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First tyrannosaur fossil discovered with its last meal perfectly preserved in its stomach
Researchers have found a tyrannosaur’s last meal perfectly preserved inside its stomach cavity.
What was on the menu 75 million years ago? The hind legs of two baby dinosaurs, according to new research on the fossil published Friday in the journal Science Advances.
Dinosaur guts and hard evidence of their diets are rarely preserved in the fossil record, and it is the first time the stomach contents of a tyrannosaur have been uncovered.
The revelation makes this discovery particularly exciting, said co-lead author Darla Zelenitsky, a paleontologist and associate professor at the University of Calgary in Alberta.
“Tyrannosaurs are these large predatory species that roamed Alberta, and North America, during the late Cretaceous. These were the iconic apex or top predators that we’ve all seen in movies, books and museums. They walked on two legs (and) had very short arms,” Zelenitsky said.
“It was a cousin of T. rex, which came later in time, 68 to 66 million years ago. T. rex is the biggest of the tyrannosaurs, Gorgosaurus was a little bit smaller, maybe full grown would have been 9, 10 meters (33 feet).”
The tyrannosaur in question, a young Gorgosaurus libratus, would have weighed about 772 pounds (350 kilograms) — less than a horse — and reached 13 feet (4 meters) in length at the time of death.
The creature was between the ages of 5 and 7 and appeared to be picky in what it consumed, Zelenitsky said.
“Its last and second-to-last meal were these little birdlike dinosaurs, Citipes, and the tyrannosaur actually only ate the hind limbs of each of these prey items. There’s really no other skeletal remains of these predators within the stomach cavity. It’s just the hind legs.
“It must have killed … both of these Citipes at different times and then ripped off the hind legs and ate those and left the rest of the carcasses,” she added. “Obviously this teenager had an appetite for drumsticks.”
The two baby dinosaurs both belonged to the species called Citipes elegans and would have been younger than 1 year old when the tyrannosaur hunted them down, the researchers determined.
The almost complete skeleton was found in Alberta’s Dinosaur Provincial Park in 2009.
That the tyrannosaur’s stomach contents were preserved wasn’t immediately obvious, but staff at the Royal Tyrrell Museum in Drumheller, Alberta, noticed small protruding bones when preparing the fossil in the lab and removed a rock within its rib cage to take a closer look.
“Lo and behold, the complete hind legs of two baby dinosaurs, both under a year old, were present in its stomach,” said co-lead author François Therrien, the museum’s curator of dinosaur paleoecology, in a statement.
The paleontologists were able to determine the ages of both the predator and its prey by analyzing thin slices sampled from the fossilized bones.
“There’s growth marks like the rings of a tree. And we can essentially tell how old a dinosaur is from looking at those, the structure of the bone,” Zelenitsky said.
Changing appetites of top predators
The fossil is the first hard evidence of a long-suspected dietary pattern among large predatory dinosaurs, said paleoecologist Kat Schroeder, a postdoctoral researcher at Yale University’s department of Earth and planetary science, who wasn’t involved in the research.
The teen tyrannosaur didn’t eat what its parents did. Paleontologists believe its diet would have changed over its life span.
“Large, robust tyrannosaurs like T. rex have bite forces strong enough to hit bone when eating, and so we know they bit into megaherbivores like Triceratops,” Schroeder said via email. “Juvenile tyrannosaurs can’t bite as deep, and therefore don’t leave such feeding traces.”
She said that scientists have previously hypothesized that young tyrannosaurs had different diets from fully developed adults, but the fossil find marks the first time researchers have direct evidence.
“Combined with the relative rarity of juvenile tyrannosaur skeletons, this fossil is very significant,” Schroeder added. “Teeth can only tell us so much about the diet of extinct animals, so finding stomach contents is like picking up the proverbial ‘smoking gun.’”
The contents of the tyrannosaur’s stomach cavity revealed that at this stage in life, juveniles were hunting swift, small prey. It was likely because the predator’s body wasn’t yet well-suited for bigger prey, Zelenitsky said.
“It’s well known that tyrannosaurs changed a lot during growth, from slender forms to these robust, bone-crushing dinosaurs, and we know that this change was related to feeding behavior.”
When the dinosaur died, its mass was only 10% of that of an adult Gorgosaurus, she said. How juvenile tyrannosaurs filled a niche
The voracious appetite of teenage tyrannosaurs and other carnivores has been thought to explain a puzzling feature of dinosaur diversity.
There are relatively few small and midsize dinosaurs in the fossil record, particularly in the Mid- to Late Cretaceous Period — something paleontologists have determined is due to the hunting activities of young tyrannosaurs.
“In Alberta’s Dinosaur Provincial Park, where this specimen is from, we have a very well sampled formation. And so we have a pretty good idea of the ecosystem there. Over 50 species of dinosaurs,” Zelenitsky said.
“We are missing mid-sized … predators from that ecosystem. So yeah, there’s been the hypothesis that, the juvenile tyrannosaurs filled that niche.”
注释：
Cretaceous: n
表示" 白垩纪"，如：The story takes place 6500 years ago in the late Cretaceous period. 故事发生在6500万年前的白垩纪晚期。
skeletal: adj
表示"骨骼的；梗概的；骸骨的"，如：These foods replenish the skeletal needs of the body. 这些食物补充身体骨骼的需要。
curator: n
表示"(博物馆、展览馆等的)馆长；管理者"，如：Curator conducted the visitors round the museum. 馆长领着游客们在博物馆中参观。
proverbial: adj
表示"众所周知的"，如：He seems to have 9 lives, like the proverbial cat. 他就像格言中所说的猫一样，似乎有九条命。
voracious: adj
表示"贪婪的；贪吃的"，means "excessively greedy and grasping"，如：After swimming, I find that I have a voracious appetite. 游完泳后,我发现我的食欲大增。
中文简要说明：
2亿年前恐龙曾经称霸地球，长期以来，科学家也陆续挖出不少化石，不过却很少发现与恐龙饮食有关的证据。最近这类研究总算有所突破，加拿大学者在一具暴龙的胃里发现2只幼龙的尸体，不过只有后腿、没有躯体，分析它们也懂得挑「好吃的」来吃，颠覆大众对它饥不择食的印象。
美媒CNN报导，这次研究的主角是一只长约4公尺、重约350公斤，年龄介于5至7岁的蛇发女妖龙（Gorgosaurus libratus，属于暴龙科），7500万年前生活在现今加拿大埃布尔达省的森林中。
有趣的是，科学家在它的胃里发现2只不到一岁的文雅捷足龙（Citipes elegans）后腿，而且是在不同时间吃下，成为生前的最后两餐。加拿大卡加立大学（University of Calgary）古生物学副教授泽伦尼斯基（Darla Zelenitsky）形容这只蛇发女妖龙相当懂吃，「它扯下捷足龙的后腿并吃掉，丢弃尸体的其他部位」，「显然这个少年对大腿肉情有独钟。」
不仅如此，从这只恐龙身上也能看出它们独特的饮食习惯，那就是随着年纪增长，它们的饮食内容会跟着改变，父母和幼龙所吃的东西完全不同。
美国耶鲁大学古生态学家施罗德（Kat Schroeder）表示，成年的暴龙咬合力道够大，足以咬断骨头，因此会猎杀三角龙之类的大型草食恐龙；相较之下，捷足龙的体型娇小有如大型鸟类，成龙长度最多约2公尺，因此成为年幼暴龙的合理目标，加上大型草食恐龙的化石上从未出现年幼暴龙的咬痕，因此推测它们在成长过程中的饮食不同，罕见的胃容物化石也提供了证据。
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