A recent paper in Palaeobiodiversity and Palaeoenvironments Smith and Scanferla (2016) report a fossil snake from the middle Eocene (48 million years ago) Messel Pit, in whose stomach is a lizard, in whose stomach is an insect. This is the second report of a vertebrate fossil containing direct evidence of three trophic levels. The snake is identified as a juvenile of Palaeopython fischeri on the basis of new characters of the skull; the lizard is identified as Geiseltaliellus maarius, a stem-basilisk; and the insect, despite preserved structural colouration, could not be identified. The lizard, G. maariusis is thought to have been an arboreal species, but like its extant relatives may have foraged occasionally on the ground. Another, larger specimen of G. maarius preserves plant remains in the digestive tract, suggesting that omnivory in this species may have been common in larger individuals, as in extant Basiliscus and Polychrus. A general picture of the trophic ecology of P. fischeri is not yet possible, although the presence of a lizard in the stomach of a juvenile individual suggests that this snake could have undergone a dietary shift, as in many extant boines.
Smith KT, Scanferla A. Fossil snake preserving three trophic levels and evidence for an ontogenetic dietary shift. Palaeobiodiversity and Palaeoenvironments. 2016:1-1.