The Mesozoic Era is renowned for the evolution of dinosaurs. Among these were the iconic giants typically portrayed in mainstream media, such as T. rex and Triceratops, but also a host of species with strange adaptations. This article focuses on some of the strangest dinosaurs, exploring the evolutionary features that set them apart from other dinosaurs.

1. Spinosaurus: “Spined Lizard”

Spinosaurus, distinguished by its iconic sail-backed silhouette, is known to be the largest land carnivore ever discovered, surpassing even the Tyrannosaurus rex. It was three times longer than an African elephant. Native to Late Cretaceous North Africa, Spinosaurus exhibited unique adaptations for a semiaquatic lifestyle (allegedly). It featured a long, narrow skull and conical teeth ideal for catching slippery prey. Its nostrils were placed high on its snout to facilitate breathing while catching fish.

It featured a distinctive sail, potentially used for display or thermoregulation, and was supported by enormous neural spines. It had a paddle-like tail, akin to modern crocodiles, whose function has been subject to speculation. Initial theories proposed that the tail might have been used for underwater propulsion. However, recent research suggests that Spinosaurus was not semi-aquatic and the tail was merely for display, similar to modern basiliscus. Spinosaurus likely hunted both in water and on land, using its imposing strength to consume a variety of prey.

2. Oryctodromeus: “Digging Runner”

Oryctodromeus was a small, agile dinosaur from the Late Cretaceous period, approximately 95 million years ago. Unearthed in Montana, this unique herbivorous dinosaur displayed an extraordinary adaptation for burrowing, a rare behavior among dinosaurs. It stood about 2.1 meters long and weighed around 45 kilograms, sporting a physique optimized for speed and digging. The dinosaur’s skull structure and large eyes were ideal for a burrowing lifestyle, likely aiding in foraging within dim environments. Oryctodromeus’ discovery alongside juveniles in a burrow suggests it engaged in parental care, indicating a complex social structure potentially involving family groups.

3. Pachycephalosaurus: “Thick-Headed Lizard”

Pachycephalosaurus was an ornithischian from the Late Cretaceous period, approximately 100-66 million years ago. Recognizable by its unique dome-shaped skull, which could be up to 10 inches thick, it roamed modern-day Montana and Wyoming. This bipedal herbivore stood about 5 meters long and weighed around 400 kilograms. Its skull, adorned with bony knobs and spikes, has sparked debate among scientists regarding its use. Some suggest it was employed in head-butting contests for dominance, while others believe it was more for display. Despite Pachycephalosaurus’ herbivorous diet, the shape of its front teeth suggests it may have consumed meat from time to time.

4. Pachyrhinosaurus: “Thick-Nosed Lizard”

Pachyrhinosaurus was a centrosaurine dinosaur distinguished by its unique cranial features. This genus lacked traditional horns but possessed a large, flattened bony mass on its nose and smaller bosses above its eyes. Roaming North America during the Late Cretaceous, this ceratopsid measured about 8 meters long and weighed around 2 to 4 tons. The structure of its skull, with a frilled neck shield and upward-extending horns from its frill, suggests it might have used its head for combat or display, similar to the modern-day rhinoceros. Primarily a herbivore, Pachyrhinosaurus migrated through the forested areas and river floodplains of regions like Alberta, Canada, and Alaska, feeding on tough, fibrous plants. Social behaviors inferred from fossil evidence indicate that Pachyrhinosaurus likely lived in herds, which provided protection against predators and enabled complex social interactions.

5. Deinocheirus: “Terrible Hand”

Deinocheirus is among the most distinctive dinosaurs discovered, notable for its massive size and unusual appearance. Known as the “terrible hand” due to its large, clawed forelimbs, Deinocheirus was an ornithomimosaur that roamed Mongolia during the Late Cretaceous period, around 70 million years ago. This dinosaur grew approximately 11 meters in length and exhibited a mix of features that have puzzled paleontologists. With a humped back similar to a camel’s and a duck-like beak, Deinocheirus was built for a specialized lifestyle. Initially thought to be a carnivore, further findings suggested it was omnivorous, feeding on plants and possibly fish.

6. Concavenator: “Cuenca Hunter”

Concavenator was a small carcharodontosaurid from Early Cretaceous Spain. Notable for its unusual back, which featured a prominent, sail-like hump supported by elongated vertebrae, Concavenator stretched around 6 meters long and moved bipedally. This unique structure might have served purposes ranging from thermoregulation to species recognition. Intriguingly, the presence of quill knobs on its forearms suggests the possibility of feathers or similar structures, challenging our understanding of feather evolution in non-avian dinosaurs. Its diet likely included smaller dinosaurs and possibly aquatic creatures, leveraging its strong jaws and sharp teeth.

7. Nothronychus: “Slothful Claw”

Nothronychus was a medium-sized therizinosaur from Late Cretaceous North America. This animal stood out due to its “sloth-like” claws and a body structure far removed from the typical carnivorous theropods from which it descended. With a long neck, robust body, and a pot-bellied abdomen, this dinosaur was primarily herbivorous, employing its 12-inch long curved claws to forage vegetation​​. Uniquely adapted to a slow-paced, browsing lifestyle, Nothronychus‘ physical form included stocky hindlimbs with four-toed feet. This anatomical feature suggests a significant shift in weight distribution necessary for its new diet. Nothronychus‘ tail was shorter and more flexible than its theropod relatives, reflecting adaptations that likely aided in balance rather than speed.

8. Nigersaurus: “Niger Lizard”

Nigersaurus, known as the “Mesozoic cow”, was a peculiar sauropod from the Middle Cretaceous Niger. With a broad snout and over 500 active and replacement teeth, this dinosaur is famed for its grazing specialization, feeding close to the ground akin to modern cattle. Its body structure supported a head-down, ground-level feeding posture.

