Procoptodon

Credit: Nix Illustration.

*Procoptodon* is an extinct genus of short-faced kangaroo that lived in Australia during the Pleistocene.

## Description

*Procoptodon* likely looked and moved similarly to kangaroos, however Procoptodon was massive compared to modern relatives. *P. goliah* was the largest of the bunch, being about 2.7 meters (8 feet 10 inches) tall and 240 kilograms (530 pounds) tall. The smallest specie is *P. gilli*, standing about 3 meters (3 feet, 3 inches) tall. *Procoptodon* coexisted with other genera of kangaroos, but specialize in tree leaves and shrubs. *P. goliah* is known by its flat face and forward-pointing eyes. Each foot bore a single clawed digit, which would have likely looked like hooves. Their paws were strange, each having two extended clawed digits. These traits made *Procoptodon* able to quickly stride through open plains, grasping at branches, and bringing them toward the animals mouth.

## Paleoecology

*Procoptodon* lived in dry, semiarid areas, located in South Australia and New South Wales. These vast areas are harsh, consisting of large treeless plains and sand dunes blown by the wind. However, Lake Menindee had a wetter and cooler climate during the time *Procoptodon* populations existed. Surrounding Lake Menindee, was a mosaic of sclerophyll forests, woodlands, savannahs and vast plains, where sand dunes formed around the edges of the lake. Fossilized footprints have been discovered on Kangaroo Island.

### Extinction

The reason *Procoptodon* fell into extinction is unclear, though there are multiple current theories. *Procoptodon* went extinct about 45,000 thousand years ago, though evidence states the genus may have prevailed as early as 18,000 thousand years ago. One theory states climate changes challenged the genus into extinction, while others state that *Procoptodon* fell victim to over hunting by humans. The main evidence for the overhunting theory is that the first humans crossed over to Australia around the same time *Procoptodon* went extinct, a time where the climate was relatively stable. However, no evidence of human predation and consumption has been found in the fossil record. New evidence suggests humans arrived in Australia between 10,000 and 15,000 years before the species became extinct.

Another theory states that the replacement of nutritious flammable plants with less flammable, less nutritious vegetation brought by humans caused increased forest fires, which may have had a toll on *Procoptodon* populations about 50,000 years ago. This statement is rivaled by *P. goliah*'s diet of chenopod saltbushes, particularily of the genus *Atriplex* being less flammable than most vegetation, being virtually unaffected by raging fires. This theory stems from *Procoptodon*'s main diet disappearing, causing the species to become extinct. At some point, kangaroos evolved prolonged breeding cycles, which limits *Procoptodon*'s from producing as many children than before the advancement was made.

## Paleobiology

### Locomotion

*P. goliah* was much too large to accelerate rapidly, which made the traditional hopping method of transportation impossible. To counteract this, the species hips and ankles were strengthened to resist torsion and twisting motions. It was more upright than others, which supports a bipedal one foot in front of the other mode of physical transport. These added modifications include wide thighs, which, in-turn made the species buttocks larger, which happens to be a trait bipedal animals share. Other sources claim that P. goliah was capable of hopping, which makes the species the largest hopping mammal on record. Further research says a 50-60 kilogram weight is optimal for large hopping marsupials. Hopping as a mode of transport for *P. goliah* and other large marsupials would risk snapping a tendon. If *P. goliah* were capable of hopping, the highest balance of height and weight would have peaked, due to the size of its body being the largest possible to support this form of locomotion.

On the more likely side, based on the bone structure and anatomy allowed by said bone structure, which are plantigrade hoppers at high speed and pentapedal at lower speeds, *P. goliah* may have walked in a fashion closer to hominids rather than kangaroos. This type of locomotion has been studied via musculoskeletal scaling patterns. As allowed by its body, the largest P. goliah could have peaked at would have likely been 2.7 meters (8 feet 10 inches) and been 240 kilograms (530 pounds). The team noticed increased stress in the tendon, which further points out the limited abilities for *P. goliah*, and body mass/locomotion rates. Ruptures spotted in the tendons show extensive elasticity in the limbs' muscles, making the ability to hop even more unlikely. Due to its transportation methods, the species may have had a high predation rate by humans.

### Feeding Patterns

Unlike the modern grazer kangaroos, *Procoptodon* was specialized to a diet of tree leaves and shrubs. The form of their robust craniums suit this type of diet, especially their flat molars and shortened faces, which supports larger masseter muscles. Masseter muscles allow for chewing. The microwear in P. goliah's teeth support a browsing diet. Large bicuspids, crenulated teeth crowns and and a large bony jaw present in *P. goliah* made for the ability to process, ingest, and digest large amounts of plant matter. Stable isotopic data suggests *P. goliah*'s diet consisted of plant matter consisting of a photosynthetic C4 pathway. Plants falling in this category are usually assumed to be grasses.

In the case of *Procoptodon*, the chenopod saltbushes attributed to semiarid Australian grasslands are a more likely source of C4. An intensification of arid climate in the second half of the Pleistocene caused *Procoptodon* to adapt to am abundance of dry plants. The fact that *P. goliah* was one of the most widespread macropodids in Australia presents further evidence that *P. goliah* was adapted to tougher vegetation. Admittedly, determining the preferences of extinct herbivores is very difficult. By analyzing teeth, wear, isotops, bone structure and biomeachanics, clues as to *P. goliah*'s diet have been deduced. *Procoptodon* would have eaten fibrous vegetables, and needed to consume salt, which may have been found near water sources, which would have made *P. goliah* able to travel to and from viable water sources, though the idea may need to be challenged.

## Species

* *P. browneorum*
* *P. cegsa*
* *P. gilli*
* *P. goliah*
* *P. maddocki*
* *P. mccoyi*
* *P. oreas*
* *P. otuel*
* *P. pusio*
* *P. rapha*
* *P. texasensis*
* *P. williamsi*

## Gallery

### Reconstructions

**Credit: Gredinia on DeviantArt.****Credit: Roman Uchytel.**
## References

https://en.wikipedia.org/wiki/Procoptodon