially thought, which combined with its large size and strong arms would have made it one of the prominent predators of the time.
Finally, the researchers are keen to acknowledge the people of the Navajo Nation in welcoming the scientists and making palaeontological research possible on their lands, highlighting the need for any type of scientific research to respect and embrace indigenous cultures.
The question of what exactly caused the extinction of (non-avian) dinosaurs has puzzled palaeontologists for over a century, but ongoing discoveries have narrowed it down to two likely culprits at the end of the Cretaceous, 66 million years ago.
One suggests that a series of protracted volcanic eruptions occurred in India, forming what is now known as the Deccan traps, released greenhouse gases that caused rapid global warming. The other is the impact of an asteroid with Earth that left a giant crater which is now buried under the Yucatán Peninsula in Mexico.
Scientists have continued to debate whether it was the volcanism, asteroid impact, or a combination of the two which killed off non-avian dinosaurs. New work led by Alessandro Chiarenza, a researcher at University College London, and colleagues has combined climatic and ecological modelling to finally settle this age-old question.
Chiarenza and colleagues first applied models used to predict future global warming, known as global circulation models, to simulate the effects of the Deccan volcanism and asteroid impact on Late Cretaceous climate. They then looked at the Late Cretaceous fossil record in order to establish the environmental conditions that made for prime dinosaur habitat.
By then combining these data, it allowed the researchers to assess how each natural disaster would have affected the dinosaurs employing a technique that is normally used by conservationists to predict how living animals will respond to climate change.
The team found that climatic changes caused by Deccan volcanism were insufficient to have caused the extinction of the dinosaurs. Instead, the release of carbon dioxide by these eruptions led to long-term global warming, which would have produced conditions very hospitable to dinosaurs.
By contrast, the dust and gas thrown into the atmosphere by the asteroid impact would have blocked out the sun, leading to severe global cooling, as temperatures on land would have plunged by up to 35ᵒC following the catastrophic impact. This was sufficient to cause the complete collapse of most suitable dinosaur habitat.
These results firmly point to the asteroid impact causing the demise of non-avian dinosaurs at the end of the Cretaceous. The prolonged 'impact winter' triggered by this cataclysm would have condemned the dinosaurs to starve to death in freezing temperatures, as the food chains and climatic conditions they depended upon collapsed.
Rather than causing extinction, the global-warming from the Deccan traps eruptions may instead have countered some of the asteroid-driven cooling, helping life to recover more quickly than it otherwise would. This highlights the sometimes-unexpected ways in which Earth systems interact with each other, but also warns that the fates of even the mightiest creatures rest on the health of the environment.