Ornithorhynchus anatinus

Photo by Michael Jerrard on Unsplash

We're continuing the animal trend with a look at the Ornithorhynchus anatinus, or duck-billed platypus. Or just platypus. These guys also have several Aboriginal Australian names, as well as some interesting stories, which I encourage you to check out. There are two here to start you off :)

Overview

- Platypus Basics: What even is a platypus, actually.

- Etymology (What's the real plural form?)

- Taxonomy and History

- Habitat n' Feeding

- Funky Features (But wait, there's more)

- Citations

Platypus Basics (What even is a platypus?)

You've probably heard of the platypus as an egg-laying mammal that seems like an amalgamation of other animals, often including the duck and beaver. Their sizes between regions vary, but males are an average of 50 cm (20 in) with females being slightly smaller. Average adults weigh anywhere from 0.7 to 2.4 kg (1lb 5 oz to 5lb 5 oz) and can reportedly live up to 23 years old (Fenner et al., 1992). They are native to eastern Australia and semiaquatic, hunting in the water but living in burrows. They have some similarities with reptiles (eggs, for example) and some with mammals (they lactate!) but contrary to ABC News' headline, they are not bird-reptile-mammals (I wouldn't recommend reading the article, it's from 2008 and there's practically no information). They also have a lower body temperature than most mammals at 32°C.

They have a soft bill, brown fur, and webbed feet, which help them hunt. They eat small invertebrates, which they find using their bills - their eyes and nostrils are closed and their ears are protected in a groove that closes when they are underwater.  10-12 hours per day are spent hunting, mostly at night. This time is composed of dives up to ten minutes long, but usually not more than three (The Australian Museum, n.d.), paddling with the front feet and steering with the back (Queensland, 2016). They are mostly solitary.

Etymology

A quick disclaimer: the names I will be discussing here are not the original names of the platypus. I don't feel that I have the authority or knowledge to write about the Aboriginal names, but I definitely suggest reading about them. I will be using the word platypus because it is the most widely recognized name, but I believe that biology needs to move towards restoring Indigenous and Aboriginal names in taxonomy (here's an article on it!).

The term "platypus" is from Greek, like many other words in biology. It comes from the word πλατύπους, or platúpous, from πλατύς, or platús (broad or flat) and πούς, or poús (foot). 

The scientific name has gone through a few iterations. It was first scientifically described by George Shaw in 1799 as Platypus anatinus, and then independently by J. F. Blumenbach as Ornithorhynchus paradoxus in 1800. However, Platypus was already a genus of beetles, so Ornithorhynchus stuck (San Diego Zoo Wildlife Alliance Library, 2023). The platypus is a weird animal and caused a lot of debate around its taxonomy, but generally it's agreed that there is one species of platypus and it is Ornithorhynchus anatinus. Ornithorhynchus is yet another Greek word, meaning bird-like, and anatinus is Latin, meaning duck-like.

The plural form of "octopus" is a common debate. Octopi? Octopuses? Dare you venture into the world of ... octopodes? Less frequently (at least where I live) do we discuss the all-important issue of the correct plural form of "platypus." You may have heard platypi, platypuses, or simply platypus. I thought of "platyplural" or "platyplurals" while I was reading about these, but sadly did not find any documentation of either. If you type the different pluralisations out, as I have, "platypi" has the red squiggles that indicate a typo. The reason it is incorrect is because "platypus" comes from Greek, whereas "platypi" is pseudo-Latin. "Platypus" and "platypuses" are the most common plural forms. They're perfectly fine, but my favourite is platypodes. That's the correct plural form going by the Greek roots of "platypus" so it seems fitting to use it. Plus it's a fun word. Platypodes!

Let's say that you want to refer to a young platypus. You could call it a Young Platywan or some variation of "young platypus." However, you could also refer to it as a puggle, which is what a young echidna is called. I quite enjoy "platypup" and use it, because, as far as I can tell, there isn't a consensus on an official term.

TL;DR - It's platypodes for adults and platypups for the younguns. "Platypuses" is the most commonly used plural form and "puggle" may be used to refer to a young platypus ("puggle" is the word for a young echidna) but in my opinion, platypodes is more correct because of the roots of the word "platypus" and "platypups" is just a cute word.

Puggle photo! Courtesy of SciTech Daily

Taxonomy and History

You might be wondering what an echidna is and why I referenced it in the etymology section. 

