Gillicus was a relatively small, 2 metres (6.6 ft) long ichthyodectiform ray-finned fish that lived in central North America (Western Interior Seaway), Europe and East Asia, from the late Albian to the early Maastrichtian.

[4] The Gillicus bones have not been digested so the larger fish must have died soon after eating its prey.

[4] The specimen can be seen at the Sternberg Museum of Natural History in Hays, Kansas.

[5] Nearly all of the Gillicus specimens collected from the Smoky Hill Chalk are adults or subadults, which suggests that the early stages of their life were spent elsewhere.

[2] In 2021, the children's book The Plesiosaur's Neck[6] coined the common name "pug fish" for the Gillicus.