Carnivores in Amber

Carnivorous leaves from Eocene Baltic amber. (A) Overview of the leaf enclosed in amber showing the adaxial tentacle-free side in slightly oblique view and stalked glands at the margin and on the abaxial side; arrowhead points to the exceptional long tentacle stalk with several branched oak trichomes attached. (B) Overview of the leaf enclosed in amber, showing abundant tentacles on the abaxial side. (C) Margin of abaxial leaf surface with tentacles of different size classes and nonglandular trichomes [SOURCE]

Carnivorous plants are marvels of evolution. Adapting to nutrient poor conditions, these botanical curiosities have evolved myriad ways of capturing and digesting prey. For all of their extant diversity, the fossil record of carnivorous plants over the eons is pretty much non existent save for some highly contentious fossils from China as well as some fossilized seeds of the aquatic carnivore, Aldrovanda. However, a recent discovery out of Russia changes everything. Beautifully preserved in amber, we now have the first conclusive fossil evidence of a carnivorous plant.

The amber was found in a mine in Russia and is estimated to be between 35 and 47 million years old, during an epoch known as the Eocene. Inside are beautifully preserved leaves of what seems to be a species of Roridula. The leaves clearly show specialized stalked glands with a pore at the tip. The researchers who discovered the amber also found evidence of the sticky secretions that were used to capture its prey.

Overviews showing the tentacle-free adaxial surface and tentacles along the leaf margins (B & C). (D) Partial leaf tip showing different size classes of stalked glands. [SOURCE]

The resemblance of these leaves to the leaves of extant Roridula is uncanny. Modern Roridula do not directly digest their prey. Instead, they rely on a symbiotic relationship between a species of bug, which lives on the leaves without getting stuck. The bugs hunt down and eat trapped insects. As they eat, the bugs defecate and it is their nitrogen-rich feces that the plants absorb for sustenance. It is quite possible that the fossilized Roridula also relied on these insects as well, though no direct evidence of this was found. 

The most interesting aspect of this discovery is its location. Today, Roridula is found only in South Africa. Its presence in Russia hints at a historic distribution that is much wider than previously thought. It has long been assumed that Roridula is a neoendemic to South Africa, with the family having arisen there and nowhere else. This discovery now shows Roridula to be a paleoendemic, once having a much wider distribution but currently restricted to South Africa. This discovery is an excitingly huge step in our understanding of carnivorous plant evolution. 

Morphological comparison of the carnivorous leaf fossils from Baltic amber (Left) and extant Roridula species (Right). (A and B) Leaf tip ending in a sole tentacle. (C and D) Stalked glands of different size classes. (E and F) Hyaline unicellular nonglandular trichomes. (G and H) Epidermal cells and stomata. (I–L) Multicellulartentacles. (A, C, E, and G) (I and J). (B, D, K, and L) R. gorgonias. [SOURCE]

Photo Credit: Alexander R. Schmidt, University of Göttingen

Further Reading: [1]