Organism · Ray-finned fishes
Phareodus encaustus
Source time context (not species duration) · ≈ 56–33.9 Ma
Inferred life reconstruction
Phareodus encaustus
Overview
Phareodus encaustus is a sharp-toothed fish from Eocene lakes. It is an ancient relative in the family Osteoglossidae, which includes living arowanas. Small fish preserved in the mouths and bellies of Phareodus fossils tell the story of a predator’s meals.[2]
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Key facts
Did its lifestyle differ between youth and adulthood? Juvenile Phareodus occur as fossils of several individuals that died together, whereas adults are usually found alone. Researchers interpreted this contrast as a clue to a shift from schooling as juveniles to solitary hunting as adults.[2]
Time and place
This fish is known from Eocene Fossil Lake, approximately 52 million years ago. The Green River Formation at Fossil Butte in present-day Wyoming, United States, preserves fossils from that lake. It is a place to encounter everything from tiny fry to large predators.[3]
The time range describes source context, not the complete duration of this species.
Size, form and skeleton
Its upper and lower jaws are longer, and its mouth corners lie farther back, than in testis of the same genus. Specimen FOBU790 of encaustus in US National Park Service material is 57.8 cm long. Long jaws, large teeth, and fins concentrated toward the rear stand out.[1][2]
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Habitat and reproduction
Some Phareodus fossils preserve smaller fishes in their mouths or bellies. Together with large pointed teeth, these provide evidence of predatory feeding. Considering the lake’s various fishes together brings predator–prey relationships into clearer view.[2]
Fossil discovery
A 1997 study compared North American Phareodus species. It described differences in the head and jaws alongside very similar tail skeletons. Many specimens in museums and national parks support these comparisons.[1][2]
References
- Li, Grande & Wilson1997 — Comparison of North American Phareodus species
- National Park Service — Fossil fishes of Fossil Butte
- National Park Service — Exhibits and ecology of Fossil Lake
- National Park Service — Exhibits and ecology of Fossil Lake
- Royal Ontario Museum — A new fossil in bat evolution
- Simmons et al. (2008) — Early bats from Wyoming and the evolution of flight
- National Park Service — Fossil fishes of Fossil Butte
Research questions
Can jaws differ while tails remain similar? Different body regions can change in different ways even within one genus. When young fishes began hunting alone is another question explored by comparing fossils.[1][3]
Observation
Move your gaze from the long jaws and sharp teeth to the rear fins. Connect the parts of the body and imagine this lake predator swimming.[1][2][3]
Related organisms
Onychonycteris finneyiPlacental mammalsSource time context (not species duration) · ≈ 56–33.9 MaFishes and bats of the Green River Formation
Phareodus and Onychonycteris are known from the Eocene Green River Formation in present-day Wyoming, United States. Connect very different organisms, such as fishes and early bats, to explore the formation’s diverse fossils.