Working with Baltic amber from the Eocene epoch, researchers have discovered fossilized carnivorous plant traps for the first time ever. These leaves from insect-eating flowering plants are between 35 and 47 million years old, and they likely belong to the same family as a South African flypaper trap plant. The findings were published in Proceedings of the National Academy of Sciences this week.
Fossil tree resin (or amber) is remarkably good at preserving microscopic details of small organisms; fossils enclosed in amber are oftentimes absent everywhere else. But compared to insects and other animals, plants are rarely trapped this way. The only exception are seeds from the aquatic carnivorous plant Aldrovanda, which can be found floating in multiple continents today. No carnivorous plant traps have been reported in the fossil record, yet.
Now, an international team led by Alexander Schmidt from the University of Göttingen in Germany revealed two carnivorous leaf fossils enclosed in a piece of Baltic amber that was previously extracted from a mine near Kaliningrad, Russia. They both have relevant characteristics that are similar to Roridula, an adhesive flypaper trap plant found only in the southwestern cape of South Africa. These plants have sticky, resinous trapping glue and differently-sized tentacles organized hierarchically. The longest tentacles make the first contact with the prey, which then gets stuck to the medium-sized tentacles; finally, the smallest tentacles immobilize the prey.
Modern Roridula are unique among carnivorous plants: In a complex mutualistic association, they rely on symbiotic insects to digest and derive nutrition from entrapped prey. Two resident species of “Roridula bugs" feed on the trapped animals, and the plants get their nutritional uptake through the bugs’ feces. “We didn't expect to find these leaves in the European fossil record, because Roridula is restricted to South Africa," Schmidt tells ABC Science.
The new fossil leaves are about five millimeters long and 0.2 millimeters wide at the base, and like modern Roridula species, they’re strewn with unicellular hairs and multicellular stalked glands (or tentacles) with a pore at the apex. The fossil leaves also show evidence of five different tentacle size classes, and the apex of each narrow, tapered leaf ends in a single tentacle. The team also found adhered organic remains that indicate how the plants excreted a sticky secretion just like the adhesion traps of modern carnivorous plants.
These morphological similarities suggest that the new fossils are early members of Roridulaceae. "Carnivorous plants are found in many modern plant families, each with their own way of catching prey," Schmidt adds. "This specific trap is unique to the plant in South Africa." However, this lineage was previously thought to be of Gondwanan origin -- that is, mostly in the southern hemisphere -- so it looks like the new fossils also widen the distribution of roridulid plants.