A hospital CT scanner traces an Iguanodon's shin swelling to a sore in the skin above it
The lesion stops short of the marrow cavity, and that is what sends the Spanish team's diagnosis outward into soft tissue rather than inward to a fracture or a tumour, though the bacteria themselves are inferred from modern ulcers.
The Scientist · Science desk
What happened
- Researchers in Spain working on two Early Cretaceous Iguanodon bernissartensis carcasses from the Mas de la Parreta quarry in Morella, eastern Spain, found an odd swelling on one shinbone.
- The overgrowth runs 17.4 centimetres along the middle of the shaft and covers about 17 percent of the bone's total length.
- They took the bone to a hospital scanner and built 3D digital models of its interior, which showed the lesion sitting on the outside of the shaft and not reaching the central marrow cavity.
- Checked against catalogued fractures, tumours and bone diseases the images matched nothing, while they did fit the reaction bone shows when an open skin sore lies directly on top of it.
- The authors' published diagnosis, in Royal Society Open Science, is an infected skin ulcer that inflamed and thickened the tissue and bone beneath it.
Why it matters
- What's now possible capability Disease in skin that never fossilised can now be argued from the shape of the bone underneath it, which opens a class of soft-tissue diagnoses that fossil surfaces were not previously read for.
- What it limits constraint Because the diagnosis is reached by elimination and the polymicrobial label comes from how modern ulcers behave, the central claim cannot be tested against the specimen itself.
- Who has to decide decision Collections managers now have a reason to spend hospital scanner time on long bones filed under unexplained swelling, in a record where trauma has absorbed most of the attention.
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Confinement to the outer shell is the load-bearing observation here, because it points the search away from the bone. The scans describe a low thickening and moderate expansion of the cortical bone, the dense outer casing of a long bone [7], and the authors read a lesion that never reaches the marrow space as one that began in the tissue lying over the bone [8]. The mechanism they invoke is specific: when an infected skin ulcer works down to the tissue covering the bone, it can set off inflammation and new bone formation at the surface [15].
The exclusions came from the same images. No pattern of fracture or bone bruising appeared, and neither did the reparative phase that follows those injuries [9]. Nothing indicated a malignant tumour, which took neoplasia off the list [10]. On scale, the reported 17.4 cm overgrowth spanning about 17 percent of the shaft implies a tibia of roughly 102 cm [20], and the patch is about 11.7 cm across at its widest [19] on that metre of bone.
The word carrying the most weight is in the paper's title, which reports a first occurrence of polymicrobial ulcer in dinosaurs [1]. That word is the one the specimen cannot supply. In living patients, tropical ulcer infection is typically polymicrobial, involving a variety of microorganisms [14], and a tropical ulcer is defined clinically as a painful, rapidly enlarging sore that usually appears on a lower limb in hot, humid conditions [16]. Europe in the Early Cretaceous was warm and humid, subtropical to warm-temperate, which the authors note suited such ulcers [17]. That is a chain of analogy and setting rather than a recovered pathogen, which is why the body of the paper is more guarded than its title: the claim as written is that this is, to the authors' knowledge, the first report of this type of pathological response to a bacterial infection in a dinosaur [13].
The denominator is one. The swelling turned up on a single shinbone from one of two carcasses recovered at the quarry [3], so the study says nothing about how often Iguanodon carried open sores, or how long this one lasted. It is also worth knowing what the surrounding literature looks like: fractures and trauma dominate the recorded pathologies of non-avian dinosaurs, according to a 2020 study in Scientific Reports [22], and firsts in this field arrive with tools and attention as much as with new disease. The first dinosaur osteosarcoma was only named in 2020, in the fibula of a Centrosaurus that lived about 76 million years ago [18].
What the work does buy is a template. A surface reaction with a healthy marrow cavity beneath it is now a described signature that points to skin, and that is a route into disease of tissue that does not fossilise. On consequence for the animal, the authors stay narrow: the progression of ulceration towards the periosteum "may have caused persistent pain, which was aggravated by normal walking and muscle pressure" [21].
What to watch
- Whether other long bones already in museum drawers, logged as unexplained surface overgrowth, get rescored against this skin-sore signature.
