The skeleton of a Psittacosaurus dinosaur is displayed during the Collector Exhibition at the Grand Palais Museum in Paris September 10, 2009.
| Photo Credit: Reuters

A new fossil of the Cretaceous Period dinosaur Psittacosaurus, a dog-sized herbivore with a parrot-like beak, that was donated to a Chinese university came with a surprise – one revealed only after scientists viewed it under ultraviolet light.

It retained large patches of beautifully preserved skin, down to its cellular structure, providing new insight into skin evolution in feathered dinosaurs. The fossil points to “zoned development” in the skin of these dinosaurs, researchers said, with Psittacosaurus and probably other feathered dinosaurs possessing scaly, reptile-like skin on body regions without feathers, with soft, bird-like skin on areas with feathers.

“Initially we didn’t really have much hope of finding any soft tissues because, to the naked eye, our specimen appears to preserve only the bones. We didn’t give up, though, because we knew that during fossilization soft tissues can be replaced by minerals, which may blend in with the sediments,” said Zixiao Yang, a postdoctoral researcher in paleontology at University College Cork in Ireland and lead author of the study published on Tuesday in the journal Nature Communications.

“When I turned on the UV light, I could feel my heart almost skip a beat. Large patches of scaly skin, covering the chest and belly, were glowing in a striking golden-yellow color under the UV. The fossil skin looked really exquisite, covered by tiny, rounded scales of about one millimeter wide,” Yang said.

Fossils of any soft tissues are rare. Skin fossils of this quality are rarer still.

Unearthed in northeastern China, the nearly complete fossil, dating to roughly 130 million years ago, is of a juvenile Psittacosaurus (pronounced SIT-ak-oh-sawr-us), about 2-1/4 feet (66 cm) long and approximately 3 years old when it died. It was donated in 2021 to Nanjing University from a private collection.

Psittacosaurus is an early member of the horned dinosaur lineage, called ceratopsians, that later produced large beasts like Triceratops. Psittacosaurus itself lacked horns. Its name means “parrot lizard” based on its protruding beak, adapted for eating plants.

Many dinosaurs had feathers. In fact, birds evolved from small feathered dinosaurs. The first rudimentary feathers are thought to have evolved from reptilian scales nearly 250 million years ago in animals ancestral to dinosaurs and the flying reptiles called pterosaurs.

Psittacosaurus had simple, bristle-like feathers atop its tail. The rest of its body was covered by scaly skin. The fossil did not have skin from the dinosaur’s feathered regions, but the researchers think these areas had bird-like skin.

“This discovery adds nuance to our understanding of feather evolution. The acquisition of modern, bird-like skin happened only locally on the body. Tough, reptile-style skin remained essential in body regions not protected by feathers,” said University College Cork paleontology professor and study co-author Maria McNamara.

The skin of birds exhibits multiple adaptations for feathers.

Birds have a dermal network of microscopic muscles that encircles each feather and acts like a hydraulic system, including muscles that pull feathers in different directions. There also is a network of smooth muscles under the skin that keeps feathers separated, as well as deposits of fatty tissue anchored to the base of the skin that create an even skin surface and feather orientation. In addition, feathers are connected by a system of sensory nerve fibers.

“Until now, we haven’t known whether the skin of dinosaurs and their relatives evolved these skin adaptations first and feathers later, or whether they evolved at the same time, and in which parts of the body,” McNamara said.

The Psittacosaurus fossil “strongly suggests that evolution of feathers – and the new skin adaptations – happened at the same time,” McNamara said.

The dinosaur’s scaly skin closely resembled the skin of today’s reptiles.

“They are similar in many aspects, including the shape, size, arrangement and composition of skin cells, and the way the skin produces color patterns,” Yang said.

Museum visitors walk beneath the skeleton of Patagotitan mayorum as it goes on display as part of the new ‘Titanosaur: Life as the Biggest Dinosaur’ exhibit at Natural History Museum in London, Britain April 1, 2023. Image for Representation.
| Photo Credit: Reuters

You’re probably familiar with classic sauropod dinosaurs – the four-legged herbivores famous for their long necks and tails. Animals such as Brachiosaurus, Apatosaurus and Diplodocus have been standard fixtures in science museums since the 1800s.

With their small brains and enormous bodies, these creatures have long been the poster children for animals destined to go extinct. But recent discoveries have completely rewritten the doomed sauropod narrative.

I study a lesser known group of sauropod dinosaurs – the Titanosauria, or “titanic reptiles.” Instead of going extinct, titanosaurs flourished long after their more famous cousins vanished. Not only were they large and in charge on all seven continents, they held their own amid the newly evolved duck-billed and horned dinosaurs, until an asteroid struck Earth and ended the age of dinosaurs.

The secret to titanosaurs’ remarkable biological success may be how they merged the best of both reptile and mammal characteristics to form a unique way of life.

Moving with the continents

Titanosaurs originated by the Early Cretaceous Period, nearly 126 million years ago, at a time when many of the Earth’s landmasses were much closer together than they are today.

Over the next 75 million to 80 million years, the continents slowly separated, and titanosaurs drifted along with the changing formations, becoming distributed worldwide.

There were nearly 100 species of titanosaurs, making up more than 30% of known sauropod dinosaurs. They varied greatly in size. From the largest known sauropods ever discovered, including Argentinosaurus, Patagotitan and Futalognkosaurus, whose weight exceeded 60 tons (54.4 metric tons) and were bigger than a semitruck, to the smallest known sauropods, including Rinconsaurus, Saltasaurus and Magyarosaurus, which were around only 6 tons (5.4 metric tons) and about the size of an African elephant.

Babies to titans

Like many reptiles, titanosaurs began life comparatively tiny, hatching from eggs no bigger than grapefruits.

The best data on titanosaur nests and eggs comes from a site in Argentina called Auca Mahuevo, featuring 75 million-year-old exposed rocks. The site contains hundreds of fossilized nests containing thousands of eggs, some of which are so well preserved, scientists recovered skin impressions from ancient embryos.

The sheer number of nests found together, in multiple geological layers, suggests titanosaurs returned to this site repeatedly to lay their eggs. The nests are so closely spaced, it’s unlikely an adult titanosaur would have been able to move freely through the nesting ground. Titanosaurs likely had a hands-off parenting style, similar to many reptiles that lay numerous eggs and don’t spend much time tending the nest or taking care of hatchlings.

A titanosaur hatchling would have been roughly 1 foot (30 centimeters) tall, 3 feet (1 meter) long and 5-10 pounds (2.5-5 kg). Recent evidence from a site in Madagascar suggests these tiny titans were born ready to rumble.

Fossilized bones from the species Rapetosaurus suggest that by the time they would have been just knee high to a modern human, they were likely fending for themselves. Microscopic details recorded deep within the bones indicate baby Rapetosaurus likely foraged independently for plants and moved much more nimbly than their lumbering adult relatives.

For the first century of dinosaur science, palaeontologists imagined titanosaurs as giant, overgrown reptiles – and used reptilian growth rates to predict their milestones. In this slow-growth model, even the smallest titanosaurs would have taken nearly a century to reach their full size, meaning they would have been relatively small for a good chunk of their lives. New evidence suggests this growth pattern is unlikely.

Scientists like me study titanosaurs’ bones at high magnification to better understand their growth. We look at the microscopic patterns of bone minerals as well as the density and architecture of the spaces that held blood vessels and cells.

The more dense the blood supply is to a bone, the faster that animal grows. These signatures are also present in living animals and can accurately reflect growth rates, anomalies and even age.

Bone data shows titanosaur growth rates were on par with mammals like whales – much, much faster than any living reptile – meaning they would have reached their enormous adult sizes in just a few decades. Scientists can’t know for sure how long titanosaurs lived, but based on large land animals living today, titanosaurs lived possibly 60 or more years.

Fuelled by plants

The rapid growth rates of sauropods was partly due to their body temperatures. By studying the chemistry of fossilized teeth and eggshells, scientists have determined titanosaurs had body temperatures ranging from about 95 to 100.5 degrees Fahrenheit (35 to 38 degrees Celsius). That’s higher than that of crocodiles and alligators, about the same as modern mammals and a bit lower than most birds, whose bodies can regularly get as warm as 104 F (40 C).

Titanosaurs’ rapid growth rates were also powered by their prodigious appetites for plants. Microscopic patterns of scratches, wear and pits on their teeth indicate titanosaurs in Argentina fed on a diverse diet rich in grit, suggesting they were dining on plants found lower to the ground, where sediment would be more commonly found.

In India, chunks of fossilized feces, otherwise known as coprolites, show titanosaurs there ingested everything from ground-level plants all the way up to the leaves and branches of trees.

Like all dinosaurs, titanosaurs replaced their teeth throughout life. But data shows they replaced each tooth about every 20 days for maximum efficiency, one of the highest tooth-replacement rates known for dinosaurs.

Had it not been for the asteroid impact 66 million years ago, these long-lived, incredibly diverse and wildly successful animals probably would have kept on thriving, in places as distant as Madagascar, Romania, North America and even Antarctica. Instead, titanosaurs were among the witnesses to – and victims of – the most recent mass extinction on Earth.