Monotreme Monday: the Platypus

Welcome to Monotreme Monday! This platform is a short, written series focusing on the incredible adaptations of Monotremes!

Monotremes make up one out of the three main groups in the class Mammalia , where they are most popularly known for their egg-laying capabilities. In today’s edition of Monotreme Monday, we will be focusing on the Platypus, one of the five species of monotremes still alive today.

Once being a very popular character in Phineas and Ferb, Perry the Platypus was possibly one of the very first introductions of Monotremes for many. Although depicted as a blue, beaver tailed, duck billed creature in the show, the actual appearance of platypuses is more subdued.

© Hans and Judy Besage—Mary Evans Picture Library Ltd/age fotostock

The platypus, Ornithorhynchus anatinus, is endemic to most of the eastern Australian coast along with Tasmania and King Island, seen in Figure 1; there is also a small group of platypuses that were introduced to Kangaroo Island (Bino et al., 2019). As you can see from the map, a majority of recorded sightings from the Australian government atlas shows high concentrations of Platypuses at the southeastern coast where many permanent river systems span from tropical to alpine environments (Bino et al., 2019). The river systems allow for dispersal of young to new areas of their habitat, which is a common behavior seen often in juveniles ranging from 7-8 months of age (Furlan et al., 2013).

Figure 1. Distribution of Platypus based on Australian state government records between 1760-2017 (Bino et al., 2019).

Platypuses often inhabit areas near fresh bodies of water, including a range from fast moving streams to slow-moving pools with coarse layers of substrate on the bottom. The substrate usually consists of pebbles or gravel. Here, the platypus will create an underground burrow, constructed between mangled and submerged tree roots right above water level (Bino et al., 2019). An example image of what the burrows look like can be seen in Figure 2 and 3. The platypus diet primarily consists of aquatic invertebrates including insects, shrimp, and crayfish. Less often they can also be seen enjoying other aquatic animals, including tadpoles, small fish, and aquatic snails (Grant 2015).

Figure 2. An example of a Platypus burrow hole (Art done by  David Nockels © Look and Learn).
Figure 3. A platypus emerging from its burrow near a bank (Thomas et al. 2019).

Although classified as mammals, a number of characteristics reflected in the platypus can be see in fish, birds, and reptiles. Some of these characteristics include egg laying capabilities, venomous spurs, and an electroreceptive bill.

Egg laying is not a common character seen in mammals. In fact, this trait is one of the main classifiers for Monotremes. Female Platypuses will go through a gestation period of about 21 days, where the offspring will begin to develop. After the gestation period, the female will lay her eggs in the burrow, usually producing between 1-3 eggs each breeding season. The mother will then start the incubation stage, where the eggs will be curled up to the mothers abdomen and tail for about 10 days (Grant 2015). Offspring will then start to hatch from the eggs, breaking through the eggshell with teeth that will later be lost. After hatching, the babies will experience large scale developmental changes, including the development of a bill after five days, webbed feet after 24 days, and fur growing in within the first 11 weeks of life (Manger et al., 1998). For the first three to four months, offspring will remain in the burrow protected from outside dangers. Here they will start to feed on milk produced from the mothers mammary glands. These glands are located under the skin of the mother and occupy most of the abdomen . As the lactation period begins to close around 114-145 days after hatching, the juvenile platypuses will lose their teeth and replace them with grinding pads made out of keratin (Grant 2015).

All platypuses are born with venomous spurs that are used later in life. These spurs are present in both males and females when hatched, contained within a sheath until about 9-12 months of age. At that point, females will permanently shed these spurs while the males will retain them and start producing venom (Whittington and Belov 2014). It is speculated that males use these spurs primary during matting season, causing seasonal production of venom. The platypus is the only mammal currently known to produce venom seasonally (Grant 2015, Wong et al., 2012). Although capable of causing extreme pain, and in certain cases causing paralysis to other male platypuses, the venom will only be fatal to smaller animals (Bino et al., 2019).

One of the most well known features of the Platypus is the ‘duck-like’ bill. Although their bill can resemble that of a duck’s, it is actually much more similar to that of a shark’s nose. The Platypus bill is made up of a 40,000+ mucous receptor glands that can conduct electric signals and acts as an antenna when searching for prey. This type of electroreception has been originally observed in fish and some aquatic amphibians. Because of this, the Platypus uses its bill as a primary tool for hunting prey (Czech-Damal et al. 2013, Fjallbrant et al. 1998). The Platypus will rely solely on its bills electroreceptive capabilities while hunting underwater and because of this has a groove on either side of its head that will shut, concealing its eyes and ears underwater (Bino et al., 2019).

Figure 3. Up close look at Platypus bill and head (© San Diego Zoo Wildlife Alliance).

Unfortunately, the platypus has faced several threats over history starting in the late 19th and early 20th century when platypus populations were being hunted for their high quality fur. This was before scientific interest really took off, and only until 1912, when the platypus became legally protected, did studies of their unique anatomy and ecology start (Bino et al., 2019). Although there have been many studies done on the anatomy, ecology, and evolution of the platypus there has been little research interest in their conservation. The platypus faces many synergistic threats to its habitat including the increase in pollutants, changes in river/stream structure and hydrology, and the creation of dams and roads. Due to these issues, platypuses have been and continue to be displaced from their natural habitats and suffer consequences from the drastic change in its ecology (Bino et al., 2019). In 2016 the platypus was marked as a ‘Near Threatened’ species by the International Union for Conservation of Nature (IUCN).

There were several names the aboriginal peoples developed for the platypus, including ‘Mallangong’, ‘Tambreet’, ‘Gaya-dari’, ‘Boonaburra’, and ‘Lare-re-lar’. Along with these names, the aboriginal people also developed folk-lore that included biocultural and ecological connections to the platypus. One of the stories begin with Ancestral Spirits deciding on a totem’s formation. As the fish, birds, and marsupials of the land plead and reasoned with the platypus to join them in their group, the platypus consulted with an echidna and decided that it was not a part of any of these groups. The platypus explained to the fish, birds, and marsupials that since it shared traits with all the groups, it would remain friends with all of them instead of picking one identity over the other. Here, the platypus is commemorating the Great Spirit for its wisdom and creation of different animals (Bino et al., 2019).

Thanks for reading all about the wonders of platypuses! We hope to see you back for the next edition of Monotreme Monday!

Did you learn anything new? Feel free to share with us below!

References

https://ielc.libguides.com/sdzg/factsheets/platypus/summary

https://www.britannica.com/animal/platypus

Bino, G., Kingsford, R. T., Archer, M., Connolly, J. H., Day, J., Dias, K., … Whittington, C. (2019). The platypus: evolutionary history, biology, and an uncertain future. Journal of Mammalogy, 100, 308–327.

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