The Platypus, Part 1

A platypus. Photograph modified from an image found on Wikimedia Commons. Photograph by Maria Grist.

Several posts ago, I wrote about placozoans, a unique type of simple animal. I began wondering, what is one of the more unusual animals? Something that when people learn about it, they think, “That thing is weird”? I also wanted it to be a more “familiar” type of animal, something that, while unusual, is not so exotic as to be a completely different form of animal.

I settled on the platypus.

Now, I know what you are thinking. “We already know why the platypus is unusual. It is an odd hodge-podge of different types of animals.” There is the familiar trope that a platypus is “an egg-laying mammal that has the beak of a duck and the tail of a beaver.” That sums up its weirdness right there, doesn’t it?

Well, not quite. For one, the platypus is stranger than “an egg-laying mammal that has the beak of a duck and the tail of a beaver.” For another, “an egg-laying mammal that has the beak of a duck and the tail of a beaver” is not a very “good” description of a platypus. Let me explain.

A platypus does not have the “beak of a duck.” Technically, it doesn’t have a beak. Sure, its mouth is called a bill, but it lacks a key characteristic of all beaks: it is not hard. Whether it is the beak of a bird, the beak of a turtle, or even the beak of a dinosaur, the beak is always a hard part with a bony core covered in keratin (a type of protein). The platypus does not have these features. Instead, much of the bill of the platypus is composed of soft tissue. It is made of soft tissue because it has a different use. In a duck, the beak is used for capturing and processing food, so it must be hard to withstand the forces of eating. A platypus processes (chews its) food using grinding pads which are located back in the mouth. Instead, the bill is full of electroreceptors, structures that are sensitive to changes of electricity in the water. It uses these electroreceptors to find its prey in the water.

There is also an external feature of the platypus that distinguishes it very easily from that of a duck. The nostrils of a duck are located towards the back of the beak while the nostrils of a platypus are located towards the front of the bill.

Skull of a platypus. The view is from above, the front of the skull is pointed up. Note that the bones of the skull do not fill the bill completely: much of the bill is soft tissue. Also, note the two dashed ovals in the bill. Those are the nostrils, which are located toward the tip of the bill.
The skull of a duck. The view is from the side. The front of the skull is toward the right. Notice that the bones in the beak have the same shape as the duck beak. Just add a layer of keratin and you have a beak. Notice also the nostrils, which are located toward the back of the beak.

In summary, in terms of function, structure, and even external features, the bill of a platypus is very different and easily distinguishable from the beak of a duck.

While the platypus does have a broad, flat tail like a beaver’s tail, the similarity ends there. The tail of a beaver is covered with scales while the tail of a platypus is covered in fur. While the tail of a beaver is used in swimming (it acts like a rudder), the tail of a platypus is primarily used to store fat (the hind-feet of a platypus act as rudders instead).

By this point, we are starting to see that the platypus has its own unique features suited to its own unique way of life. It just so happens that some of these features bear superficial similarities to the anatomy of other animals. I have heard some people refer to the platypus as a “mosaic animal.” I believe that calling the platypus a “mosaic animal” creates a false impression. It creates the impression that the anatomy of a platypus is cobbled together from the anatomy of other animals. As we have seen, the platypus does not have the bill of a duck and does not have the tail of a beaver, so it is not a mosaic of different traits. Rather, it is its own unique animal, which happens to be unfamiliar to most people, so we end up describing it in terms of more familiar animals.

Let me elaborate a little bit on that last part. Part of the reason that the platypus seems like an animal that is a hodge-podge of other animal parts is because we have not seen a living platypus (I am pretty sure none of you have seen a living platypus: aside from being native to Australia, there is only one zoo outside of Australia that houses platypuses, and that is the San Diego Zoo Safari Park[1]). However, all of us (here in the United States) have seen ducks and many of us have seen beavers. It is simply “too easy” to compare the unfamiliar platypus to the familiar duck and beaver. Suppose the situation were reversed, and we were familiar with platypuses but ducks were considered unusual. Would we describe ducks as “birds with the bill of a platypus”? Probably.

The point is that platypus is its own unique kind of animal. It is not a mosaic, it is not a hodge-podge, it is not a mixture. It is a platypus, and if it is unusual to us, it is simply because we are unfamiliar with it and because there are few animals like it.

Noting that there are few animals like the platypus, I want to address one more topic. I plan on giving some details about the life and anatomy of a platypus, and we will see that some features of a platypus actually do cross what we consider to be “normal” animal boundaries. For example, the shoulder girdle of a platypus is much more like that of a reptile than that of a typical mammal. It is still its own unique shoulder girdle with its own unique purpose, but in its anatomy, it does not look like the shoulder girdle of a mammal but instead looks like the shoulder girdle of a reptile. I think this is why the platypus is sometimes called a “mosaic animal”: calling it a mosaic blunts the impact of the evolutionary claim that the platypus is a “primitive” mammal with “reptilian” features. Once again, such a claim is unnecessary: reptiles and mammals do not exist except as man-made conventions.

Before I explain, let me clear some things up. First of all, I use the terms “mammal” and “reptile” all the time. It is simply convenient to do so. There is a large number of animals with similar characteristics (scales and sprawling legs) and we call these animals reptiles, and there is another large group of animals with similar characteristics (hair and mammary glands), and we call these mammals. In that sense, the terms “mammal” and “reptile” help us describe the world around us. However, it is tempting to think that mammals make a natural group and all mammals must be alike and that reptiles are a natural group and that all reptiles must be alike. From a creationist perspective, there is simply no reason to think that mammals and reptiles are natural groups. The only groups of animals that are truly natural are kinds. We are repeatedly told in Genesis 1 that animals (and plants) were made according to their own kinds. That is it. We are not told that animals were made according to their own classes (in the Linnaean hierarchy, “mammal” and “reptile” lie closest to the level of class).

Now, some may point out that Genesis 1 actually does mention groups aside from kinds. These are groups like birds (vs. 20-22), livestock, creeping things, and beasts of the earth (vs. 24-25). However, we should be cautious with these groups: they do not necessarily correspond to groups that we use today. Take birds, for example. Genesis 1 does not describe what birds are in any detail, aside from the fact that they a winged. However, if we look elsewhere in the Bible, we can find more descriptions of what God considers to be birds. Leviticus 11 details the clean animals that the Hebrews were permitted to eat and the unclean animals they were not permitted to eat. Verses 13-19 lists the unclean birds. The very last bird mentioned is the bat. Apparently, the words “bird” and “fowl” in the Bible simply mean “flying animals,” rather than “flying animal with wings made of feathers,” which is closer to our definition of a bird. The point is, our definition of bird is different from that used in the Bible, so we should not be dogmatic that God’s pattern of creation must have followed our definition of animals. Thus, there is no reason to explain the reptilian features in the mammalian platypus. As long as the platypus is its own kind, it can have any features that God gave it for its particular lifestyle, regardless of whether we think those features belong in another group.

Well, that is just an introduction. As I already mentioned, I plan on talking more about the anatomy of the platypus and explaining how it is unusual compared to more familiar animals, but that will be left for later posts.

Thoughts from Steven