| Shastasauridae | |
|---|---|
 | |
| Skeleton ofShastasaurus sikanniensis | |
 | |
| Scale diagram ofShonisaurus | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | †Ichthyosauria |
| Node: | †Merriamosauria Motani, 1999 |
| Family: | †Shastasauridae Merriam, 1895 |
| Genera | |
Shastasauridae is an extinctfamily ofichthyosaurs from theLate Triassic with a possibleEarly Jurassic record.[1] The family contains the largest known species of ichthyosaurs, which include some of and possibly the largest knownmarine reptiles.[2]
Shastasauridae was named by American paleontologistJohn Campbell Merriam in 1895 along with the newly described genusShastasaurus. In 1999, Ryosuke Motani erected the cladeShastasauria to includeShastasaurus,Shonisaurus, and several other traditional shastasaurids, defining it as astem-based taxon including "allmerriamosaurians more closely related toShastasaurus pacificus than toIchthyosaurus communis." He also redefined Shastasauridae as anode-based taxon including "the last common ancestor ofShastasaurus pacificus andBesanosaurus leptorhynchus, and all its descendants" andShastasaurinae, which Merriam named in 1908, as a stem taxon including "the last common ancestor ofShastasaurus andShonisaurus, and all its descendants."[3] In an alternative classification scheme, paleontologist Michael Maisch restricted Shastasauridae to the genusShastasaurus and placedShonisaurus andBesanosaurus in separate families, Shonisauridae and Besanosauridae, respectively.[4][5] In various studies, the grouping of Shastasauridae has been variously found to be eithermonophyletic orparaphyletic. Studies that have recovered the group as monophyletic generally includeShastasaurus,Besanosaurus,Guanlingsaurus,Guizhouichthyosaurus,Shonisaurus and‘Callawayia’wolonggangense within the group.[6]
Shastasaurids as typically defined have elongate bodies, with over 55 presacral vertebrae.[6] They were the largest ichthyosaurs, with even some of the smaller species likeGuanlingsaurus measuring over 8 metres (26 ft) in length.[7] One of the largest specimens was discovered in England in May 2016,[8] when researcher and fossil collector Paul de la Salle discovered a partial jawbone measuring 96 centimeters (3.15 ft) long which was catalogued as BRSMG Cg2488, also referred to as the Lilstock specimen. In 2018, Dean Lomax, de la Salle, Judy Massare, and Ramues Gallois identified the Lilstock specimen as a shastasaurid. While its incompleteness made the size of the animal difficult to suggest, it clearly was very large. UsingShonisaurus sikanniensis as a model, the researchers estimated the ichthyosaur to have been 26 meters (85 ft) long, nearly the size of ablue whale. Scaling based onBesanosaurus, however, found a shorter length estimate of 22 meters (72 ft).[9] In 2024, the Lilstock specimen was referred to the newly described speciesIchthyotitan, with a length estimate of up to 25 meters (82 ft).[2]
Unlike otherTriassicichthyosaurs, which fed almost exclusively oncephalopods,[10] shastasaurians fed on a variety ofprey.[11] Evidence for this prey diversity includes gut contents fromGuizhouichthyosarus tangae,Shonisaurus popularis, and an unnamed specimen from theBrooks Range ofAlaska.[11]
Although older studies have suggested that shastasaurids were suction-feeders, current research indicates that the jaws of shastasaurid ichthyosaurs do not fit the suction-feeding profile, since their short and narrow hyoid bones are unsuitable to withstand impact forces for such kind of feeding,[12] and since some species likeShonisaurus had robust sectorial teeth with gut contents of mollusk shells and vertebrates.[13][11]
