The Insane Biology of: The Platypus

When the platypus first came to the attention of European scientists in 1798 not everyone was convinced that the creature before them was even real where some thought a prankster had mashed together separate parts of different animals to create a fake not an uncommon occurrence at this boom time of natural discovery but the platypus was a very real animal and one that confused anatomists for some time.

These European scientists were asking the same questions that the Aboriginal people of Australia had been asking for a long time before them where there are several Aboriginal stories about the origins of the platypus one of which tells of a union between a duck and a water rat.

In science terms we’ve ultimately classed the platypus as a mammal or more specifically a monotreme an egg-laying mammal of which there are only two kinds of animals in the world.

The platypus nurses its young with milk which is a defining mammalian characteristic but it has no nipples where instead the milk is secreted directly through pores in the skin in a mammary patch on the mother’s abdomen where the baby platypuses called puggles lap up the milk from their mother’s fur where this unusual lactation system represents an intermediate evolutionary stage between the mammary glands of advanced mammals and the complete absence of milk production in reptiles and birds.

Around 340 million years ago the first amniotes appeared on Earth in the form of small lizard-like creatures where amniotes are four-legged vertebrates that are defined by the membrane or amnion that protects the embryo during development where the amniotic egg was an evolutionary invention that first allowed reptiles to colonize dry land where fish and amphibians must lay their eggs in water but thanks to the amniotic egg reptiles can lay their eggs nearly anywhere on dry land.

The monotremes or egg-laying mammals split off from the mammalian lineage around 200 million years ago where they never gained the ability to have an internal pregnancy and never lost their egg laying ability.

Genome sequencing of platypus sex cells have shown there are a large number of shared genes between platypuses and birds where in particular the platypus retains copies of the vitellogenin gene which codes for egg protein that is a precursor to egg yolk which helps sustain growing embryos where platypuses have fewer copies of the gene than birds and reptiles but most mammals don’t have the gene at all.

The female platypus digs an elaborate burrow into a riverbank that can be up to 20 meters long where she creates a nesting chamber at the end and lays typically two leathery eggs where she then incubates the eggs by curling her body around them for about ten days until they hatch where this egg incubation behavior is similar to many reptiles and demonstrates the platypus’s evolutionary link to its reptilian ancestors despite being a mammal.

Marsupials originated in what is now South America and migrated over to what is now Australia via the supercontinent Gondwana around 70 million years ago where their bodies were more efficient at locomotion and their internal pregnancies meant they could better protect their young and thus they out-competed the monotremes on almost every front and slowly all but two the echidna and the platypus went extinct.

One hypothesis as to how the platypus persisted in the face of intense competition from the marsupials is its ability to take to the water a domain where the marsupials could not follow where marsupials could not colonize water environments because when they’re born they have to live inside their mother’s pouch for weeks to suckle milk where the babies would drown if their mothers ever had to venture into the water but with their eggs secure in a nest the platypus can happily stay in the water avoiding predation and exploiting their very own environmental niche.

The platypus has fully webbed front feet that provide propulsion when swimming where the webbing extends beyond the claws and the animal uses an alternating paddling motion where remarkably when on land the webbing folds back to expose the claws allowing the platypus to walk normally and dig burrows where the broad flat tail also acts as a rudder for steering underwater and stores fat reserves similar to a beaver tail making the platypus highly adapted for both aquatic and terrestrial environments.

The platypus bill which looks ridiculous actually houses about 70,000 electro-receptors that can detect electrical impulses from shrimp muscle contractions through the water where these receptors are similar to those found in sharks and allow the platypus to hunt effectively underwater with its eyes and ears closed where the platypus sweeps its bill side to side detecting prey through electrical signals alone making it an incredibly effective predator in murky water conditions.

The platypus bill also contains about 40,000 mechanoreceptors called push rods that are arranged in columns of stacked cells where these receptors can detect the pressure waves created by a moving shrimp from about 15 to 20 centimeters away where the combination of electroreception and mechanoreception creates a dual sensory system that allows the platypus to precisely locate and capture prey in complete darkness underwater making it one of the most sophisticated sensory hunters among mammals.

The platypus evolved its electroreception independently from fish making it a remarkable example of convergent evolution where it is one of only three types of mammals that have this ability alongside echidnas and dolphins where the receptors are completely different in structure from those found in sharks and other fish demonstrating that evolution can arrive at similar solutions to the same problem of hunting in low-visibility aquatic environments through entirely different developmental and genetic pathways.

Male platypuses have venomous spurs on their hind feet that can deliver an extremely painful sting where the venom is produced from genes that were duplicated from ancient reptilian defensins where this represents another example of convergent evolution because while the genes are reptilian in origin the venom delivery system and the specific venom cocktail evolved independently in the platypus lineage where the spurs are thought to be used primarily during mating season for male combat rather than for defense or hunting.

Scientists discovered just last year that platypus fur exhibits biofluorescence under ultraviolet light where the fur glows a bright greenish color where the purpose of this trait is currently unknown though it could potentially be used for communication between individuals where this discovery adds yet another bizarre feature to an already extraordinary animal and raises questions about whether platypuses can see ultraviolet light and use this fluorescence for social signaling or mate selection.