Discovery of dinosaurs and their biomes at Hanauma Bay

Hanauma Bay on the southern coast of Victoria, Australia is a famous source of dinosaur fossils on the Australian continent, but it is not easy to discover fossils here. Although fossils are often well preserved here, they are buried in hard sandstone, siltstone and mudstone and can only be unearthed with suitable excavation tools such as sledgehammers, drills and even blasting equipment.

plesiosaur

In 1987, an Australian excavation team conducted a long and boring field work here. Two months have passed, and despite using various methods such as drilling and blasting, not many fossils have been found.

Seeing that this field season is coming to an end, the expedition team decided to try their luck in the last few days. They dug two parallel tunnels in a cliff along an ancient stream channel to search for and excavate bones that were deposited in that ancient stream channel 100 million years ago. After the two parallel tunnels were dug, they decided to dig another tunnel perpendicular to them to connect them. This was really a lucky decision, because just when the expedition team was digging this third horizontal tunnel, they finally discovered the dinosaur fossils they had been longing for.

After drilling and blasting to remove the covering rocks, the team members carefully took out the fossilized rock blocks from the floor of the "Dinosaur Mine" as if they were dealing with newborn babies, for fear of damaging even a little bit. specimen.

On this day, an excavation team member was surprised to find an unusual fossil while inspecting the newly split rock in the dark tunnel. Because the space in the tunnel is narrow, dark and humid, the specimen itself is brown in color and difficult to find among the dark gray rocks, so it was ignored during previous inspections. After careful observation, it was determined that this was the fossil on the top of the skull of a small dinosaur that might have been smaller than a chicken. The exposed section shows that there should be more things related to this fossil around. After careful search, the excavation team found the corresponding part in a once-abandoned stone, that is, a fragment of the top of another skull, which was inadvertently peeled off like an orange peel during the excavation. . After the two fossils were bonded together, a rather large brain fossil of a dinosaur was clearly visible. Of note is the large size of the pineal foramen, the pituitary gland part of the brain responsible for vision. This condition is extremely rare among all other known species of dinosaurs.

Then, the excavation team dug out all the preserved skulls. Their good luck continued the next day. Less than 1 meter away from the skull fragments, they found some remaining fossils of vertebrae, belts and leg bones. The size, shape and burial conditions of the fossils told them that these postcranial bones and the skull belonged to the same dinosaur individual. This conjecture was confirmed by subsequent laboratory research and repair and mounting work. Research shows that this smart dinosaur with big eyes was small, walked on two legs and moved quickly. It lived 160 million years ago and fed on plants and insects.

The discovery of this precious dinosaur fossil and its subsequent discoveries have provided scientists with important clues about the life that existed in this area 160 million years ago.

Prior to this, the fossil record of dinosaurs and other terrestrial vertebrates in the Australian continent from about 65 million to 220 million years ago was almost blank. As early as 1900, a geologist discovered the first dinosaur bone fossil on the coast of Victoria. However, more than 90 years have passed, and no new dinosaur bone fossils have been discovered here before this excavation; there are only two jaw fragments that can reflect the evidence of mammals that survived on the Australian continent during that period. The large number of imprinted fossils and the small number of bone fossils found indicate that the dinosaur family on the Australian continent was once very prosperous and dominant at that time. However, the available skeletal fossil evidence is surprisingly sparse. Since the 1960s, Australian scientists have begun some explorations, hoping to discover some specimens to fill the gaps in this aspect of the Australian continent and increase their understanding of the paleontological history of the region.

Hanauma Bay is a major fossil-producing area in southern Australia. The rocky outcrops along Melbourne's southeast and southwest coast are less affected by climate and their fossils are therefore less susceptible to the intense weathering that is common in other parts of the continent. The area where dinosaur fossils are found on this coastal stretch of Victoria covers only a few square kilometers. Here, waves crash against the rocks, gradually exposing dinosaur skeleton fossils. Less than 100 meters further inland, the same rock was severely eroded, making it difficult to find fossilized bones.

To the north of Hanauma Bay is the lower Otway Mountains, to the south is the vast South Australian Sea; less than 3,000 kilometers to the south is the Antarctic continent across the sea. When dinosaurs lived here, the landscape was completely different than it is now. At that time, the South Australian Sea did not exist, and Hanauma Bay was nothing more than the bottom of a rift canyon. At exactly that time, Australia and Antarctica, two plates that had long been connected as part of Gondwana, began to separate. The terrain at the bottom of this Grand Canyon is relatively flat. If you lived at that time, you could hike from what is now Hanauma Bay to Antarctica, and then stand there and look back to the north. You can see Australia on the horizon in the distance. side of the canyon cliff.

