Open Paleo

Hesperornithoides

Hartman et al., 2019 HESS-per-OR-nee-THOY-deez

From Greek 'Hesperis' meaning 'western', 'ornis' meaning 'bird', and '-eides' meaning 'form', hence 'western bird form'. The species name honors the Miessler family.

154.8–143.1 million years ago Kimmeridgian–Tithonian, Late Jurassic
Late Jurassic stages

Hesperornithoides is a genus of troodontid theropod dinosaur that lived in North America during the Late Jurassic period.

Under dispute

Hesperornithoides, the oldest definitive troodontid, is recovered in a basal position by its describers (Hartman and colleagues, 2019) — though within their tree it falls in a derived clade with Daliansaurus, Xixiasaurus, and Sinusonasus — and as the basalmost troodontid by Sellés and colleagues (2021). It is not assigned to a named subfamily and is placed at Troodontidae incertae sedis.

Diagnosis

  1. Pneumatic jugal
  2. Short posterior lacrimal process (<15% of ventral process length)
  3. Quadrate forms part of lateral margin of paraquadrate foramen
  4. Small external mandibular fenestra (<12% of mandibular length)
  5. Humeral entepicondyle >15% of distal humeral width
  6. Manual ungual III subequal in size to ungual II
  7. Mediodistal corner of tibia exposed anteriorly

Species

Hesperornithoides miessleri Hartman et al., 2019

Type species

Named for the Miessler family, in recognition of their support of the research project that described the specimen.

Holotype
WYDICE-DML-001 , Wyoming Dinosaur Center
Material
Partially articulated skeleton comprising most of an articulated skull and mandibles, five cervical vertebrae, first dorsal vertebra, portions of 12 caudal vertebrae, five chevrons, partial scapula and coracoid, portions of humeri, left ulna and radius, radiale, semilunate carpal, left metacarpals I-III, manual phalanges, manual unguals I-III, ilial fragment, incomplete femur, tibiae and fibulae, left astragalus and calcaneum, metatarsal packets, left pedal phalanges III and IV, and pedal unguals II-IV
Horizon
middle Morrison Formation, Kimmeridgian–Tithonian, Late Jurassic , 154.8–143.1 million years ago
Locality
Jimbo Quarry, Wyoming, United States Hartman and colleagues (2019) place the holotype in the sandstone overlying the Jimbo Quarry bonebed, and report the Morrison as undivided in central Wyoming.

References

  1. Hartman, S.; Mortimer, M.; Wahl, W. R.; Lomax, D. R.; Lippincott, J.; Lovelace, D. M. (2019). A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight. PeerJ 7: e7247. PeerJ. doi:10.7717/peerj.7247 hartman2019a
  2. Paul, G. S. (2024). The Princeton Field Guide to Dinosaurs (3rd ed.). Princeton University Press.

    Source of the mass estimate.

    paul2024a
  3. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Theropods. Princeton University Press.

    Source of the hip height estimate, and the appearance features.

    jones2026c
  4. Sellés, A. G.; Vila, B.; Brusatte, S. L.; Currie, P. J.; Galobart, À. (2021). A fast-growing basal troodontid (Dinosauria: Theropoda) from the latest Cretaceous of Europe. Scientific Reports 11(1). Springer Science and Business Media LLC. doi:10.1038/s41598-021-83745-5

    Recovered Hesperornithoides as the basalmost troodontid.

    sellés2021a