JOOPITER PRESENTS:
An adult and a juvenile Maiasaura peeblesorum.
Seventy-six million years ago, their bones were laid down in the same Montana bonebed.
Now they stand again.
MAIASAURA
Maia — "GOOD MOTHER" / saura — "LIZARD"
In the late 1970s, on ranch land near Choteau in Teton County, Montana, a rare dinosaur nest came out of the ground
In 1979, John R. Horner and Robert Makela published the find in Nature. They read it as the first tangible evidence of social behavior in dinosaurs, and gave the animal a name that stated the argument outright: Maiasaura peeblesorum—a composite of “good mother lizard,” and “Peebles” for the families on whose land it was found.
It was a radical idea at the time. Prior to that, prevailing scientific belief held that dinosaurs simply reproduced and moved on, but this discovery posed something very different: that their young could have depended on, and even been nurtured by, their parents.
The thinking changed how dinosaurs were studied, and literature has since described it as revolutionary for what it inferred about family life in a non-avian dinosaur.
Nearly 50 years later, JOOPITER is proud to offer Hank and Koda as two individual lots from that same species–and the same Montana formation.
AN EVOLUTIONARY NEST
The scientific revelation that began with the nest’s discovery has continued to expand in scope and significance.
In 2025, a study in Scientific Reports, co-authored by the paleontologist who named the species, found that newborn Maiasaura were comparable to birds that hatch helpless and depend on their parents, and that the young remained in the nest for weeks while gaining strength and independence.
In 2026, a study of tooth wear found that juveniles and adults ate differently. Its authors read that as further evidence of the young being fed and nurtured by their parents.
Maiasaura has served as a model organism for extinct vertebrate population biology too, with growth dynamics and survivorship assessed across large samples.
This is unusual in paleontology. Most extinct animals are known from fragments or isolated individuals. Maiasaura is known from enough individuals, and enough different ages, to be studied as a population.
Which begs the question: how did so many individuals end up preserved together in Teton County?
THE GROUND IS THE PROVENANCE
In the foothills of the Rocky Mountain Front, near Bynum, Montana the Linster Quarry stands. A prolific, family-run dig site, it is embedded within the Late Cretaceous Two Medicine Formation, dating back roughly 73 to 84 million years.
The quarry has yielded several milestone discoveries that have reshaped modern paleontology. It is the home of the holotype of Bambiraptor feinbergi, as well as one of the most complete and pristine Gorgosaurus specimens ever found.
It also contains Maiasaura peeblesorum specimens of multiple ages, which has allowed paleontologists to map an ontogenetic, or growth-stage, series in an unprecedented manner.
But the importance of Linster Quarry is not simply that these dinosaurs were found there. It is what happened to them after they died.
AN ACCIDENT IN PRESERVATION
During the Late Cretaceous period, the region that is now western Montana was characterized by dynamic seasonal floodplains and a large river system that was flanked by active volcanic ranges. The area became a favored nesting and living ground for massive herds of Maiasaura peeblesorum.
Sudden environmental shifts, floods, or volcanic ash accumulation caused massive die-offs of the prehistoric species.
Then a second, gentler event occurred. The remains were moved and stacked together in a way that naturally protected them against scavengers and the elements. Over millions of years, these dense layers of bone beds were compressed into the hard sandstone strata of the Two Medicine Formation—resulting in an extraordinary array of single species individuals of many ages in one place, in exceptional condition.
As McFeeters, Evans and Maddin record of the site, “there is no evidence for a second hadrosaurid taxon in this bonebed.”
In other words, the bonebed is not a random accumulation of dinosaurs. It is a record of Maiasaura.
In 2021, five partial Maiasaura skulls from this bone bed—subadult through mature adult—were published as an ontogenetic series.
AN ENTIRE POPULATION, IN PIECES
Because the animals came apart before the bones were moved and stacked, no element can be assigned with certainty to one individual over another.
That means any and all mounts from these sites are composites–including Hank and Koda.
Koda is 68% original fossil bone by bone count. Hank is 62%. Where original bone is absent, elements have been fabricated by 3D printing integrated with epoxy resin.
A complete bone list identifies every element—from the axial column and ribs to the individual phalanges of the hands and feet—as original, restored or printed.
It is a distinction worth making precisely because the story of this bonebed is not about one perfect dinosaur. It is about an entire population that happened to survive in pieces, and their contribution to the advancement of paleontology.
Koda — THE ADULT
Koda is the more mature of the offering.
Standing 20.7 feet nose to tail, and 8.5 feet tall.
Judging from the overall size of the material and the degree of bone development, it can be determined that Koda represents a fully mature adult stage of growth, within a species that reached full adult size at about eight.
Mounted mid-stride with the head lowered, on a custom-fabricated steel armature.
At this scale, Koda is a double-height object: taller than a standard doorway, and a foot and a half short of a basketball rim.
Hank — THE YOUNG ONE
Then there is Hank.
Standing 13 feet long, 6.3 feet tall, it can be determined that Hank represents a juvenile stage of growth.
Juvenile dinosaur material of this caliber is scarce in the fossil record; concentrations of it occur only in exceptional circumstances. Histological work on the species found mortality to be very high in the first year of life—which is why an animal of this growth stage, fully mounted, is seldom seen.
At this scale, Hank greets you eye to eye. But his importance is not simply his size—it is his growth stage.
FROM BONE TO BODY
Koda and Hank come from the same deposit. The variable is growth stage. That makes direct comparison possible, and compelling: the proportional change in the limb bones, the development of the skull, the mechanics of the animal through maturity — a juvenile and an adult of one species, from one floodplain.
For collectors, the significance is straightforward. Whether acquired together or as separate lots, these are not simply two mounted dinosaurs. They are two stages of one species, preserved in the same place, offering a rare opportunity to see evolutionary change made physical on a remarkable scale.
Offered with full title and license; all intellectual property transfers with the specimen.
