Pollen-feeding in a giant pelobatid tadpole from the late Oligocene of Enspel, Germany

Abstract

We examined the gut contents of a fossil giant pelobatid tadpole from the late Oligocene of Enspel, Germany, and discovered that it contains mainly pollen from spruce (Picea) but also pollen from pine (Pinus), beech (Fagus), and elm (Ulmus). Pollen in the gut of the fossil tadpole and other plant fossil records from this locality suggest that the regional vegetation around Enspel was characterised by mixed conifer and broadleaved forests with a prominent deciduous angiosperm component. Palaeoclimatic estimations indicate that the area endured a fully humid warm temperate climate with a hot to warm summer and a distinct temperature difference between seasons. The pollination period of potential modern analogues of the plant taxa discovered in the gut of the fossil tadpole hints that it was feeding on pollen floating on the water surface of the ancient Enspel Lake during late spring or earliest summer. Comparable analyses from the guts of extant pelobatid tadpoles have shown a broad spectrum of food remains, including whole/or parts of algae, protists, protozoans, macrophytes, rotifers, crustaceans, and pollen. It seems that living pelobatid tadpoles are indiscriminate and opportunistic feeders able to adapt and change their feeding behaviour according to the available food source. The time of origin and evolution of pollen feeding in tadpoles is obscure. Our discovery indicates that pelobatid tadpoles were already feeding on pollen in the late Oligocene, and the amount and purity of pollen filling the gut suggests intentional surface feeding.