Bite marks, not body size: crocodylians ran the large-prey trade in Miocene Colombia

A paper in the Journal of Vertebrate Paleontology reports physical evidence of crocodylian predation on ungulates in the Middle Miocene of Colombia ^[1]. On the authors' reading, that makes crocodylians the most significant predator group in the habitat, ahead of the saber-toothed mammals and flightless terror birds working the same shoreline ^[2][3].

The setting deserves stating plainly, because it is what makes the result interesting. More than 10 million years ago a vast lake covered much of South America, holding giant turtles and crocodylians ^[4]. The shore supported anacondas, saber-toothed mammals, terror birds and sebecids, the terrestrial relatives of crocodylians ^[3]. The herbivore list is equally crowded: giant ground sloths, glyptodonts, and several ungulate groups including astrapotheres and toxodontids ^[7], animals that could weigh well over a tonne ^[8]. The largest predator of the period was Purussaurus neivensis, a relative of modern caimans measuring 7 metres and weighing 1,800 kilograms ^[9].

The method is the part operators should note. The work is an analysis of fossils already sitting in museum collections ^[11], and the evidence class is bite and tooth marks on herbivore bone, which the researchers describe as the only direct evidence of interactions between species ^[12]. The examined material spans 10.5 million to 16 million years ^[13], a window of 5.5 million years ^[15]. That is a slow, cheap, retrospective read on food-web structure, and it does something body-size inference cannot.

Consider what size alone would have delivered here. A 1,800-kilogram predator against prey of a tonne or more is a margin under roughly 1.8 to 1 ^[16], which is not a decisive gap, and the summary account of the study gives no body masses at all for the mammalian carnivores in the same system ^[17]. Ranking that cast by dimensions would have been an argument rather than a measurement. Damage on bone, by contrast, is an observable: something bit this animal, and the marks carry the geometry of the mouth that made them.

Oscar Wilson of the University of Helsinki, a postdoctoral researcher on the study, frames the ecological logic as one of surplus: "There was so much prey available that mammalian predators couldn't have eaten it all" ^[6]. He puts the conclusion as crocodylians being the region's most important predators, "especially when it came to hunting large prey" ^[5]. The study further suggests Purussaurus sat at the top of the chain and may have influenced the size of herbivore populations ^[10].

The hedges are in the researchers' own wording. Wilson refers to "the frequency of marks likely made by Purussaurus" ^[14], which is an attribution of probability, not an identification, and the summary account describes that frequency qualitatively without giving counts of marked specimens ^[17].

What to watch: whether the published counts in the paper are large enough to carry the word "most" ^[14], whether the same collections yield comparably frequent marks attributable to sebecids, terror birds or saber-toothed mammals ^[3], and whether anyone repeats the exercise on museum material outside Colombia ^[11]. The transferable result is procedural. If trophic rank can be read from tooth traces across a 5.5 million-year window of shelved fossils ^[13][15], other apex-predator assignments made from body size are open to the same audit.