Short answers, pulled from the story.
Proboscidea is the taxonomic order of mammals that includes the elephants and their extinct relatives, formally described by J. Illiger in 1811. Three living species are currently recognised: the African bush elephant, the African forest elephant, and the Asian elephant.
The earliest known proboscideans, such as Eritherium, are found in Paleocene rocks in Africa dating to around 60 million years ago. These early members were much smaller than modern elephants.
The mammutid "Mammut" borsoni is estimated to have had an average adult male body mass of 16 tonnes, making it one of the largest land mammals ever documented. A fragmentary femur of Palaeoloxodon namadicus has led to speculative estimates as high as 22 tonnes, though that figure rests on a single partial specimen.
The longest tusk ever recorded was 5.02 metres long and belonged to the mammutid "Mammut" borsoni, found in Greece. Some mammoth tusks are thought to have weighed over 200 kilograms.
Island dwarfism in proboscideans is attributed to limited food resources and the absence of large predators, which reduced the survival advantage of large body size. Most dwarf proboscidean cases date to the Pleistocene, when fluctuating sea levels isolated elephant populations on islands across the Mediterranean, Indonesia, and the Channel Islands of California.
The collision of the Afro-Arabian plate with Eurasia during the Early Miocene, around 18-19 million years ago, opened a land corridor that allowed proboscideans to disperse out of Africa. They later crossed into North America via the Bering Land Bridge around 16-15 million years ago, and gomphotheres reached South America as part of the Great American interchange.