Chimaera

Chimaeras are special kinds of fish called cartilaginous fish. This means they have cartilage instead of bones, like sharks and rays. They belong to a group known as Chimaeriformes. People often call them "ghost sharks," rat fish, spookfish, or rabbit fish. These names can also refer to other fish groups, so it’s important to know which one people are talking about.

In the past, chimaeras were very common and diverse, as we can see from fossils. Today, most living chimaera species live deep in the ocean, far from shore. They are closely related to sharks and rays, but their last common ancestor with these fish lived almost 400 million years ago.

Chimaeras look quite different from sharks and rays. Some have long, whip-like tails, while others have unique features like large heads or unusual body shapes. They are fascinating creatures that help scientists learn more about how different kinds of fish have evolved over time.

You can find out more about chimaeras by looking at the cartilaginous fish or reading about the [Chimaera (genus)](/wiki/Chimaera_(genus), the [Chimera (mythology)](/wiki/Chimera_(mythology), and other related topics like rattails, Opisthoproctidae, and Siganidae. There’s also a fun film called Ghost Shark if you’re interested in stories that use this name.

Anatomy

Chimaeras are soft-bodied, shark-like fish with big heads and long, thin tails. They can grow up to 150 cm (about 4.9 feet) long. Unlike sharks, their skeletons are made entirely of cartilage, a flexible material.

These fish have special features that help them move through the water. Their large chest fins can help them glide, making them look like they are flying. They also have smaller belly fins and, in some types, a fin near the tail. Some chimaeras even have a sharp, stinging spine on their back for protection.

Chimaeras have a unique way of sensing their surroundings. Their snouts can detect electric signals from prey. They also have strong, permanent tooth-plates that work like a beak, perfect for crushing food.

Behavior

Chimaeras, also called ghost sharks or ratfish, live on the ocean floor, often in deep water. Some species, like the rabbit fish and the spotted ratfish, can sometimes be found in shallower water and are seen in public aquaria. They live in all oceans except the Arctic and Antarctic.

Chimaeras eat small sea creatures like crabs, brittle stars, and molluscs. They usually live close to the bottom of the ocean.

When it’s time to have babies, chimaeras lay eggs in tough, spindle-shaped cases.

Conservation and threats

Some chimaera species are at risk because they can be caught when people are fishing for other fish, or sometimes on purpose for their meat. Even though no chimaera species are in danger of disappearing completely, several might be at risk because we do not know enough about them. Many of these fish live in special areas, and we still have a lot to learn about how they move.

Some chimaeras are caught for food, and there are now rules to help control how many can be caught. But some groups of them have gone down a lot. Other kinds are often caught by accident, which can also make their numbers go down. Chimaeras are usually not affected by the trade that takes fins from sharks.

Losing their homes is also a worry. Building along coastlines and things like deep-sea mining and trawling can hurt the places where chimaeras live. Species that live close to shore might also be affected by climate change, because stronger storms and warmer water can damage their eggs.

Classification

Main article: List of chimaeras

Chimaeras are special kinds of fish. They are part of a group called cartilaginous fishes, which also includes sharks and rays. They share some traits with regular bony fishes, too.

Scientists have found many new kinds of chimaeras by studying deep water and old museum samples. There are now more than 50 different living types of chimaeras, split into three families. These families are Callorhinchidae, Rhinochimaeridae, and Chimaeridae. Callorhinchidae is the most basic group.

Evolution

Studying how chimaeras evolved has been hard because there are not many good fossils. Scientists now use DNA sequencing to learn more about these fish.

Chimaeras and their close relatives split from Elasmobranchii, which includes sharks and rays, during the Devonian period, over 380 million years ago. The oldest known chimaera-like fish, Protochimaera, lived in the Early Carboniferous period in Russia. Modern chimaeras appeared in the Early Jurassic in Europe. Older chimaeras often lived in shallower waters, unlike today’s deep-water ones. Many modern groups evolved during the Mesozoic Marine Revolution. They were most diverse in the mid-Cretaceous period, developing many types of teeth.

