Spicomellus
- 13 hours ago
- 2 min read
MEANING: Spike collar
PERIOD: Middle Jurassic
CONTINENT: Africa
Spicomellus is the earliest known ankylosaurian dinosaur, and has forced paleontologists to rethink many aspects of the group, including distribution, lifestyle, and evolutionary trends. Striking features include the meter long spikes fused directly to the skeleton, and evidence of a tail weapon existing before the ankylosaurid/nodosaurid split.
Spicomellus is from the Middle Jurassic. The Middle Jurassic, spanning from approximately 174 to 163 million years ago, was a period of increasing tectonic activity and evolutionary innovation. By this time, the supercontinent Pangaea had begun to split more significantly, with Laurasia in the north and Gondwana in the south drifting apart. This movement created new coastlines, shallow seas, and rift valleys that fostered diverse ecosystems. The climate remained generally warm and humid, promoting the spread of lush vegetation, including ferns, cycads, and conifers, which blanketed much of the land and supported a wide variety of herbivorous dinosaurs.
Though less well known than the Late Jurassic, the Middle Jurassic was an important evolutionary chapter. Several major dinosaur groups began to diversify, including the stegosaurs and more derived long-necked sauropods that would later dominate the landscape. Theropods also continued to evolve, giving rise to new lineages like the megalosaurids and the early ancestors of more derived carnivores. Fossil evidence from this interval is relatively scarce compared to later stages, but what we do have paints a picture of an increasingly complex world, setting the stage for the iconic ecosystems of the Late Jurassic.
Spicomellus is an ankylosaur. Ankylosauria is a group of herbivorous, armored ornithischian dinosaurs known for their heavily built bodies and protective coverings. The group is traditionally divided into two main families: the tail-club-wielding Ankylosauridae and the spike-covered Nodosauridae. These derived forms are well known from the Cretaceous, and represent the height of ankylosaur evolution in terms of defensive adaptations and body size. However, the evolutionary story of ankylosaurs begins earlier, with more basal forms that lack many of the extreme traits seen in their later relatives.
Basal ankylosaurians were generally smaller and less heavily armored than their descendants. While they still possessed osteoderms embedded in their skin, these were arranged in simpler patterns and offered more modest protection. These early members often retained more gracile builds and longer limbs, suggesting they may have been slightly more agile and less tank-like. Many lacked the wide skulls, fused body armor, and tail clubs seen in ankylosaurids, and some retained relatively primitive features like simple teeth and unspecialized hips. Fossils of these basal forms are known from both the Jurassic and Early Cretaceous, and they provide crucial insight into how ankylosaurs gradually developed their hallmark traits over time.
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