Necrophagy by insects in Oculudentavis and other lizard body fossils preserved in Cretaceous amber

Abstract

When a vertebrate carcass begins its decay in terrestrial environments, a succession of different necrophagous arthropod species, mainly insects, are attracted. Trophic aspects of the Mesozoic environments are of great comparative interest, to understand similarities and differences with extant counterparts. Here, we comprehensively study several exceptional Cretaceous amber pieces, in order to determine the early necrophagy by insects (flies in our case) on lizard specimens, ca. 99 Ma old. To obtain well-supported palaeoecological data from our amber assemblages, special attention has been paid in the analysis of the taphonomy, succession (stratigraphy), and content of the different amber layers, originally resin flows. In this respect, we revisited the concept of syninclusion, establishing two categories to make the palaeoecological inferences more accurate: eusyninclusions and parasyninclusions. We observe that resin acted as a “necrophagous trap”. The lack of dipteran larvae and the presence of phorid flies indicates decay was in an early stage when the process was recorded. Similar patterns to those in our Cretaceous cases have been observed in Miocene ambers and actualistic experiments using sticky traps, which also act as “necrophagous traps”; for example, we observed that flies were indicative of the early necrophagous stage, but also ants. In contrast, the absence of ants in our Late Cretaceous cases confirms the rareness of ants during the Cretaceous and suggests that early ants lacked this trophic strategy, possibly related to their sociability and recruitment foraging strategies, which developed later in the dimensions we know them today. This situation potentially made necrophagy by insects less efficient in the Mesozoic.

Extinct and extant termites reveal the fidelity of behavior fossilization in amber

“…The amber consists of multiple layers that are characteristic of successive resin flows ( 13 , 28 ), and both termites are found in the same flow layer ( Movies S1 and S2 ). Thus, these two termites are eusyninclusions ( 11 ), preserved at the same time. An opaque cloud of bubbles visually obscured the ventral posterior parts of the abdomens of the two termites.…”

“…Red imported fire ants cover sticky surfaces with soil particles to access food resources ( 38 ), and granivorous desert ants remove sticky spider webs from nestmates to rescue them ( 39 ). Scavenging insects can be attracted by large animals trapped on a sticky surface ( 11 , 35 ), and the spatial distribution of these insects may have reflected their foraging behavior. Thus, future studies on behavioral responses to sticky objects by animals will increase our understanding of fossil records in amber, as well as shed light on the behavioral capacity of extant insects.…”

“…Amber, or fossil resin, provides uniquely detailed soft-body preservation with three-dimensional (3D) features ideal for capturing snapshots of “frozen behaviors,” fossils with animals preserved in action ( 9 , 10 ). The co-occurrence of multiple individuals [i.e., syninclusions, or specifically eusyninclusions ( 11 )] is a valuable source of information for tracking behavioral interactions between extinct organisms, including predator–prey relationships ( 12 – 14 ), mating behaviors ( 14 ), and host–parasite associations ( 15 , 16 ). Nevertheless, the preservation process in tree resin is not instantaneous and induces a range of behavioral responses that interfere with the behavior performed immediately before entrapment.…”

Group mating in Cretaceous water striders

“…Among them, two pairs and a single male appear to have been preserved on the same layer at the upper surface of the amber (electronic supplementary material, figure S7), suggesting they were probably trapped simultaneously, documenting a microevent. The amber is composed of distinct layers, each potentially representing resin flows occurring at various times [ 59 ]. The additional pair, located in the lowest layer, likely documented a separate microevent, potentially occurring minutes, hours, or even days apart [ 59 ].…”

“…The amber is composed of distinct layers, each potentially representing resin flows occurring at various times [ 59 ]. The additional pair, located in the lowest layer, likely documented a separate microevent, potentially occurring minutes, hours, or even days apart [ 59 ]. However, all syninclusions present in consecutive layers might be spatially very close to each other.…”