Polar dinosaurs in Australia
Encyclopedia
The South Polar dinosaurs proliferated during the Early Cretaceous
(145-100 Ma) while the continent
of Australia
was still linked to Antarctica to form East Gondwana
, a continent that had rifted from Africa
and drifted southward. Much of this southern continent lay inside the Antarctic Circle
, and the climate
there was unlike any that exists today. This led to fauna and flora that were unique to the time. Much of what is known about the fauna of Polar Australia comes from fossil beds found in Dinosaur Cove
and Flat Rocks on the Victoria
n coast of southeast Australia.
Several techniques have been used to deduce the ancient climate of Gondwana in the Early Cretaceous
. One technique involves looking at the levels of oxygen isotope
s in the rocks from the time. These have suggested estimated mean annual temperatures of between 0 and 8 °C (32 and 46.4 F). The rocks with associated mammal
and dinosaur
fossil
s show evidence of permafrost
, features such as ice wedging
, patterning and hummocked ground. Permafrost today occurs in temperature ranges of between -2 C.
Another method used to deduce the climate of the time is to use the types of plant
s found in the fossil record. The fossil record shows a floral community dominated by conifers, ginkgo
es, fern
s, cycad
s, bryophyte
s, horsetail
s and a few flowering plant
s. The plants indicated, through structural adaptations, a seasonal cold period and a mean annual temperature around 10 °C (50 °F) (higher than found by the oxygen isotope data) and the presence of ferns and bryophytes indicates rainy conditions. A large inland sea that extended into central Australia modified its continental climate.
The very lopsided distribution of land and ocean around the South Pole would have forced the ocean current
s and seasonal winds (monsoon
s) to flow across the polar area, stopping a cold pool from forming around the pole.
These studies show that during the Cretaceous
there were no polar ice cap
s, and forest
s would have extended all the way to the South Pole
, and life could have flourished there during the summer. However, the Earth's axial tilt
means that the regions inside the Antarctic circle
would still have experienced a polar night
: a period of sunless darkness and cold of up to six months, during which only the hardiest life forms could survive. This combination of a habitable terrain with a long polar night is an ecological circumstance that has no present day analogue.
animals, which included many relict species of families that had gone extinct in the rest of the Cretaceous world, among them giant Amphibian labyrinthodonts, such as Koolasuchus
. It is thought that since they survived in Gondwana, they could survive the cold, in regions where it was too cold in winter for their competitors, the crocodile
s.
Mammals, including monotreme
s and possible placentals, have been found, and fragmentary remains of flying pterosaur
s. The teeth of plesiosaur
s (long-necked fish-eating reptiles) have also been found, suggesting that they lived in the rivers of Gondwana. Lungfish and possible crocodile teeth have also been found; both taxa are associated with distinctly non-polar conditions today, which further confuses our understanding of the climatic conditions of these fossil localities.
Dinosaur
fossils are rare in Australia, but dinosaurs found in the Victorian deposits include relics of the Jurassic
period, such as a relative of Allosaurus
, ornithomimosaurs, ankylosaurs, and hypsilophodont
- like dinosaurs, the commonest and most diverse group found thus far. The hypsilophodont-like dinosaurs provide a clue to the habits of the dinosaurs that lived in these polar
environment
s: one skull is interpreted as having 'large eyes', and casts of the brain of one individual has been interpreted as showing enlarged optic lobes. This interpretation has been used as a supporting argument for the theory that these dinosaurs may have had acute night vision
; if this were the case it may suggest that the hypsilophodont-like dinosaurs may have lived in the polar areas for most if not all of the year, including the weeks or months-long polar night
.
However these features may be a feature of ontogeny of the single taxon represented by a single skull fragment, and thus these characteristics may bear no indication of visual acuity of the adults of this taxon, for which no skull has been described. These polar conditions would've been exposed to 6 months of near-endless daylight during the summer also, where enlarged eyes and optic lobes would not have proven necessarily advantageous.
(65.5 Ma) which exterminated the non-avian dinosaurs and so many other of the world's species at the time. At the present time, this is merely speculation, but Australia may yet prove to be the best shot at finding fossils of post-Cretaceous, non-avian
dinosaurs.
