Recent research compared the variation between all of the described Diprotodon species with the variation in one of Australia's largest living marsupials, the eastern grey kangaroo, and found the range was comparable, with a near continent-wide distribution.
This left only two possible Diprotodon species differing only in size with the smaller being around half the size of the larger.
According to Gause’s "competitive exclusion principle", no two species with identical ecological requirements can coexist in a stable environment.
However, both the small and large diprotodonts coexisted throughout the Pleistocene and the size difference is similar to other sexually dimorphic living marsupials.
Further evidence is the battle damage common in competing males found on the larger specimens, but absent from the smaller.
Dental morphology also supports sexual dimorphism, with highly sexually dimorphic marsupials, such as the grey kangaroo, having different tooth sizes between males and females, but both sexes having the same dental morphology.
An identical dental morphology occurs in the large and small Diprotodon.
The taxonomic implication is that Owen's original Diprotodon optatum is the only valid species.


A single sexually dimorphic species allows behavioural interpretations.
All sexually dimorphic species of over 5 kg (11 lb) exhibit a polygynous breeding strategy.
A modern example of this is the gender segregation of elephants, where females and the young form family groups, while lone males fight for the right to mate with all the females of the group.
This behaviour is consistent with fossil finds where adult/juvenile fossil assemblages usually contain only female adult remains.

Cyclic variations in the strontium isotope ratios within the tooth enamel of a 300,000-year-old fossil imply that a population of Diprotodon undertook regular, seasonal migrations across the Darling Downs, making it the only known extinct or extant metatherian known to migrate annually.
The carbon-13 enamel content was found to have little variation, suggesting a relatively consistent diet through the course of a year containing a mix of both C₃ and C₄ plants.
A finite element method analysis of the skull estimated it had a bite force of around 4500 Newtons at the first molar to over 11,000 N at the fourth molar, values which were described as "exceptionally high", suggesting that Diprotodon was capable of processing tough, fibrous food.
Recent research compared the variation between all of the described Diprotodon species with the variation in one of Australia's largest living marsupials, the eastern grey kangaroo, and found the range was comparable, with a near continent-wide distribution. This left only two possible Diprotodon species differing only in size with the smaller being around half the size of the larger. According to Gause’s "competitive exclusion principle", no two species with identical ecological requirements can coexist in a stable environment. However, both the small and large diprotodonts coexisted throughout the Pleistocene and the size difference is similar to other sexually dimorphic living marsupials. Further evidence is the battle damage common in competing males found on the larger specimens, but absent from the smaller. Dental morphology also supports sexual dimorphism, with highly sexually dimorphic marsupials, such as the grey kangaroo, having different tooth sizes between males and females, but both sexes having the same dental morphology. An identical dental morphology occurs in the large and small Diprotodon. The taxonomic implication is that Owen's original Diprotodon optatum is the only valid species.

A single sexually dimorphic species allows behavioural interpretations. All sexually dimorphic species of over 5 kg (11 lb) exhibit a polygynous breeding strategy. A modern example of this is the gender segregation of elephants, where females and the young form family groups, while lone males fight for the right to mate with all the females of the group. This behaviour is consistent with fossil finds where adult/juvenile fossil assemblages usually contain only female adult remains.
Cyclic variations in the strontium isotope ratios within the tooth enamel of a 300,000-year-old fossil imply that a population of Diprotodon undertook regular, seasonal migrations across the Darling Downs, making it the only known extinct or extant metatherian known to migrate annually. The carbon-13 enamel content was found to have little variation, suggesting a relatively consistent diet through the course of a year containing a mix of both C₃ and C₄ plants. A finite element method analysis of the skull estimated it had a bite force of around 4500 Newtons at the first molar to over 11,000 N at the fourth molar, values which were described as "exceptionally high", suggesting that Diprotodon was capable of processing tough, fibrous food.
Diprotodon