In the early Cretaceous, the southeastern part of the Australian continent was still within the Antarctic Circle at that time, probably around 80o south latitude. Fossil plant and vertebrate specimens from that era collected from Hanauma Bay and other parts of Victoria show that the climate here, while not as cold as today's polar regions, was also erratic. Significant growth rings can be seen on the excavated plant fossils, reflecting obvious seasonal climate changes. The results of measuring the oxygen isotope decay rate of rocks in the Hanauma Bay area show that the average annual temperature in the southeastern part of the Australian continent in the early Cretaceous was only 5 to 6 degrees Celsius, and could even be as low as minus 8 degrees Celsius. The climate may be quite warm in the summer, but during the long winter nights the temperature is always well below freezing. Research on ancient valley sediments in this area shows that the area often experienced periodic flooding during that period, which was likely caused by the melting of snow at high altitudes due to seasonal climate changes.

Before the 1970s, except for some footprint fossils found in the Spitesbergen area, whether dinosaurs lived in the polar regions had always been a mystery. Later, hadrosaurus skeleton fossils were discovered in northern Alaska. Subsequently, many fossil specimens were discovered in high latitudes in the northern and southern hemispheres, including Alaska, Canada, Siberia, New Zealand, and the Antarctic Peninsula, providing scientists with opportunities to study and understand cold regions. The living conditions of dinosaurs are providing more and more clues.

Since Hanauma Bay and its surrounding areas provided a good living environment for a variety of organisms during the Mesozoic Era, the various animal and plant fossil specimens found in this area provide scientists with an opportunity to try to recreate what life was like at that time. Polar environment, explore how various animals and plants living in Hanauma Bay, including dinosaurs, survive long and warm summers and equally long but extremely cold winters.

In addition to dinosaurs, scientists have also discovered 150 species in Victoria, such as spiders and pterodactyls, ferns and coniferous pine trees, among others. For a region of the Antarctic Circle, such rich biodiversity must have been enough to make the landscape appear vibrant and lush. Huge gymnosperms such as Chilean cedar, ginkgo and podocarpus form the dominant population of the plant community. Prosperous ferns and mosses, some low shrubs and even herbs form the understory of the forest. Sphagnum moss and a primitive vascular plant grow in open marshes, while algae, amaranth and quills become producers in the water. New angiosperms had appeared, and although they were rare at the time, they did not become the dominant plant group on Earth until about 65 million years ago, after the dinosaurs became extinct.

In the highlands of Tasmania and the high mountains of southeastern Australia, many close relatives of those ancient plants still exist. They grow both in cold areas covered with snow in winter and in warmer environments. . Therefore, scientists speculate that their Mesozoic ancestors could also have grown in the place called Hanauma Bay by modern people and successfully adapted to the cold climate in winter at that time.

The fauna at that time also included more than 80 species of invertebrates. Fossils of aquatic shellfish, freshwater bryozoans, spiders, various crustaceans and animals similar to earthworms have been found in ancient lake sediments in the area. There are as many as 12 orders of insect fossils, with beetles, flies and bed bugs being the most numerous species, among which some well-preserved juvenile individuals are also preserved.

At that time, many fish, including lungfish, still lived in the rivers of the ancient Australian continent located in the Antarctic Circle. Modern lungfish live in a very narrow range, only in equatorial Africa, South America and the northeastern part of the Australian continent.

Fossils of amphibians, turtles and reptiles similar to lizards have also been found here, and fossilized teeth of plesiosaurs show traces of this long-necked monster. Interestingly, although plesiosaurs are basically marine creatures, the plesiosaurs on the Australian continent lived in freshwater. This phenomenon leads scientists to believe that plesiosaurs were likely to be able to often swim into inland rivers and lakes during the Cretaceous, but they just traveled farther from the ocean in Australia. In addition, some feather fossils also reveal the presence of birds in this area.

Scientists also discovered a very striking phenomenon, that is, many species such as labyrinthine amphibians and some bipedal carnivores that have become extinct in other parts of the world in older times have survived here longer. time. It is likely that it was the ancient Australian continent's location in the Antarctic region that provided a refuge for many different species of plants and animals.

Scientists also discovered that among the nearly 200 dinosaur fossils, more than half are juvenile dinosaur individuals. From this, they speculated that dinosaurs were not accidental visitors here. They probably used this place as a breeding ground, taking advantage of the rich plant resources produced by the 24 hours of sunshine a day in the polar regions in summer.

In-depth and meticulous exploration and excavation work has enabled scientists to obtain more and more abundant animal and plant fossil specimens. These discoveries have changed people's understanding of the earth's climate 100 million to 120 million years ago. Although the global temperature was generally rising at that time, life in the polar regions still faced the harsh climate during the low temperature season. Some dinosaurs adapted to such an environment and lived tenaciously in it. Understanding what kind of environment they lived in and how they adapted to this environment will undoubtedly be helpful in studying why dinosaurs completely disappeared from the earth at the end of the Cretaceous period. Studying these dinosaurs and other creatures that lived in the Antarctic climate 106 million years ago will also provide some inspiration for scientists to explore the occurrence time and development speed of various changes in the climate that led to the modern ice age.

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