Living Nematodes Found Inside Dinosaur Fossil Bones: A Microscopic Ecosystem Within Bone

After spending tens of millions of years buried underground and undergoing mineralization, dinosaur bones become fossil remains composed largely of inorganic minerals. Yet for microscopic organisms living in soil, a buried bone filled with pores and canals can still provide an accessible habitat. In recent years, several microscopy studies have reported nematode-like structures within fossil bones of ceratopsians, tyrannosaurids, and hadrosaurs. One study even succeeded in extracting actively moving nematodes directly from freshly excavated bones of Edmontosaurus annectens. These worms clearly did not survive from the Cretaceous to the present day. Current evidence instead suggests that dinosaur fossils can be recolonized by organisms living in modern soils.

Reconstruction of Edmontosaurus annectens（Image source：Connor Ashbridge， CC BY 4.0 ）

General morphology of a nematode（Image source： Database Center for Life Science (DBCLS)， CC BY 3.0 ）

Researchers collected bones from an Edmontosaurus annectens fossil site in the Lance Formation of Wyoming, USA. The samples included fragments of a partially exposed femur buried approximately 0–10 cm below the surface, as well as a tooth root, cranial bones, and a chevron recovered from different depths. Soil samples were also collected from the immediate vicinity. To determine whether living nematodes were actually present inside the bones, the researchers used the Baermann funnel method, a standard technique in nematology for extracting live nematodes.

Baermann funnel method（Image source：Indong RA et al. (2024)， CC BY 4.0 ）

The method takes advantage of the ability of nematodes to move through thin films of water. The bone fragments were first scrubbed with a brush, repeatedly rinsed with deionized water, enclosed in material that allowed small organisms to pass through, and then completely submerged in water. If active nematodes were present inside the bone, they could migrate out of the sample and eventually settle at the bottom of the funnel, where they could be collected. In some samples, highly active worms were recovered within just 15 minutes of immersion.

Not every dinosaur bone yielded living nematodes. No live worms were recovered from the tooth root, chevron, or cranial bone samples. Only the femur fragments located close to the ground surface produced living nematodes, with 18 individuals recovered in total. Live nematodes were also present in all of the surrounding soil samples. These observations support the idea that nematodes can enter dinosaur bones, although it remains unclear whether they establish long-term populations within the bones or only occasionally migrate into them from the surrounding soil.

The researchers had previously prepared 40 µm ground sections of bones from Edmontosaurus, Triceratops, and Nanotyrannus. Within the vascular canals, they observed numerous elongated, fusiform structures of varying sizes, which were interpreted as possible evidence for nematodes of different sizes inhabiting the bones. The highest density was recorded in Triceratops horn bone, whereas the lowest was found in Edmontosaurus jawbone.

(Image permission could not be obtained. Please refer to the original research paper for the figure.)

Why would nematodes enter fossilized dinosaur bones in the first place? One proposed explanation is that fungi growing inside the bones may provide a food source. In 40 µm ground sections of Triceratops and Edmontosaurus bones, the researchers observed hypha-like structures, some of which extended into compact bone. Suspected fungal structures and spores were also found in solutions produced during bone demineralization. Under electron microscopy, some fungal hyphae appeared to tunnel into the bone and extend toward still-recognizable osteocyte structures within the bone tissue. On this basis, the researchers proposed that living fungi are capable of colonizing these dinosaur bones.

(Image permission could not be obtained. Please refer to the original research paper for the figure.)

Many nematodes feed on fungi. Some species in genera such as Aphelenchus, Bursaphelenchus, and Ditylenchus, for example, are fungivores. However, the studies did not directly demonstrate a trophic relationship between the nematodes and fungi inhabiting the fossils. Whether these organisms actually form a food-chain relationship within dinosaur bones remains to be tested.

When paleontologists encounter microscopic filamentous or worm-like structures inside dinosaur bones, the question is therefore not limited to whether those structures originated while the dinosaur was still alive. Another biological history, operating on an entirely different timescale, must also be considered: tens of millions of years later, new organisms may have entered and occupied the spaces preserved within these ancient bones.

Author: Shui-Ye You

References:

1. Indong RA et al. (2024). A simple protocol for cultivating the bacterivorous soil nematode Caenorhabditis elegans in its natural ecology in the laboratory. Front. Microbiol.

2. Peterson K et al. (2025). Inorganic Cretaceous Dinosaur Remains are Colonized by Specialized Communities of Fungi that Thrive within Bones and Support Fungivore Nematodes. Microscopy and Microanalysis.

3. Peterson K et al. (2026). Duck-Billed Nematodes: What Microscopy Reveals about Dead Dinosaurs. Microscopy Today.