Its skull was unusually delicate and lightweight, with large fenestrae and a mouth packed with tightly arranged teeth. This configuration facilitated a diet primarily of ferns and other low vegetation. However, Nigersaurus was relatively small for a sauropod, only 9 meters long and weighing around 4 tons.

9. Mamenchisaurus: “Mamenchi Lizard”

Mamenchisaurus stood out among Late Jurassic sauropods primarily for its extraordinary neck, which was nearly half its total body length. It inhabited what is now China’s Sichuan Province approximately 159 to 150 million years ago. Approximately 20 meters long and weighing up to 27 tons, Mamenchisaurus is one of the largest dinosaurs ever discovered. This giant sauropod’s elongated and pneumatic cervical vertebrae featured air sacs that lightened its skeletal structure. Adapted to a herbivorous diet, Mamenchisaurus used its peg-like teeth to strip leaves from high-reaching plants, exploiting food sources beyond the reach of other herbivores.

10. Kosmoceratops: “Ornamented Horned Face”

Kosmoceratops, discovered in Utah’s Kaiparowits Formation, is known for its peculiar skull ornamentation. This animal features an array of horns over its large frill, traits that make it one of the strangest dinosaurs. This animal was roughly 4.5 meters long and weighed about 1.2 tons. Its habitat in southern Laramidia was a lush, swampy environment, supporting a rich variety of plant life that constituted its diet. Kosmoceratops likely used its intricate arrangement of frill horns for social interactions, such as competing for mates or deterring rivals, rather than purely for defense against predators.

11. Amargasaurus: “Amarga Lizard”

Amargasaurus is a distinctive Early Cretaceous sauropod that roamed Argentina 130 million years ago. Known for its striking cervical sails that could reach 60 centimeters long, Amargasaurus was relatively small for a sauropod. It only grew up to 13 meters long and weighed up to 4 tons. The animal’s double row of cervical sails might have been used for thermoregulation, display, or communication within its species.

This sauropod featured sturdy, slightly shorter forelimbs compared to its hind limbs, contributing to a sloping posture. Amargasaurus had a horselike snout equipped with pencil-like teeth suited for grazing on low vegetation, indicating a specialized feeding strategy.

12. Carnotaurus: “Meat Eating Bull”

Carnotaurus, the “meat-eating bull”, was a distinctive Late Cretaceous horned theropod that thrived 72 million years ago in modern-day Argentina. Recognizable by its bull-like horns positioned above its eyes and an unusually short snout, Carnotaurus was around 8 meters long and weighed approximately 1.5 to 2.1 tons. Its streamlined body, powerful hind legs, and robust muscular neck suggest it was capable of bursts of incredible speed. Despite its fearsome appearance, the functionality of its vestigial arms remains a puzzle, as they seem too diminutive to have been of much use. The extensive skin impressions found with the fossils indicate a scaly hide, possibly without feathers.

13. Pegomastax: “Strong Jaw”

Pegomastax is a small Early Jurassic heterodontid that inhabited what is now South Africa around 200 to 190 million years ago. Unlike most dinosaurs, the genus was rather small, measuring 60 centimeters in length and weighing less than a housecat. Despite its plant-based diet, Pegomastax sported a parrot-like beak with unusual fangs, a rare combination in herbivores that may have been used for defense or social interactions. Its jaw was robust, with a distinct set of tall teeth adapted for slicing through vegetation, and its body may have been covered with bristle-like structures. This combination of features suggests that Pegomastax was a specialist, possibly using its sharp teeth for nipping and its quills for protection, navigating the dense, river-close forests of its time.

14. Incisivosaurus: “Incisor Lizard”

Incisivosaurus is the most basal oviraptorosaur ever discovered, dating from Early Cretaceous China. This genus exhibited some of the most unusual dentition seen in dinosaurs, and the best preserved oviraptorosaur teeth yet found. This dinosaur, measuring about one meter in length, was characterized by an agile build and long hind limbs. Its most notable feature was its rodent-like incisors in the front of its mouth. Coupled with its sharp cheek teeth, Incisivosaurus could have processed a more diverse diet, from plants to small vertebrates. This combination of features indicates that Incisivosaurus might have been omnivorous.

15. Isisaurus: “Indian Statistical Institute Lizard” (I kid you not)

Isisaurus, originally known as Titanosaurus colberti, is a distinctive sauropod that lived about 100 to 65 million years ago, in Late Cretaceous India. This dinosaur is notable for its unusually short neck and longer forelimbs compared to other titanosaurs, suggesting a different feeding or locomotive strategy. Measuring up to 18 meters in length and weighing around 14 tons, Isisaurus was a large dinosaur, despite its relatively moderate size for a sauropod. It featured a robust and somewhat compact skeletal structure with especially strong limb bones. Isisaurus‘ humerus alone could grow up to 148 centimeters. Although the skull of Isisaurus has never been found, the postcranial remains are more complete than most titanosaurs.

16. Mononykus: “One Claw”

Mononykus, a small theropod from the Late Cretaceous period, was unique for its singular large claw on each forearm, leading to its name meaning “One Claw”. Found in the Nemegt Formation of Mongolia, Mononykus was about 1 to 1.5 meters long, characterized by a light build and bird-like features that indicate a highly specialized lifestyle. Its long, sharp claws were likely adapted for digging or burrowing. This implies an insectivorous diet where it might have hunted for insects or dug into termite mounds. Some scientists also speculate that Mononykus could have been omnivorous, consuming both plant material and small prey, which would make it a versatile feeder in its arid habitat.