Palaeolagus haydeni

Overview

Palaeolagus haydeni is an early lagomorph mammal from the Oligocene. It has been studied through fossils from present-day Wyoming and Nebraska, USA. Its familiar rabbitlike appearance invites a search for different features in an ancient relative.^[1]

Key facts

What can be learned by looking inside a skull without cutting it open? A 2021 study analyzed this species’ skull using CT data. Researchers compared features resembling rabbits and pikas to explore the bodies of early lagomorphs.^[1]

Time and place

This mammal lived in the early Oligocene, around 33 million years ago. Material is known from the White River Group and Brule Formation in present-day Wyoming, USA. The region allows early lagomorphs to be explored alongside other mammals.^[1][3]

The time range describes source context, not the complete duration of this species.

Size, form and skeleton

Descriptions of the head include long, flat nasal bones with forward-projecting tips. Comparative literature also discusses a hind-limb plan with a long lower leg and foot. Head and limb features together reveal the body of an early lagomorph.^[1][2]

The teeth of this rabbit relative from early Oligocene North America also suggest its small size. The upper cheek-tooth rows of 30 specimens from Nebraska were approximately 0.8–1 cm long. This measures the row from the front premolar to the last molar, not a single tooth.^[10]

Habitat and reproduction

A 2021 study described the semicircular canals of the inner ear in Palaeolagus as slender and strongly curved, like those of living rabbits and hares, unlike the more oval canals of pikas. The authors linked this shape to agile movement. Small structures inside the head thus provided a way to investigate locomotion.^[1][2][4]

Fossil discovery

Skulls and postcranial bones held in several museums provide research material for this animal. A 2021 study used CT data to analyze specimens including a skull with its lower jaw articulated. Comparing the outside and inside of old fossils revealed more about the bodies of early lagomorphs.^[1][3]

References

1. 2021 study — The skull of Palaeolagus examined with CT
2. Fostowicz-Frelik2007 — Comparing hindlimbs of fossil rabbits
3. Smithsonian — Fossil record of Palaeolagus haydeni
4. Ruf·Meng·Fostowicz-Frelik(2021). Anatomy of the Nasal and Auditory Regions of the Fossil Lagomorph Palaeolagus haydeni: Systematic and Evolutionary Implications. Frontiers in Ecology and Evolution9:636110.
5. 2021 study — The skull of Palaeolagus examined with CT
6. Smithsonian — Fossil record of Palaeolagus haydeni
7. Smithsonian — Skeletal material of Hypertragulus calcaratus
8. International Commission on Stratigraphy (2024) — Geological time chart
9. Vislobokova (2001) — Evolution and skeletal comparison of Tragulina
10. Korth & Dharmapuri (2017), Ontogenetic change in dental dimensions of the Oligocene (Orellan) leporid Palaeolagus Leidy from Nebraska

Research questions

When did the features of rabbits and pikas begin to diverge? The head of Palaeolagus is interpreted as combining features resembling both groups. Comparing the head and long hind limbs helps explore changes among early lagomorphs.^[1]

Observation

Move your gaze from the long nasal bones at the front of the head to the trunk and hind limbs. Examining teeth, skull, and elongated legs together brings the body of this ancient lagomorph into focus.^[1][2]