Photo by Enguerrand Blanchy on Unsplash

This is an echidna. Like platypodes, they are native to Australia as well as New Guinea. Platypodes (which belong to a monotypic family) and echidnas (of which there are four species) both belong to the order Monotremata.

To make it a little clearer, here's a simpler version: Animalia > Chordata > Mammalia > Monotremata > Ornithorhynchidae > Ornithorhynchus > anatinus

Or, in another way, they belong to a monotypic genus (Ornithorhynchus) in a monotypic family (Ornithorhynchidae) and are part of the order Monotremata alongside echidnas. They are mammals, which are vertebrates, which are animals. (This is in the opposite direction from the previous version).

A quick note: while today platypodes belong to a monotypic taxon, there are four known prehistoric platypus species: three from Australia and one from South America (San Diego Zoo Wildlife Alliance Library, 2023).

As if a monotypic family isn't already interesting enough, platypodes have a unique place in evolutionary history. Genetic research shows that monotremes (mammals belonging to Monotremata) split from eutharians (placental mammals) and marsupials roughly 187 million years ago, with the two monotremes (echidnas and platypodes) splitting around 55 million years ago (Zhou et al., 2021). Monotremes belong to Mammalia, meaning they are mammals, but they do have certain links to other kinds of animals. For example, in addition to the X and Y sex chromosomes observed in mammals, male birds also have Z chromosomes. One of the platypus' X chromosomes is essentially equivalent to the chicken Z chromosome, and multiple studies have found a gene associated with determining sex in birds on it (Finkel, 2008). Bet'cha didn't expect that.

While we know platypodes (and monotremes in general) offer us insight into the evolution of mammals, the details are not completely clear. Two of the leading theories I have read about are the following: monotremes offer a link between reptiles evolving into mammals, as was the theory of many 18th century biologists, or monotremes are older mammals that connect modern mammals to more reptilian (but not truly reptilian) ancestors. Two main clades in Amniota (a clade of tetrapods) are sauropsids, or reptiles and birds, and synapsids, or mammals. It is thought that the two clades evolved from a common amniote ancestor, not necessarily one from the other. Monotremes' unique characteristics give us clues about what early mammals might have been like. One way to do this is to compare the genomes of different organisms to see how closely related they are. We can use the platypus reference genome and compare it with those of other mammals, reptiles, and birds to see how similar they are and construct a phylogenetic tree.

I would have written more on the evolution of mammals but honestly, it's not as easy as you might think and I've spent far too long on this already. Shall we go meet Australian Governor John Hunter?

Here we are with some history! Again, I am not Aboriginal Australian, and this section focuses on European descriptions of the platypus.

Governor John Hunter said that "a promiscuous intercourse between the different sexes of all these different animals ” may have led to the creation of the platypus (Zarrelli, 2016). Apparently, this was an actual thought, incorrect as it is. They were thought to be the work of taxidermists for a long time, and not without reason. After all, they're extraordinarily odd creatures, and if you don't think that yet, you will after reading about their weird features.

Platypodes were first encountered by Europeans in 1797 (San Diego Zoo Wildlife Alliance Library, 2023). In 1799, George Shaw (yes, the one who would be the first scientifically described the platypus) came across it in a laboratory study, going so far as to cut open the preserved specimen in search of the stitches that would prove it was fake. Spoiler alert, he found none. Decades later, biologists were still confused. The anatomist Robert Knox (yes, that Robert Knox) wrote that the methods used alone were enough to make a scientist suspicious.

"[scientists were] aware of the monstrous impostures which the artful Chinese had so frequently practised on European adventurers; in short, the scientific felt inclined to class this rare production of nature with eastern mermaids and other works of art" 

 (Hall, 1999).

Even after biologists agreed it was real, the platypus still confused them. What is it? Literally thousands of platypus specimens (whole and organs) were sent to Europe for studying, making the platypus' survival all the more impressive. The British anatomist Everard Home found that platypodes' sexual organs were similar to an oviparous reptile's, leading him to think that they were a kind of mammal more similar to birds. He published this research in 1802 (Hall, 1999). Biologists played hot potato with the taxonomy, bouncing platypodes between both new and existing groups (Zarrelli, 2016).

