Tithonian
[8][13] The Tithonian extinction has not been studied in great detail, but it is usually attributed to habitat loss via a major marine regression (sea level fall).
[7] There is good evidence for a marine regression in Europe across the Jurassic-Cretaceous boundary, which may explain the localized nature of the extinction.
Some authors support a fundamental correlation (the so-called "common cause hypothesis"),[12] while others strongly voice doubts.
[15] Sea level fall was likely related to the Tithonian climate, which was substantially colder and drier than the preceding Kimmeridgian stage.
[13][16] Several Arctic outcrops show a moderate (up to 5‰) negative organic δ13C excursion in the middle part of the Tithonian.
During the Late Jurassic and Early Cretaceous, numerous volcanic deposits can be found along the margin of Gondwana, which was beginning to fragment into smaller continents.
A lack of earliest Cretaceous marine lagerstätten may appear as a loss of diversity, simply looking at the raw data alone.
[18][19] Sampling bias may also explain apparent extinctions in terrestrial environments, which have a similar disconnect in fossil abundance.
Only a fraction of Jurassic ammonite species survive to the Cretaceous, though extinction rates were actually lower in the late Tithonian relative to adjacent time intervals.
[7][9] Moderate diversity declines have been estimated or observed in gastropods, brachiopods, radiolarians, crustaceans, and scleractinian corals.
Conversely, the Tithonian extinction acted as a trigger for a Cretaceous diversification event for plesiosaurs in the clade Xenopsaria, namely elasmosaurids and leptocleidians.
Diplodocids, basal macronarians, and mamenchisaurids took the brunt of the extinction,[6] though a few species of each group survived to the Early Cretaceous.
[10] Theropod diversity declined through the entire Late Jurassic, with medium-sized predators such as megalosaurids being the hardest hit.
[12] Practically no earliest Cretaceous sites are known to preserve pterosaur fossils, so the precise timing of non-pterodactyloid extinctions is very uncertain.
[18] Coastal and freshwater crocodyliforms experienced high extinction rates across the J–K boundary, preceding a significant diversification of more terrestrially-adapted metasuchians in the Cretaceous.
