Based on their ability to impede theme park openings alone, dinosaurs are revered amongst children and scientists alike for their ferocious strength, imposing stature, and all-around radness. According to new evidence, though, our understanding of current fossil records may be woefully inaccurate, especially when it comes to charting size and growth patterns of those denizens of the Land Before Time. During a presentation this week at the Society of Vertebrate Paleontology in Los Angeles, paleontologist Jack Horner of Bozeman, Montana’s Museum of the Rockies revealed that when he dissected fossilized dinosaur bones in the museum’s collection and studied the inner layers, most of the specimens exhibited signs that they were still growing at the time of their likely untimely death.

Smaller fossils, which were typically labeled as “juveniles”, have outer bone layers containing canals that housed blood vessels and groups of osteocytes (cells that are used for bone formation). One can imagine Horner’s surprise when he discovered similar signs of growth in “adult” fossils, especially given the fact that in most present-day animal species, the skeleton stops growing after reaching adulthood. Horner did find specimens of adult fossils that had stopped growing, containing closely packed bone layers without any osteocytes of blood vessels – a telltale sign of arrested growth. But, overwhelmingly, the specimens at which he looked did not have any such indicators.

One of Horner’s central specimens was a thirteen year-old, ten meter-long Allosaurus, a large bipedal predator and preferred mount of Elf Warriors in Magic: The Gathering‘s “Coldsnap” collection. “It’s a big one, and it was undeniably still growing – ripping along, really – when it died,” said Horner. Also included among the specimens were six Tyrannosaurus rex fossils, all of which exhibited signs of continued growth. With results like that, it’s no small wonder that they are regarded as the King of the Dinosaurs and mortal enemy to Cadillacs.

When questioned whether any of the regal, yet terrifying specimens have displayed signs of halted growth, Horner smiled and noted, “I think all the T. rex specimens found so far were still growing when they died.” Hail to the king, baby. Now, it’s important to note that this doesn’t necessarily imply the creatures would be longer or taller; rather, their mass would increase, bulking them up to make them more physically imposing. Huh. It looks like there actually is a historical precedent for being big-boned.

University of California, Berkley paleontologist Kevin Padian is excited by the findings and their ramifications: “For years we’ve been finding robust and gracile forms of skeletons that are otherwise very similar.” While it may not have the same impact as a meteor hitting the Earth, this new evidence is certainly shaking up traditional understandings of dinosaur growth. Padian explains, “Some have suggested the robust ones were males and the gracile ones were females. Others have argued they were different species. Now it looks like they were actually just different ages.” Or, in layman’s terms, age ain’t nothin’ but a fossil record.

[HT: Nature.com]