Osteoglossiformes

Lore & Background

Osteoglossiformes first evolved in Gondwana before that continent broke up, which explains their current distribution across South America, Africa, Australia, and southern Asia. In 2008, several new species of marine osteoglossiforms were described from the Danish Eocene Fur Formation, dramatically increasing the diversity of this group and implying that Osteoglossomorpha is not a primary freshwater fish group with a typical Gondwana distribution.

Reader's Guide

The order Osteoglossiformes is significant for its primitive status among ray-finned fish and its unique anatomical features, such as toothed or bony tongues and a gastrointestinal tract that passes to the left of the esophagus and stomach, unlike all other fish where it passes to the right. Members vary greatly in size, from the tiny Pollimyrus castelnaui at 2 cm to the massive arapaima (Arapaima gigas) reaching 2.5 m. The families Gymnarchidae and Mormyridae are weakly electric fish that sense prey using electric fields. The mooneyes (Hiodontidae) are often classified here but may also be placed in a separate order, Hiodontiformes. The discovery of marine fossils from the Danish Eocene Fur Formation in 2008 challenged the view that osteoglossiforms are exclusively freshwater, suggesting a broader evolutionary history.

Did You Know?

• The name Osteoglossiformes means 'bony tongues' in Ancient Greek.
• All at least 245 living species inhabit freshwater.
• The smallest species is Pollimyrus castelnaui at 2 cm; the largest is Arapaima gigas at 2.5 m.
• Gymnarchidae and Mormyridae are weakly electric fish that sense prey using electric fields.