- Whether any geochemical or microstructural work can place actual organisms at the lesion instead of inferring them from modern tropical ulcers.
- Whether the second Iguanodon bernissartensis carcass from the same Morella quarry shows related lesions.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence58
- Adoption
- Not scored
- Hype gap+14
- Incentives45
- Confidence66
Claim ledger
Ranked by verification strength, evidence, and original report placement.
- [1]
The study is Javier Salas-Herrera et al, "First occurrence of polymicrobial ulcer in dinosaurs", published in Royal Society Open Science (2026), DOI 10.1098/rsos.261293.
- [2]
Researchers in Spain were working on two fossil carcasses of Iguanodon bernissartensis from the Early Cretaceous, discovered at the Mas de la Parreta quarry in Morella, eastern Spain.
- [3]
The team came across the strange swelling on the shinbone of one of the two sets of remains.
- [4]
The swelling is a 17.4-centimetre (6.9-inch) bone overgrowth along the middle of the shinbone, covering about 17% of its length.
- [5]
The swelling measured around 6.9 inches in length and 4.6 inches in width.
- [6]
The researchers scanned the bone with a hospital scanner to create 3D digital models revealing its inner structure.
- [7]
The digital models showed the bone growth was characterised by a low thickening and moderate expansion of the cortical bone, the dense outer shell of long bones.
- [8]
The lesion did not extend into the bone's central medullary cavity, indicating the problem likely originated in the overlying soft tissue.
- [9]
There was no indication the growth was triggered by bone fracture or bone bruises, and no signs of the reparative phase of bone healing seen with those types of injuries.
- [10]
The researchers ruled out neoplasia, as there was no evidence of malignant tumours.
- [11]
The team compared the CT images with known signs of fractures, tumours and bone diseases and found no similar patterns; instead the swelling matched how bone reacts when an open skin sore sits directly above it.
- [12]
The study authors suggest the overgrowth may have been caused by an infected skin ulcer that triggered inflammation and thickening in the tissue and bone beneath it.
- [13]
The researchers say: "This is, to our knowledge, the first report of this type of pathological response to a bacterial infection in a dinosaur."
- [14]
Infection of tropical ulcers is typically polymicrobial, caused by a variety of microorganisms, and the researchers say polymicrobial infections have not been observed in dinosaurs before.
- [15]
When an infected skin ulcer spreads down to the tissue covering the bone, it can trigger inflammation and new bone formation at the bone's surface.
- [16]
A tropical ulcer is a painful, rapidly enlarging sore that often appears on the lower limb of an individual living in a hot, humid tropical region, according to DermNet.
- [17]
The Iguanodon studied would have lived in Europe at a time when the climate was warm, humid subtropical to warm-temperate, a favourable environment for tropical ulcers to proliferate.
- [18]
In 2020 researchers identified an aggressive bone cancer (osteosarcoma) in a dinosaur for the first time, a malignant tumour in the fibula of a Centrosaurus that lived roughly 76 million years ago.
- [19]
The reported 4.6-inch width of the swelling is about 11.7 centimetres.
- [20]
A 17.4-centimetre overgrowth covering about 17% of the shaft implies a tibia roughly 102 centimetres long.
- [21]
The paper states: "The progression of ulceration towards the periosteum of the bone may have caused persistent pain, which was aggravated by normal walking and muscle pressure."
- [22]
According to a 2020 study published in Scientific Reports, the most common pathological conditions among all non-avian dinosaur species are fractures and trauma.
Sources
2 independent publishers whose own reporting we read for this story.
- discovermagazine.comSwelling on an Iguanodon Shinbone May Reveal the First Known Infected Ulcer in a Dinosaur
1 article · September 3, 2026
- phys.orgIguanodon shinbone growth may be first evidence of an infected skin ulcer in a dinosaur
1 article · September 2, 2026
Topics and entities
Topics
- CT Imaging of Fossils
- Infection in Deep Time
- Dinosaur Disease and Injury
Entities
- Javier Salas-Herrera
- Royal Society Open Science
- Iguanodon bernissartensis
- Scientific Reports
- Mas de la Parreta quarry