Dinosaurs broke ribs, developed bone infections, wore down joints and grew tumours. Some survived severe bites long enough for damaged tissue to remodel. These fossils can reveal part of one animal's biography, but they demand strict diagnosis: a swelling may be a healed fracture, infection, tumour, developmental variation or deformation caused after burial.
Palaeopathology studies disease, injury and abnormal development in organisms of the past. It usually lacks soft tissues, blood tests and a clinical history. Researchers instead combine surface form, internal bone structure, lesion position and comparison with close living and extinct relatives.
What separates the main possibilities?
A callus, rounded edges and continuous remodelled cortex show that tissue repaired after injury. They prove survival, not the exact accident or social care.
Irregular new bone, cavities and drainage channels can support osteomyelitis. A specific bacterium or fungus is rarely recoverable.
CT and histology test whether abnormal tissue invades and destroys normal cortex. Benign and malignant growths can resemble trauma externally.
Erosion and reactive growth on bones that met at one joint can support arthritis. Pain and degree of lost movement remain inferred.
Late cracks cut already formed tissue, while sediment pressure may deform several neighbouring bones in the same direction. Context is essential.
What counts as pathology?
A pathology is an abnormality produced during life: fracture, inflammatory reaction, developmental disorder, joint destruction or neoplasm. The clearest sign is the body's response. Bone grows around an injury, smooths an edge, remodels internal trabeculae or forms a channel through which inflammatory material drained.
Damage near death may show no healing. Its timing then depends on fracture geometry, crushing and edge condition. After death, bone also breaks, dissolves, is compressed by sediment and is damaged by roots or insects. These pseudopathologies must be eliminated before a medical interpretation is offered, just as preservation must be understood when explaining how fossils form.
Healing versus a later break
Fresh biological bone and mineralised fossil bone fracture differently. A wound during life can distort an element and produce a callus. A late crack crosses finished tissue without repair. Absence of a callus does not automatically mean post-mortem damage because the animal may have died immediately.
Researchers compare colour and texture across the break, follow the cortex on CT and ask whether neighbouring bones share one deformation direction. Local trauma has its own centre; geological pressure commonly affects several elements together.
Fractures and survival
Trauma is the most conspicuous part of the dinosaur pathology record. Theropods preserve healed ribs and injuries to feet, tails and facial bones. Herbivores show damaged limbs, ribs, tails, armour and spikes. A fall, collision, overload, bite or blow from another animal may be plausible, but callus shape seldom records one unique event.
The nearly complete juvenile Tenontosaurus OMNH 58340 has several injuries, including compressed ribs and large calluses, some associated with infection. Their distribution led researchers to propose a major fall. The general event is a supported reconstruction, not a preserved scene.
Healing proves only that the animal lived long enough to deposit repair tissue. It does not yield an exact number of days or prove that herd members supplied food.
Bites before and after death
Teeth leave punctures, scores, chips and aligned dents. Healing places contact during life. An unhealed mark could come from an attack, a fatal bite or feeding after death, so a bite alone seldom distinguishes hunting from scavenging.
One Daspletosaurus skull and jaw carry multiple injuries at different stages. Healed punctures fit bites from other tyrannosaurids, probably during encounters between individuals, while separate post-mortem marks record feeding on the carcass. Facial bites are more common in larger, mature tyrannosaurids, supporting repeated contact between conspecifics without revealing whether food, territory or mating prompted each conflict.
Bone infection
Osteomyelitis is inflammation of bone and marrow, commonly associated with infection entering through a wound, damaged tooth or bloodstream. Fossils may combine rough external growth, internal destruction, cavities and channels. No one feature is unique, so fracture and tumour remain alternatives.
CT examination of Tyrannosaurus rex specimen FMNH PR 2081, “Sue”, supported chronic osteomyelitis in the left fibula and two fused tail vertebrae. A Tenontosaurus hand bone contains a cavity comparable to a Brodie abscess. Both interpretations depend on internal and external architecture rather than roughness alone.
A juvenile diplodocoid nicknamed Dolly has abnormal growths where cervical vertebrae connect with air sacs. The most economical diagnosis is respiratory infection, probably airsacculitis spreading to bone. The fossil cannot identify the microorganism.
Tumours and cancer
A tumour is abnormal tissue growth; cancer is a malignant tumour that invades surrounding structures. Most soft-tissue tumours leave no skeletal trace, so the fossil sample is strongly biased towards bone lesions.
