See text Belemnotheutis is an extinct coleoid cephalopod genus from the middle and upper Jurassic, related to but morphologically distinct from belemnites.

This genus was the subject of a dispute between several eminent 19th century British paleontologists, notably between Richard Owen and Gideon Mantell.

One specimen recovered from Christian Malford, Wiltshire and currently displayed in the Paleontology Department of the Natural History Museum in London is fossilized clasping a fish.

[6] In true belemnites, the large dense rostra acted as a counterbalance, keeping the animal horizontally oriented when swimming.

Brain cartilage is observed in some specimens, as well as a pair of aragonitic statoliths which helped the animal determine horizontal orientation when swimming.

[9][20] At the center of the dorsal surface of the rostrum is a narrow V-shaped groove running about 3/5ths the length of the phragmocone from the apex, with two rounded ridges at its left and right sides.

These grooves are one of the most distinctive features of the Belemnotheutidae and are theorized to have served as attachments to terminal oval or oar-shaped fins like in some modern squids.

[22] Intestinal casts (cololites) as well as the orientations and positions of fossilized remains reveal that the animal preyed on fish and other coleoids in life.

Their great abundance in certain formations indicate that Belemnotheutis were highly gregarious animals, congregating in large monospecific or polyspecific shoals.

[21] The earliest known possible remains of belemnotheutids (genera Chitinobelus and Chondroteuthis) come from the Lower Jurassic, from phragmocones and rostra recovered from Toarcian formations in Dumbleton, Gloucestershire, and Ilminster, Somerset, England.

Most authorities like Jeletzky (1966),[7] Bandel and Kulicki (1988), and Peter Doyle (1990)[13] classify it under Belemnitida in the suborder Belemnotheutina (the classification used by this article).

Others like Donovan (1977) and Engeser and Reitner (1981) classify it as a distinct order, Belemnotheutida, based on the aragonitic constitution of the rostra,[9] the shape of the proostraca, protoconchs, and the arm crowns, among other morphological factors.

[12] Belemnotheutis has been continually spelled as Belemnoteuthis by authors who believed that Pearce had made an honest mistake in naming the specimens.

[32] In 2008, an excavation team led by the British Geological Survey in Christian Malford recovered fossilized ink sacs from several remarkably preserved remains of Belemnotheutis antiquus in the Oxford Clay that had been previously identified during the 1840s.

[19] The specimens were fossilized rapidly in apatite (calcium phosphate) through a process paleontologist Phil Wilby called "The Medusa Effect".

Bringing to mind the 19th century practices of the aforementioned early paleontologists, they used the ~150 million year old ink to draw a replica of the original illustration of Belemnotheutis as drawn by Joseph Pearce.

[34] Belemnotheutis was first described by the amateur paleontologist Joseph Pearce in 1842 in Wiltshire, South West England, two years after excavations from the construction of the Great Western Railway uncovered parts of the Oxford Clay.

Pearce responded by stating that examination by another paleontologist James Bowerbank, supported his belief that fossils did not possess the bullet-shaped guards typical of Belemnites but instead had rostra in the form of very thin sheaths.

Shortly after his death, the same paper published the support of William Cunnington, a fossil collector, for this description as opposed to Owen's conclusions.

He also described the characteristic groove on the apical dorsal surface of the Belemnotheutis for the first time (structures which Owen had attributed as artifacts of crushing).

[9][37] Mantell continued to assert his position until his death in 1852,[35] gaining supporters in other eminent paleontologists like Edward Forbes and Charles Lyell against Owen with regards to the true morphology of Belemnotheutis.

Mantell did eventually receive the Royal Medal for his work on Iguanodon to which Owen had attempted to claim another authority much in the same way that he had named Belemnotheutis after himself.