Some birds survived the asteroid that wiped out dinosaurs. A fossilized poop can help explain why

David DeMar Jr./Field Museum

Tiny feathers encased in fossilized poop are helping scientists understand why some birds made it through the mass extinction that wiped out the dinosaurs and others did not.

Unearthed in Montana, the feathery find belonged to a bird that had once been devoured and excreted by a predatory dinosaur — possibly a Tyrannosaurus rex or smaller cousin — just before the asteroid strike that unleashed the extinction event 66 million years ago, according to a new study published in the journal Current Biology. The remains include the best-preserved feather ever extracted from Mesozoic deposits, or rocks from the age of the dinosaurs, and the discovery offers a rare glimpse into a make-or-break moment for many species.

“It’s such a beautiful, well-preserved feather, from such an unexpected source, and it’s exciting that it could help us answer this huge question in paleontology,” said lead study author Jingmai O’Connor, the associate curator of fossil reptiles at Chicago’s Field Museum, in a news release.

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However, the stunning specimen likely represents a species that did not survive in the aftermath of the asteroid strike, according to the team behind the new research. Based on an examination of bones found with the feathers inside the coprolite — the scientific term for fossilized feces — the study authors believe the feathers belonged to a small, flightless diving bird similar to modern loons, which were part of a now-extinct group known as Hesperornithiformes.

Paleontologists established decades ago that birds evolved from dinosaurs. That means the bird species flapping around in backyards today are effectively the only surviving dinosaurs. Puzzlingly, however, today’s birds all descend from just one group of dinosaur-era birds called Neornithes, a close relative of Hesperornithiformes.

The hellish conditions triggered by the planet’s collision with the city-size space rock wiped out all other birds and dinosaurs, O’Connor noted. The newly found feathers could hold a clue to the downfall of the Hesperornithiformes.

O’Connor said some of the feathers looked highly similar to those present today in modern birds, with a central spine having a square cross section that would have helped make the feather stiff yet lightweight. However, others looked more primitive in structure — smaller and fuzzier — and would not have been as good at insulating as modern bird body feathers, she added.

“The primitive body feathers of hesperornithiforms were not a problem for these birds during the greenhouse world of the Mesozoic, but the asteroid impact triggered an impact winter and global temperatures dropped significantly,” she explained via email.

Scientists believe the collision released billions of tons of dust, sulfur and other gases into the atmosphere, blocking the sun and leading to a dramatic cooling of Earth’s climate. Plants were unable to photosynthesize, a biological process critical for life, for almost two years afterward, research suggests .

“Now the primitive body feathers and their less effective insulation is problematic — it takes more energy to stay warm but there is less food available through which to acquire this energy.”

Jingmai O’Connor/Field Museum

She said a similar pattern had been seen in other birds from the Cretaceous called enantiornithines. Their plumage has been preserved in globs of amber — prehistoric tree resin.

O’Connor thinks one of the main reasons the Neornithes branch of the bird family survived the mass extinction is due to differences in their feathers. Other scientists had reasoned that because Neornithes species lived near water, something about this habitat helped protect them from the devastating effects of the mass extinction. However, Hesperornithiformes also lived by water and disappeared.

To confirm her hypothesis, paleontologists would need to find a Neornithes fossil from just before the asteroid strike and examine its plumage to confirm that it does not retain feathers with primitive traits, O’Connor said.

“It would have to be preserved in amber or in another exceptionally preserved coprolite so that the feathers are preserved in 3D and with enough bone to be certain about the identification,” she noted.

“Who knows, maybe someone has already picked up a coprolite with these traces inside.”

Andrey Atuchin/Field Museum

Such well-preserved feather specimens don’t turn up often, and even those studied in the new research weren’t immediately apparent. David DeMar Jr., a paleontologist with the University of Washington in Seattle , came across the coprolite that preserved them in 2016 while collecting fish fossils in Montana, within the Hell Creek Formation.

Since no feathers had ever been found in the Hell Creek, despite a 150-year-history of fossil hunting there, O’Connor said DeMar’s first thought was maybe the crack in the reddish-brown nodule he found on a rocky outcrop contained a plant. But closer inspection revealed it was a feather.

“I picked it up and scanned its surface through my hand lens, and that’s when I couldn’t believe what I was seeing, a tiny fossil feather,” DeMar, who is a coauthor on the study, said in the news release.

However, it wasn’t until the researchers imaged the fossilized feces in a micro-CT scanner that they realized the specimen contained multiple feathers, leg bones and even remnants of the bird’s stomach contents. Many of the remains were exceptionally preserved in three dimensions.

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The fossilized dinosaur droppings also preserved two minuscule, diamond-shaped scales from a fish known as a gar that still exists today. The fish would have been too small to satisfy a dinosaur predator and thus probably formed the bird’s last meal before it was wolfed down by the T. rex, according to the study.

“If it wasn’t for the break exposing the feathers, we’d still be unaware that coprolites can be a source of this kind of information,” O’Connor said.

“I continue to marvel over the kinds of things we find in the fossil record that were never thought possible,” said Anthony Fiorillo, adjunct faculty research professor at Southern Methodist University and the executive director of the New Mexico Museum of Natural History & Science, who was not involved in the research.

