A teacher spotted two unusually large footprints. They turned out to be a first for science

Kent Hups/Denver Museum of Nature & Science

Kent Hups set out one morning on a research expedition in the famed Hell Creek Formation, a series of fossil-rich sedimentary rock layers in the western United States.

The vast formation, spanning parts of Montana, Wyoming, North Dakota and South Dakota, is abundant in Late Cretaceous dinosaur bones — but finding footprints is a different story. The area’s sediments typically eroded before the tracks could be preserved.

Courtesy Denver Museum of Nature and Science

Hiking family discovers rare T. rex fossil

Yet Hups, a high school science teacher from Northglenn, Colorado, found himself looking down at what ended up being the first known trackway left behind by a T. rex.

“My first reaction was total disbelief,” said Hups, a volunteer research associate at the Denver Museum of Nature & Science. “I sat and looked at it for a period of time before I was convinced it was a track at all.”

The two giant footprints he initially spied in July 2025 had distinct three-pronged impressions strikingly similar to other fossilized tracks . To determine which Cretaceous species would have left the marks, he measured the trace fossil from end to end.

Footprints with a length that’s greater than the width suggest the track maker was likely a meat eater, Hups explained. With each footprint about 3 feet (0.9 meter) long and 2 to 2½ feet (0.6 to 0.8 meters) wide, Hups spotted evidence not only for a carnivore but the largest, most iconic meat-eating dino that lived in what once was a lush, swampy coastal floodplain — Tyrannosaurus rex.

Tyler Lyson/Denver Museum of Nature & Science

The extraordinary footprints are described in a study published September 8 in the Journal of Vertebrate Paleontology. Unlike bones, these tracks capture live movement from 66.5 million years ago, offering clues to the prehistoric apex predator’s behavior and walking stride, researchers say.

“I hope that more people go out and look a little bit harder at those strange looking rocks and this leads to a better, more detailed understanding of what life looked like in the past,” Hups said in an email. “It is the closest thing that we have to a time machine.”

Hups, a coauthor of the new report, had found two fossilized footprints out in the open, one more eroded than the other, but study coauthor Tyler Lyson, senior curator of vertebrate paleontology at the Denver Museum of Nature & Science, was looking for stronger evidence of a pattern to be convinced this was a dinosaur trackway.

“Rocks can weather into all different shapes and sizes, you know, some that look like Florida, some that look like Texas, some that look like T. rex footprints,” Lyson said.

Lyson marked an X in the dirt where other footprints should have been. As the researchers dug, they not only found a third, but a fourth print as well. The prints had three slender toes and the middle digits were longer than the others, an anatomy similar to T. rex feet.

Also, the size was a key indicator, Lyson said. The Hell Creek Formation “is one of the best studied rock units in the world, so we think we have a really good understanding of what dinosaurs were living there, and the two dinosaurs that are big enough to make such a track are T. rex and then the duck-billed dinosaur called Edmontosaurus,” he said. “Their feet are very different.”

The four footprints are noted in the study. But this summer, the research team located a fifth print. “So, there’s no doubt in my mind that it’s a trackway that belongs to a T. rex,” Lyson said.

The discovery was a result of the dinosaur being in the right place at the right time, he added. What’s now North Dakota was a plant-rich environment where dinosaurs could thrive 66.5 million years ago. The soft, muddy earth created the conditions needed for the dinosaur tracks to be buried, brought back to the surface and exposed by erosion.

Previously, researchers had found only two isolated footprints attributed to the tyrannosaur. The first specimen was discovered by a US Geological Survey geologist in New Mexico and described in 1994, and the second was reported in a study by a University of Manchester paleontologist in 2008 from the Hell Creek Formation in Montana . Scientists have unearthed only a handful of tracks from other dinosaurs in the wider Hell Creek Formation. “Worldwide, trackways aren’t that rare, but for this interval of time in North America, they’re very rare,” Lyson said.

Rare look at the last days of the dinosaurs shows they were thriving, scientists say

Longer and more clearly preserved trackways from other large meat-eating dinosaurs are known elsewhere, but the first trackway likely attributable to T. rex is important, noted Dr. Anthony Romilio, a paleontologist and research associate with the University of Queensland’s Dinosaur Lab in Brisbane, Australia. Romilio was not involved with the study.

In the Hell Creek Formation, “even a poorly preserved example is a meaningful discovery there,” Romilio wrote in an email. “Any trackway provides a record of real behaviour that their bones cannot: a few seconds of life, 66.5 million years ago.”

Dozens of T. rex skeletons have been uncovered in the Hell Creek Formation, which preserves evidence of North America’s last dinosaur ecosystem. But tracks can give scientists clues that bones can’t, including how fast the dinosaur was moving and what its feet may have looked like.

Multiple tracks can provide more information than isolated footprints and allow scientists to estimate how fast an animal was moving when its tracks formed. In this case, the new trackway discovery provides the first direct evidence of a T. rex’s stride length — about 13 feet (4 meters) total for the four footprints — suggesting it was walking at about 3.5 to 4.5 miles (5.6 to 7 kilometers) per hour, Lyson said.

However, the number is way below its maximum speed, since preserved tracks were likely made in wet soil, and animals move fastest on firm dirt, explained Thomas Holtz Jr., a vertebrate paleontologist and principal lecturer in the department of geological, environmental and planetary sciences at the University of Maryland, College Park. He added that the footprints are still an important finding for paleontologists.

Nearly 200 Jurassic footprints unearthed on ‘dinosaur highway’

“The most important aspect is that this is perhaps the first definitive Tyrannosaurus rex trackway sequence,” said Holtz, who was not involved in the study.

The Denver Museum of Nature & Science plans to collect three prints from North Dakota to further analyze them for tissue and skin impression data, according to Lyson. The trackway’s publication gives other scientists the opportunity to analyze its measurements and reconstruct how the dinosaur moved , Romilio added. And knowing tracks like these exist could help researchers find more in the future, according to Holtz.

Taylor Nicioli is a freelance journalist based in New York.

肯特·胡普斯/丹佛自然科学博物馆

一天早上，肯特·胡普斯出发前往著名的地狱溪组进行研究考察，地狱溪组是位于美国西部的一系列富含化石的沉积岩层。

这片横跨蒙大拿州、怀俄明州、北达科他州和南达科他州部分地区的广袤地层蕴藏着丰富的晚白垩世恐龙骨骼化石，但寻找恐龙足迹却并非易事。该地区的沉积物通常在足迹得以保存之前就已被侵蚀殆尽。

图片由丹佛自然科学博物馆提供

徒步旅行的家庭发现了罕见的霸王龙化石

然而，来自科罗拉多州诺斯格伦的高中科学教师赫普斯却发现自己正低头看着最终被证实是霸王龙留下的第一条足迹。

“我的第一反应是完全难以置信，”丹佛自然科学博物馆的志愿者研究员胡普斯说。“我坐下来仔细观察了好一会儿，才确信那确实是一条赛道。”

他最初在2025年7月发现的两处巨大足迹，都具有清晰的三叉状印痕，与其他化石足迹惊人地相似。为了确定是哪种白垩纪物种留下的痕迹，他测量了足迹化石的长度。

胡普斯解释说，长度大于宽度的脚印表明留下痕迹的很可能是肉食动物。每个脚印长约 3 英尺（0.9 米），宽约 2 至 2.5 英尺（0.6 至 0.8 米），胡普斯发现的证据不仅表明存在食肉动物，而且还表明存在曾经生活在郁郁葱葱的沼泽沿海冲积平原上的最大、最具代表性的肉食恐龙——霸王龙。

泰勒·莱森/丹佛自然科学博物馆

9月8日发表在《脊椎动物古生物学杂志》上的一项研究描述了这些非凡的足迹。研究人员表示，与骨骼不同，这些足迹记录了6650万年前的活体运动，为了解史前顶级掠食者的行为和行走方式提供了线索。

“我希望更多的人能走出去，更仔细地观察那些奇形怪状的岩石，从而更好地、更详细地了解过去的生活是什么样子，”胡普斯在一封电子邮件中写道。“这是我们最接近时光机的东西。”

新报告的合著者之一 Hups 在露天发现了两个化石足迹，其中一个比另一个侵蚀得更严重，但该研究的合著者、丹佛自然科学博物馆脊椎动物古生物学高级馆长 Tyler Lyson 正在寻找更有力的证据来证明这是一个恐龙足迹。

“岩石风化后会变成各种不同的形状和大小，你知道，有些看起来像佛罗里达，有些看起来像德克萨斯，有些看起来像霸王龙的脚印，”莱森说。

莱森在原本应该有其他脚印的地方画了个“X”标记。研究人员继续挖掘，不仅发现了第三个脚印，还发现了第四个。这些脚印有三个细长的脚趾，中间的脚趾比其他脚趾长，这种解剖结构与霸王龙的脚掌相似。

莱森还表示，足迹的大小也是一个关键指标。他说：“地狱溪组是世界上研究最深入的岩层之一，所以我们认为我们对生活在那里的恐龙种类有了非常清晰的了解。能够留下如此巨大足迹的恐龙有两种：霸王龙和鸭嘴龙，也就是埃德蒙顿龙。它们的脚掌结构截然不同。”

研究中记录了这四个足迹。但今年夏天，研究团队又发现了第五个足迹。“所以，我确信这绝对是霸王龙的足迹，”莱森说道。

他补充说，这一发现是恐龙恰好出现在正确地点和时间的结果。如今的北达科他州在6650万年前曾是一片植物茂盛的地区，非常适合恐龙生存。松软的泥土为恐龙足迹的埋藏、重见天日以及最终因侵蚀作用而暴露出来创造了必要的条件。

此前，研究人员仅发现过两处被认为是霸王龙留下的孤立足迹。第一处足迹标本由美国地质调查局的一位地质学家于1994年在新墨西哥州发现并描述；第二处足迹则由曼彻斯特大学的一位古生物学家于2008年在蒙大拿州的赫尔克里克组地层中发现并发表。科学家们在更广阔的赫尔克里克组中仅挖掘出过少量其他恐龙的足迹。“在全球范围内，足迹并不罕见，但在北美这一时期，足迹却非常罕见，”莱森说道。

科学家称，罕见的恐龙末期影像显示，它们当时正处于繁荣时期。

昆士兰大学恐龙实验室的古生物学家兼研究员安东尼·罗米利奥博士指出，其他大型肉食恐龙的足迹更长、保存更清晰，在其他地方也曾发现过，但第一条可能属于霸王龙的足迹意义重大。罗米利奥博士并未参与这项研究。

罗米利奥在一封电子邮件中写道，在地狱溪组，“即使是保存状况不佳的足迹也是一项意义重大的发现。任何足迹都记录了骨骼无法展现的真实行为：6650万年前短短几秒钟的生命历程。”

在赫尔克里克组地层中，人们发现了数十具霸王龙骨骼，该地层保存着北美最后一个恐龙生态系统的证据。但足迹可以为科学家提供骨骼无法提供的线索，例如恐龙的移动速度以及它的脚部可能是什么样子。

多条足迹比孤立的脚印能提供更多信息，使科学家能够估算出动物形成足迹时的移动速度。莱森表示，此次新发现的足迹首次直接证实了霸王龙的步幅——四个足迹总长约13英尺（4米）——这表明它当时的行走速度约为每小时3.5至4.5英里（5.6至7公里）。

然而，这个数字远低于其最大速度，因为保存下来的足迹很可能是在潮湿的土壤中形成的，而动物在坚实的泥土上移动速度最快，马里兰大学帕克分校地质、环境和行星科学系的脊椎动物古生物学家兼首席讲师小托马斯·霍尔茨解释说。他补充说，这些足迹对古生物学家来说仍然是一项重要的发现。

在“恐龙高速公路”上发现近200个侏罗纪时期的足迹

“最重要的一点是，这可能是第一个确凿无疑的霸王龙足迹序列，”霍尔茨说道，他并未参与这项研究。

据莱森称，丹佛自然科学博物馆计划从北达科他州采集三枚足迹，以便进一步分析其组织和皮肤印痕数据。罗米利奥补充说，足迹的发表使其他科学家有机会分析其测量数据，并重建恐龙的运动方式。霍尔茨表示，了解此类足迹的存在有助于研究人员在未来发现更多足迹。

泰勒·尼乔利是一位居住在纽约的自由撰稿人。