공룡 배설물에서 7천만 년 전 풀 발견 > 미스테리

6천500만년 전 공룡이 멸종한 지 한참 뒤에야 지구상에 풀이 자라기 시작했을 것이라는 학계의 지배적인 추론을 뒤집고 당시 공룡의 배설물 화석에서 풀 성분이 발견돼 학자들을 놀라게 하고 있다.

사진#01
The lump of dung

스웨덴 자연사박물관의 카롤리네 스트롬베르크(Caroline E.A. Stromberg, of the Swedish Museum of Natural History in Stockholm )등 연구진은 인도 학자들이 중부지역에서 발견해 보내온 거대공룡 티타노사우루스의 배설물 화석을 분석한 결과 풀에만 들어있는 `파이톨리스(phytoliths)'란 이름의 규토 성분이 들어있는 것을 확인했다.


지금까지 학자들은 지구상에서 발견된 가장 오래된 풀 화석이 5천500만년 전 것이라는 이유로 초식공룡들이 나뭇가지나 잎 등을 먹었을 것으로 추정해 왔지만 티타노사우루의 배설물에서 나온 성분들은 6천500만~7천100만년 전에 나타났던 여러 종류의 풀로 밝혀졌다.


연구진은 이중 어떤 풀들은 오늘날의 벼와 대나무, 꼴풀 등과 친척뻘 되는 모습을 갖고 있었다고 밝혔다.


이들은 이 시기의 공룡들이 이처럼 다양한 풀을 먹었다는 것은 8천만 년 이상 전에 풀이 등장해 인도대륙 전역에서 진화했음이 분명하다는 것을 말해주는 것이라고 강조했다.


긴 목과 긴 꼬리에 작은 머리로 유명한 거대한 몸집의 티타노사우루스는 나뭇가지처럼 단단한 먹이를 갈아 잘게 부수는 이빨은 갖고 있지 않아 이들이 풀을 뜯었을 것이라는 가설에 더욱더 무게를 실어주고 있다.


스트롬베르크는 공룡과 같은 시대에 살았던 설치류 비슷한 포유동물들의 치아가 말처럼 풀을 뜯는 오늘날의 동물들 것과 비슷한 점이 의문이었는데 이번 발견으로 의문이 풀리게 됐다고 말했다.


미국 스미소니언 연구소의 고식물학자 돌로레스 피퍼노 (Dolores Piperno) 는 "이는 후기 백악기에 풀이 등장했을 뿐 아니라 다양한 종을 이루고 있었다는 의심할 수 없는 증거"라고 지적했다.


피퍼노를 비롯한 고식물학자들은 사이언스 최신호에 이들의 연구보고서와 함께 실린 논평에서 "오랫동안 정설로 굳어져 온 추론 중 많은 것들이 재검토될 수밖에 없다"고 말하고 이번 발견은 당시 약 1만 종의 풀들이 초식 공룡들과 함께 살았음을 뜻하는 것이라고 말했다.

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Dinos would eat even grass -
Fossils near Nagpur reveal new insight into feeding habits
Friday, November 18, 2005

New Delhi, Nov. 17: Fist-sized lumps of fossilised dinosaur dung scattered on a hillside about 150 km south of Nagpur have provided scientists the first evidence to show that dinosaurs sometimes ate grass.

The discovery by scientists in Chandigarh and Lucknow with a collaborator in Sweden will change long-standing beliefs about both the evolution of grasses on earth and the feeding habits of the dinosaurs.

Until now, plant-eating dinosaurs had been portrayed as feeding exclusively on trees because there had been no fossil evidence to show that grasses had even existed during the era of the dinosaurs.

The earliest grass fossils detected so far are about 56 million years old, a period long after the extinction of the dinosaurs 65 million years ago. But in tomorrow’s issue of the US journal Science, the Indian and Swedish researchers will report their discovery of undigested remains of grass in fossilised dinosaur dung between 65 and 70 million years old.

Studies of dinosaur dung in the past have revealed residues of trees such as conifers and cycads, micro-organisms and algae. “These grass residues tell us that herbivorous dinosaurs were indiscriminate eaters. They’d eat whatever vegetation they’d get,” said Vandana Prasad, a scientist at the Birbal Sahni Institute of Paleobotany in Lucknow who detected the microscopic grass residues called phytoliths in the dung.

“But the small amounts of grass residues in the fossilised dung clearly shows that grass was not the primary food of these dinosaurs,” Prasad said.

“This finding pushes back the antiquity of grass on earth,” said paleontologist Ashok Sahni, a co-author at Punjab University in Chandigarh who had picked up the dung samples during field trips to Pisdura, a village south of Nagpur.

“We’re lucky Pisdura has the world’s highest abundance of fossilised dinosaur dung,” Sahni said. Dung exposed to air is rapidly degraded by micro-organisms and vanishes in days. “Something must have happened there — perhaps a flood — to quickly bury the dung and allow it to fossilise,” he said.

Studies of the dung samples suggest that they belonged to Titanosaurids, large herbivorous dinosaurs that roamed in India at the time, Sahni said.

The Titanosaurids belonged to a family of giant to medium-sized dinosaurs — typically about 20 metres in length — whose fossils have been detected in lake and river sediments across Madhya Pradesh and Gujarat in the past.

Scientists elsewhere have hailed the new find as the first “unambiguous evidence” that grasses had become widespread much before the demise of the dinosaurs.

“These remarkable results will force reconsideration of many long-standing assumptions about grass evolution, dinosaurian ecology, and early plant-herbivore interactions,” scientists Dolores Piperno and Hans-Dieter Sues at the National Museum of Natural History in Washington DC said in a commentary in the same issue of Science.

The grass residues in dinosaur dung also solve a puzzle about primitive mammals called Gondwanatheres that existed in India, Madagascar and Argentina during the dinosaur era.

In 1997, Indian and US fossil-hunters had detected high-crowned teeth — associated with grass-grazing — in Gondwanathere fossils.

“With no grass to graze, we had no idea why these primitive mammals had high crowned teeth,” Sahni said.

“Now it appears very likely that the high crowned teeth in these mammals was a response to the evolution of grasses at about the same time,” Sahni said.

Grasses today cover 25 per cent of the earth’s surface and make up an important source of food for humans and animals.

Sahni said the site near Pisdura has hundreds of fossilised remains of dinosaur dung and turtles and other ancient animals. “I’m uncomfortable with giving away details of the exact location,” he said.

A few years ago, Sahni had conducted an expedition in which he had marked several sites near Jabalpur that had fossilised dinosaur eggs. “Over time, people carried them away, perhaps as souvenirs.”1

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