Ankylosaurids are a group of dinosaurs often called “armored dinosaurs” due to their remarkable defensive adaptations. These herbivores were characterized by their low-slung, robust bodies covered in extensive bony armor. Their broad stance and heavily shielded form provided significant protection. They inhabited Earth for millions of years, leaving behind a fossil record that continues to intrigue paleontologists.
Distinctive Features
Ankylosaurids possessed an elaborate bony armor, known as osteoderms or scutes, embedded directly within their skin. These varied in size and shape, from wide, flat plates to smaller, rounded nodules, providing a formidable protective covering across their back, neck, and hips. This armor was often supplemented by collagen fibers, which provided additional strength while keeping the overall weight manageable.
Many ankylosaurids had a large, bony tail club. This club was formed by several enlarged osteoderms fused to the last few tail vertebrae, creating a heavy, bulbous structure. The “handle” of the club consisted of stiffened vertebrae, allowing for powerful side-to-side swings. A swing from a large tail club could generate enough force to shatter bones, making it a powerful defensive weapon.
Ankylosaurids had a broad, robust body supported by four short, powerful limbs. Their hind limbs were longer than their forelimbs, contributing to their low-slung posture. The skull was wide and low, often adorned with horn-like protrusions on the top and back of the head, enhancing their armored defense. Their jaws featured a beak at the front, followed by rows of small, leaf-shaped teeth, designed for processing plant material.
Life and Times
Ankylosaurids were obligate herbivores. Their small, leaf-shaped teeth were suitable for cropping low-lying vegetation. The broad muzzle of some species suggests they were non-selective browsers, consuming ferns and other ground-level plants.
The large hyoid bones found in their skeletons suggest they had long, flexible tongues, which would have aided in gathering plant material. Their expanded gut region implies they relied on hindgut fermentation to digest fibrous plant matter. While their social behavior is still debated, their formidable defenses suggest they may have lived solitarily or in small groups.
Ankylosaurids first appeared in the Middle Jurassic period, with early specimens found in North Africa. They persisted until the end of the Late Cretaceous period, approximately 66 million years ago, making them among the last non-avian dinosaurs before the Cretaceous-Paleogene extinction event. Fossil evidence indicates a wide geographical distribution, with specimens discovered across North America, Europe, and Asia.
Major Families
Ankylosaurids are primarily categorized into two main families: Ankylosauridae and Nodosauridae, which exhibit distinct morphological differences. Ankylosauridae, exemplified by Ankylosaurus, is characterized by a prominent bony tail club. Members of this family had broader skulls with wedge-shaped osteoderms and two collars of armor plates on their neck, unlike nodosaurids.
Ankylosaurids often had complex respiratory pathways within their cranium. Their osteoderms along the torso were often filled with smaller ossicles, creating a fused shield.
Nodosauridae, on the other hand, lacked the distinctive tail club. These often had more slender body builds and sometimes longer snouts. Nodosaurids are identifiable by three collars of armor plates on their neck, in contrast to the two found in Ankylosauridae. Their armor included thick, triangular plates projecting from their sides and parallel rows of keeled oval plates on their back.