Apternodus mediaevus

Overview

Apternodus mediaevus is a Late Eocene mammal. It was first described from lower-jaw and dental material from present-day Montana, USA. Beginning with a small jaw, research expanded to comparisons of the head and several partial body bones.^[1]

Key facts

A lower jaw bearing two molars can serve as the reference for a species name. The Apternodus type specimen AMNH9601 is such material. Comparisons beginning with small teeth led to research on other skulls and body bones.^[1]

Time and place

It is a Late Eocene animal from around 35 million years ago. Important material is known from Chadronian strata in present-day Montana, USA. It formed part of a world inhabited by diverse North American mammals.^[1]

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

Size, form and skeleton

The type jaw preserves the first and second molars. Other specimens include skulls and partial bones of the vertebral column, arms, legs, and feet. Comparisons across several body regions reveal this mammal’s anatomical features.^[1]

Jaw specimen MPUM 7820 of Apternodus mediaevus preserves a second molar measuring 2 mm in both length and width. These figures show the size of one tooth in a small jaw, rather than the size of the whole body.^[2]

Habitat and reproduction

How can a body’s handling of food be studied? Molars, jaws, and partial limb bones are compared with those of other small mammals. Viewing material from several Montana localities side by side allows exploration of this animal’s life and distribution.^[1]

Fossil discovery

Matthew described this species in 1903 from jaw fragments from Pipestone Springs, Montana. A 2002 study compared several skulls and body bones together. Larger specimens were also provisionally retained in the same species based on tooth shape and anatomical consistency.^[1]

References

1. 2002 study — The morphology and relationships of Apternodus
2. Asher et al. (2002) — Morphology and relationships of Apternodus and other extinct, zalambdodont, placental mammals
3. Turnbull2004 — Taeniodonta of the Washakie Formation, Southwestern Wyoming

Research questions

Does a difference in body size automatically mean a different species? Researchers considered tooth form and consistency across several bones as well as size. Comparing small and large specimens explores variation within one species and differences between species.^[1]

Observation

Move your gaze from the molars in the jaw to the head and limbs. Consider together what information the small teeth and other body bones each provide.^[1]