Troodontid specimens from Montana and validity of Troodon formosus (free pdf)
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Ben Creisler
May 13, 2025, 11:00:16 AM5/13/25
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Ben Creisler
David J. Varricchio, Jason D. Hogan & Jacob D. Gardner (2025)
Troodontid specimens from the Cretaceous Two Medicine Formation of Montana (USA) and the validity of Troodon formosus
Journal of Paleontology (advance online publication)
DOI: https://doi.org/10.1017/jpa.2024.67
https://www.cambridge.org/core/journals/journal-of-paleontology/article/troodontid-specimens-from-the-cretaceous-two-medicine-formation-of-montana-usa-and-the-validity-of-troodon-formosus/3E58F1FDA3FE53DE569E0D0B20E79F22
In 1855, Ferdinand Hayden collected a single tooth from the Judith River badlands of central Montana. Joseph Leidy named this specimen the following year as Troodon formosus. We describe troodontid material from the coeval Two Medicine Formation of Montana that compares closely to the recently resurrected and previously synonymized Stenonychosaurus inequalis from the lower Dinosaur Park Formation of Alberta. We uphold that synonymy but recognize T. formosus as the senior synonym. Troodon formosus is distinguished from other troodontids by a maxilla with an anteriorly more broadly rounded maxillary fenestra, low-angled nasal process with stepped anterior portion, large palatal shelf, and 23 teeth; more pronounced basioccipital tubera; L-shaped to triangular frontal; and relatively shorter metatarsal III with convex to flat anterior face at maximum breadth. Phylogenetic analysis places T. formosus within the Troodontinae, a clade with poor within-group resolution. The T. formosus holotype was diagnostic at time of description. Despite numerous complications over the taxon’s long history, the original name of 1856 has come to encompass a robust and specific species concept despite originally fragmentary material. Troodon formosus best satisfies the International Code of Zoological Nomenclature’s tenants of priority and stability. Recent proposals to re-establish Stenonychosaurus inequalis as the proper name encounter an equally problematic and undiagnostic type specimen. Instead of either of these types, we propose that material from the Two Medicine Formation (Museum of the Rockies, MOR 553) would best serve as a neotype for Troodon formosus.
Non-technical Summary
In 1855 Ferdinand Hayden collected a single tooth from the Judith River badlands of central Montana. Joseph Leidy in Philadelphia named this specimen the following year as Troodon formosus, “beautiful wounding tooth.” So began the somewhat troubled history of the dinosaur Troodon. Over the next 130 years, Troodon would be considered a lizard, possibly a pachycephalosaur (a thick-headed dinosaur), or simply too incomplete to understand. Resolution of Troodon’s true nature did not come until Philip Currie in the 1980s described more material, including jaws with teeth, and correctly identified Troodon formosus as a species of small, carnivorous dinosaur close to the ancestry of birds. We know Troodon now as possibly one of the smartest dinosaurs, or at least one of the brainiest. But because of the fragmentary nature of the original discovery, some scientists think that the name Troodon formosus should be thrown out.
We present previously undescribed material from Montana that helps to clarify Troodon’s true nature, much as Currie envisioned. We propose that these new specimens should be used to formally ground the definition of the species. Based upon these new specimens, as well as a reading of the International Code of Zoological Nomenclature, we argue that Troodon formosus remains valid as the senior synonym of Stenonychosaurus inequalis and captures the species concept first envisioned by Leidy 165 years ago for an unknown animal with unusual teeth in the Cretaceous of Montana. Preservation of the name means that Troodon formosus remains among the earliest dinosaurs named from North America.
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A new paper:
Free pdf:
David J. Varricchio, Jason D. Hogan & Jacob D. Gardner (2025)
Troodontid specimens from the Cretaceous Two Medicine Formation of Montana (USA) and the validity of Troodon formosus
Journal of Paleontology (advance online publication)
DOI: https://doi.org/10.1017/jpa.2024.67
https://www.cambridge.org/core/journals/journal-of-paleontology/article/troodontid-specimens-from-the-cretaceous-two-medicine-formation-of-montana-usa-and-the-validity-of-troodon-formosus/3E58F1FDA3FE53DE569E0D0B20E79F22
In 1855, Ferdinand Hayden collected a single tooth from the Judith River badlands of central Montana. Joseph Leidy named this specimen the following year as Troodon formosus. We describe troodontid material from the coeval Two Medicine Formation of Montana that compares closely to the recently resurrected and previously synonymized Stenonychosaurus inequalis from the lower Dinosaur Park Formation of Alberta. We uphold that synonymy but recognize T. formosus as the senior synonym. Troodon formosus is distinguished from other troodontids by a maxilla with an anteriorly more broadly rounded maxillary fenestra, low-angled nasal process with stepped anterior portion, large palatal shelf, and 23 teeth; more pronounced basioccipital tubera; L-shaped to triangular frontal; and relatively shorter metatarsal III with convex to flat anterior face at maximum breadth. Phylogenetic analysis places T. formosus within the Troodontinae, a clade with poor within-group resolution. The T. formosus holotype was diagnostic at time of description. Despite numerous complications over the taxon’s long history, the original name of 1856 has come to encompass a robust and specific species concept despite originally fragmentary material. Troodon formosus best satisfies the International Code of Zoological Nomenclature’s tenants of priority and stability. Recent proposals to re-establish Stenonychosaurus inequalis as the proper name encounter an equally problematic and undiagnostic type specimen. Instead of either of these types, we propose that material from the Two Medicine Formation (Museum of the Rockies, MOR 553) would best serve as a neotype for Troodon formosus.
Non-technical Summary
In 1855 Ferdinand Hayden collected a single tooth from the Judith River badlands of central Montana. Joseph Leidy in Philadelphia named this specimen the following year as Troodon formosus, “beautiful wounding tooth.” So began the somewhat troubled history of the dinosaur Troodon. Over the next 130 years, Troodon would be considered a lizard, possibly a pachycephalosaur (a thick-headed dinosaur), or simply too incomplete to understand. Resolution of Troodon’s true nature did not come until Philip Currie in the 1980s described more material, including jaws with teeth, and correctly identified Troodon formosus as a species of small, carnivorous dinosaur close to the ancestry of birds. We know Troodon now as possibly one of the smartest dinosaurs, or at least one of the brainiest. But because of the fragmentary nature of the original discovery, some scientists think that the name Troodon formosus should be thrown out.
We present previously undescribed material from Montana that helps to clarify Troodon’s true nature, much as Currie envisioned. We propose that these new specimens should be used to formally ground the definition of the species. Based upon these new specimens, as well as a reading of the International Code of Zoological Nomenclature, we argue that Troodon formosus remains valid as the senior synonym of Stenonychosaurus inequalis and captures the species concept first envisioned by Leidy 165 years ago for an unknown animal with unusual teeth in the Cretaceous of Montana. Preservation of the name means that Troodon formosus remains among the earliest dinosaurs named from North America.
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