At this point, it seems like platypodes might just be a cosmic practical joke. Thirty years after they were first described, biologists still didn't know how they were reproducing and whether they lactate or not. It was the German anatomist Johann F. Meckel who described the platypus' mammary glands in detail in 1826 (Hall, 1999). After this discovery, scientists were so strongly convinced that platypodes must be mammals that they disregarded any reports of platypus eggs, despite Aboriginal Australian and early colonists' knowledge. The idea that all mammals give live birth was deeply entrenched in their minds at the time, even with Home's observations and other knowledge supporting the idea that platypodes lay eggs.

(editorial note: I found Meckel's original paper! It's here, but I was not able to read it because it is in Latin. If you want to go into biology, highly recommend learning Latin and Greek roots, at least. Thank you to another friend from biology club for translating portions).

So at this point, it was confirmed that platypodes lay eggs but also lactate. How would you classify them? Let me tell you some more. They lack wings or feathers, so they cannot be birds. They're warm-blooded and have diaphragms, which reptiles lack. They lactate but lay eggs, which ... doesn't that mean they aren't mammals?

Well, we know they're mammals now, but the confusion around them is entirely understandable.

Platypodes have historically been hunted for their fur, in addition to being hunted for scientific purposes, but they are now legally protected in all Australian states where they can be found and have been since 1912. Their numbers have been decreasing, likely due to habitat loss, and while they are currently not considered threatened, organizations such as the Australian Conservation Foundation are pushing for them to be classified as threatened (Australian Conservation Foundation).

Habitat n' Feeding

Blogspot seems to think I'm a platypus. That is, it seems to think I am inhabiting the coast of New South Wales (the southeastern of Australia), the natural habitat of the platypus.

As I mentioned earlier, platypodes are semiaquatic, so they live in places with ample amounts of freshwater. This could be near a river or lake, or sometimes dams. They'll tolerate water anywhere from 0-31°C and are more often found in the water than out of it (San Diego Zoo Wildlife Alliance Library, 2023). Their burrows are made near the water, often in riverbanks or the edges of ponds.

Now, how do they feed? Remember, their eyes and ears are closed underwater. The key is the bill. Around 40,000 electroreceptor skin cells are arranged in stripes on it (American Museum of Natural History, 2018). That means, in addition to being able to sense pressure, it is able to pick up tiny amounts of electric pulses produced by the movement of the platypus' prey (Scheich et al., 1986). To my knowledge, monotremes are the only mammals that use electroreceptors for hunting (the Guiana Dolphin has some electroreception but I'm not sure how much). It works particularly well for platypodes because water is a much better conductor of electricity than air - this is why there are far more fish that use forms of electrolocation than land animals.

A platypus will dive for 30-140 seconds, collecting its prey from the riverbed and storing the invertebrates in its cheek-pouches. It chews the food once it returns to the surface (The Australian Museum, n.d.).

Funky Features

Rapid-fire!

- Venomous ankle spurs

- Fur

- Jaws

- Reproduction

- Lactating

Venomous Ankle Spurs

"« hey bbg, check out my ✨venom✨ » - a platypus, somewhere" - a friend from my biology club.

So far, it seems like platypodes do not use their venom for hunting or defense. Only male platypodes have venomous spurs (about 12 mm long), which they can move to some extent, and the venom glands are most active during mating season. This has led many people to believe that the venom serves an offensive purpose to assert dominance.

Platypus venom is a cocktail of different bits and bobs, including a nerve growth factor protein that is found in a number of snake venoms and some other components that are found in various marine organisms - however, that does not mean that platypodes evolved from reptiles. According to Whittington et al. (2008), through genetic analysis (Warren et. al, 2008) it seems that platypus venom and reptilian venom evolved convergently (separately). It's theorized that the nerve growth factor is responsible for the heightened sense of pain that platypus-envenomed people experience (Whittington et al., 2009). The venom is interesting - it is very hard to treat, even with narcotics (Fenner et al., 1992). Platypus venom is associated with swelling, extreme pain, nausea...not fun.

Fur

Platypus fur is dense and frequently described as "mole-like" in early research. Apparently it's nice enough that they were hunted for their fur 🤷. However, the most interesting thing about the fur is that it's biofluorescent. It doesn't glow by itself (that would be bioluminescent), instead absorbing light and re-emitting longer wavelengths. In this case, platypus fur absorbs ultraviolet (UV) light and re-emits it as a greenish-bluish light. This could be because some of the platypus' natural predators use UV light to hunt - if the platypus absorbs it and re-emits a different kind of light, this may render it invisible to certain predators (Anich et al., 2020). Of course, there's no guarantee that it does serve a purpose. If the conditions in which platypodes fluoresce aren't usually met in their environment, then the likelihood that the fluorescence is significant to their lifestyles is drastically lower.