However, small dinosaur fossils (teeth, bits of bone) found after the K/T boundary are likely to be derived fossil
s washed out of eroded Mesozoic
deposits, or remains of dinosaurs that died in the Cretaceous-Tertiary extinction event that were later washed into a lake or the sea.
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
(145-100 Ma) while the continent
Continent
A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...
of Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
was still linked to Antarctica to form East Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
, a continent that had rifted from Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
and drifted southward. Much of this southern continent lay inside the Antarctic Circle
Antarctic Circle
The Antarctic Circle is one of the five major circles of latitude that mark maps of the Earth. For 2011, it is the parallel of latitude that runs south of the Equator.-Description:...
, and the climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...
there was unlike any that exists today. This led to fauna and flora that were unique to the time. Much of what is known about the fauna of Polar Australia comes from fossil beds found in Dinosaur Cove
Dinosaur Cove
Not to be confused with the children's book series of the same name.Dinosaur Cove in Victoria, Australia is a fossil bearing site in south-east of the continent where the Otway Ranges meet the sea to the west of Cape Otway, adjacent to Great Otway National Park .The inaccessible ocean-front cliffs...
and Flat Rocks on the Victoria
Victoria (Australia)
Victoria is the second most populous state in Australia. Geographically the smallest mainland state, Victoria is bordered by New South Wales, South Australia, and Tasmania on Boundary Islet to the north, west and south respectively....
n coast of southeast Australia.
Gondwana’s climate
During the Cretaceous, Earth on average was warmer than it is now, making the polar regions more habitable.Several techniques have been used to deduce the ancient climate of Gondwana in the Early Cretaceous
Early Cretaceous
The Early Cretaceous or the Lower Cretaceous , is the earlier or lower of the two major divisions of the Cretaceous...
. One technique involves looking at the levels of oxygen isotope
Isotope
Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...
s in the rocks from the time. These have suggested estimated mean annual temperatures of between 0 and 8 °C (32 and 46.4 F). The rocks with associated mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
and dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s show evidence of permafrost
Permafrost
In geology, permafrost, cryotic soil or permafrost soil is soil at or below the freezing point of water for two or more years. Ice is not always present, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of...
, features such as ice wedging
Ice wedge
An ice wedge is a crack in the ground formed by a narrow or thin piece of ice that measures up to 3-4 metres wide at ground level and extends downwards into the ground up to several metres. During the winter months, the water in the ground freezes and expands...
, patterning and hummocked ground. Permafrost today occurs in temperature ranges of between -2 C.
Another method used to deduce the climate of the time is to use the types of plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s found in the fossil record. The fossil record shows a floral community dominated by conifers, ginkgo
Ginkgo
Ginkgo , also spelled gingko and known as the Maidenhair Tree, is a unique species of tree with no close living relatives...
es, fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s, cycad
Cycad
Cycads are seed plants typically characterized by a stout and woody trunk with a crown of large, hard and stiff, evergreen leaves. They usually have pinnate leaves. The individual plants are either all male or all female . Cycads vary in size from having a trunk that is only a few centimeters...
s, bryophyte
Bryophyte
Bryophyte is a traditional name used to refer to all embryophytes that do not have true vascular tissue and are therefore called 'non-vascular plants'. Some bryophytes do have specialized tissues for the transport of water; however since these do not contain lignin, they are not considered to be...
s, horsetail
Horsetail
Equisetum is the only living genus in the Equisetaceae, a family of vascular plants that reproduce by spores rather than seeds.Equisetum is a "living fossil", as it is the only living genus of the entire class Equisetopsida, which for over one hundred million years was much more diverse and...
s and a few flowering plant
Flowering plant
The flowering plants , also known as Angiospermae or Magnoliophyta, are the most diverse group of land plants. Angiosperms are seed-producing plants like the gymnosperms and can be distinguished from the gymnosperms by a series of synapomorphies...
s. The plants indicated, through structural adaptations, a seasonal cold period and a mean annual temperature around 10 °C (50 °F) (higher than found by the oxygen isotope data) and the presence of ferns and bryophytes indicates rainy conditions. A large inland sea that extended into central Australia modified its continental climate.
The very lopsided distribution of land and ocean around the South Pole would have forced the ocean current
Ocean current
An ocean current is a continuous, directed movement of ocean water generated by the forces acting upon this mean flow, such as breaking waves, wind, Coriolis effect, cabbeling, temperature and salinity differences and tides caused by the gravitational pull of the Moon and the Sun...
s and seasonal winds (monsoon
Monsoon
Monsoon is traditionally defined as a seasonal reversing wind accompanied by corresponding changes in precipitation, but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea...
s) to flow across the polar area, stopping a cold pool from forming around the pole.
These studies show that during the Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
there were no polar ice cap
Ice sheet
An ice sheet is a mass of glacier ice that covers surrounding terrain and is greater than 50,000 km² , thus also known as continental glacier...
s, and forest
Forest
A forest, also referred to as a wood or the woods, is an area with a high density of trees. As with cities, depending where you are in the world, what is considered a forest may vary significantly in size and have various classification according to how and what of the forest is composed...
s would have extended all the way to the South Pole
South Pole
The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is one of the two points where the Earth's axis of rotation intersects its surface. It is the southernmost point on the surface of the Earth and lies on the opposite side of the Earth from the North Pole...
, and life could have flourished there during the summer. However, the Earth's axial tilt
Axial tilt
In astronomy, axial tilt is the angle between an object's rotational axis, and a line perpendicular to its orbital plane...
means that the regions inside the Antarctic circle
Antarctic Circle
The Antarctic Circle is one of the five major circles of latitude that mark maps of the Earth. For 2011, it is the parallel of latitude that runs south of the Equator.-Description:...
would still have experienced a polar night
Polar night
The polar night occurs when the night lasts for more than 24 hours. This occurs only inside the polar circles. The opposite phenomenon, the polar day, or midnight sun, occurs when the sun stays above the horizon for more than 24 hours.-Description:...
: a period of sunless darkness and cold of up to six months, during which only the hardiest life forms could survive. This combination of a habitable terrain with a long polar night is an ecological circumstance that has no present day analogue.
Gondwana’s ancient fauna
Much as in Australia today, East Gondwana played host to many endemicEndemic (ecology)
Endemism is the ecological state of being unique to a defined geographic location, such as an island, nation or other defined zone, or habitat type; organisms that are indigenous to a place are not endemic to it if they are also found elsewhere. For example, all species of lemur are endemic to the...
animals, which included many relict species of families that had gone extinct in the rest of the Cretaceous world, among them giant Amphibian labyrinthodonts, such as Koolasuchus
Koolasuchus
Koolasuchus is an extinct genus of brachyopoid temnospondyl in the family Chigutisauridae. Fossils have been found from Victoria, Australia and date back 120 Ma to the Aptian stage of the Early Cretaceous. Koolasuchus is the latest known temnospondyl. Koolasuchus is known from several fragments of...
. It is thought that since they survived in Gondwana, they could survive the cold, in regions where it was too cold in winter for their competitors, the crocodile
Crocodile
A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...
s.
Mammals, including monotreme
Monotreme
Monotremes are mammals that lay eggs instead of giving birth to live young like marsupials and placental mammals...
s and possible placentals, have been found, and fragmentary remains of flying pterosaur
Pterosaur
Pterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
s. The teeth of plesiosaur
Plesiosaur
Plesiosauroidea is an extinct clade of carnivorous plesiosaur marine reptiles. Plesiosauroids, are known from the Jurassic and Cretaceous Periods...
s (long-necked fish-eating reptiles) have also been found, suggesting that they lived in the rivers of Gondwana. Lungfish and possible crocodile teeth have also been found; both taxa are associated with distinctly non-polar conditions today, which further confuses our understanding of the climatic conditions of these fossil localities.
Dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
fossils are rare in Australia, but dinosaurs found in the Victorian deposits include relics of the Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
period, such as a relative of Allosaurus
Allosaurus
Allosaurus is a genus of large theropod dinosaur that lived 155 to 150 million years ago during the late Jurassic period . The name Allosaurus means "different lizard". It is derived from the Greek /allos and /sauros...
, ornithomimosaurs, ankylosaurs, and hypsilophodont
Hypsilophodont
Hypsilophodonts were small ornithopod dinosaurs, regarded as fast, herbivorous bipeds on the order of 1–2 meters long . They are known from Asia, Australia, Europe, New Zealand, North America, and South America, from rocks of Middle Jurassic to late Cretaceous age...
- like dinosaurs, the commonest and most diverse group found thus far. The hypsilophodont-like dinosaurs provide a clue to the habits of the dinosaurs that lived in these polar
Geographical pole
A geographical pole is either of the two points—the north pole and the south pole—on the surface of a rotating planet where the axis of rotation meets the surface of the body...
environment
Natural environment
The natural environment encompasses all living and non-living things occurring naturally on Earth or some region thereof. It is an environment that encompasses the interaction of all living species....
s: one skull is interpreted as having 'large eyes', and casts of the brain of one individual has been interpreted as showing enlarged optic lobes. This interpretation has been used as a supporting argument for the theory that these dinosaurs may have had acute night vision
Night vision
Night vision is the ability to see in low light conditions. Whether by biological or technological means, night vision is made possible by a combination of two approaches: sufficient spectral range, and sufficient intensity range...
; if this were the case it may suggest that the hypsilophodont-like dinosaurs may have lived in the polar areas for most if not all of the year, including the weeks or months-long polar night
Polar night
The polar night occurs when the night lasts for more than 24 hours. This occurs only inside the polar circles. The opposite phenomenon, the polar day, or midnight sun, occurs when the sun stays above the horizon for more than 24 hours.-Description:...
.
However these features may be a feature of ontogeny of the single taxon represented by a single skull fragment, and thus these characteristics may bear no indication of visual acuity of the adults of this taxon, for which no skull has been described. These polar conditions would've been exposed to 6 months of near-endless daylight during the summer also, where enlarged eyes and optic lobes would not have proven necessarily advantageous.
Post K/T dinosaurs?
Given that the dinosaurs and other fauna of Cretaceous were well adapted for living in long periods of dark and cold weather, it has been postulated that this community might have survived the Cretaceous-Tertiary extinction eventCretaceous-Tertiary extinction event
The Cretaceous–Paleogene extinction event, formerly named and still commonly referred to as the Cretaceous-Tertiary extinction event, occurred approximately 65.5 million years ago at the end of the Maastrichtian age of the Cretaceous period. It was a large-scale mass extinction of animal and plant...
(65.5 Ma) which exterminated the non-avian dinosaurs and so many other of the world's species at the time. At the present time, this is merely speculation, but Australia may yet prove to be the best shot at finding fossils of post-Cretaceous, non-avian
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
dinosaurs.
- "Reports earlier this year that dwarf mammoths survived to early historical times, in islands off the coast of Siberia, give force to such speculation. If dinosaurs found a similar haven in which they outlived the rest of their kind, then we think polar Gondwana, including southeastern Australia, is a likely place to look for it."
However, small dinosaur fossils (teeth, bits of bone) found after the K/T boundary are likely to be derived fossil
Derived fossil
A derived fossil or reworked fossil is a fossil found in rock made later than when the fossilized animal or plant died: it happens when a hard fossil is freed from a soft rock formation by erosion and redeposited in a currently forming sedimentary deposit....
s washed out of eroded Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
deposits, or remains of dinosaurs that died in the Cretaceous-Tertiary extinction event that were later washed into a lake or the sea.
See also
- Dinosaur DreamingDinosaur DreamingDinosaur Dreaming is a Palaeontological site situated near Inverloch, Victoria, Australia. Remains of primitive mammals from the Cretaceous Age were first uncovered there in 1997 by researchers from Museum Victoria and the Monash University Science Centre....
- Dinosaur CoveDinosaur CoveNot to be confused with the children's book series of the same name.Dinosaur Cove in Victoria, Australia is a fossil bearing site in south-east of the continent where the Otway Ranges meet the sea to the west of Cape Otway, adjacent to Great Otway National Park .The inaccessible ocean-front cliffs...
- Geology of AntarcticaGeology of Antarctica-Geological history and paleontology:More than 170 million years ago, Antarctica was part of the supercontinent Gondwana. Over time Gondwana broke apart and Antarctica as we know it today was formed around 25 million years ago.-Paleozoic era :...
, including paleontology