Species: Presbyornis or Gallinuloides?
Geologic Era: Eocene (53.5-48.5 million years old)
Location Found: Green River Formation
Size: Duck to goose sized (assuming identification of Gallinuloides or Presbyornis like animal)
Estimated Range: Eocene
Extinction Date: End of Eocene
This is a small piece of sediment from the famous Green River Formation. This formation is one of the most productive fossil sites in the world, and we do have several specimens from this formation in our collection. This is a bird trackway, which is considered a trace fossil. I honestly can’t tell how many individual tracks are present, but I would say at least 10 appear to be preserved. One can’t tell what species made the tracks, but it would have been a medium sized bird, perhaps comparable to a modern duck or goose. I have seen a few similar fossils online, and most list trackways such as this one as being made by Presbyornis, a distant ancestor of modern ducks and geese.
The Green River Formation has produced not only trackways such as this one, but also countless other vertebrate fossils. Some of the most common are Knightia fish, which can be found in nearly every rock shop that sells fossils. Other species that have been found include primitive bats, freshwater stingrays, snakes, crocodiles, and plants. If crocodiles were present, the Green River area must have been a fairly warm, humid environment (perhaps comparable to modern Florida/Louisiana). The little bird pictured below is an undescribed species from the Green River Formation, beautifully preserved.
Unidentified Green River Bird: “Fossil bird Field Museum” by Matt Mechtley from Tempe, Arizona, USA – Fossil early birdUploaded by FunkMonk. Licensed under CC BY-SA 2.0 via Commons – https://commons.wikimedia.org/wiki/File:Fossil_bird_Field_Museum.jpg#/media/File:Fossil_bird_Field_Museum.jpg
Presbyornis: “Presbyornis Enhancement” by Smokeybjb – Own work. Licensed under CC BY-SA 3.0 via Commons – https://commons.wikimedia.org/wiki/File:Presbyornis_Enhancement.jpg#/media/File:Presbyornis_Enhancement.jpg