Shastasauridae is an extinct family of Ichthyosauria from the Late Triassic with a possible Early Jurassic record.
Taxonomy
Shastasauridae was named by American paleontologist John Campbell Merriam in 1895 along with the newly described genus
Shastasaurus. In 1999, Ryosuke Motani erected the clade
Shastasauria to include
Shastasaurus,
Shonisaurus, and several other traditional shastasaurids, defining it as a
stem-based taxon including "all
more closely related to
Shastasaurus pacificus than to
Ichthyosaurus communis." He also redefined Shastasauridae as a
node-based taxon including "the last common ancestor of
Shastasaurus pacificus and
Besanosaurus leptorhynchus, and all its descendants" and
Shastasaurinae, which Merriam named in 1908, as a stem taxon including "the last common ancestor of
Shastasaurus and
Shonisaurus, and all its descendants."
In an alternative classification scheme, paleontologist Michael Maisch restricted Shastasauridae to the genus
Shastasaurus and placed
Shonisaurus and
Besanosaurus in separate families, Shonisauridae and Besanosauridae, respectively.
In various studies, the grouping of Shastasauridae has been variously found to be either
monophyletic or
paraphyletic. Studies that have recovered the group as monophyletic generally include
Shastasaurus,
Besanosaurus,
Guanlingsaurus,
Guizhouichthyosaurus,
Shonisaurus and
'Callawayia'
wolonggangense within the group.
Description
Shastasaurids as typically defined have elongate bodies, with over 55 presacral vertebrae.
They were the largest ichthyosaurs, with even some of the smaller species like
Guanlingsaurus measuring over in length.
One of the largest specimens was discovered in England in May 2016,
when researcher and fossil collector Paul de la Salle discovered a partial jawbone measuring 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. Using
Shonisaurus sikanniensis as a model, the researchers estimated the ichthyosaur to have been long, nearly the size of a
blue whale. Scaling based on
Besanosaurus, however, found a shorter length estimate of .
In 2024, the Lilstock specimen was referred to the newly described species
Ichthyotitan, with a length estimate of up to .
Feeding habits
Unlike other
Triassic Ichthyosauria, which fed almost exclusively on
Cephalopod,
shastasaurians fed on a variety of
Predation.
Evidence for this prey diversity includes gut contents from
Guizhouichthyosarus tangae, Shonisaurus popularis, and an unnamed specimen from the
Brooks Range of
Alaska.
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,
