Scelidosaurus: Unveiling the Early Jurassic Herbivore

Scelidosaurus may not be as familiar as the mighty Tyrannosaurus or the elegant Brachiosaurus, yet it holds a unique place in the annals of paleontology. Discovered in the mid-19th century, this herbivorous dinosaur from the Early Jurassic Period offers a fascinating glimpse into a world long gone. Its discovery in the cliffs of Lyme Regis, a place already steeped in paleontological lore, adds to the intrigue surrounding this ancient creature.

Scelidosaurus Key Facts

Scelidosaurus Origins, Taxonomy and Timeline

Scelidosaurus, whose name translates from Greek as ‘Limb Lizard’, offers a fascinating insight into dinosaur nomenclature. The name is a combination of ‘skelis’ (rib of beef) and ‘sauros’ (reptile/lizard) in order to reflect its distinctive physical characteristics.

Belonging near the ancestors of the Ankylosauria group, Scelidosaurus is a prime example of early armored dinosaurs. It belongs to the family Scelidosauridae and is a primitive relative of the later armored dinosaurs. While the type species stands alone in its genus, its distinct traits make it a subject of great interest in paleontological studies.

The timeline of Scelidosaurus spans the Early Jurassic Period, specifically from the base of the Hettangian to the top of the Early/Lower Pliensbachian Epochs. This places it in a time frame of approximately 201.3 to 183.0 million years ago, a period rich in evolutionary developments as dinosaurs just began to conquer the Earth.

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Discovery & Fossil Evidence of Scelidosaurus

The story of Scelidosaurus begins in the 1850s with quarry owner James Harrison of Charmouth, West Dorset, England. Harrison discovered fossils in the cliffs of Black Ven, between Charmouth and Lyme Regis, an area known for its rich Jurassic deposits. These fossils, initially quarried possibly for cement manufacturing, included fragmentary limb bones, which Harrison, along with collector Henry Norris, sent to Professor Richard Owen of the British Museum (Natural History) in London.

Among these fossils was a left thighbone, specimen GSM 109560, which played a pivotal role in the identification of Scelidosaurus. In 1859, Owen named the genus Scelidosaurus in an entry about paleontology in the Encyclopædia Britannica. Despite a vague definition and no specific specimens identified, the genus was validly named. Owen’s inspiration for the name, a mix-up between the Greek words for ‘hindlimb’ and ‘rib of beef’, reflected the strong development of the hind leg in this dinosaur. In 1861, Owen named the type species Scelidosaurus harrisonii, in honor of Harrison. 

A case of mistaken identity

The story of Scelidosaurus’s identification took a twist when Richard Lydekker, in 1888, designated some hindlimb fragments as the type specimen, or lectotype. However, these fragments were later discovered to be part of a Theropod dinosaur, not Scelidosaurus. This mix-up wasn’t rectified until 1968 by Bernard Newman. In 1994, the International Commission on Zoological Nomenclature officially designated a new lectotype for Scelidosaurus. This decision corrected the earlier misidentification and established a more accurate reference for the dinosaur.

The new lectotype, a rather complete skeleton with skull and lower jaws, was found in marine deposits dating back about 191 million years. While the skeleton was largely intact, certain parts like the snout tip, neck base, forelimbs, and tail end were missing. Hundreds of osteoderms were discovered in connection with the skeleton, many in their original position.

From the 1960s, Ronald Croucher further prepared this fossil using acid baths using a technique refined for Charmouth fossils. However, this method, along with some mishandling, led to the deterioration and breakage of the bones. Despite these challenges, recent work by Norman and others has shed new light on Scelidosaurus, offering a more complete understanding of this early Jurassic herbivore.

Scelidosaurus Size and Description

This early dinosaur was a creature of modest size, especially when compared to the colossal dinosaurs that roamed the Earth in later periods. Yet, in the context of the Early Jurassic Era, it stood as a medium-sized species, significant in its own right. With its hindlimbs longer than its forelimbs, this quadrupedal dinosaur presents an intriguing study in early dinosaur posture and movement. Its body was covered in a protective layer of armor, indicative of the survival challenges of its time.

Size and Weight of Type Species

In terms of size, Scelidosaurus was relatively modest. Estimates suggest a length of approximately 13.0 feet, with some sources like Gregory S. Paul in 2010 proposing a slightly smaller size of 12.5 feet. In terms of weight, it is believed to have weighed around 600 pounds. This size positions Scelidosaurus as a notable presence in the Early Jurassic landscape, neither dominating in size like the giants of later eras nor diminutive.

The posture of Scelidosaurus is particularly fascinating. While primarily quadrupedal, there is evidence to suggest that it could have reared up on its hind legs to browse foliage, a behavior that would have added to its height. Intriguingly, a trackway discovered in the Holy Cross Mountains of Poland reveals a Scelidosaur-like animal walking bipedally, suggesting that Scelidosaurus may have been more adept at bipedalism than previously thought. This ability to switch between quadrupedal and bipedal movement reflects a significant evolutionary adaptation and offers insights into the diverse and dynamic world of Early Jurassic dinosaurs.

