Ic
- Icarosaurus,
†Red Ichthyopterygia Owen, 1840
- †Apatodonosaurus Mehl 1928
- †Baptanodontidae Marsh 1879
- †Cetarthrosaurus Seeley 1873
- †Chonespondylus Leidy 1868
- †Ghuizhouichthyosaurus
- †Grippiidae Wiman 1929
- †Guanlingichthyosaurus
- †Hueneosauria Maisch and Matzke 2000
- †Ichthyosaurus Koenig 1818
- †Ichthyosaurus polyptychodon Koken 1883
- †Ichthyosaurus strombecki Meyer 1862
- †Isfjordosaurus Motani 1999
- †Macropterygius Huene 1922
- †Mixosauria Motani 1999
- †Mixosauridae Baur 1887
- †Naanchangasaurus
- †Omphalosauridae Merriam 1906
- †Pachygonosaurus von Huene 1916
- †Parvinatatoridae McGowan and Motani 2003
- †Pessosaurus Wiman 1910
- †Platypterygiidae Bardet 1995
- †Proteosauridae Hay 1902
- †Quasianosteosauridae Maisch and Matzke 2003
- †Rachitrema Sauvage 1883
- †Shastosauroidea Tatarinov 1964
- †Sphaerodontes Torre and Cuervo 1939
- †Stenopterygius grandis Cabrera 1939
- †Svalbardosaurus Mazin 1981
- †Thaisauridae Maisch 2010
- †Undorosauridae Efimov 1999
- †Utatsusauridae McGowan and Motani 2003
Animalia → Chordata → Reptilia → Diapsida
- Ichthyosauridae †
†Klada Ichthyosauriformes Motani et al. 2015
- †Ichthyopterygia Owen, 1840
- †Nasorostra Jiang et al. 2016
Diapsida → Neodiapsida → Ichthyosauromorpha
†Klada Ichthyosauromorpha Motani et al. 2015
- Hupehsuchia Carroll and Dong 1991
- Ichthyosauriformes Motani et al. 2015
- Ichthyosaurus De la Beche & Conybeare, 1821 †
Ig
- Ignotosaurus,
- Igua,
- Iguana,
- Iguania,
- Iguanidae,
- Iguaninae,
Ik
- Ikanogavialis †
- Ikechosaurus,
Il
- Ilchunaia †
Ir
- Irenosaurus,
Is
- Iserosaurus,
- Isfjordosaurus Motani, 1999 †
- Isochirotherium,
- Isodontosauridae,
- Isodontosaurus,
- Istiodactylidae Howse, Milner & Martill, 2001 †
- Istiodactylus Howse, Milner & Martill, 2001 †
It
- Itasuchus †