Pack hunting in theropods is debated science — we have circumstantial evidence but no smoking gun. Paleontologists have found intriguing traces: multiple skeletons at kill sites, trackways showing coordinated movement, and bite marks suggesting organized predation. But absence of evidence is not evidence of absence, and we must be careful about projecting modern animal behavior onto extinct species.
The Evidence Stack
- Multiple skeletons at single sites — Sites like the Yixian Formation in China and various western US locations show multiple theropod individuals (often similar size, suggesting similar age/cohort) preserved near herbivore remains. Deinonychus at the Cloverly Formation shows 3-4 individuals around an Iguanodon carcass. This hints at coordinated feeding, though scavenging or coincidental death cannot be ruled out.
- Trackways showing parallel movement — Some fossil trackways show multiple theropods moving in roughly the same direction at similar speeds. Interpretation: coordinated hunting. Counter: they could be following the same food source independently, or the tracks could have been made at different times.
- Bite-mark patterns — Some herbivore fossils (Psittacosaurus, Protoceratops) show multiple bite marks from different-sized teeth, suggesting multiple attackers. This is suggestive but not definitive — scavenging by different animals over time produces similar patterns.
- Brain size and intelligence — Deinonychus and Velociraptor had relatively large brains for their size (high encephalization quotient). Modern pack hunters (wolves, orcas, lions) are intelligent. Larger brains enabled coordination, but do not prove it happened.
- Weapon specialization — Deinonychus had that famous sickle claw, which some argue was a coordinated hunting weapon (one animal slashing while others wrestled prey). Alternatively, it was a climbing claw or display structure.
The Honest Assessment
The strongest case comes from Deinonychus. Yale paleontologist John Ostrom's 1969 interpretation of the Cloverly site made pack hunting famous. But later analysis by Philip Currie and others shows the site is complex — bones are jumbled, dating is uncertain, and it is hard to know if all skeletons died at once or over years. More recent work suggests Tyrannosaurus was likely solitary (based on fossil site frequency and bite-mark spacing on prey), though juveniles may have been more social.
The problem with fossil evidence: we see endpoints (skeletons, tracks, bite marks) but not behavior. A lion pride and a hyena clan both leave multiple predators at kills, but their hunting tactics differ entirely. We infer behavior from bones, and inference is not certainty.
Pro tip: When reading dinosaur papers, look for the phrase 'consistent with' rather than 'evidence for' — that is the mark of honest paleontology. A fossil trackway is 'consistent with pack behavior' but does not prove it. The field has matured past the 1990s certainty that Velociraptors hunted like wolves.