Hadrorhachia (lit. "stout spine") is a clade of Acanthopodia, common to pelagic environments and analogous to cartilaginous fish on Earth.
Description[]
Hadrorhachia first emerged around 4060ma, when it diverged from the Orthorhachia branch.
The first Hadrorhachids used subcarangiform swimming, having a truncate caudal fin, and measured around 2 meters in length. While some species retain this form of locomotion, other species have evolved to use the other two forms of body-driven swimming. Native to pelagic environments, all observed Hadrorhachids employ some form of counter-shading.
Hadrorhachids dominated the pelagic ecosystem for over 150 million years, until the global climate shift resulted in the disruption of the oceanic ecosystem. While the Hadrorhachids survived, their top-level roles in the food chain were mostly overtaken by the Thalattotheres. However, the Hadrorhachids remain dominant in deeper waters due to their gill-based respiration.
Branches[]
- Ptilopoda: Filter feeders, comprise the largest Acanthopods ever seen
- Teleopterida: Pelagic predators
