Hesperornithoides

Credit: Gabriel Ugueto.

*Hesperornithoides*, nicknamed Lori, is a genus of troodontid theropod dinosaur that lived in Wyoming during the Late Jurassic.

## History

A field crew supervised by William Wahl in 2002 unexpectedly unearthed *Hesperornithoides* at Jimbo Quarry, Morrison Formation. It overlying the excavation of *Supersaurus vivianae* near Douglas, Wyoming. In Lovelace, 2006, the stratigraphic position was carefully documented, finally being announced in 2003 at a Society of Vertebrate Paleontology meeting. Phylogenetic analysis in 2005 was presented in a Journal of Vertebrate Paleontology abstract. Lori was donated to the Big Horn Basin Formation, who joined the Wyoming Dinosaur Center in 2016.

*H. miessleri* was named in 2019 by Scott Harman, Mickey Mortimer, William Wahl, Dean R. Lomax, Jessica Lippincott and David M. Lovelace, 18 years later. The genus derives from the Greek Ἑσπερίς (Hesperis), meaning "western", ὄρνις (ornis), meaning "bird", and eides, meaning "form". The species epithet honours the Miessler family, who supported the project. The holotype is WYDICE-DML-001, which was found in the middle Morrison, Tithonian-aged. It is a partial skeleton, which contains the rear skull, lower jaws, hyoids, 5 neck vertebrae, the first back vertebra, 12 tail vertebrae, one rib, chevrons, a left shoulder girdle, a right humerus, the left arm, a partial thighbone and both lower legs (not including the e right toes). Lori is partially articulated, and is likely a subadult or adult.

## Description

The holotype individual was 89 centimeters (35 inches) long, which is limited for a troodontid. The cranial and postcranial material has proportions associated with juveniles. However, the size difference would not be by very much. For example, the adult estimate would be 1 meter (3.3 feet). The authors found derived apomorphic traits similar to paraves. The jugal is pneumatized, the rear lacrimal branch is less than 15% of the descending branch (measured from the inner corner, down). The ridge on the humerus closer to the inner condyle is more than 15% of the full distal width. The hand's third claw is close to the size of the second claw. The shinebone's lower inner corner projects to the front.

## Classification

Phylogenetic analysis in 2005 classified thee specimen as a close relative of *Sinornithoides*. SVP 2017 brought unpublished phylogenetic results, which recovered Lori as a relative of *Sinovenator*. *Hesperornithoides* existing along many maniraptorans (*Anchiornis*, *Eosinopteryx*...) was used a strong refutation to the arguments presented by those who refuse dinosaurs evolved into birds. In 2019, *Hesperonithoides* was assigned a relatively basal position in Troodontidae, in a clade alongside *Daliansaurus*, *Xixiasaurus* and *Sinusonasus*:

## Paleoecology

Although many large dinosaurs from the Morrison have been excavated, *Hesperornithoides* proves more species could be undiscovered. The Morrison *Hesperornithoides* lived in was open and well-watered with low growths and rare trees. Additionally, this ecosystem had lacustrine and wetland environments. Most paraves, aside from avialans, had few members that had some flight capability. All the exceptions were likely arboreal, which indicates flight evolved many times when species had traits and behaviours adapted for climbing trees and near-vertical surfaces. This includes wing-assisted incline running.

## References

https://en.wikipedia.org/wiki/Hesperornithoides