Choristodera
Extinct semiaquatic reptiles with diverse body forms.
Choristodera is an extinct order of semiaquatic diapsid reptiles that ranged from the Middle Jurassic, or possibly the Triassic, to the Miocene, existing for approximately 168 to 20 million years ago, with a possible extension to 11.6 million years ago. The group is morphologically diverse, with the most famous members being the crocodile-like neochoristoderes, such as *Champsosaurus*, which resembled modern gharials with long, thin snouts and conical teeth. Other choristoderans exhibited lizard-like or long-necked morphologies, the latter including genera like *Shokawa*, *Khurendukhosaurus*, and *Hyphalosaurus*, which possessed plesiosaur-like necks. The lizard-like body form is considered the ancestral morphology, making the grouping of non-neochoristoderes paraphyletic. Choristoderes appear to have been confined to the Northern Hemisphere, with fossils recovered from North America, Asia, and Europe, and possibly also North Africa. They are generally thought to be derived neodiapsids closely related to or part of Sauria. The order was established in 1876 by Edward Drinker Cope as a suborder of Rhynchocephalia, initially containing only *Champsosaurus* from the Late Cretaceous of Montana. A second genus, *Simoedosaurus*, was described in 1877 from the Upper Paleocene of France. For over a century, these remained the only recognized choristoderes until new taxa were described from the Lower Cretaceous of Mongolia in the late 1970s and from the Middle Jurassic of Britain in the late 1980s and early 1990s, the latter revealing a small, lizard-like form distinct from the previously known crocodile-like species. Choristoderes share nine synapomorphies, including a unique skull bone called the neomorph, which is not found in other reptiles. Their skulls ancestrally had elongated upper and lower temporal fenestrae, though in many non-neochoristoderes the lower fenestrae closed secondarily. The braincase of *Champsosaurus* suggests good olfactory capabilities but only average vision, and its inner ear indicates sensitivity to low-frequency sounds. Most choristoderes had simple, homodont teeth with striated enamel, while neochoristoderes had more complex, hooked teeth with enamel infolding.
- Order
- Choristodera
- Known from
- North America, Asia, Europe, possibly North Africa
- Largest known species
- Kosmodraco dakotensis, estimated length ~5 m
- Smallest known genera
- Cteniogenys and Lazarussuchus, length ~30 cm
Lore & Background
A year later, Paul Gervais described Simoedosaurus from Upper Paleocene deposits in France. For over a century, these remained the only recognized choristoderes. In the late 20th century, new taxa were described from Lower Cretaceous sediments in Mongolia by Soviet-Mongolian teams, and Susan E. Evans described new material of Cteniogenys from the Middle Jurassic of Britain, revealing it to be a small, lizard-like choristodere.
Reader's Guide
Choristoderes are significant for their long temporal range and morphological diversity, offering insights into the evolution of semiaquatic reptiles in the Northern Hemisphere. They are generally thought to be derived neodiapsids close to or within Sauria. The group includes both crocodile-like neochoristoderes and smaller lizard-like forms, with some long-necked species resembling plesiosaurs. Their fossils are exclusively found in freshwater deposits, often alongside turtles, fish, and crocodyliformes, suggesting a warm temperate climate preference. The discovery of skin impressions and soft tissue in some specimens provides rare details about their integument and aquatic adaptations. Choristoderes likely occupied distinct ecological niches, with neochoristoderes coexisting with blunt-snouted crocodyliformes but not narrow-snouted ones.
Did You Know?
- Choristoderes possess a unique skull bone not found in other reptiles, called the neomorphic bone.
- The largest known choristodere, Kosmodraco dakotensis, reached an estimated length of about 5 m.
- Champsosaurus had a heart-shaped skull when viewed from above due to expanded temporal fenestrae.
- Some choristoderes, like Hyphalosaurus, had webbed feet and a tail fin for swimming.
Frequently Asked Questions
What is Choristodera?
Choristodera is an extinct order of semiaquatic diapsid reptiles that inhabited freshwater environments across the Northern Hemisphere. They survived from the Middle Jurassic (possibly as early as the Triassic) all the way through the Miocene before vanishing entirely.
What did Choristodera look like?
Their body plans varied enormously, ranging from crocodile-shaped predators like Champsosaurus to more lizard-like builds and species with notably elongated necks. This morphological diversity made them one of the most visually varied groups of extinct reptiles.
Where did Choristodera live?
Fossils have been recovered from North America, Asia, and Europe, with some evidence possibly pointing to North Africa as well. They were restricted to the Northern Hemisphere and never appear in the fossil record of the Southern Hemisphere.
How big could Choristodera get?
The size range was striking: the largest known species, Kosmodraco dakotensis, stretched to roughly five meters in length, while the smallest genera such as Cteniogenys and Lazarussuchus measured only around thirty centimeters. That means some were roughly the size of a house cat while others rivaled large crocodilians.
Why are Choristodera important to paleontology?
Their survival spanning over a hundred million years of geological time makes them a key group for studying how semiaquatic reptile lineages adapted and diversified across multiple mass-extinction boundaries. Their presence on three continents also helps researchers map ancient freshwater ecosystems and faunal connections between regions.
More in Prehistoric Extinct Animals 1-24
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