The best-tested malignant case in a non-avian dinosaur occurs in the fibula of Centrosaurus apertus TMP 1989.018.0108. Once considered a fracture callus, it was re-examined with radiography, micro-CT, thin sections and comparison with normal centrosaur bone and human osteosarcoma. Cortical destruction, disorganised new tissue and invasive growth supported osteosarcoma.
An expanded jaw region in juvenile Telmatosaurus transsylvanicus was diagnosed as an ameloblastoma, normally a benign tumour associated with tooth development. A survey of more than 10,000 dinosaur vertebrae found tumour-like lesions only among sampled Cretaceous hadrosaurs, but collection and preservation bias prevent a claim that other dinosaurs were protected.
Joints, spine and chronic wear
Joint surfaces may show bony growth, erosion, fusion and sclerosis. Patterns across the accessible skeleton are needed to distinguish osteoarthritis, septic arthritis, old trauma and normal variation. In a New Jersey hadrosaur, destructive and reactive changes affected both bones of an elbow, supporting septic arthritis rather than an isolated lump.
A badly healed limb redistributes load and can alter neighbouring joints. These secondary changes reveal prolonged mechanical compensation, but they do not show the animal's gait directly.
Injuries as behavioural evidence
Repeated distribution can be more informative than one spectacular lesion. About 22 per cent of examined adult pachycephalosaurid domes carried lesions concentrated near the top, a pattern compatible with head-to-head impacts. Infection may have followed trauma.
Healed damage to the armour of the ankylosaur Zuul clusters along the flanks near the pelvis. That placement fits lateral blows from another tail-clubbed ankylosaur better than randomly distributed predator attacks. Location, repetition and healing support the hypothesis, while the actual encounter remains unobserved.
A changing diagnosis in tyrannosaur jaws
Large rounded holes in the rear lower jaws of several tyrannosaurids illustrate scientific revision. A 2009 study compared them with lesions in living birds and proposed a trichomonosis-like infection. A 2022 analysis found no characteristic inflammatory response and considered healed trauma, perhaps bites, more likely.
Both studies examine real lesions but disagree about cause. Until a diagnostic microscopic sign or pathogen is found, the aetiology remains disputed.
How a fossil diagnosis is made
- Measure and photograph the lesion and compare it with normal anatomy.
- Compare the matching bone, other individuals and close relatives.
- Use radiography and CT to map density, cavities, channels and fracture lines.
- Use histology when justified to examine tissue growth and invasion.
- Test trauma, infection, tumour, developmental variation and burial damage as alternatives.
Histology is powerful but removes a sample from a rare fossil. Chemical tests can separate bone from sediment, although fossilisation changes original composition. Living birds and crocodilians constrain possible tissue responses but are not exact medical copies of a non-avian dinosaur.
What the bone can and cannot reveal
Healing demonstrates survival. Repeated injuries in one anatomical region can support behaviour. Linked lesions may reveal the path of an infection, while joint remodelling records long-term load. These conclusions apply to the individual and observed structures.
Bone almost never supplies the intensity of pain, exact pathogen, duration of illness, cause of death or social assistance. A severe lesion may have been chronic but survivable, while a small wound could kill too quickly to leave healing. Growth and repair are also related, making bone histology and dinosaur growth essential context.
Frequently asked questions
How can scientists tell that a dinosaur was injured while alive?
The strongest sign is a biological response such as a callus, rounded edges, remodelled internal tissue or inflammatory bone growth. Without healing, fracture pattern and geological context help, but timing is less certain.
Did dinosaurs get cancer?
Yes. Osteosarcoma has been diagnosed in a Centrosaurus bone using CT, histology and comparative samples. Benign tumours are also known, but rare fossils cannot reveal cancer frequency across all dinosaurs.
Does a healed fracture prove that a herd cared for an injured dinosaur?
No. It proves survival long enough for bone to repair. The animal may have fed itself, while social assistance would require independent evidence.
Can one fossil bone identify the exact infection?
A lesion may support a process such as chronic osteomyelitis, but normally cannot identify the microorganism. CT, histology, the distribution of lesions and exclusion of tumours or burial damage improve confidence.
Palaeopathology is most reliable when several methods agree and the diagnosis retains alternatives. It can reconstruct the boundaries of an individual life, not issue a complete medical record for an entire species.