A 2011 genetic study showed that examined M. columbi specimens were grouped within a subclade of woolly mammoths. This suggests that the two populations interbred and produced fertile offspring. It also suggested that a North American form known as Mammuthus jeffersonii may be a hybrid between the two species.
Larry Agenbroad, a respected researcher, believes that the M. imperator is a non-valid name given to unusually large M. columbi. Given that that proboscidean tusks grow throughout the animal's life, older animals will tend to have longer tusks, and so are more likely to cross. He has also mooted the alternative interpretation that M. imperator represents a subspecies of large M. columbi. This has also been accepted by other scientists.
The Columbian mammoth was one of the last members of the American megafauna to go extinct, with the date of disappearance generally set at approximately 12,500 years ago. However, several specimens have been dated to 9,000 years ago or less, and one near Nashville, Tennessee, was dated to only about 7,800 years ago. However, dates younger than 11,000 BP have not been viewed as credible.
The earliest known proboscideans, the clade which contains the elephants, existed about 55 million years ago around the Tethys Sea area. The closest relatives of the Proboscidea are the sirenians and the hyraxes. The family elephantidae existed six million years ago in Africa, and includes the living elephants and the mammoths. Among many now extinct clades, the mastodon is only a distant relative of the mammoths, and part of the separate mammutidae family which diverged 25 million years before the mammoths evolved. The following cladogram shows the placement of the Columbian mammoth among other proboscideans, based on hyoid characteristics:
The Columbian mammoth was a savanna and grassland inhabitant, similar to the modern African elephant. Large males ranged from 3.7–4.0 m (12.1–13.1 ft) and weighed between 7–9 metric tons (7.7–9.9 short tons) with spiralled tusks that could grow up to 4.25 metres (13.9 ft) long.
It was a herbivore, with a diet consisting of varied plant life ranging from grasses to conifers. It is also theorized that the Columbian Mammoth ate the giant fruits of North America such as the Osage-orange, Kentucky coffee and Honey locust as there was no other large herbivore in North America then that could ingest these fruits. Using studies of African elephants, it has been estimated that a large male would have eaten approximately 700 pounds (320 kg) of plant material daily. The average Columbian mammoth ate 300 pounds of vegetation a day.
Hair believed to have belonged to the Columbian mammoth has been discovered in the Bechan Cave, Utah, where mammoth dung has also been found. Some of this hair is coarse, and identical to that known to belong to woolly mammoths. Since this location is so far south, it is unlikely the hair belonged to woolly mammoths. The distribution and density of this fur on the living animal is unknown.