Scientists used to think chimaeras moved to deep water to survive big events, but newer research suggests they mostly lived in shallow water and only moved deeper after a big event at the end of the Cretaceous period. The plough-nosed chimaeras are the only group that still live in shallower waters like their ancestors.

Taxonomy

Extinct groups of chimaeras include:

• †Suborder Echinochimaeroidei Lund, 1977
  • †Family Echinochimaeridae Lund, 1977
    • †Genus Echinochimaera Lund, 1977 United States, Lower Carboniferous (Serpukhovian)
• †Suborder Squalorajoidei Patterson, 1965 (Lower Carboniferous–Early Jurassic)
  • ?†Genus Sulcacanthus Itano & Duffin, 2023 United States, Lower Carboniferous (Viséan)
  • Family †Squalorajidae Woodward, 1886
    • †Genus Squaloraja Riley, 1833 Europe, Early Jurassic (Hettangian–Sinemurian)
• †Suborder Myriacanthoidei Patterson 1965 (Late Triassic–Late Jurassic; possible Carboniferous records)
  • †Family Chimaeropsidae
    • †Chimaeropsis Zittel 1887 Belgium, Early Jurassic (Sinemurian), Germany, Late Jurassic
  • †Family Myriacanthidae Woodward 1889
    • †Acanthorhina Fraas 1910 Posidonia Shale Formation, Germany, Early Jurassic (Toarcian)
    • †Agkistracanthus Duffin and Furrer 1981 Austria, England and Switzerland, Late Triassic–Early Jurassic (Rhaetian–Sinemurian)
    • †Alethodontus Duffin 1983 Germany, Early Jurassic (Sinemurian)
    • †Halonodon Duffin 1984 Belgium and Luxembourg, Early Jurassic (Sinemurian)
    • †Metopacanthus Zittel 1887 Posidonia Shale Formation, Germany, Early Jurassic (Toarcian)
    • †Oblidens Duffin and Milàn 2017 Hasle Formation, Denmark, Early Jurassic (Pliensbachian)
    • †Myriacanthus Agassiz 1837 United Kingdom, Late Triassic-Early Jurassic (Rhaetian–Sinemurian)
    • †Recurvacanthus Duffin 1981 United Kingdom, Early Jurassic (Sinemurian)
• †Suborder Protochimaeroidei Lebedev & Popov in Lebedev et al., 2021
  • †Family Protochimaeridae Lebedev & Popov in Lebedev et al., 2021
    • †Genus Protochimaera Lebedev & Popov in Lebedev et al., 2021 Moscow Region, Russia, Lower Carboniferous (Viséan–Serpukhovian)
• Suborder Chimaeroidei Patterson 1965
  • †Eomanodon Ward and Duffin 1989 United Kingdom, Early Jurassic (Pliensbachian)
  • Family Callorhinchidae Garman, 1901
    • †Brachymylus A. S. Woodward 1894 Germany, Early Jurassic (Pliensbachian)
    • †Bathytheristes Duffin 1995 Posidonia Shale Formation, Germany, Early Jurassic (Toarcian)
    • †Ottangodus Popov, Delsate & Felten, 2019 France, Middle Jurassic (Bajocian)
    • †Moskovirhynchus Russia, Upper Jurassic
    • †Pachymylus United Kingdom, France, Middle Jurassic
  • Family †"Edaphodontidae"
    • †Ischyodus (40 species) Worldwide, Middle Jurassic–Miocene (also placed in Callorhinchidae)
    • †Elasmodectes Europe, Jurassic–Cretaceous
    • †Elasmodus Worldwide, Cretaceous–Paleogene
    • †Edaphodon Worldwide, Cretaceous–Neogene
    • †Ptyktoptychion Australia, Early Cretaceous
    • †Lebediodon Europe, Cretaceous
  • Family Chimaeridae Bonaparte, 1831
    • †Canadodus Popov, Johns & Suntok, 2020 Sooke Formation, Canada, Oligocene
  • Family Rhinochimaeridae Garman, 1901
    • †Amylodon Europe, Late Cretaceous–Oligocene