Barsboldia: the hadrosaur with an unusually high back

Barsboldia sicinskii is a large hadrosaurid from the Nemegt Formation of Mongolia. It is recognised by a partial skeleton whose vertebrae carry unusually tall neural spines, especially across the sacrum and the front of the tail. No skull is known. As a result, the fossil cannot tell us whether this dinosaur had a hollow head crest, and it leaves several aspects of its classification less certain than they are in hadrosaurids with complete skulls.

Quick facts

From an expedition find to a new genus

A Polish–Mongolian palaeontological expedition found the skeleton in 1970 at North Sayr, within the Nemegt locality. The bones came from sandy deposits of the Nemegt Formation. They were initially identified as Saurolophus angustirostris, a well-known hadrosaur from the same region.

Teresa Maryańska and Halszka Osmólska reconsidered the specimen while studying Saurolophus. Its tall vertebral spines and the construction of the sacrum differed from the material assigned to that genus. In 1981, they named Barsboldia sicinskii. The genus honours Mongolian palaeontologist Rinchen Barsbold; the species name honours Wojciech Siciński, who prepared the fossil and assisted the authors over many years.

The holotype is held by the Institute of Paleobiology of the Polish Academy of Sciences in Warsaw as ZPAL MgD-I/110. It remains the only specimen securely referred to the genus. With a sample of one, researchers cannot measure variation among individuals, distinguish age-related changes from species traits, or test whether the animal’s unusual proportions were typical.

What the skeleton preserves

The associated vertebral series includes nine dorsal vertebrae, nine fused sacral vertebrae and fifteen caudal vertebrae. Fragments of ribs, part of the left ilium, pieces of the pubic bones, incomplete hind-limb bones and portions of the foot are also preserved. This is a substantial postcranial sample, but it is not a complete skeleton.

The skull, lower jaws and most of the forelimbs are absent. We therefore cannot directly inspect the muzzle, the tooth batteries of this individual, or any cranial crest. Reconstructions that show a complete head borrow its general shape from other hadrosaurids. A hollow lambeosaurine crest would be especially speculative because no skull roof or crest bones are known.

The pelvis and vertebral column indicate a very large animal. They do not provide a complete body length or a secure mass estimate. Familiar claims that Barsboldia exceeded ten metres scale missing parts against relatives; they should not be mistaken for measurements of the preserved skeleton. It is safer to describe a large-bodied hadrosaurid than to call it a record-holder on this evidence.

The tall vertebral spines

The neural spines on the dorsal, sacral and front caudal vertebrae rise conspicuously above their centra. On the sacrum, the spines are at least about four times the height of the centra and broaden toward their tips, producing a club-shaped outline in side view. The front of the tail also carries tall spines, which become lower farther back.

In life, these bones were covered by muscle, ligaments and other tissues; they did not stand exposed above the skin. The extended spine series could have raised the contour over the pelvis and tail base, but the exact profile depends on soft tissues that do not fossilise here. A narrow muscular ridge and a thicker hump are alternative reconstructions, not structures preserved directly. The bones do not demonstrate a sail.

The unusual spines originally encouraged comparison with lambeosaurines, whose members often carry elaborate hollow cranial crests. But the back spines are not the same structure as a skull crest. Albert Prieto-Márquez’s 2011 reassessment found that tall neural spines occur in more than one hadrosaur lineage and are not, on their own, a reliable marker of close relationship.

Pelvis and locomotion

The ilium is incomplete, yet it provides a useful character for phylogenetic comparison. Its central blade is relatively shallow, with a depth-to-length ratio below 0.8, and its upper rear margin lacks a strong separate ridge. In the 2011 analysis, this combination helped place Barsboldia among basal saurolophines rather than within Lambeosaurinae.

Like other large hadrosaurids, it could probably use both two-legged and four-legged postures. That inference comes from the broader anatomy of the family, not from a complete set of Barsboldia limb bones. The vertebral profile does not reveal its ordinary walking speed or prove that the raised back was an adaptation for a particular gait.

Classification: from lambeosaurine to saurolophine

The 1981 description called Barsboldia the first lambeosaurine known from the Nemegt Formation. That proposal relied chiefly on the high vertebral spines and the sacrum. However, the skull – the part that would provide direct evidence of the characteristic hollow crest in a lambeosaurine – was missing.

In 2011, Prieto-Márquez added the genus to a phylogenetic dataset containing 47 hadrosauroids. His analysis recovered it among early saurolophines, a branch that lacks the typical hollow cranial crest of lambeosaurines. The result depended on pelvic characters, especially the ilium, rather than on the height of the vertebral spines. The reassessment helps place it alongside other hadrosaurids.

This placement is a hypothesis, not a final answer. The skull and many bones used to score other hadrosaurids are missing in Barsboldia; a new specimen preserving the head could change the analysis. The genus is still diagnosed by a distinctive combination of pelvic and sacral features, even while its exact position remains open.

Age and Nemegt environments

The Nemegt Formation was deposited by river channels, floodplains and wet lowlands late in the Cretaceous. Its absolute age has been refined over time. It is commonly placed in the late Campanian or early Maastrichtian, with many modern comparisons supporting a Maastrichtian age. The formation-level estimate should not be presented as an exact date for the Barsboldia individual.

Remains of Saurolophus angustirostris are abundant in the formation. Other named dinosaurs include Tarbosaurus, Deinocheirus, Therizinosaurus and several titanosaurs. These fossils show that the Nemegt ecosystem supported a diverse large-bodied fauna. They do not prove that a particular Barsboldia encountered every one of those animals.

No teeth of Barsboldia are preserved, but its placement in Hadrosauridae points to a plant-based diet and the complex dental batteries characteristic of the family. The type specimen cannot identify the plants it selected or the height at which it fed. Those questions require direct dental or ecological evidence that this skeleton does not provide.

Growth and maturity

A histological study of Mongolian Late Cretaceous hadrosaur bones sampled a rib and a metatarsal of ZPAL MgD-I/110. Their microstructure contributed to a discussion of prolonged growth in large hadrosaurids. One individual can inform that comparison, but it cannot produce a complete growth curve for the genus or show how much variation existed between animals.

The fused sacrum and robust bones are consistent with a large, mature individual. Its age in years is unknown, and the sample cannot show whether it represents an average adult or an unusually large member of the species. A claim about sex or maturity beyond those limits would go beyond the evidence.

What a reconstruction can show

The fossil directly supports a large hadrosaurid with a strong pelvis and an elevated vertebral profile above the sacrum and front of the tail. The familiar duck-billed head, forelimbs and much of the trunk are restored by comparison with better-known hadrosaurids. That comparison gives a plausible overall body plan while leaving details of Barsboldia itself unresolved.

The head crest, colour, skin pattern and precise soft-tissue outline of the back are unknown. Tall spines justify a raised contour but do not establish a sail. Any specific colour scheme or thickness of tissue belongs to artistic reconstruction. A fuller skull, a second skeleton and more complete limbs would test its classification and body proportions. Until then, the dinosaur catalogue entry should show the high spinal profile without presenting the absent anatomy as a discovery.