This is mildly interesting already, but other mammals also fluoresce under UV light. Biofluorescence in mammals was observed in New World flying squirrels (placental mammals) which are also most active between dusk and dawn (Kohler et al., 2019). It was also found in small marsupials (opossums) as early as 1983 (Kohler et al., 2019) and more recently in larger marsupials. (Koumoundouros, 2020). The important thing to note here is that this covers the three major groups of mammals, which may indicate that biofluorescence is an ancestral mammalian trait.

Jaws

Did you know that platypodes lack teeth? The living adults, at least. Platypups are born with teeth, which then drop out as they age. Adult platypodes still chew, using hard pads of keratin to crush their food. Asahara et al. (2016) showed that platypodes lack space for tooth roots. This may be due to the angle of their bills, which are optimized for bottom-feeding, and/or because of their greater reliance on electroreception and mechanoreception (touch), which has changed their proportions and reduced the available space for tooth roots (Asahara et al., 2016).

Reproduction

Platypodes have 52 chromosomes total, including 10 sex chromosomes. Males have 5X and 5Y, which in meiosis split into a chain of 5X and a chain of 5Y (Warren et al., 2008). Of course, the most famous part of platypus reproduction is that they lay eggs. The eggs are leathery and small, less than 2 cm in diameter, and hatch in an early stage of development (after 10-12 days of incubation outside of the body, following 15-21 days of gestation) (Enjapoori et al., 2014). This means that the growth of the infant (like in marsupials) is dependent on lactation. A clutch generally comprises of 1-3 eggs.

After hatching, platypups stay in the burrow for 3-4 months, after which their teeth fall out and are replaced by the keratin pads they will use in their adult lives. They reach adult size approximately a year after leaving the mother's burrow.

(San Diego Zoo Wildlife Alliance Library, 2023)

Lactating

Platypodes do not have nipples. They secrete milk through their skin. It's been proposed that the original purpose of lactation was to prevent desiccation of the eggs or for antimicrobial purposes, only later evolving for nutritional purposes (Enjapoori et al., 2014). There have been several antimicrobial components found in platypus milk, including one that is specific to monotremes (Enjapoori et al., 2014). This may be because platypus hatchlings live in burrows that are not terribly hygienic, and due to their immaturity, require assistance to survive.

That was a doozy. Congratulations if you've made it this far, and thank you for reading. I would suggest reading about platypodes if you (somehow) have quite a lot of time to burn, but let me tell you, it's quite the rabbit hole (platypus burrow?) to venture down. If you ever encounter one and (for some reason) really need to pick it up, the Fenner paper (regarding the effects of platypus venom and treatment attempts) suggests picking up a platypus by the tip of the tail, as to avoid potentially getting envenomed.

I'll leave you to do with that information what you will.

Citations

Featured in this post!

Platypus stories:

https://www.unsw.edu.au/research/platypus-conservation-initiative/the-platypus

ABC News article:

https://abcnews.go.com/Technology/story?id=4828261&page=1

Restoring Indigenous and Aboriginal names in taxonomy:

https://doi.org/10.1038/s42003-020-01344-y

Johann F. Meckel's paper on platypus anatomy:

https://nla.gov.au/nla.obj-32735030/view?partId=nla.obj-32742480#page/n12/mode/1up

Actual Citations

American Museum of National History. (2018, January 12). To hunt, the platypus uses its electric sixth sense | AMNH. American Museum of Natural History. https://www.amnh.org/explore/news-blogs/news-posts/to-hunt-the-platypus-uses-its-electric-sixth-sense

Anich, P., Anthony, S., Carlson, M., Gunnelson, A., Kohler, A., Martin, J. & Olson, E. (2020). Biofluorescence in the platypus (Ornithorhynchus anatinus). Mammalia, 85(2), 179-181. https://doi.org/10.1515/mammalia-2020-0027

Asahara, M., Koizumi, M., Macrini, T. E., Hand, S. J., & Archer, M. (2016). Comparative cranial morphology in living and extinct platypuses: Feeding behavior, electroreception, and loss of teeth. Science Advances, 2(10). https://doi.org/10.1126/sciadv.1601329

Brian K. Hall. The paradoxical platypus. BioScience, 49(3), 211–218 (1999). https://doi.org/10.2307/1313511

