Genus: Nanotyrannus BAKKER, WILLIAMS & CURRIE, 1988
Etymology: Greek, nanos “dwarf, pigmy” and Greek, tyrannos, “king”, Pigmy tyrant.
= Chicagotyrannus BAKKER & CURRIE , (nomen nudum)
Etymology: In reference to the Field Museum in Chicago, and Greek, tyrannos “king”.

Note: Note: Clevelanotyrannus was a name in a citation by CURRIE, et al in CURRIE, 1987 (Bakker, R.T., Williams, M., and Currie, P.J. in preparation. The Tyrant Dinosaurs--a redefinition of Tyrannosaurus, Albertosaurus, Gorogsaurus, Daspletosaurus, Tarbosaurus, and a new genus of dwarf tyranosaurine, Clevelanotyrannus; with a discussion of head-neck posture, prey-attacking adaptations and head-butting behavior. Submited to Hunteria. This was later changed when the official paper of Nanotyrannus was published.).

Species: lancensis (GILMORE, 1946) BAKKER, WILLIAMS & CURRIE, 1988
= Gorgosaurus lancensis GILMORE, 1946
Etymology: In reference to the Lance Formation.
= Albertosaurus lancensis (GILMORE, 1946) RUSSELL, 1970
= Albertosaurus (Nanotyrannus) lancensis (GILMORE, 1946)
= Deinodon lancensis (GILMORE, 1946) KUHN, 1965

Holotype: CMNH 7541

Locality: Sand Creek, Carter County, Montana.

Horizon: Lower Hell Creek Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material: Nearly complete skull and lower jaws in occlusion. The skull is missing the squamosal, postfrontal, quadratojugal, and the upper half of the quadrate of the right side; there is some disarrangement of the bones of the palate, and many of the teeth are either missing or incomplete.

Note: A CAT scan has shown that this specimen is even less complete than originally thought, much is plaster and stone.

Top and middle after Bakker, et al, 1988.

Referred material:

Locality: Corson County, South Dakota.

Horizon: Lance Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

Uncataloged specimens at Denver Museum of Natural History: Three Teeth broken at the crown-root junction.

 

LUPTON, GABRIEL & WEST, 1980

Locality: McCone County, Montana.

Horizon: Hell Creek Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

Number: Not given: Five isolated teeth.

 

LANGSTON, 1955, field notes.

Locality: Cochrane Paskapoo, Alberta Province, Canada.

Horizon:

Biostratigraphy:

Age: Late Cretaceous.

Material:

Number: Not given: Skull and Skeleton.

 

LARSON, 1997 (pers. comm.)

Locality: Field Museum "Sue" locality, Maurice Williams’s Ranch, Cheyenne River Indian Reservation, near Faith, Meade County, South Dakota.

Horizon: Hell Creek Formation, about 15 feet above the contact with the Fox Hills Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

BHI: Jugal, 3 teeth.

Possible lachrymal, but may belong to Tyrannosaurus rex.

Note: Found with “Sue”. Once thought to have been a juvenile Tyrannosaurus rex.

 

SNYDER, McLAIN, WOOD & CHADWICK, 2020

Locality: Hanson Ranch (HR), northern Niobrara County, Eastern Wyoming.

Horizon: Lance Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

Number: Not given: 135 teeth.

 

= Nanotyrannus sp SPENCER, TURNER & CHADWICK, 2001

Locality: Niobrara County, Wyoming.

Horizon: Lance Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

Number: Not given: Teeth.

 

STENERSON & O’CONNER, 1994

Locality: Northwestern South Dakota.

Horizon: Hell Creek Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

Number: Not given:

 

STEIN, 2021

Locality: Tooth Draw Deposit, Butte County, South Dakota.

Horizon: Hell Creek Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

TD-16-033: Rooted right dentary tooth.

TD-13-247: Pre-maxillary tooth.

TD-17-182: Adult right dentary tooth.

TD-12-262: Juvenile right dentary(?) tooth.

Numbers: Not given: 418 teeth, and dozens of unnumbered specimens.

TD-11-121: Manual claw.

 

YUN, 2019

Locality: Harding County, South Dakota.

Horizon: Hell Creek Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

KPM-NNV00003: tooth.

 

 

ZANNO & NAPOLI, 2025

Locality: Near Jordan, Garfield County, Montana.

Horizon: Hell Creek Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

NCSM 4000: Nearl complete skull and skeleton.

Note: One of the Dueling Dinosaurs.

 

Locality: Montana.

Horizon: Hell Creek Formation.

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material:

KUVP 156375: Partially disarticulated skull and associated postcranial skeleton.

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Species: lethaeus ZANNO & NAPOLI, 2025
Etymology: Latin, lethaeus, adjectival form of Lethe, the mythological River Lethe of the Underworld in Greco-Roman mythology. The name referes both the Hell Creek Formation in which the speicmen was found and the depiction of the Lethe in Virgil's Aeneid, from which souls must drink to forget thier previous life and be reincarnated, in recognition of oru reinterpretation of this specimen as neither Nanotyrannus lancensis nor a juvenile Tyrannosaurus rex, contrary to all previous literature.
= Nanotyrannus lancensis HENDERSON, 2005

Holotype: BMRP (Burpee Museum Rockford Paleontology) 2002.4.1

Locality: Burpee Museum Locality number K-12, public land under jurisdiction of the Federal Bureau of Land Management, northwestern Carter County, Montana.

Horizon: Hell Creek Formation (unknown level).

Biostratigraphy:

Age: Lancian age, upper Maastrichtian Stage, uppermost Senonian subepoch, Upper Gulf Epoch, Late Cretaceous.

Material: Fragmentary skull and fragmentary skeleton of a juvenile.

Note: Nicknamed "Jane."

Note: Has a brodie abscess (Paleopathology) on a phalanx (VITTORE & HENDERSON, 2005, 2013)

Note: Has evidance for face bitting (PETERSON, HENDERSON, VITTORE & SCHERER). Possible penetrating holes made by pes claws on the scapula and ilium (ROTHSCHILDS, 2013).

Note: Nicknamed Jane.