Fossilized ecological interactions

Who could forget the famous “fish-in-a-fish” fossil of the Portheus that died right after eating an Ichthyodectes? (Of course, taxonomy being far from fossilized, it is now considered to be a Xiphactinus that died right after eating a Gillicus. Oh, well)

By James St. John - Xiphactinus sp. with Gillicus sp. in its stomach (fossil fishes) (Niobrara Formation, Upper Cretaceous; Gove County, Kansas, USA) 2, CC BY 2.0,

It may be rare to find an ecological interaction fossilized, but when such finds are made, they would seem to be in some ways more valuable than a perfect, single specimen – they tell us something definite about paleoecology, without us having to surmise it from preserved anatomy.

I am fortunate that I currently reside just blocks (in two directions!) from Green Mill Run, an internationally known fossil site. My web search just now for “green mill run fossils” turned up a plethora of trip reports and other articles, including one in Dutch. Of course, shark teeth are the big draw, but the creek bed is full of all sorts of marine fossils. Today, I came upon this one – the first (and will probably be the only) fossil I uploaded to iNat:

Image description: a fossil Exogyra shell with numerous sponge-like holes. End image description.

I uploaded this because although Exogyra is an oyster, it has a spiral shell which at first glance would be taken for a gastropod shell. It looks a bit like an abalone without the row of holes. It is the fifth Exogyra observation on iNat – there are three others from the Southeastern Coastal Plain of the United States and one from South Africa. However, it is the first Exogyra observation on iNat which shows parasitization by boring sponge (Clionaidae, if the Cretaceous ones were in the same family as extant ones). This excited me so much, I added the observation field:

Image description: A screenshot from showing the lower right corner of an observation page. It reads, "Observation fields (2). Fossil: yes. Interaction->Parasitized by: Boring Sponges (Family Clionaidae). Top Identifiers of Exogyra: None found. End image description.

So for all you paleonaturalists out there, what fossilized ecological interactions have you found?


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