Enjapoori, A. K., Grant, T., Nicol, S. C., Lefèvre, C., Nicholas, K. R., & Sharp, J. A. (2014). Monotreme lactation protein is highly expressed in monotreme milk and provides antimicrobial protection. Genome Biology and Evolution, 6(10), 2754–2773. https://doi.org/10.1093/gbe/evu209

Fenner, P. J., Ja, W., & Myers, D. L. (1992). Platypus envenomation — a painful learning experience. Medical Journal of Australia, 157(11), 829–832. https://doi.org/10.5694/j.1326-5377.1992.tb141302.x

Finkel, E. Genome Speaks to Transitional Nature of Monotremes. Science 320, 730-730 (2008). https://doi.org/10.1126/science.320.5877.730

Gerritsen, V. B. (2002, December 1). Platypus poison. Protein Spotlight. https://www.proteinspotlight.org/back_issues/029/

Kohler, A. M., Olson, E. R., Martin, J. G., Anich, P. S. (2019, February 28). Ultraviolet fluorescence discovered in New World flying squirrels (Glaucomys), Journal of Mammalogy, 100(1), 21-30. https://doi.org/10.1093/jmammal/gyy177

Koumoundouros, T. (2020, November 27). Stop everything - it turns out wombats also have biofluorescent fur : ScienceAlert. ScienceAlert. https://www.sciencealert.com/it-s-not-just-the-platypus-wombats-and-other-australian-mammals-biofluoresce-too

Platypus: A Darwinian cautionary tale. (2021, April 6). Truth in Science. https://truthinscience.uk/platypus-a-darwinian-cautionary-tale/

Platypus. (n.d.). Australian Conservation Foundation. https://www.acf.org.au/platypus

Platypus. (n.d.). The Australian Museum. https://australian.museum/learn/animals/mammals/platypus/

Queensland, C. O. S. O. (2016, April 29). Platypus. Environment, Land and Water | Queensland Government. https://www.qld.gov.au/environment/plants-animals/animals/discovering-wildlife/platypus

San Diego Zoo Wildlife Alliance Library. (2023, May 17). LibGuides: Platypus (Ornithorhynchus anatinus) Fact Sheet. International Environment Library Consortium.

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

Scheich, H., Langner, G., Tidemann, C. et al. Electroreception and electrolocation in platypus. Nature 319, 401–402 (1986). https://doi.org/10.1038/319401a0

Warren, W. C., Hillier, L. D. W., Graves, J. a. M., Birney, E., Ponting, C. P., Grützner, F., Belov, K., Miller, W., Clarke, L., Chinwalla, A. T., Yang, S. P., Heger, A., Locke, D. P., Miethke, P., Waters, P. D., Veyrunes, F., Fulton, L. L., Fulton, B., Graves, T., . . . Wilson, R. K. (2008). Genome analysis of the platypus reveals unique signatures of evolution. Nature, 453(7192), 175–183. https://doi.org/10.1038/nature06936

Whittington, C. M., Koh, J., Warren, W. C., Papenfuss, A. T., Torres, A. M., Kuchel, P. W., & Belov, K. (2009). Understanding and utilising mammalian venom via a platypus venom transcriptome. Journal of Proteomics, 72(2), 155–164. https://doi.org/10.1016/j.jprot.2008.12.004

Whittington, C. M., Papenfuss, A. T., Bansal, P. S., Torres, A. M., Wong, E. S., Deakin, J. E., Graves, T., Alsop, A. E., Schatzkamer, K., Kremitzki, C., Ponting, C. P., Temple-Smith, P., Warren, W. C., Kuchel, P. W., & Belov, K. (2008). Defensins and the convergent evolution of platypus and reptile venom genes. Genome Research, 18(6), 986–994. https://doi.org/10.1101/gr.7149808

Zarrelli, N. (2016, April 21). Why 19th-century naturalists didn't believe in the platypus. Atlas Obscura. https://www.atlasobscura.com/articles/why-19th-century-naturalists-didnt-believe-in-the-platypus

Zhou, Y., Shearwin-Whyatt, L., Li, J. et al. Platypus and echidna genomes reveal mammalian biology and evolution. Nature 592, 756–762 (2021). https://doi.org/10.1038/s41586-020-03039-0

 P.S. If you made it down all the way to the end of the citations, here's a little present for you. One of the lighter chapters of Loving Reaper by Jenny Jinya, featuring our dear friend the platypus. Hope you enjoy as much as I did!