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| Chimaeras | |
|---|---|
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| Hydrolagus colliei | |
| Scientific classification | |
| Unrecognized taxon (fix): | Holocephali |
| Order: | Chimaeriformes Obruchev, 1953 |
| Families | |
Chimaeras are cartilaginous fish in the order Chimaeriformes. They are sometimes known informally as 'ghost sharks'.
They may be the "oldest and most enigmatic groups of fishes alive today". Their closest living relatives are sharks, though in evolutionary terms they branched off from sharks nearly 400 million years ago and have remained isolated ever since.
At one time they were a diverse and abundant group, as shown by the fossil record. They are now found mainly to deep water. There are fifty living species in six genera and three families. Studying the evolution of these species has been problematic because there are few good fossils. DNA sequences have become the preferred approach to understanding speciation.
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