A reconstruction of a Patagotitan in comparision to a human, which is a out ten times smaller.

Titanosaurs, such as this Patagotitan, were the largest land animals ever to have evolved, yet we know very little about how they grew © Mariolanzas/Wikimedia Commons

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Dinosaur diaries: the first-ever 3D fossil of a titanosaur embryo

The first 3D scan of an embryo of a titanosaur reveals that they had an egg tooth-like structure on the end of their nose.

Read more about this extraordinary discovery, as well as how the dinosaur family tree is getting another shakeup and how some researchers are trying to age a 125 million year old dinosaur. 

Palaeontologists know relatively little about baby dinosaurs. Their bodies are rarely preserved as fossils, partly because they weren't big enough and their skeletons were still a bit too soft to fossilise, but also because they were more likely to be eaten by predators.

A new paper by Martin Kundrát and colleagues reports on the first-ever 3D preserved sauropod embryo, revealing some very unusual details about its face.

The team worked on a newly discovered Argentinian dinosaur egg that contained a very well-preserved 3cm long fossil embryo skull. It belonged to a titanosaur, a group that includes some of the largest land animals to ever have lived, with some species reaching an incredible 37 metres long. 

The skull of the titanosaur embryo, showing a small protrution at the front of its nose.

The skull of the embryo is preserved in exquisite detail, showing the curious proportions of the baby titanosaur 

The fossil was carefully prepared and cleaned, then scanned using a powerful type of X-Ray which let them build up a detailed 3D image of the skull without damaging it.

These scans have revealed some amazing features. The embryo was about 80% grown in the egg so wasn’t quite ready to hatch yet, but it had already developed a bony horn-like structure on the end of its snout. This may have helped it break out of the egg whilst hatching, similar to the egg tooth used by the chicks of most modern birds. The horn could have also been used for foraging, or even self-defence.

The team also found that the eyes were more forward-facing than they would have been in an adult titanosaur. This may have given the young dinosaur improved binocular vision until it grew larger, helping it to search for food and avoid predators looking for an easy meal.

Finds like this are exceptionally rare, and this is one of the best-preserved dinosaur embryos ever found. It gives us an insight into how some of the biggest ever dinosaurs developed when they were still very small. 

A reconstruction of the sauropod embryo, showing it had big, bluging eyes, and a small horn on the end of its nose.

It is likely that the young titanosaur had an egg tooth-like horn on its snout, possibly to help it break out of the egg. 

The dinosaur family tree gets another shakeup

The family tree of the dinosaurs is constantly being reviewed in the light of new data. In its latest shake up, a new study has suggested that a group of reptiles called silesaurids are actually dinosaurs, challenging what we thought we knew about early dinosaur evolution. 

The bird-hipped dinosaurs, which includes iconic forms like Stegosaurus and Triceratops, are a group so named because the bones in their hips superficially look like those found in birds. But the early evolution of these dinosaurs has been shrouded in mystery.

They appear fully formed in the Jurassic period, and there are no transitional fossils that show how they developed from their Late Triassic meat-eating cousins the lizard-hipped dinosaurs, the group which includes animals such as Tyrannosaurus rex.

Now, Rodrigo Müller and Maurício Garcia from the Universidade Federal de Santa Maria in Brazil have carried out a new analysis that suggests a group of reptiles called silesaurids might in fact be the earliest bird-hipped dinosaurs.

A reconstruction of a silesaurid walking on all fours, with scaly skin, a lizard like head and a row of spikes along its back.

Silesaurids have traditionally not been included within dinosaurs, but that might now be about to change © Nobu Tamura/Wikimedia Commons

The silesaurids are from the Middle and Late Triassic periods, which means that they would fill in the time gap between the first lizard-hipped dinosaurs and the first bird-hipped dinosaurs.

The earliest 'silesaurids' may have actually been meat-eaters or perhaps omnivores. This new hypothesis helps palaeontologists to answer key questions about the evolution of the bird-hipped dinosaurs, like how and when they became plant eaters.

Many palaeontologists will be rushing to scrutinize this study as any shake-up of the dinosaurian family tree is always controversial. Only new discoveries and new methods of analysis will determine if this hypothesis stands the test of time. 

How to age a dinosaur

As animals grow, their bones change drastically not just in size, but also in their shape. But despite this, the age of a dinosaur when it died is still not clear just by looking at its bones. This has proven to be a long-standing problem for palaeontologists interested in how dinosaurs grew.

The answers, however, may be hidden inside the bones themselves.

In early development the changes in the shapes of bones occur very quickly. But once an animal has reached sexual maturity, this bone growth slows until the animal reaches its full adult size.

This record of bone growth can be examined by studying the bones under a microscope.

In a new study, Fenglu Han and colleagues have looked at the microscopic growth patterns within the bones of a small, plant-eating dinosaur from the Early Cretaceous (~125 million years ago) of China called Jeholosaurus

The fossil of a Jeholosaurus, next to a section of the limb bone and finally a thing slice through it, showing a layer of rings within the bones structure.

By taking thin sections through the bones of the Jeholosaurus fossils, the researchers were able to count the rings in the older specimens to determine their ages © Modified from Han et al. (2020). Silhouette by V. Sinkkonen

While some dinosaurs are only represented by a single fossil, Jeholosaurus is known from over a half-dozen individuals, showing a wide range of body lengths. The size differences between these specimens may indicate different ages, but they may also be due to natural variation within a population or even sexual dimorphism.

In order to accurately work out the age range of these Jeholosaurus fossils, Han and colleagues needed to look at the internal patterns of bone growth.

To do this the team cut out thin slices from the leg bones of five Jeholosaurus individuals, which were then prepared into even thinner slices that could be looked at under a microscope.

They found that the bones from the smaller individuals had lots of canals, which in life would have been providing the blood and nutrients required for fast bone growth.

The bones from the larger individuals, however, had growth lines, which, like tree-rings, are thought to be caused by a pause in growth during the harsher winter months and so can indicate the age at death.

From this, the researchers were able to tell that the Jeholosaurus specimens ranged in age from early juveniles to sexually mature subadults. By counting these growth rings in the bones of the largest specimen of Jeholosaurus, Han and colleagues found that it was probably five years old at the time of its death.

This study shows that Jeholosaurus probably reached sexual maturity as early as two years old, a comparatively early age to many other dinosaurs previously looked at. Perhaps this rapid early growth was an important evolutionary adaption that helped Jeholosaurus and other bird-hipped dinosaurs became so successful throughout the rest of the Cretaceous.