The South Polar region of the Cretaceous comprised the continent of East Gondwana–modern day Australia, Zealandia, and Antarctica–a product of the break-up of Gondwana in the Cretaceous Period. The southern region, during this time, was much warmer than it is today, ranging from perhaps in the latest Cretaceous Maastrichtian in what is now southeastern Australia. This prevented permanent ice sheets from developing and fostered polar forests, which were largely dominated by conifers, cycads, and ferns, and relied on a temperate climate and heavy rainfall. Major fossil-bearing geological formations that record this area are: the Santa Marta and Sobral Formations of Seymour Island off the Antarctic Peninsula; the Snow Hill Island, López de Bertodano, and the Hidden Lake Formations on James Ross Island also off the Antarctic Peninsula; and the Eumeralla and Wonthaggi Formations in Australia.
The South Polar region housed many endemic species, including several relict forms that had gone extinct elsewhere by the Cretaceous. Of the dinosaur assemblage, the most diverse were the small Elasmarian ornithopod dinosaurs. The South Polar region also was home to the last labyrinthodont amphibian, Koolasuchus. The isolation of Antarctica produced a distinct ecosystem of marine life called the Weddellian Province.
Landscape Geology
The Latady Basin in the southern Antarctic Peninsula–Palmer Land–contains volcanic rock, evidencing a large magmatic event in the Middle Cretaceous referred to as the Palmer Land event. This area has yielded an array of both macro- and micro- plant and mollusk fossils representative of the Early Cretaceous, as well as the Middle to Late Jurassic. The area that is now the Antarctic Peninsula, throughout the Mesozoic, was subducting the proto-Pacific plate, causing volcanic activity.
An important fossil-bearing formation is the Santa Marta Formation at James Ross Island off the Antarctic Peninsula, one of the most significant formations of the Southern Hemisphere, representing a high diversity terrestrial flora and fauna of the Late Cretaceous polar region. Seymour Island is similar in this respect, the area of discovery for vertebrate and invertebrate creatures–such as plesiosaurs–of the Late Cretaceous, extending into the Eocene. Other Cretaceous fossil-bearing formations in Antarctica are the Snow Hill Island Formation, the López de Bertodano Formation, and the Hidden Lake Formation, also on James Ross Island.
The Eumeralla Formation of Dinosaur Cove and the Wonthaggi Formation in Victoria, Australia, contain a number of dinosaur fossils and tracks from the Early Cretaceous. The Tahora Formation represents the reptile assemblage of Cretaceous New Zealand.
The Eromanga Sea was an inland sea across what would be Australia that formed in the Early Cretaceous. The sea reached the Eromanga Basin from the north via the Carpentarian Basin. The southern end of the sea comprised lagoons and rivers, and to the east in Surat Basin a bay. When India drifted away from Australia in the Early Cretaceous, the Perth Basin also filled with seawater. The area that would be the Coral Sea was a rift valley. As Australia and Antarctica drifted apart throughout the Cretaceous, a sea formed in between them.
Vegetation
The Cretaceous is characterized by warm global temperatures caused by the high amounts of carbon dioxide and possibly methane greenhouse gases in the atmosphere. This caused a lack of permanent ice coverage in the polar regions, though the carbon dioxide level dropped between 115 and 66 million years ago (mya), possibly allowing some permanent ice cover. It is possible that, throughout the Cretaceous, several small ice sheets developed. Increased tectonic activity, causing more geothermal heat, may have prevented glaciation and increased global temperatures. Temperatures may have been up to 15 °C (27 °F) warmer than they are in the modern age.
Jurassic The landscape of the Middle Jurassic polar region has been reconstructed from the remains of forests exposed in New Zealand, which were between 70 and 80°S during the Jurassic. The vegetation was largely made up of conifers, cycads, and other gymnosperms, as well as ferns; on the forest floor grew lycopods, bryophytes, fungi, and algae. It had a temperate climate with heavy rainfall.
Early Cretaceous In the Early Cretaceous, East Gondwana (Australia, Antarctica and Zealandia) had started to split away from South America, and India and Madagascar also began to separate at around the same time. The tropical zone may have extended, during the Cretaceous, to 32°S, allowing year-round tree growth in the Antarctic in polar forests. The discovery of several mature evergreen and deciduous trees indicate a warm-to-cool temperature with moderate seasons lacking widespread freezing, at least between the latitudes 70 and 85°S. However, it is also possible that the plant life may only be representative of the warm summer months. Much of what is known of the plant life of East Gondwana during the Cretaceous consists of pollen remains and leaf compressions from the northern Antarctic Peninsula. Depending on the latitude, the polar winters may have lasted from six weeks to four and a half months.
However, rocks from the Early Cretaceous Wonthaggi Formation in southeastern Australia evidence seasonally frozen ground. Its geographical positioning in the Early Cretaceous at around 78°S indicates this area experienced one to three months of darkness in winters, and this area is representative of a glacial-fed floodplain. Evidence of Early Cretaceous glaciation and cold climates was discovered in sediments in the Eromanga Basin in modern-day central Australia, or 60 to 80°S in the Early Cretaceous. This basin was a large inland sea in the Cretaceous. Nonetheless, similar formations could have been created by simply debris flow, and so it is possible that glaciation did not ever occur there. The total polar ice coverage during the Mesozoic may have been a third of the size as it is in modern times, though cold snaps of subfreezing temperatures possibly occurred throughout the Early Cretaceous.
Late Cretaceous The canopy of the polar forests around present-day Alexander Island, which was around 75°S in the Middle Cretaceous, were predominantly evergreen, and likely most South Polar forests were as well, and comprised mainly araucarian and podocarp conifers. It is thought that these trees remained dormant throughout the polar winters until summers under the midnight sun.
Evidence of flowering plants dating to around 80 Ma in the Late Cretaceous suggests the existence of temperate forests–similar to those in present-day Australia, New Zealand, and southern South America. Some flower remains were discovered near 60°S, and it is possible at such a low latitude that this area was subject to polar winters and seasonal weather, though the flowers suggest an annual temperature range of and a rainy climate.
Pollen remains from southeastern Australia are identical to living plant species of Australia: conifers, flowering plants that inhabit areas with high rainfall and a Mediterranean climate, and sclerophyllous scrublands, indicating a unique landscape of rainforest and open bushland. Indicated by the size of the tree rings on fossil trees, the Antarctic polar forests featured a cooling trend throughout the Maastrichtian age 72 to 66 mya, from a mean annual temperature of to a more seasonally extreme . These plants likely survived the Cretaceous–Paleogene extinction event, which killed off most life 66 Ma, on the volcanic Antarctic Peninsula; plant fossils dating to 60 Ma in the Paleocene from Seymour Island off this peninsula are recognized as being the ancestors of temperate plants inhabiting modern-day Australia and South America.
The Late Cretaceous (Campanian) Zamek and Half Three Point Formations of King George Island were located at 60°S and display a rich assemblage of fossil flora, such as Podocarpus; Araucaria; the leptosporangiate ferns Cladophlebis and Clavifera; and a variety of Magnoliopsida flowering plants, Dicotylophyllum, Myrciophyllum santacruzensis, Nothofagus, Sterculiaephyllum australis, Monimiophyllum, and so forth.Zamek Hill assemblage at Fossilworks.orgSkua Bay assemblage at Fossilworks.orgHalf Three Point assemblage at Fossilworks.org The Sobral Formation of Seymour Island spanning the Cretaceous–Paleogene boundary at a paleolatitude of 63°S provided a new genus of fossil flower in the family Cunoniaceae, Eucryphiaceoxylon eucryphioides.Sobral Formation at Fossilworks.org
Ecology
Much as in Australia today, East Gondwana played host to many endemic animals, which included many relict species of families that had gone extinct in the rest of the Cretaceous world. It is possible the polar regions of the Late Cretaceous had been inhabited by groups of plants and animals whose ancestry can be traced back to the Ordovician. The gradual isolation of Antarctica in the Late Cretaceous created a distinct group of aquatic creatures called the Weddellian Province.
Dinosaurs Birds
The remains of the ancestor of modern birds, the Neornithes, are uncommon in the Mesozoic, with a large radiation occurring in the Neogene of Antarctica. However, the discovery of the Late Cretaceous Vegavis, a goose-like bird, on Vega Island indicates that the major modern bird groups were already common in the Cretaceous. A femur belonging to an unidentified seriema-like bird was also discovered on Vega Island. Bird footprints were preserved in Dinosaur Cove, and, being larger than most Cretaceous bird species, indicate an abundance of larger enantiornithe or ornithurine birds during the Early Cretaceous.
Two diving birds, possible primitive divers, were discovered in Late Cretaceous Chile and Antarctica: Neogaeornis and Polarornis. Polarornis may have been capable of both diving and flight. The earliest penguins, Crossvallia and Waimanu, are known from 61–62 Ma in the Paleocene, however molecular data suggests penguins first evolved in the Late Cretaceous. Given that these penguins were dated so close to the Cretaceous–Paleogene extinction event, the group either evolved before the event or very rapidly afterwards.
Non-avian
Dinosaur fossils are rare from the South Polar region, and major fossil-bearing locations are the James Ross Island group; Beardmore glacier in Antarctica; Roma, Queensland; Mangahouanga stream in New Zealand; and Dinosaur Cove in Victoria, Australia. The dinosaur remains of this region, such as those found in Victoria, consist only fragmentary pieces, making identification controversial. For example, disputed identifications include an allosaurid, which is more likely to be a Megaraptoran, the ceratopsian Serendipaceratops, which was likely to have been an ankylosaur, and the difficult-to-classify theropod Timimus have consequently been made.