Why did armoured jawless vertebrates probably disappear after the Devonian Period?

Armoured jawless vertebrates, often referred to as ostracoderms, likely disappeared after the Devonian Period because they were replaced by more efficient and aggressive jawed vertebrates.

During the Devonian, these primitive agnathans faced increasing competition from emerging groups, including placoderms, acanthodians, sharks, and early bony fishes. These newer groups possessed evolutionary advantages, such as jaws and more effective feeding mechanisms, which allowed them to outcompete the armoured jawless forms.12

Additionally, the Devonian Period was marked by a series of mass extinction events that eliminated 70 to 80 percent of all animal species. These extinctions were driven by significant environmental stresses, including rapid global warming or cooling, anoxic conditions in the oceans, and fluctuating sea levels. While these environmental pressures contributed to widespread faunal turnover, the primary cause for the disappearance of the armoured jawless vertebrates is attributed to their replacement by more advanced, competitive fish groups.3451