The Lonely Island

            Part of what draws my research to far-away lands is studying how the history of different geographic regions have shaped the flora and fauna found within, known as the study of biogeography. This time around, I find myself in Australia – technically the largest island in the world (not going to delve into the island versus continent argument, technically Europe is just a series of peninsulas off Asia but I digress…) that has one of the most distinctive assortments of plants and animals found anywhere on our planet. Typically when we think of this uniqueness, termed endemism, it is measured by how many species are found only in a certain geographic region, country, island, or continent. In Australia, it is an astonishing 80% of all the plants and animals are found nowhere else in the world – with an even more impressive 7 entire families of mammals, 4 families of birds, and 12 flowering plant families that are endemic. This all adds up to 7% of the world’s total number of species – a number that is greater than double the amount found in Europe and North American together!

            So it has been established that Australia has an impressive number of species, but what led to this phenomenal amount of uniqueness? Australia was once part of the supercontinent Gondwana connected 140 million years ago to what is present day South America, Africa, India, and Antarctica. As continental plates began to shift, Gondwana split apart leaving only Australia and Antarctica connected until around 50 million years ago, they split as well. After this point in time, many of the Australian plants and animals found themselves in isolation – when other diverse families such as Bovidae (cows, gazelles, etc..) spread across much of the rest of the world and formed new species, they never made it to Australia before the split from Antarctica, leaving them absent. Instead, Australian families such as the Dasyuridae (carnivorous marsupials), Macropodidae (kangaroos and kin), Menuridae (Lyrebirds), among many others diversified into a variety of forms and niches that world have normally been occupied by entire other families. Thus, it is Australia’s long history of isolation in the southern ocean distant from other continents that has led to its amazing array of endemic plants and animals.

            Mentioned briefly, some of the most fascinating aspects of Australia’s wildlife are the convergence, or the similarities between 2 or more unrelated groups of animals in their traits or features. On Australia, the majority of the larger forms are originated from marsupials instead of placental mammals as in the rest of the world. Some of these include –

  • Tasmanian Tiger (Marsupial, Dasyuridae) and Red Fox (Placental,
  • Sugar Glider (Marsupial, Petauridae) and Flying Squirrels (Placental, Sciuridae)
  • Planigale (Marsupial, Dasyuridae) and Deer Mice (Placental, Cricetidae)
  • Hopping Mice (Placental, Muridae) and Kangaroo Rats (Placental, Heteromyidae)
  • Tasmanian Devils (Marsupial, Dasyuridae) and Hyenas (Placental, Hyaenidae)

Quite an amazing example of convergent evolution when you consider that tiny Planigale is in the same family and the wolf sized Thylacine!


 

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