Monotremes have the sprawling gait and skeleton of a lizard along with the lower jaw and inner-ear structure of a therian mammal. For example, the acidic stomach may be of limited value in digesting a diet rich in the calcium carbonate that forms the exoskeleton of many aquatic invertebrates, as this basic compound neutralises acid. Given that the common ancestor of the extant monotremes was aquatic and that this phenomenon is also common amongst fishes, it may ultimately reflect a diet associated with an aquatic lifestyle. In what may be considered a classic case of “use it or lose it”, the monotremes have essentially lost their stomachs, instead having an oesophagus that connects directly with the intestine. Being toothless, an uncommon feature amongst mammals, the bits of coarse sediment it gathers along with its prey help to mash its mouthful before swallowing. The platypus uses both mechanoreceptors (that provide touch sensitivity) and electroreceptors (that detect electrical currents) in its bill to locate the freshwater invertebrates that it feeds upon. The monotremes are famous for their mishmash of ancestral reptilian and derived mammalian traits, as well as a few altogether unique features. Genome analysis of the platypus reveals unique signatures of evolution. From Warren, W., Hillier, L., Marshall Graves, J. et al. Mammal lineages are in red diapsid reptiles, shown as archosaurs (birds, crocodilians and dinosaurs), are in blue and lepidosaurs (snakes, lizards and relatives) are in green. Geological eras and periods with relative times (Myr ago) are indicated on the left. Therian mammals with common characters split into marsupials and eutherians around 148 Myr ago (dark-red text). Monotremes diverged from the therian mammal lineage ∼166 Myr ago and developed a unique suite of characters (dark-red text). These small early mammals developed hair, homeothermy and lactation (red lines). In parallel, the highly derived therians, which includes the placental and marsupial mammals, evolved many of the traits that we now commonly associate with the class Mammalia, such as viviparity (live birth).Īmniotes split into the sauropsids (leading to birds and reptiles) and synapsids (leading to mammal-like reptiles). The common ancestor of the monotremes (traditionally also known as prototherians) diverged from this lineage around 166 Mya but retained a number of their ancestral reptilian characteristics, including egg-laying. Lactation – a trait that unifies all mammals – evolved within these primitive therapsids. The sauropsids, the lineage that gave rise to reptiles (including birds), and the lineage that gave rise to therapsids (mammal-like reptiles) split around 315 million years ago (Mya). The platypus ( Ornithorhynchus anatinus) belongs to the mammalian order of Monotremata, whose members (the platypuses and the echidnas) are distinct from all other mammals chiefly because they lay eggs. National Museums of World Culture, Wikimedia commons, CC4. Image: Original artist unknown bark painting c1900-1966 Arnhem Land, Northern Territory. ![]() ![]() They all agree, and from that time onward Platypus has been known as very wise and very special.Įach animal group has its own special traits, but the platypus has been classed a very special creature ever since the Dreamtime – and I’m inclined to agree. “But it’s not only me - ” he says, “each of us has something that makes us special in our own very special way”. He explains that he shares characteristics with each group, and therefore does not need to join any one group to be special. However, after much deliberation and consultation with his friend Echidna, he respectfully declines all offers. Each of the groups holds its own special meetings, and each invites shy Platypus to join their special family. It begins with the Ancestor Spirits of the birds, of the land creatures, and of the water creatures, telling of why each group is special – flight and laying eggs for the birds, fur and running fast for the land creatures, and swimming for the water creatures. There is a dreaming that tells the story of “ why Platypus is special”. The Australian aboriginal Dreamtime stories describe the events that mark the creation of the natural world and its inhabitants. This week in the wide world of venom series, we introduce the enigmatic platypus.Ī truly unique species - the platypus (Ornithorhynchus anatinus ). Believe it or not, this creature actually exists! With its unusual combination of reptilian and mammalian traits, it’s easy to see it has evoked wonder and disbelief in many of those who have encountered it. Try to imagine an egg-laying, lactating, nipple-less, toothless, stomach-less, venomous mammal.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |