Dinosaurs are the “calling cards” of paleontology, captivating people’s attention for nearly two centuries. These remarkable reptiles have become ingrained in our culture, inspiring books, films, video games, and even making appearances in advertisements and design.

The first dinosaur was described in 1824 from fossils discovered in Oxfordshire, England. It was named “Megalosaurus,” meaning “great lizard.” As more fossils were unearthed, species like Iguanodon and Hylaeosaurus were also identified. These animals did not fit into the existing biological classification system at the time. In 1842, zoologist Richard Owen grouped them together under the new term “dinosaurs.”

In modern taxonomy, dinosaurs are defined as all animals that are descendants of the last common ancestor of Triceratops, the house sparrow, and Diplodocus carnegiei. This means that birds are technically dinosaurs as well. To avoid confusion, however, in this article, “dinosaurs” will specifically refer to non-avian dinosaurs.

Today, over a thousand species of dinosaurs are known, though this is just a fraction of the total number that once existed. Modern paleontology allows us to reconstruct with high accuracy the appearance, movement, and dietary habits of these creatures. Some fossils even allow us to determine body temperature, coloration, or vocalization. However, dinosaurs earned their popularity not through the color of their feathers but through their record-breaking feats. In this article, we will explore some of these remarkable achievements and intriguing facts.

Before discussing the earliest dinosaurs, it’s worth mentioning their ancestors. Dinosaurs belong to a group of diapsid reptiles known as archosaurs. Archosaurs themselves are divided into two evolutionary branches. The first, Crurotarsi, led to the emergence of crocodiles. The second branch, Ornithodira, split into pterosaurs and dinosaurs.

The early ancestors of dinosaurs lived in what would become southern and eastern Africa, a part of Gondwana. These were small, graceful creatures with lightweight bodies and long limbs. The earliest known dinosauriform is Asilisaurus kongwe, whose remains were found in Tanzania. Asilisaurus lived 245 million years ago, reaching up to 3 meters in length and moving quickly on all fours. It fed on plants, insects, and small vertebrates.

The evolution of dinosaur ancestors progressed rapidly, spurred by high competition from other archosaurs and cynodonts, the ancestors of mammals. By the middle Triassic period, around 242-237 million years ago, a new type of reptile appeared: small, fast-moving omnivores that walked on their hind legs and used their shorter forelimbs for foraging. These early dinosaurs had four-chambered hearts, high metabolic rates, and some even had bristle-like structures on their skin, which would later evolve into feathers.

Dinosaurs are divided into three major groups: Ornithischia, Sauropodomorpha, and Theropoda. Early representatives of all three groups are known from at least the Carnian age (237-227 million years ago). Their classification is complex due to the significant similarities between them and the presence of shared traits with other dinosauriforms. An example is Eoraptor lunensis, a small dinosaur from Argentina, about 1 meter in length, with agile forelimbs. Eoraptor was omnivorous and lived in dense forest undergrowth. The features of its skeleton make it resemble both theropods and sauropods, complicating its precise classification.

Dinosaurs thrived for about 175 million years—a span 2.6 times longer than the entire Cenozoic era. Such longevity would not have been possible without adaptations that increased their biological efficiency, one of which was a high metabolism.

Traditionally, dinosaurs were depicted as cold-blooded, sluggish reptiles. However, John Ostrom’s studies of Deinonychus in the 1960s revolutionized our understanding of dinosaur physiology and behavior. Today, it is believed that dinosaurs were warm-blooded to varying degrees, though metabolic rates differed greatly among families. Differences also existed in how they maintained their body temperatures. The large size of sauropods allowed them to retain heat effectively. Small and medium-sized theropods likely used feathers to regulate their body temperature. Bony plates and frills, such as those in stegosaurs, ceratopsians, and ankylosaurs, may have also played a role in thermoregulation.

Is it possible to measure a dinosaur’s body temperature? Yes, modern techniques allow for this. A comprehensive analysis of the isotopic composition of tooth enamel, eggshells, and growth rates determined from fossil bone cross-sections can provide such insights.

For example, the body temperature of oviraptors has been estimated at 31-32°C, lower than that of birds but still 5-6°C higher than the ambient temperature. An increase in size naturally leads to a higher body temperature. The body temperature of Camarasaurus is estimated at 36-38°C, while Brachiosaurus may have had a temperature of 38-39°C. It seems that sauropods were giant “furnaces” radiating heat, and one of their challenges was not retaining heat but rather shedding the excess. The air sacs along their long necks may have acted as radiators to help dissipate this heat.

The ability to maintain a high body temperature allowed dinosaurs to inhabit even polar regions. Fossils have been found in Chukotka and Alaska, as well as in southern Australia and even Antarctica.

Of course, there is a temptation to attribute all of this to changes in geography and climate. It is known that the positions of the lithospheric plates were different in the past, and the climate was milder than it is today. But was this true for the entire Mesozoic era?

As Pangaea broke apart, the continents began to drift apart, and by the end of the Cretaceous period, the planet’s geography was quite recognizable. Chukotka and Alaska were located slightly further north than they are today. Australia and Antarctica formed a single landmass, not yet separated from South America. The global climate was generally warmer than it is today, with average annual temperatures in polar latitudes of 10-13°C. This is slightly lower than in Sochi, which means frost and snowfall would have been common in winter. Nevertheless, both carnivorous and herbivorous dinosaurs lived in these regions.

One of the most famous Antarctic dinosaurs is Cryolophosaurus, which lived during the early Jurassic period (199-182 million years ago). It was a large predator up to 6.5 meters long, with a distinctive crest on its skull. Its neighbors in the Antarctic forests included sauropodomorphs, pterosaurs, and rat-like synapsids. Fossils of Arctic dinosaurs from the late Cretaceous period are more diverse, including hadrosaurs, ankylosaurs, ceratopsians, and predators such as tyrannosaurids. For instance, a fragment of a young dromaeosaur’s jaw, related to Saurornitholestes, was recently discovered in Alaska. Fossils of juvenile hadrosaurs have been found in eastern Siberia and Chukotka.

High metabolism wasn’t the only factor that helped dinosaurs dominate the Mesozoic era. A significant innovation was the unique structure of their limbs. Unlike reptiles and amphibians, which have limbs positioned to the sides of their bodies, dinosaurs evolved limbs that were positioned directly beneath their bodies. This shift reduced the strain on muscles and joints and allowed dinosaurs to breathe while running. Speed and endurance became key advantages in the struggle for survival. The drive to move even faster eventually led to bipedalism, first as a temporary adaptation and later as a permanent mode of locomotion. As some dinosaurs grew larger, they reverted to quadrupedal movement. Bipedal locomotion was retained by theropods, and it is among them that we find the fastest runners.

The fastest dinosaur is believed to be Struthiomimus. This slender dinosaur, about the size of an ostrich and similar in appearance, had a lightweight skeleton, a long neck with a small head, and powerful legs. A 1988 study estimated its speed at 50-80 km/h, comparable to that of an ostrich.

Studies of dinosaur tracks yield comparable results. For example, a set of tracks found in Texas, left by two theropods weighing around 500-600 kg, indicates a speed of 43 km/h (12 m/s). This is the highest recorded speed, but it’s unlikely that these tracks were left by the fastest dinosaurs. The speed of large theropods, such as Tyrannosaurus rex, would have been lower. Modern estimates place it between 17 and 29 km/h. The slowest dinosaurs were the giant sauropods, with estimated speeds of 3-4 km/h.

To maintain high activity levels and stay in top shape, every dinosaur needed a healthy diet—and a good diet requires a well-developed mouth.

One important innovation that appeared among archosaurs was teeth set in specialized sockets, or alveoli. This anchored the teeth in the jaw and prevented them from being lost during a bite, allowing for greater bite force. Another significant adaptation was the differentiation of teeth, with different shapes serving different functions, enhancing feeding efficiency. The teeth of carnivorous dinosaurs, like those of mammals, could include several types in a single mouth. The teeth of different dinosaur species are so distinctive that they can be used to classify the animals even without a complete skeleton.

The largest teeth among dinosaurs belonged to the most famous Mesozoic predator, Tyrannosaurus rex. With roots included, they could reach up to 30 cm in length! Equally impressive was T. rex‘s bite force, estimated to be around 30 tons per square centimeter. This was powerful enough to crush the bones of even large Triceratops.

The dental systems of herbivorous dinosaurs were much more complex. Many species had well-developed beaks to help them snip tough branches. Some herbivorous dinosaurs swallowed stones, which helped grind food in their stomachs. Others could chew their food with complex jaw movements.

Hadrosaurs and ceratopsians had unique dental “batteries.” A hadrosaur battery consisted of columns of teeth, where the bottom tooth was alive and the 3-5 upper teeth were already dead. Such columns could number up to 60, and there were four such batteries in the mouth.

Triceratops had a dental battery with 36-40 teeth, and there could be 3 to 5 such batteries on each side of its long jaw. This totals up to 800 teeth!

But dinosaurs were not just about teeth, speed, and hot blood—they were also about bright colors. Or were they? Can we really make conclusions about the skin coverings, let alone the colors, of these animals based on fossils?

It’s often said that the appearance of dinosaurs is nothing more than the fantasy of artists. The internet is filled with paleo-art, and anyone can choose dinosaurs in any style and color they like. However, it’s important to distinguish between artistic renderings and scientific reconstructions. Paleoartists are always limited by specific scientific facts and general principles.

Paleontologists have access to skin impressions from various dinosaur species, revealing the diversity of their coverings. Almost all species had scales and osteoderms, which are bony plates embedded in the skin. These osteoderms could grow into spikes, dorsal plates (as in stegosaurs), or even a complete armor like that of Ankylosaurus.

Another important skin element was feathers. Well-developed feather coverings were common among many theropod species, and there is evidence of feather-like structures in ornithischians as well. Feathering was more common in small dinosaurs and less so in large ones. Nevertheless, a large theropod, Yutyrannus, up to 9 meters long and weighing about 1.4 tons, was covered in feathers. Feathers also provide crucial information—they help us reconstruct the color of dinosaurs. If melanosomes, the organelles responsible for pigment, are preserved in the fossils, we can determine the colors of the feathers.

For instance, the feathers of the small theropod Caihong were black, but on its chest and head, they shimmered with all the colors of the rainbow, like those of a hummingbird or a trumpeter bird.

Sinosauropteryx was the first dinosaur confirmed to have a feathered covering. In 2010, its coloration was reconstructed. The body of Sinosauropteryx was reddish-brown with a white belly and a “bandit mask” around its eyes, like that of a raccoon. Its tail had alternating white stripes.

We’ve discussed metabolism, speed, feeding habits, and even the appearance of dinosaurs. Now let’s talk about their inner world.

It’s commonly believed that dinosaurs were not very intelligent, a conclusion often drawn from the relatively small size of their brains compared to their bodies. However, there are numerous examples of social behavior among dinosaurs, such as nest-building and caring for offspring. Even the bright coloration of feathers could indicate complex courtship rituals, which would require a certain level of cognitive ability. Complex behavior is also observed in crocodiles, and some birds have been shown to possess intelligence that surpasses that of many mammals.

One way to assess cognitive abilities is through the encephalization quotient (EQ), which compares the brain mass to the expected average brain mass for animals of a similar size. In humans, the EQ is 7.7, in hedgehogs it’s 0.3, and in crocodiles, it’s 0.036.

A 2013 study investigated the EQ of several dinosaur species. Among large theropods, the EQ ranged from 0.14 (in Carcharodontosaurus) and 0.25 (in Allosaurus) to 0.41 (in Tyrannosaurus) and 0.58 (in Nanotyrannus). Nigersaurus, which was 9 meters long and not the largest sauropod, had an EQ of 0.1. The study’s leaders were Troodon, with an EQ of about 0.85, and Bambiraptor, with an EQ of 0.8-1.1, which is comparable to the intellectual capabilities of a cat or horse.

As for the brain-to-body mass ratio, one of the records for small brains belonged to Stegosaurus. For its two to three-ton body, it had a brain weighing just 70 grams.

Dinosaurs might not have been known for their brain size, but when it comes to body size, they were unmatched. Dinosaurs were the largest land animals in Earth’s history.

Of course, not all dinosaurs were enormous. The average size of a dinosaur was about that of a dog or a sheep, and the smallest dinosaur, Epidexipteryx, weighed just 164 grams. But these tiny creatures lived alongside animals of truly colossal size.

Giant sauropods roamed the plains of the Jurassic and Cretaceous periods. Their massive bodies were supported by four columnar legs; their long necks allowed them to graze over vast areas without moving, and their lengthy tails acted as both a counterbalance and a defensive weapon.

Their bones are astounding in their dimensions. But how can we accurately estimate their size? The situation is complicated by the atypical anatomy of sauropods. Their vertebrae were lightweight, with large cavities for air sacs, making them poorly preserved. The fragmentary nature of their remains makes it difficult to determine their length. The presence of air sacs and cavities in their bones complicates weight estimates.

Amphicoelias altus is one of the contenders for the title of the largest dinosaur, and indeed, the largest land animal ever. Discovered in the Morrison Formation (USA) in 1878, its remains date back to the Jurassic period. These remains included fragments of femurs and a vertebra 2.3-2.4 meters high. Modern estimates suggest Amphicoelias reached up to 32 meters in length and weighed more than 78 tons. Unfortunately, its remains were lost, and scientists must rely on drawings and descriptions. So, is there a possibility of exaggeration or even deliberate falsification of the data?

In fact, Amphicoelias is not the only giant, and the fossilized bones of other large sauropods show similar sizes. One example is Argentinosaurus huinculensis, from which pelvis, femur, and part of the vertebrae have been preserved. Argentinosaurus lived during the late Cretaceous period (96-92 million years ago) in what is now Argentina. Its length is estimated at 35 meters, and its weight at 65-75 tons. This makes Argentinosaurus the longest vertebrate, surpassing even the blue whale in length.

Dinosaurs are so fascinating that we unconsciously want to extend their existence. By the end of the Cretaceous period, 66 million years ago, there were several hundred species of these animals. While some data suggest a gradual decline in their diversity, others indicate that the late Cretaceous was a time of flourishing, particularly for hadrosaurs and ceratopsians. One thing is certain: dinosaurs did not plan to go extinct during the Maastrichtian age (72-66 million years ago) and abruptly disappeared from the geological record at the Cretaceous-Paleogene boundary. But what if some dinosaurs survived longer than their peers?

The causes of the catastrophic extinction are a topic for another discussion. What’s important for us is that the absence of dinosaur fossils does not necessarily indicate their extinction but rather a decline in population numbers. Extinction could have continued into the Paleogene for tens of thousands of years, with small dinosaur populations possibly surviving. However, the chances of finding their fossils are virtually nil. Yet, such discoveries have been made.

The most significant find is a femur of a hadrosaur from the Ojo Alamo Formation in New Mexico. The bone was found in sandstone layers dating to about 64.5 million years ago. Direct dating of the bone gives an age of 64.8 million years, corresponding to the Danian age of the Paleocene. There are doubts due to the river deposits and the lack of other skeletal fragments, suggesting the bone could have been re-deposited from earlier geological layers. However, if the dating is accurate, a population of hadrosaurs may have outlived their relatives by 1.5 million years.

Similar fossils have been found in India and China, as well as on the Chatham Islands in the southwest Pacific Ocean. The rarity of these finds and their concentration in the early Paleocene suggest a prolonged extinction process for dinosaurs. The discovery of Paleocene dinosaurs would be sensational, but for now, this remains a hypothesis.