The Dinosaur in Detail

This dinosaur’s anatomy, from the unique structure of its skull to the intricate arrangement of its armor, offers a glimpse into the evolutionary adaptations of early dinosaurs. Interestingly, Owen’s initial interpretation of Scelidosaurus’s lifestyle in 1861 vastly differs from current views, as he suggested it was a fish-eater and partially sea-dwelling.

The skull was small and elongated, measuring about twenty centimeters in length. It was triangular in shape from above, mirroring the characteristics of earlier Ornithischians. The snout was flat on top and dominated by nasal bones. The skull was marked by five pairs of fenestrae, or openings in the bone. These openings were not closed or overgrown as seen in many later armored dinosaurs. The large upper temporal fenestrae, in particular, were crucial for muscle attachment and suggest a powerful bite. The eye socket featured a brow ridge, initially thought to be the prefrontal bone but later identified as a fused palpebral bone, with the upper rim formed by the supraorbital bone.

The most striking aspect of this herbivore was its armor. The body was covered with bony scutes, or osteoderms, embedded in the skin and arranged in horizontal rows. These osteoderms varied in size and shape and some of the latest Scelidosaurus specimens show variations in osteoderms. These features indicate a possible diversity within the species or an evolutionary adaptation. The larger scutes were aligned in regular rows along the body with three rows on each side of the torso. Between the bony scutes, fossilized skin impressions have revealed that Scelidosaurus had rounded, non-overlapping scales akin to those of the modern Gila monster. 

Interesting Points about Scelidosaurus

Scelidosaurus in its Natural Habitat

Unlike some of its later Ornithischian cousins, Scelidosaurus didn’t boast complex, grinding teeth. Instead, it was equipped with smaller, leaf-shaped teeth that were adept at cropping vegetation. This dinosaur’s jaws were designed for a simple yet effective vertical movement, a trait that set it apart in its approach to feeding. Its method for feeding, reminiscent of the Stegosaurids’ feeding habits, was perfectly suited for a diet primarily composed of ferns and conifers.

The narrow head of Scelidosaurus hints at a preference for high-quality food. However, Paul Barrett, a notable paleontologist, suggested that for a creature of Scelidosaurus’ size with a large gut capable of efficient fermentation, the need for easily digestible, high-energy food was less critical compared to smaller animals. This insight paints a picture of Scelidosaurus as a less selective feeder, comfortably sustaining itself on low, scrubby vegetation. While it’s conceivable that Scelidosaurus could have raised itself on its hindlimbs to extend its feeding range, this behavior, as speculated by paleontologist David Norman, might not have been a significant aspect of its lifestyle. Instead, it likely thrived within a meter of the ground, making the most of the resources within its reach in a world where its dietary needs dictated its daily routines and habitat choices.

Contemporary Dinosaurs

Scelidosaurus’ life was a constant quest for ferns and low-lying plants. This was a task made challenging not just by the scarcity of these resources but also by the presence of contemporaries like Iguanodon. Iguanodon was larger and more robust and often roamed the same areas. Imagine the tension as these two herbivores encountered each other, non-aggressive yet competitive, silently vying for the same patches of foliage. Their interactions were a delicate dance of coexistence and competition where each used their unique physical attributes to access food.

But the challenges for Scelidosaurus didn’t end with finding food. Predators lurked in the shadows of this ancient world. Enter the formidable carnivorous Megalosaurus, larger and more menacing than our Scelidosaurus. This predator-prey relationship added a layer of constant vigilance to the herbivore’s life. Picture the heart-pounding chases as Megalosaurus, driven by hunger, set its sights on the relatively smaller Scelidosaurus. These encounters were not just about survival but were a testament to the agility and defensive strategies of Scelidosaurus. It relied on its armored body and quick thinking to escape these terrifying predators.

In this prehistoric drama, another player, Sinosaurus also played a significant role. Sinosaurus, though smaller and not as directly confrontational with Scelidosaurus as Megalosaurus, contributed to the ecosystem’s dynamic. The presence of Sinosaurus possibly influenced the behavior and migratory patterns of Scelidosaurus as it navigated a landscape where danger from similarly sized carnivores was ever-present. This intricate web of interactions, from competition for food to the threat of predation, paints a vivid picture of Scelidosaurus’ life–a testament to the resilience and adaptability required to survive in such a diverse and challenging ecosystem.

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Sources

The information in this article is based on various sources, drawing on scientific research, fossil evidence, and expert analysis. The aim is to provide a comprehensive and accurate overview of Scelidosaurus. As new discoveries are made, this article might be updated to reflect new facts.

Article last fact-checked: Joey Arboleda, 01-15-2024

Featured Image Credit: Jack Mayer Wood, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons