Scientists say they’ve found the strongest evidence yet of red blood cells in a dinosaur bone

Traces of prehistoric blood could reveal unprecedented clues about dinosaur biology, but they’ve been notoriously difficult to confirm. Now, researchers studying a 115 million-year-old dinosaur bone say they’ve found the strongest evidence yet of red blood cells in a fossil.

Tissues , cells and other soft biological samples rarely ever survive the fossilization process and thus make for controversial discoveries. A few previous studies, dating back to the late 1990s, have reported structures resembling red blood cells in dinosaur and other reptile fossils, but researchers have fiercely debated their legitimacy.

The new study , published Monday in the journal Proceedings of the National Academy of Sciences, used a combination of new microscopic imaging and chemical analyses to find not only microscopic structures resembling red blood cells preserved within the dinosaur bone, but also chemical evidence of heme — a molecule in hemoglobin, the protein in red blood cells that carries oxygen. According to the study’s authors, it is the first time heme has been detected in situ, or within the structures themselves, in a dinosaur fossil.

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The well-preserved Early Cretaceous bone and new research approach bolster the argument that biological structures and molecules can survive in prehistoric fossils, said lead author Kliti Grice, organic geochemist and John Curtin Distinguished Professor at Curtin University in Perth, Australia.

“The exciting implication is not just what we have found in this dinosaur. It is that we now have approaches that can be applied to other fossils to ask how much original biological information may still be hidden within them,” Grice said in an email.

However, not all experts are convinced that the microscopic structures are truly red blood cells.

If researchers find similar evidence of red blood cells in more fossil specimens, it “could potentially help us ask much more sophisticated questions about the physiology of extinct animals,” Grice said.

The fossil is a partial hind limb of Aratasaurus museunacionali, a theropod dinosaur that lived during the Early Cretaceous. Paleontologists dug up the leg bone in 2008 at the geological site Mina Pedra Branca in northeastern Brazil within the Romualdo Formation, a rocky area known for its exceptionally preserved fossils. Scientists believe stagnant waters limited oxygen and slowed the decomposition of remains buried in this region.

Within the bone’s vascular canals — microscopic tubes that carry contain blood vessels and nerve fibers — the study authors found an abundance of oval-shaped microstructures that looked similar to red blood cells. The team then used a combination of imaging and chemical analysis to identify whether the structures contained signatures consistent with red blood cells.

Past research may have separately described red blood cell-like structures and possible remnants of blood chemistry in dinosaur fossils, but this study brings together multiple lines of evidence, including the structures’ location, appearance, mineral composition and associated chemical signals, Grice said.

The researchers suggest that low-oxygen burial conditions at the site may have limited the breakdown of organic material, helping the structures survive. Along with heme, the study authors found the bone contained traces of manganese oxides, minerals that may have further helped stabilize and preserve the cells.

“Bones provide extraordinary information about anatomy, growth, locomotion and evolution. But cellular and molecular preservation potentially gives us access to a different layer of biological information: the chemistry of the living animal and its tissues,” Grice said.

However, she emphasized that it is too early to draw conclusions about the physiology of Aratasaurus based on one specimen.

“One of the first questions is whether this is an extraordinarily rare occurrence or whether similar preservation has simply been overlooked in other fossils,” she said. “There may therefore be fossils sitting in museum collections around the world that contain molecular and cellular information that has simply never been investigated.”

Grice and her team plan to expand their research to other fossils from different species, geological time periods and environments to better understand how widespread this type of well-preserved molecular evidence might be.

In the future, more molecular clues could help researchers investigate how dinosaurs transported oxygen through their bodies, how their tissues functioned and how their biology compared with that of animals alive today.

But does finding red blood cells from a dinosaur bring scientists any closer to recreating its DNA, as seen in books and movies like “Jurassic Park”? Not necessarily, said Timothy Cleland, a physical scientist at the Smithsonian Institution’s Museum Conservation Institute. Heme and DNA are different molecules, and they would fossilize in bone in different ways, he explained. Finding evidence of one does not mean the other has survived.

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“This study opens new research avenues to explore heme b preservation within bone, especially in exceptional sites like this one,” Cleland said in an email, referring to the most common form of heme. “Additionally, this study begs the question, does this kind of preservation extend beyond this single dinosaur to other species within the Romualdo Formation as well as to other locations with exceptional preservation?”

The structures also differed in size and shape from red blood cells in living birds and crocodilians, the authors noted in the study. But they cautioned that modern species may not be the best comparison for non-avian dinosaurs — and that the cells they found in Aratasaurus museunacionali may not retain their original shape from when the animal was alive.

Cleland, who was not involved in the new study, said future research could help scientists better understand how red blood cells might change after an animal dies, which could possibly explain Aratasaurus’ odd cell shapes.

It’s also possible that the structures might not be remnants of red blood cells at all.

The findings do not meet established standards for identifying fossilized blood cells, said Mary Schweitzer, professor emeritus in the department of biological sciences at North Carolina State University. She was not involved in the study.

She questioned whether the structures’ shape and size sufficiently match red blood cells in living relatives of dinosaurs as well as the significance of hausmannite, the type of manganese oxide the study authors predominantly found. Schweitzer noted that this substance is not detected in living red blood cells.

But Grice said the team does not consider hausmannite an original component of the cells. Rather, they believe it formed during fossilization and may have helped preserve the structures and associated molecular evidence.

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Still, Schweitzer said in an email that the authors’ use of multiple analytical techniques is an exciting advancement for the field. Based on the data, she said she is hopeful that some molecules from the dinosaur itself remain preserved in the bone.

“The usability of fossil molecules preserved in deep time is only just beginning to be explored, as conventional wisdom states preservation like this is not possible,” Schweitzer said. “The more studies we can do on very old fossils, the more we can learn about the interaction between the burial environments and the degrading organism.”

Further research could eventually help scientists answer much bigger questions, including what prehistoric molecules can reveal about disease, biological processes and how molecules have evolved over time, she added.

“If we can get beyond ‘It can’t’ to ‘What if it can?’, there is no telling what may lie ahead!” Schweitzer said.

Taylor Nicioli is a freelance journalist based in New York.

史前血液痕迹或许能揭示恐龙生物学前所未有的线索，但一直以来，证实这些痕迹都极其困难。如今，研究人员在研究一块距今1.15亿年的恐龙骨骼时表示，他们发现了迄今为止在化石中发现红细胞的最有力证据。

组织、细胞和其他软性生物样本极少能在化石化过程中保存下来，因此相关的发现往往充满争议。一些早期研究，最早可追溯到20世纪90年代末，报告称在恐龙和其他爬行动物化石中发现了类似红细胞的结构，但研究人员对其真实性一直争论不休。

这项周一发表在《美国国家科学院院刊》（PNAS）上的新研究，结合了新型显微成像技术和化学分析方法，不仅在恐龙骨骼中发现了类似红细胞的微观结构，还发现了血红素的化学证据——血红素是血红蛋白（红细胞中负责携带氧气的蛋白质）中的一种分子。据研究作者称，这是首次在恐龙化石中原位检测到血红素，即在化石结构内部检测到血红素。

在出人意料的地方，人们发现了已知体型最大的恐龙的化石蛋。

澳大利亚珀斯科廷大学有机地球化学家兼约翰·柯廷杰出教授、论文第一作者克利蒂·格莱斯表示，保存完好的早白垩世骨骼和新的研究方法强化了生物结构和分子可以在史前化石中保存下来的论点。

格莱斯在一封电子邮件中表示：“令人兴奋的意义不仅在于我们在这只恐龙身上发现了什么，更在于我们现在拥有可以应用于其他化石的方法，从而探究其中可能还隐藏着多少原始的生物学信息。”

然而，并非所有专家都确信这些微观结构真的是红细胞。

格莱斯说，如果研究人员在更多化石标本中发现类似的红细胞证据，“可能会帮助我们提出关于已灭绝动物生理学的更复杂的问题”。

这块化石是早白垩世时期一种兽脚类恐龙——博物馆阿拉塔龙（Aratasaurus museunacionali）的部分后肢。古生物学家于2008年在巴西东北部罗穆阿尔多组（Romualdo Formation）地质遗址的米纳佩德拉布兰卡（Mina Pedra Branca）挖掘出了这块腿骨。罗穆阿尔多组地层以保存异常完好的化石而闻名。科学家认为，当时的静水环境限制了氧气供应，减缓了埋藏于此的化石遗骸的分解速度。

研究人员在骨骼的血管管（输送血管和神经纤维的微小管道）内发现了大量椭圆形微结构，这些微结构看起来与红细胞相似。随后，研究团队结合成像和化学分析技术，确定这些结构是否含有与红细胞一致的特征。

格莱斯说，过去的研究可能分别描述了恐龙化石中类似红细胞的结构和可能的血液化学残留物，但这项研究将多方面的证据结合起来，包括这些结构的位置、外观、矿物成分和相关的化学信号。

研究人员认为，该遗址的低氧埋藏环境可能限制了有机物的分解，从而帮助骨骼结构得以保存。除了血红素外，研究作者还发现骨骼中含有微量的锰氧化物，这些矿物质可能进一步帮助稳定和保存了细胞。

格莱斯说：“骨骼提供了关于解剖结构、生长、运动和进化方面的非凡信息。但细胞和分子层面的保存可能让我们接触到不同层面的生物信息：活体动物及其组织的化学成分。”

然而，她强调，仅凭一个标本就对阿拉塔龙的生理特征得出结论还为时过早。

“首先要问的问题之一是，这究竟是极其罕见的现象，还是其他化石中类似的保存状况只是被忽略了，”她说。“因此，世界各地的博物馆藏品中可能保存着一些化石，其中包含着从未被研究过的分子和细胞信息。”

格赖斯和她的团队计划将研究范围扩大到不同物种、地质时期和环境的其他化石，以更好地了解这种保存完好的分子证据的普遍程度。

未来，更多的分子线索可以帮助研究人员研究恐龙如何通过身体输送氧气，它们的组织如何运作，以及它们的生物学特性与现存动物的生物学特性有何不同。

但是，从恐龙化石中发现红细胞，是否就能让科学家更接近于重现恐龙的DNA，就像《侏罗纪公园》等书籍和电影中展现的那样呢？史密森学会博物馆保护研究所的物理学家蒂莫西·克莱兰德表示，未必如此。他解释说，血红素和DNA是不同的分子，它们在骨骼中形成化石的方式也不同。发现其中一种的证据并不意味着另一种也保存了下来。

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克莱兰德在一封电子邮件中表示：“这项研究为探索骨骼中血红素b的保存开辟了新的研究途径，尤其是在像这样的特殊遗址中。”他指的是最常见的血红素形式。“此外，这项研究也引出了一个问题：这种保存方式是否不仅限于这具恐龙化石，还存在于罗穆阿尔多组的其他物种以及其他保存状况异常完好的地点？”

研究作者指出，这些结构在大小和形状上也与现存鸟类和鳄鱼的红细胞不同。但他们也提醒说，现代物种可能并非非鸟类恐龙的最佳参照对象——而且他们在博物馆阿拉塔龙（Aratasaurus museunacionali）体内发现的细胞可能并未保留其生前的原始形状。

克莱兰德并未参与这项新研究，他表示，未来的研究可以帮助科学家更好地了解动物死后红细胞可能发生的变化，这或许可以解释阿拉塔龙奇特的细胞形状。

也有可能这些结构根本不是红细胞的残余物。

北卡罗来纳州立大学生物科学系荣誉教授玛丽·施韦策表示，这些发现不符合既定的化石血细胞鉴定标准。她并未参与这项研究。

她质疑这些结构的形状和大小是否与恐龙近亲的红细胞足够吻合，以及研究作者主要发现的锰氧化物——豪斯曼石——的意义。施韦策指出，这种物质在活体红细胞中并未被检测到。

但格莱斯表示，研究团队并不认为硼氢化钙是细胞的原始成分。相反，他们认为硼氢化钙是在化石形成过程中产生的，可能有助于保存细胞结构及其相关的分子证据。

关于恐龙的一个长期存在的根本性问题或许终于有了答案。

不过，施韦策在邮件中表示，作者们运用多种分析技术是该领域的一项令人振奋的进展。她表示，根据这些数据，她希望恐龙骨骼中能够保存一些来自恐龙自身的分子。

施韦策说：“人们对保存在远古时期的化石分子的利用价值才刚刚开始探索，因为传统观点认为这种保存方式是不可能的。我们对非常古老的化石进行的研究越多，就越能了解埋藏环境与降解生物体之间的相互作用。”

她补充说，进一步的研究最终可能有助于科学家解答更大的问题，包括史前分子可以揭示哪些关于疾病、生物过程以及分子如何随时间演变的信息。

“如果我们能从‘不可能’转变为‘如果可以呢？’，那么未来会发生什么，谁也无法预料！”施韦泽说道。

泰勒·尼乔利是一位居住在纽约的自由撰稿人。