In 2000, Chinese and German expedition teams unearthed a large number of vertebrate fossils such as turtles, crocodiles, dinosaurs and mammals on the southern edge of the Junggar Basin, China, dating back about 160 million years – late Jurassic.
Twenty years later, from this fossil block, German scientists describe the oldest known evidence that mammals had “eaten” dinosaurs from the tooth markings on their ancient ribs. Mamenchisaurus dinosaurs.
Excavation site in the Junggar Basin.
In the late Jurassic fossils unearthed in the Junggar Basin, there is a fragmented ancient rib fossil, which the scientists believe may have belonged to the Mamenchisaurus that was more than 20 meters long. However, at first, scientists did not discover the special feature of these ancient rib fossils, only when they re-examined the fossils, they found that there were small and elongated marks on the bone. of these marks about 0.5-1.5 mm and width about 30–250 μm.
Mamenchisaurus is a prominent Sauropoda dinosaur with a long neck – more than half its length. Most of the species in this genus lived 160 to 145 million years ago, in the Oxford to Tithonus period, the late Jurassic period, the largest species reaching a length of 35 m and can weigh between 50 and 75 tons. The long necks were a distinctive feature of Mamenchisaurus dinosaurs because they had a neck that was two-thirds to half its length. Mamenchisaurus dinosaur neck formed by 19 ancient vertebrae, of which the longest burning was more than 2 meters in size. The bones are tightly linked together, so their necks are not flexible, move slowly and difficult. According to the speculation of scientists, the neck muscles of this dinosaur are relatively developed, otherwise it will not be able to support such a long neck.
When discovering small and thin marks on bones, researchers speculate that there are 3 main reasons leading to this phenomenon, firstly due to sediment friction or trampling of vertebrates, the second is due to insect infestation and, ultimately, vertebrate teeth marks. Therefore, the researchers compared the traces on the fossil’s ancient ribs with a large number of other fossilized samples with similar traces to find an answer.
Fossils of Mamenchisaurus neck ribs with biological traces, abc are photos taken from different angles.
The friction of sediment and the trampling of vertebrates will leave small streaks on the surface of bones, often appearing in parallel clusters. The length is usually less than a few hundred µm (micrometres) and the width is only a few microns.
But the traces left on the ancient rib fossil sample are not distributed in parallel clusters so this cannot be traces left by the trampling of the animal. As mentioned above, the fossil traces are about 0.5-1.5 mm long and 30–250 μm wide (1 mm = 1000 μm), much larger than the friction of the sediments.
The second reason is that these traces appear from insect infestation, which is one of the most common reasons in the fossil record and the traces they leave behind are also varied. Most intrusion marks are pore-shaped and have long lines. The main culprit of this phenomenon is termites.
In the past, there have been many biological relics on dinosaur bones that are suspected to be related to ancient termite nests, the feature of the trail left by the termite is the deepest part of the tooth mark at the middle end. Both ends are pointed, the middle is wide, in addition, small tooth marks often have ridges.
However, the biological trace on the cervical fossils is teardrop-shaped, pointed at one end and blunt on the other, the deepest part of the trace is close to the blunt end. Therefore, these traces cannot be left by insect infestation.
Traces on fossils due to insect infestation.
After eliminating the above possibilities and analyzing in depth, the researchers finally determined the extent of the mammal group based on the size of the fossil traces, as well as the size and shape. of teeth, tooth type.
After comparing the teeth of the ancient mammals of this area, scientists believe that the larger markings on fossils of the ancient ribs of the Mamenchisaurus species are likely to come from the Chinese species Sineleutherus. Because the incisors width of this species is 200μm this size corresponds to the teeth mark on the cervical fossils with a width of 30-250μm.
The incisors of the Sineleutherus species in China, the width of the tip of the tooth is 200μm.
Sineleutherus lived in Late Triassic to Early Cretaceous and shaped like a squirrel or a house mouse. Until now, there are still many female paintings surrounding this species, some people think they are mammals, and some people think that they are just a sub-branch.