Presbyornis isoni

Overview

Presbyornis isoni is a large duck relative from the Late Paleocene. Although this bird is known from only a few wing bones, comparison with abundant fossils of the same genus leads us into the world of a group combining long legs with duck-like heads.^[1][3]

Key facts

It has been suggested that two left wing bones found several years apart might belong to a single bird. A humerus and a wing finger bone were connected through their discovery location and form. This is one scene from fossil research in which small discoveries are linked together.^[1]

Time and place

This North American bird lived in the Late Paleocene, around 60 million years ago. Important fossils came from the Aquia Formation at Blue Banks, Charles County, in present-day Maryland, USA. Marine sediments of the time preserved the bird's wing bones.^[1][2]

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

Size, form and skeleton

The reference humerus lacks its upper end, but its lower end is 23.3 mm wide. A wing finger bone studied alongside it is 40.6 mm long. These dimensions are smaller than a direct measurement of whole-body height would be, but they provide a starting point for size comparisons with other Presbyornis.^[1]

Habitat and reproduction

Presbyornis pervetus, a species in the same genus, is presented as a long-legged bird that filtered small food items from water. The possibility that it nested in groups beside lakes has also been studied. Considering the life of this relative alongside isoni brings the bird group to which it belonged more vividly into view.^[3]

Fossil discovery

In 1994, Olson introduced this large species while studying bird fossils from the Aquia Formation. Even without a complete skeleton, a distinctive wing bone can serve as the reference for a new name. As comparative specimens accumulate, the form represented by that name becomes clearer.^[1]

References

1. Olson (1994), A Giant Presbyornis (Aves: Anseriformes) and Other Birds from the Paleocene Aquia Formation of Maryland and Virginia. Proceedings of the Biological Society of Washington 107(3):429–435.
2. ICS geologic time chart2024/12
3. AMNH — Presbyornis pervetus
4. Clarke et al.2005 — Vegavis as evidence of modern bird lineages in the Cretaceous
5. Olson (1994), A Giant Presbyornis (Aves: Anseriformes) and Other Birds from the Paleocene Aquia Formation of Maryland and Virginia. Proceedings of the Biological Society of Washington 107(3):429–435.
6. AMNH — Presbyornis pervetus
7. ICS geologic time chart2024/12

Research questions

How much can wing bones alone reveal about a bird's size and relationships? Comparing several species within the same genus helps distinguish shared features from distinctive differences in size. This bird also invites anticipation of the next discovery that might reveal more of its body.^[1][3]

Observation

Begin by examining the combination of wings and legs.^[1][3]