A strange fossil from the Bromacker fossil site in Germany has provided scientists with rare evidence of the relationship between predator and prey in terrestrial ecosystems about 290 million years ago. The specimen, designated MNG 17001, initially appeared to be just some densely packed light-colored bone fragments in sandstone, but paleontologists soon realized that it was actually a ball of "vomit" that was spit out by ancient predators and eventually petrified.
The research team discovered the fossil in Bromack in 2021, which dates to the early Permian period. The specimen is an irregular three-dimensional mass, approximately 5 cm long, 3 cm wide, and 1.4 cm thick, with internal bone fragments compacted together. To avoid damaging the sample, the researchers used micro-CT scans to digitally segment and reconstruct the internal structure of the mass.
The results showed that the clump of fossils contained at least 41 small bones, all less than 20 millimeters in length, from at least three different animals. With the help of rich excavation data in the Bromark area over the past 30 years, the research team compared and identified these bone fragments with known fossils.
Among the identifiable species, a portion of the skeleton belongs to the small reptile Thuringothyris mahlendorffae; another upper arm bone comes from Eudibamus cursoris, a reptile that is “iconic” in the area because of its ability to walk on two legs. The third larger bone was identified as the limb bone of some kind of diadectid. It is estimated that the individual body was about 60 centimeters long and relatively stout.
Because the bones were so densely packed together, the researchers concluded that they were the result of a predator that had eaten and partially digested at least three different prey species, then regurgitated and vomited the undigested bones together. However, similar bone aggregations could also be the result of fossilized feces, known as coprolites, so the team needed to further distinguish whether these were coprolites or regurgitalites.
To this end, the researchers performed X-ray fluorescence analysis of the matrix surrounding the specimen. In the case of coprolites, the matrix is usually enriched with phosphorus due to intestinal microbial activity; however, the analysis showed no significant increase in phosphorus concentration around the bones. This is consistent with the fact that the vomitus remains in the digestive system for a short time and does not form significant phosphorus enrichment, thus supporting the interpretation of "vomit fossils". Research suggests that this is the earliest known evidence of vomiting in a terrestrial vertebrate.
Judging from the differences in the size of the regurgitated prey, it is clear that the predators that dominated this feeding event were "opportunistic" feeders - they were not picky eaters and ate whatever they could catch. Such findings can help reconstruct the structure of food webs between predators and a variety of small prey in ancient ecosystems. William Freimuth, a scholar at North Carolina State University who was not involved in the study, pointed out that in such an important early Permian terrestrial ecosystem as Bromac, such vomit fossils are one of the key nodes in understanding the structure of the food web.
Such vomit fossils and coprolites are considered "time capsules" by researchers: they seal the remains of multiple species in the same mass, directly proving that these animals coexisted in the same place at the same time and were connected to each other through predatory relationships. As for which predator spit out the skeleton, the study suggests two possible candidates for the apex predator - Dimetrodon teutonis and Tambacarnifex unguifalcatus, both of which are synapsids, ancient ancestors of mammals.
The researchers emphasized that although vomit fossils are relatively rare in the fossil record, their paleoecological significance is quite significant. This latest study on MNG 17001, published in the journal Scientific Reports, provides new direct evidence for the predatory structure and animal behavior of early Permian terrestrial ecosystems.