A new 2026 study reports evidence of scavenging among tyrannosaurids in Montana’s Judith River Formation: tooth marks on a metatarsal suggest a smaller tyrannosaurid fed on the carcass of a much larger relative, highlighting size‑asymmetric feeding behavior.
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| Artistic reconstruction of juvenile and adult tyrannosaurids feeding on a larger carcass, illustrating size‑asymmetric scavenging behavior. Image composition © Artifacts. |
🦖 Key Findings from the Study
- Specimen: BDM 124, a partial left metatarsal II from the Judith River Formation (Campanian age, ~75 million years ago).
- Marks: 16 distinct tooth marks identified using high‑resolution 3D surface scanning and the Category‑Modifier (CM) classification system.
- Producers: The small size and spacing of the marks indicate they were made by a juvenile or small tyrannosaurid.
- Behavior: Evidence points to scavenging late in carcass consumption, not active predation.
- Implication: Suggests size‑asymmetric feeding, where smaller tyrannosaurids exploited carcasses of larger conspecifics or closely related taxa. Directory of Open Access Journals
📊 Context and Significance
| Aspect | Details |
|---|---|
| Formation | Judith River Formation, Montana, USA – rich fossil assemblage of tyrannosaurids |
| Dating | Campanian stage of the Late Cretaceous (~75 Ma) |
| Methodology | 3D scanning, morphometric analysis, NMDS (Non‑metric Multidimensional Scaling) |
| Interpretation | Tooth marks consistent with scavenging, not combat |
| Ecological Insight | Adds evidence for intraspecific interactions and possible cannibalism among tyrannosaurids |
🔍 Why It Matters
- Trophic dynamics: This is one of the clearest fossil records showing different size classes of tyrannosaurids interacting via feeding, expanding our understanding of their ecological roles.
- Cannibalism debate: While cannibalism in tyrannosaurids has been suggested before, this study strengthens the case by showing smaller individuals feeding on larger carcasses.
- Methodological advance: The use of systematic tooth mark classification and quantitative analysis provides a replicable framework for future paleoecological studies.
⚠️ Limitations & Considerations
- Single specimen: Evidence comes from one metatarsal, so broader ecological conclusions remain tentative.
- Scavenging vs. predation: Marks indicate late‑stage carcass consumption, but cannot fully rule out opportunistic feeding during life.
- Comparative data: More specimens across formations are needed to confirm whether this behavior was widespread.
🌍 Broader Paleontological Context
- Similar evidence of cannibalism has been documented in Majungatholus (Madagascar) and debated in Tyrannosaurus rex.
- This Montana find adds to the growing dataset suggesting complex feeding strategies among theropods, including intraspecific competition and opportunism. scilit.com
✅ In short: The Judith River Formation metatarsal shows that smaller tyrannosaurids scavenged on larger relatives, offering rare fossil evidence of size‑asymmetric feeding and enriching our picture of Late Cretaceous predator ecology.
Source: ScienceDirect – Investigating size‑asymmetric feeding among tyrannosaurids using tooth marks on a metatarsal from the Judith River Formation, Montana, USA https://www.sciencedirect.com/science/article/pii/S2950117226000038
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