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dailytelegraph.com.au/classmate Triassic, Jurassic and Cretaceous woodlands Ancient trees: A cycad plant (above) and the limb of a rare, prehistoric Wollemi pine tree (below) The world’s forests slowly recovered from the Permian extinctions. In the hot and dry Triassic Period (248-206 mya), there were primitive conifers, ferns and gingkos. One common variety of primitive conifers was the Araucariae. The world became more humid during the Jurassic Period (206-144 mya), helping the growth of conifer, fern and cycad forests in the tropics, while conifers dominated the forests toward the polar regions. Flowering plants began to evolve in the late Jurassic but began to dominate the landscape during the Cretaceous Period (144-65 mya). At the end of the Cretaceous Period there was another mass extinction of species, brought on by a range of factors, including a cooling of the planet, and exacerbated by what is thought to be the impact of a massive asteroid. NN IVER S British novelist John Fowles Did you know? Plant fossils Herbivores: An artist’s impression of the dinosaur Abydosaurus mcintoshi feeding on conifer trees A h The first trees C E T Evolution did not intend trees to grow singly. Far more than ourselves they are social creatures, and no more natural as isolated specimens than man is as a marooned sailor or hermit SS M A A L T 10t Ancient forests he forests we see around the world today are not the same forests inhabited by our prehistoric ancestors. Many of the plant and animal inhabitants of forests have evolved as a result of the changing landforms and climates that shape a forest. However other species have not changed significantly over millions of years. In the Silurian Age, 443 to 416 million years ago (mya), there were no forests as we now know them. Most plant life was short and restricted to narrow bands near the edge of water. In the Devonian Period (416-354 mya) larger plants began to evolve. Archaeopteris (below left) is the first known modern tree, growing up to 30m with a trunk diameter of 1m. Unlike previous plants, it developed a deep root system and thick trunk, enabling it to survive winds and drought. It had broad fern-like leaves that created shade and its shed leaves would have covered the ground with organic matter, allowing other plants and animals to thrive in the shade of the trees, creating a new biome. It reproduced from two different kinds of spores — large egg and small sperm spores. The fossilised remains of Archaeopteris have been found all around the world, showing that it was capable of surviving in many different environments, from tropical to sub-polar. Fossils also show there was usually a single dominant species of Archaeopteris in a given forest area. It became extinct in the late Devonian and the forest biome temporarily disappeared. Relation: A 135 millionyear-old fossil alongside a living conifer metasequoia branch RY 6 Series 11 A w Evidence of what forests looked like in the past comes from plant fossils. When prehistoric plants died they either left impressions in mud, or were covered by layers of silt, which then hardened into stone. Sometimes the plant simply rotted away leaving other silts or chemicals to fill the cavity and harden into stone, or in some cases the plant itself was transformed by chemical reactions into stone. Some plant fossils are little more than leaf patterns in the middle of sedimentary rocks, while others are complete trees or plants preserved in stone (see Petrified forests). n Although common across the world in Triassic and Jurassic forests, Araucarias died out in the northern hemisphere and became native only to areas of the southern hemisphere. Surviving species include the Norfolk Island pine (Araucaria heterophylla), the monkey puzzle tree (A. araucana) and also the Wollemi pine (Wollemia nobilis). n The evolution of larger trees with deeper roots made the land more hospitable to animal life. Without trees there would have been nothing for herbivorous land-dwelling animals to eat and few places for them to be protected from the glare of the sun. Living fossils There are several species of plants that are considered living fossils because they are found in the fossil records from millions of years ago and many only exist in small remnant populations. Ginkgo trees (left), native to China, are known from the fossil record dating back to the Permian Period. There is an 840-year-old ginkgo tree in Seoul. Australia also has a living fossil, the Wollemi pine, which has fossil ancestors dating back to the Jurassic era. It was thought to be extinct until it was found in the Wollemi National Park in 1994. Petrified forests Carboniferous ferneries to Permian deserts In the Carboniferous Period (354-290 mya) Earth became hotter and more humid, allowing new kinds of plants to evolve to replace the forests made extinct at the end of the Devonian. These were not forests that we would recognise, they were populated mostly by giant ferns, horsetails and huge lycopsids. Lycopsids were gigantic, weird-looking plants as tall as 50m. An ice age at the end of the Carboniferous shrank the forests. When the ice sheets receded in the Permian Period (290-248 mya), the world became hotter and drier, with sparse forests populated by small stands of ferns and primitive conifers. A major extinction event wiped out 95 per cent of all land vegetation. Carboniferous is from carbo, the Latin word for coal, and the period was named after the fact that coal comes from the fossilised remains of the forests of this time. Cenezoic forests In the Cenezoic Era (65 mya to the present), the plants quickly recovered and thick forests spread across the globe. There were even lush forests in what is today Antarctica and across what is today the desert of Central Australia. These began to thin out when the climate became cooler and drier about 43 million years ago and Antarctica’s thick forests were covered with an ice sheet. The separation of the continents resulted in isolated southern continents with distinctive forests. About 25 million years ago grasslands started to spread, eventually dominating large areas of the planet. By about two million years ago, this encouraged some of the great ape species to leave the trees and the forests and to forage in the grasslands. At the start of the Pleistocene, the planet entered an ice age. Several alternating periods of warmer weather and ice ages made significant changes to the forests. At the end of the last ice age, about 10,000 years ago, the forests of the Taiga spread northward, creating what is still the world’s largest forest. AP Photo Prehistoric vegetarians The evolution of forests on land made possible animal life on land. There is plenty of evidence for prehistoric creatures munching on trees from primeval forests. The earliest forests would have provided rotting leaves for microbes to break down and primitive species of insects to make homes in. The earliest herbivores are believed to have evolved about 320 million years ago but these merely tore leaves off plants and swallowed them whole, allowing their gut to process the leaves. About 290 million years ago, the first herbivores capable of efficiently digesting plant matter began to appear. The earliest known was a synapsid — a reptilian ancestor of mammals known as Suminia getmanovi — which had sharp teeth capable of shredding the leaves to process them better. It was also well adapted to climbing to the tops of trees to reach the tender leaves. When dinosaurs roamed Earth between 215 and 65 million years ago, most evolved as plant eaters. Unique: mammal bones have been found in fossilised tree resin from more than 18 million years ago Around the world there are various places where prehistoric forests have left remnants known as petrified forests. There are petrified forests in places such as Lake Macquarie in NSW, Bridgewater in Victoria and Chinchilla in Queensland. On the island of Lesbos in Greece, there is also a stone forest. In the US the most famous example is the Petrified Forest National Park in Arizona. Petrified means literally turned to stone or rock — from the Greek “petros” meaning stone — which happens when the wood is fossilised (see Plant fossils). The stone in petrified forests still resembles wood but is actually stone. Enduring: Petrified remains of trees in South Australia’s Canunda National Park Amber n The monkey puzzle tree (above) was first seen by Europeans in 1780 and initially called the Chile pine. In about 1850 someone remarked that it would “puzzle a monkey to climb it’’ after which it became known as the monkey-puzzler or the monkey puzzle tree. n Petrified wood is the state gem of Washington in the US. It is often made into jewellery and other decorative objects. n Because the cellulose in plants was hard to digest, some species of dinosaurs swallowed stones to help grind up the material. Known as gastroliths, these have been found with the remains of dinosaurs. n Mosquitoes have been found trapped in amber dating from the time of the dinosaurs, causing some to speculate that they may hold the blood of dinosaurs, making it possible to clone the beasts. Author Michael Crichton used this as the basis for his novel Jurassic Park. Sources and further study The forests of prehistoric times have left interesting traces in the form of amber. This is fossilised tree sap that has become altered over time, by heat and pressure that causes the chemical composition to change, making it more stable and longer-lasting. Often the amber has been found with animals or plant matter trapped inside. The oldest known deposits of amber come from the Carboniferous Period 320 million years ago. But the most significant deposits are those from the shores of the Baltic Sea dating back 60 million years. Fossil, by Paul Taylor (Penguin/DK) Prehistoric Life, by William Lindsay (Penguin/DK) The Complete Guide To Prehistoric Life, by Tim Haines and Paul Chambers (BBC Books) First Life (BBC/Roadshow DVD) The Complete Walking With series (BBC/Roadshow DVD) The First Forests devoniantimes.org/opportunity/ forests.html Cl@ssmate For free teacher resources visit dailytelegraph.com.au/classmate EVERY TUESDAY Email: [email protected] Phone: 9288 2542 Editor: Troy Lennon Graphics: Paul Leigh and Will Pearce