大卫·德马尔二世/菲尔德博物馆

化石粪便中包裹着的细小羽毛正在帮助科学家们了解为什么有些鸟类在导致恐龙灭绝的大灭绝中幸存下来，而另一些鸟类却没能幸存下来。

根据发表在《当代生物学》杂志上的一项新研究，在蒙大拿州出土的这件羽毛化石属于一只鸟类，它曾被一只掠食性恐龙——可能是霸王龙或其体型较小的近亲——吞食并排出体外。这只恐龙的遭遇发生在6600万年前的小行星撞击地球引发灭绝事件之前不久。这件化石是迄今为止从中生代地层（即恐龙时代的岩石）中提取出的保存最完好的羽毛，这一发现让我们得以窥见许多物种生死攸关的时刻。

“这是一根非常漂亮、保存完好的羽毛，而且来源也出乎意料，令人兴奋的是，它或许能够帮助我们解答古生物学中的这个重大问题，”该研究的主要作者、芝加哥菲尔德博物馆化石爬行动物副馆长景迈·奥康纳在一份新闻稿中说道。

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。

然而，据这项新研究的团队称，这件令人惊叹的标本很可能代表着一个在小行星撞击后未能幸存的物种。研究人员通过对粪化石（即化石化的粪便）中与羽毛一同发现的骨骼进行分析，认为这些羽毛属于一种小型、不会飞的潜水鸟，类似于现代的潜鸟，它们属于现已灭绝的黄昏鸟类（Hesperornithiformes）。

古生物学家几十年前就已证实鸟类是由恐龙进化而来。这意味着如今在后院里飞来飞去的鸟类实际上是唯一幸存的恐龙。然而，令人费解的是，现存的鸟类都起源于恐龙时代的一类鸟类——新鸟类（Neornithes），它们是黄昏鸟类（Hesperornithiformes）的近亲。

奥康纳指出，这颗行星与那颗城市大小的太空岩石相撞后引发的炼狱般的环境，导致所有其他鸟类和恐龙灭绝。新发现的羽毛或许能为黄昏鸟类的灭绝提供线索。

奥康纳表示，有些羽毛看起来与现代鸟类的羽毛非常相似，中央的脊刺呈方形横截面，这使得羽毛既坚硬又轻盈。然而，另一些羽毛的结构则显得更为原始——更小更蓬松——而且隔热性能不如现代鸟类的体羽。

她通过电子邮件解释说：“在中生代的温室世界里，黄昏鸟类的原始体羽对这些鸟类来说不是问题，但小行星撞击引发了撞击冬天，全球气温显著下降。”

科学家认为，这次碰撞向大气层释放了数十亿吨尘埃、硫磺和其他气体，遮蔽了阳光，导致地球气候急剧降温。研究表明，此后近两年时间里，植物都无法进行光合作用——这是生命至关重要的生物过程。

“现在，原始的羽毛及其较差的隔热性能带来了问题——保持温暖需要更多的能量，但可用于获取这些能量的食物却越来越少。”

景迈·奥康纳/菲尔德博物馆

她说，在白垩纪的其他鸟类——反鸟类中也发现了类似的模式。它们的羽毛被保存在琥珀——史前树脂中。

奥康纳认为，新鸟类之所以能在大灭绝中幸存下来，主要原因之一是它们羽毛的差异。其他科学家则认为，由于新鸟类生活在水边，这种栖息地的某些特性帮助它们免受了大灭绝的毁灭性影响。然而，黄昏鸟类也生活在水边，最终却灭绝了。

奥康纳说，为了证实她的假设，古生物学家需要找到小行星撞击地球之前的新鸟类化石，并检查其羽毛，以确认它没有保留具有原始特征的羽毛。

她指出：“它必须保存在琥珀中，或者保存在其他保存异常完好的粪化石中，这样羽毛才能以三维形式保存下来，并且有足够的骨骼，才能确定其身份。”

“谁知道呢，也许已经有人捡到过含有这些痕迹的粪化石了。”

安德烈·阿图钦/菲尔德博物馆

保存如此完好的羽毛标本并不常见，即使是这项新研究中研究的标本，最初也并非显而易见。西雅图华盛顿大学的古生物学家小戴维·德马尔 (David DeMar Jr.) 于 2016 年在蒙大拿州地狱溪组 (Hell Creek Formation) 采集鱼类化石时，偶然发现了保存这些羽毛的粪化石。

尽管地狱溪已有150年的化石勘探历史，但从未发现过羽毛，奥康纳说，德马尔最初的想法是，他在岩石露头上发现的红棕色结核的裂缝里可能藏着植物。但仔细检查后发现，那其实是一根羽毛。

“我捡起它，用放大镜扫描它的表面，那时我简直不敢相信自己的眼睛，那是一根微小的化石羽毛，”该研究的合著者德马尔在新闻稿中说道。

然而，直到研究人员使用微型CT扫描仪对化石粪便进行成像后，他们才意识到该标本中包含多根羽毛、腿骨，甚至还有鸟类胃内容物的残余。许多遗骸的三维结构都保存得异常完好。

化石揭示了一种奇特的滑翔生物，它于1.2亿年前捕食鸟类

这些恐龙粪便化石中还保存了两片微小的菱形鳞片，它们来自一种名为雀鳝的鱼类，这种鱼至今仍然存在。研究表明，这种鱼体型太小，不足以满足恐龙捕食者的需求，因此很可能是这只鸟在被霸王龙吞食前的最后一餐。

奥康纳说：“如果不是因为破损导致羽毛暴露出来，我们可能至今都不知道粪化石可以作为这类信息的来源。”

“我对我们在化石记录中发现的那些以前从未想过会存在的东西感到惊叹不已，”南方卫理公会大学兼职研究教授、新墨西哥州自然历史与科学博物馆执行主任安东尼·菲奥里洛说道，他并未参与这项研究。