Research topics - fossil behavior

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

Amber inclusion provides detailed and vivid records of extinct life, but the fossilization process may distort the true picture of past organisms. How can we refine the behavioral inference of fossilized animal behavior? The taphonomic experiment on living animals is the key.
We studied a 38-million-year-old piece of Baltic amber containing a pair of termites, Electrotermes affinis. Our micro-CT scanning revealed that the fossilized pair was a female and a male, seemingly a termite tandem running behavior.
However, the female and male within the amber were positioned side-by-side. This is unlike living termites, in which the leader and follower are in a single file. We hypothesized that termites struggled on the sticky surface before being completely trapped by tree resin.

In a previous study, Solórzano Kraemer et al. (2018) demonstrated that arthropod assemblages entrapped in tree resin are like those in sticky traps. Inspired by this, we investigated how sticky traps catch termite mating pairs during tandem runs.
When tandem leaders of Coptotermes formosanus entered the sticky trap and stopped free walking, most followers were also caught. Interestingly, after struggling, they often ended up in a side-by-side position like a fossilized pair.
We further estimated which partner was the leader in the fossilized pairs from body postures of trapped and untrapped living pairs using DeepLabCut (http://deeplabcut.org). We estimated that the male was the leader in 74%. Such quantification is rare in fossil studies.
This estimation is consistent with the ancestral state reconstruction of termite tandem running behavior performed in our previous study (Mizumoto et al., 2022 PNAS). It estimated that both females and males played the leader role in this fossil species.
In summary, our study demonstrated how inference of fossilized behavior can be refined by accounting for behavioral response during fossilization events. This experimental approach allowed us to quantify the uncertainty in reconstructing behavior from amber fossils.
Mizumoto et al., 2024 PNAS

Inferring collective behaviors from the fossilized fish school

Fossils can be the only direct record of past behaviors performed by extinct animals. In this study, we found evidence consistent with the interaction rules for coordinated collective motion in a fossilized group of the fish Erismatopterus levatus. By inferring the next moment of the fossilized conditions, we found the traces of two rules for social interaction: repulsion from close individuals and attraction towards neighbors at a distance. This study highlights the possibility of exploring the social communication of extinct animals, which may help the understanding of the evolution of collective behaviors.
Mizumoto et al., 2019 Proc R Soc B