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As I’m sure some of you are aware, Tyrannosaurus mcraensis (Dalman et al., 2023) was not the first Tyrannosaurus species named from material discovered in the southern United States. There was almost another, T. “vannus”.

In an unpublished master’s thesis, Douglas Lawson assigned the name Tyrannosaurus “vannus” to a partial left maxilla (TMM 41436-1) from the upper Javelina Formation (lower Tornillo Group) in Big Bend National Park, Texas (Lawson, 1972). The maxilla displayed an unusual morphology that Lawson at the time considered distinct from that of T. rex. The rostral margin terminates abruptly and the second antorbital fenestra is proportionally very large, these features along with the overall small size were enough for Lawson to tentatively assign a novel name to the specimen. Since this name was never formerly published it fell into obscurity. And in a subsequent publication Lawson revised his interpretation and referred TMM 41436-1 to T. rex, citing ontogenetic immaturity as the explanation for the unusual shape of the specimen (Lawson, 1976).

In 1990 Kennith Carpenter suggested that TMM 41436-1 belonged to a new species or even a new genus, noting that the sharp downward arc of the rostral margin suggests “a face considerably shorter than in T. rex” (Carpenter, 1990). Carr & Williamson (2000) rejected Carpenter’s interpretation, referring the maxilla “unequivocally” to T. rex. Brochu (2003) considered the morphology of TMM 41436-1 consistent with that of T. rex or at least a very close relative. Finally, a recent re-examination of the specimen revealed a low dorsoventral ridge around the second antorbital fenestrae, a feature indictive of immaturity (Wick, 2014).

Regardless of whether the Javelina maxilla represents a distinct species or simply belonged to an immature T. rex, the informal name T. “vannus” remains an interesting but often overlooked footnote in the study of Tyrannosaurus.

References:

Brochu, C. A. (2003). Osteology of Tyrannosaurus rex: insights from a nearly complete skeleton and high-resolution computed tomographic analysis of the skull. Journal of vertebrate Paleontology, 22(4), 1-138.

Carpenter, K. (1990). Variation in Tyrannosaurus rex. Dinosaur systematics: perspectives and approaches, 141-145.

Carr, T. D., & Williamson, T. E. (2004). Diversity of late Maastrichtian Tyrannosauridae (Dinosauria: Theropoda) from western North America. Zoological Journal of the Linnean Society, 142(4), 479-523.

Lawson, D. A. (1972). Paleoecology of the Tornillo Formation, Big Bend National Park, Brewster County, Texas (Doctoral dissertation, University of Texas at Austin).

Lawson, D. A. (1976). Tyrannosaurus and Torosaurus, Maastrichtian dinosaurs from Trans-Pecos, Texas. Journal of Paleontology, 158-164.

Wick, S. L. (2014). New evidence for the possible occurrence of Tyrannosaurus in West Texas, and discussion of Maastrichtian tyrannosaurid dinosaurs from Big Bend National Park. Cretaceous Research, 50, 52-58.

Description

As I’m sure some of you are aware, Tyrannosaurus mcraensis (Dalman et al., 2023) was not the first Tyrannosaurus species named from material discovered in the southern United States. There was almost another, T. “vannus”.

In an unpublished master’s thesis, Douglas Lawson assigned the name Tyrannosaurus “vannus” to a partial left maxilla (TMM 41436-1) from the upper Javelina Formation (lower Tornillo Group) in Big Bend National Park, Texas (Lawson, 1972). The maxilla displayed an unusual morphology that Lawson at the time considered distinct from that of T. rex. The rostral margin terminates abruptly and the second antorbital fenestra is proportionally very large, these features along with the overall small size were enough for Lawson to tentatively assign a novel name to the specimen. Since this name was never formerly published it fell into obscurity. And in a subsequent publication Lawson revised his interpretation and referred TMM 41436-1 to T. rex, citing ontogenetic immaturity as the explanation for the unusual shape of the specimen (Lawson, 1976).

In 1990 Kennith Carpenter suggested that TMM 41436-1 belonged to a new species or even a new genus, noting that the sharp downward arc of the rostral margin suggests “a face considerably shorter than in T. rex” (Carpenter, 1990). Carr & Williamson (2000) rejected Carpenter’s interpretation, referring the maxilla “unequivocally” to T. rex. Brochu (2003) considered the morphology of TMM 41436-1 consistent with that of T. rex or at least a very close relative. Finally, a recent re-examination of the specimen revealed a low dorsoventral ridge around the second antorbital fenestrae, a feature indictive of immaturity (Wick, 2014).

Regardless of whether the Javelina maxilla represents a distinct species or simply belonged to an immature T. rex, the informal name T. “vannus” remains an interesting but often overlooked footnote in the study of Tyrannosaurus.

References:

Brochu, C. A. (2003). Osteology of Tyrannosaurus rex: insights from a nearly complete skeleton and high-resolution computed tomographic analysis of the skull. Journal of vertebrate Paleontology, 22(4), 1-138.

Carpenter, K. (1990). Variation in Tyrannosaurus rex. Dinosaur systematics: perspectives and approaches, 141-145.

Carr, T. D., & Williamson, T. E. (2004). Diversity of late Maastrichtian Tyrannosauridae (Dinosauria: Theropoda) from western North America. Zoological Journal of the Linnean Society, 142(4), 479-523.

Lawson, D. A. (1972). Paleoecology of the Tornillo Formation, Big Bend National Park, Brewster County, Texas (Doctoral dissertation, University of Texas at Austin).

Lawson, D. A. (1976). Tyrannosaurus and Torosaurus, Maastrichtian dinosaurs from Trans-Pecos, Texas. Journal of Paleontology, 158-164.

Wick, S. L. (2014). New evidence for the possible occurrence of Tyrannosaurus in West Texas, and discussion of Maastrichtian tyrannosaurid dinosaurs from Big Bend National Park. Cretaceous Research, 50, 52-58.