Kretase’de Yaşayan Bazı Timsah Türleri Dinozorlarla Beslenmiş
Sahra Çölü’nde Godvana kıtasına ait birimlerinin egemen olduğu yerlerde Kretase döneminde yaşadığı düşünülen 5 farklı timsaha ait kafatası fosili bulundu. Bulunan kafataslarına verilen takma adlar yabandomuzu çeneli timsah, fare çeneli timsah, köpek çeneli timsah, ördek çeneli timsah ve uzun yassı çeneli timsah şeklinde sıralanıyor. Fosiller, Fas’ın Kem Kem Yatağı adlı bölgesinde ve Nijer’in Gadoufaoua (Tr. Develerin gitmeye korkutuğu yer) adlı bölgelesinde bulundu.
Burada görüntü var, göremiyorsanız http://www.youtube.com/watch?v=E4B2lKNE-_s
Bu fosilleri bulan Paul Sereno’nun (Şikago Üniversitesi) ve Hans Larsson’un (MekJil Üniversitesi) yorumuna göre ilk timsahlar küçük ve ayakları üzerinde dört nala koşabiliyormuş. Bu yorumun ışığında bu timsahların çevik olduğu ve karada çok hızlı hareket ettiği söyleniyor. Aynı zamanda timsahların kuyruklarının geçirdiği evrim sayesinde kazandığı çeviklik ile de suda daha hızlı yüzebilidiği söyleniyor. Düşünülen iki durumun, 200 milyon yıl öncesi timsahlarının geçirdiği evrim için ayırı özellikler olduğu belirtiliyor.
Fosilleri bulunan bazı timsahları diğerlerinden farklı kılan en önemli özellikse milyonlarca yıl önce Kretase döneminde küçük dinozorlarla (örneğin T-rex) beslenmeleri olarak gösteriliyor. Bulunan timsahların her birinin farklı beslenme alışkanlıklarına ve davranışlara sahip olduğu belirtiliyor. Tarih öncesi timsahların, Afrika bataklıklarında, göllerinde ya da nehirlerinde küçük dinozorlar, balık ve bitki kökleri yiyerek beslendikleri belirtiliyor.
A flesh model of the head of PancakeCroc (above) and its fossil lower jaw. PancakeCroc was a fish eater with a 3-foot-long, pancake-flat skull. It likely rested motionless for hours, its open jaws waiting for prey. Photo by Mike Hettwer, courtesy National Geographic.
A flesh model of the head of RatCroc (above) and its fossil lower jaw. RatCroc used its pair of buckteeth to dig for food — plants and grubs. Other fossil bones, not pictured, helped flesh out RatCroc’s features. Photo by Mike Hettwer, courtesy National Geographic.
A flesh model of the head of DuckCroc (above) and its fossil skull. DuckCroc had a broad, overhanging snout and long, pointed nose. Photo by Mike Hettwer, courtesy National Geographic.
A flesh model of the head of DogCroc (above) and its fossil skull. DogCroc had a soft, doglike nose and would have been an agile galloper and swimmer. Photo by Mike Hettwer, courtesy National Geographic.
A flesh model of the head of BoarCroc (above) and its actual fossil skull discovered in the Sahara by a team led by paleontologist Paul Sereno, a professor at the University of Chicago. BoarCroc was a 20-foot-long meat eater with three sets of dagger-shaped fangs. Photo by Mike Hettwer, courtesy National Geographic.
Daha fazla bilgi için birkaç adres
BoarCroc, RatCroc, DogCroc, DuckCroc, PancakeCroc
5 “Oddball” Crocs Discovered, Including Dinosaur-Eater
BoarCroc, RatCroc, DogCroc, DuckCroc and PancakeCroc Cousins of Prehistoric SuperCroc Inhabit Lost World of Sahara
Students Help Prepare Croc Fossils
Behind the Scenes Interview: Building the Five Ancient Crocs at the UC Fossil Lab
Introducing: BoarCroc, RatCroc, DogCroc, DuckCroc and PancakeCroc
Five ancient crocs, one with teeth like boar tusks and another with a snout like a duck’s bill, have been discovered in the Sahara by National Geographic Explorer-in-Residence Paul Sereno and McGill Professor Hans Larsson. The five fossil crocs, three of them newly named species, are remains of a bizarre world of crocs that inhabited the southern land mass known as Gondwana some 100 million years ago.
Sereno, a professor at the University of Chicago, and his team members, including Larsson, unearthed the strange crocs in a series of expeditions beginning in 2000. “These species open a window on a croc world completely foreign to what was living on northern continents,” Sereno said. These crocs, along with a closely related sixth species, are detailed in a paper published in the journal ZooKeys and appear in the current issue of National Geographic magazine.
At 40 feet in length and weighing 8 tons, Sarcosuchus imperator, or SuperCroc, was the first and largest of the crocs Sereno found in the Sahara, but it was not the strangest, Sereno said. He and his teams soon discovered key fossils of five previously unknown or poorly understood species, most of them walking “upright” with their arms and legs under the body like a land mammal instead of sprawled out to the sides, bellies touching the ground.
New species:
BoarCroc: Kaprosuchus saharicus; fossils found in Niger. Twenty-foot-long upright meat eater with an armoured snout for ramming and three sets of dagger-shaped fangs for slicing. Closest relative found in Madagascar.
RatCroc: Araripesuchus rattoides; fossils found in Morocco. Three-foot-long, upright plant and grub eater. Pair of buckteeth in lower jaw used to dig for food. Closest relative in South America.
PancakeCroc: Laganosuchus thaumastos; fossils found in Niger and Morocco. Twenty-foot-long, squat fish eater with a three-foot pancake-flat head. Spike-shaped teeth on slender jaws. Likely rested motionless for hours, its jaws open and waiting for prey. Closest relative from Egypt. The scientific paper also names a close relative discovered by the team in Morocco, Laganosuchus maghrebensis.
New fossils:
DuckCroc: Previously named species, Anatosuchus minor; fossils found in Niger. Three-foot-long upright fish-, frog- and grub-eater. Broad, overhanging snout and Pinocchio-like nose. Special sensory areas on the snout end allowed it to root around on the shore and in shallow water for prey. Closest relative in Madagascar.
DogCroc: New fossils of named species, Araripesuchus wegeneri; fossils found in Niger include five skeletons, all next to each other on a single block of rock. Three-foot-long upright plant and grub eater with a soft, doglike nose pointing forward. Likely an agile galloper, but also a capable swimmer. Closest relative in Argentina.
“We were surprised to find so many species from the same time in the same place,” said Larsson, who along with a team member discovered the bones of BoarCroc and PancakeCroc. “Each of the crocs apparently had different diets, different behaviours. It appears they had divided up the ecosystem, each species taking advantage of it in its own way.”
Based on interpretation of the fossils, Sereno and Larsson hypothesize that these early crocs were small, upright gallopers. They suggest that the more agile of their new croc menagerie could not only gallop on land but also evolved a swimming tail for agility and speed in water, two modes of locomotion suggested to be evolutionary hallmarks for the past 200 million years.
To study the crocs’ brains, Sereno CT-scanned the skulls of DuckCroc and DogCroc and created digital and physical casts of the brains. The result: Both DogCroc and DuckCroc had broad, spade-shaped forebrains that look different from those of living crocs. “They may have had slightly more sophisticated brain function than living crocs,” Larsson said, “because active hunting on land usually requires more brain power than merely waiting for prey to show up.”
To collect the croc fossils, Sereno and teams endured temperatures topping 125 degrees F, living for months on dehydrated food. Logistics were challenging: For the 2000 expedition, they transported trucks, tools, tents, five tons of plaster, 600 pounds of water and four months’ worth of other supplies.
Kaynakça
Lee, C., 2009. Introducing: BoarCroc, RatCroc, DogCroc, DuckCroc and PancakeCroc, Newsroom, McGill University, Montreal, Canada, http://www.mcgill.ca/newsroom/news/item/?item_id=112310, accessed at November 20th 2009.
TRT, 2009. Timsahlar Dinozor da Yiyormuş, Çevre, Türkiye Radyo Televizyon Kurumu, Ankara, Türkiye, http://www.trt.net.tr/Haber/HaberDetay.aspx?HaberKodu=84906b58-8442-4714-b1dc-a18973729ef5, 20 Kasım 2009 tarihinde ulaşılmıştır.
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