Aggressive tumor found on 150-million-year-old leg bone of young Jurassic giant (2025)

New evidence adds to a 2020 finding that dinosaurs had bone tumors and other conditions seen in modern-day vertebrates.

In 2014, researchers discovered a 150-million-year-old ulna of a mamenchisaurid in northeastern Thailand with unusual characteristics. They’ve now honed in on some possible explanations, according to an April 24 study published in the Journal of Anatomy.

The forelimb, with a “bulge” of abnormal bone growth near the shaft, belonged to a “subadult” that had completed its most rapid growth phase but was still growing, according to researchers.

Diagnostic imaging determined that in life, the young mamenchisaurid suffered from an osteogenic tumor, or a tumor that originates in bone-forming cells.

This is the first report of an osteogenic tumor in an early Eusauropod, the taxonomic group to which mamenchisauridae belong, according to the study.

Researchers said based on the tumor’s size, location and connection to muscles that controlled the movement of the dinosaur’s toes and elbow, it is “highly likely” the young dinosaur experienced “severe discomfort” and reduced function of its forelimb.

Researchers could not make a definitive diagnosis, including whether the tumor was malignant or benign, because it shared characteristics with many other tumors, including osteoblastoma and osteosarcoma, according to the study.

The tumor had aggressive features, including evidence of reactive bone growth, and non-aggressive characteristics, such as well-defined borders, according to researchers.

The ulna was discovered in Kalasin province in northeastern Thailand.

The research team includes Siripat Kaikaew, Suravech Suteethorn and Anusuya Chinsamy.

First malignant dinosaur bone tumor discovered in 2020

Scientists only recently confirmed that dinosaurs had malignant bone cancer after finding osteosarcoma — a cancer associated with rapid bone development — in the leg bone of a Centrosaurus apertus, according to a 2020 study published in the journal The Lancet Oncology.

Researchers said dinosaurs likely had many of the same cancers seen in vertebrates today, particularly those impacting the bones, given many dinosaur species’ enormous size and accelerated growth rates, NPR reported.

More about mamenchisauridae

Mamenchisauridae, which roamed the Earth during the late Jurassic period alongside the stegosaurus and the brachiosaurus, were sauropods — the largest dinosaurs to ever exist.

According to researchers, mamenchisauridae “have the distinction of being the sauropods with the longest necks.”

A mamenchisauridae species discovered in China in 2023 has a neck nearly 50 feet long.