The Duck-Billed Platypus
Figure 1: Image of adult Platypus (Source: http://www.dailymail.co.uk/sciencetech/article-1018650/Its-bird-beaver---actually-platypus-scientists-decode-DNA-time.html)
The Duck-Billed Platypus is only found in Australia and they are semi-aquatic animals (they live in both water and on land). They live in fresh water systems in tropical rain forests to the high altitude of the Australian alps and make themselves burrows in the bank of the river or creek. Their ideal environment would incude lots of vegetation with logs and rocks lining the bottom of the river so the platypus can use its bill for foraging. The platypus has to be careful when they leave the burrow for food as they are leaving their babies open to predators and they are leaving the safety of their homes making themselves vulnerable to predators.
Figure 2: Male Platypus diving through the water. (Source: http://www.reed.edu/biology/professors/srenn/pages/teaching/web_2010/EmilyFong/adaptation.html)
Fertilisation in platypi is very unique as they are one of the two mammals that lay eggs (the other being echidnas).There are two parents involved and after much persistance by the male trying to impress the female by rolling sideways and diving through the water (Figure 2) copulation then joins the two individuals. The egg is fertilised inside the female, this occurs in the water usually between june and october. The female then makes herself a nest in a long complex burrow in less then a week, she then spends the next few days collecting material to prevent her eggs and hatchlings from drying out. Once the eggs are laid they are quite soft, white and are about the same size as a sparrow's egg. This strategy is quite effective as two parents are involved and being an endangered species, with two sets of DNA the offspring are not going to be direct copies with the same weaknesses as their parents.
Figure 3: Young platypus feeding (source: http://www.acuteaday.com/blog/2013/08/14/adorable-baby-platypus-eating)
The platypus displays oviparity(lays an egg) when their young develop both externally and internally in a hard shelled egg called an amniote. Being semi-aquatic animals, the platypus lay eggs in their burrows right on the edge of the water which is a difficult place for some predators to reach and it ensures a safer environment for their young to develop. The fertilised egg develops inside the mother for about 2-3 weeks and then the egg is laid and the embryo develops for a further 10 days. When the egg is inside the female most of the nervous, cardiovascular and excretory system are developing. Once the egg is laid the brain then starts to develop. If the embryo completely developed internally it would make getting around for the mother harder, already being an easy target, extra weight and shape would increase the chances of becoming another animals meal. This way of development is quite affective as the baby is always being protected by the mother or a shell.
Figure 4: Baby platypus without hair (source:http://amazing-creature.blogspot.com.au/2011/05/platypus-egg-laying-mammal.html)
There is quite a high level of parental care recquired to ensure the survival of a baby platypus. The male platypus leaves directly after fertilisation so the parental care is all up to the female platypus. As only a few eggs are fertilised at a time the the female needs to put all their energy into nurturing the baby platypus. The young platypus will drink thick milk from two patches of skin under the mothers belly. This will go on for up to 5 months where the babies then start to follow the mother out of the burrow and forage for food themselves. The platypus is a k-selection animal as they take good care of their young for a long time and they only produce a small amount of eggs. This means that there is a great deal of parental care involved in looking after a baby platypus because the offspring are completely defenceless and the only way a platypus can ever defend themselves is by the male's poisonous spurs. This method of care is good in the sense that the young platypus are looked after very well for the start of their life. But this also means that they completely rely on their mother therefore if she was to get injured or even killed the chances of the babies surviving are very slim.
Did You Know?
The platypus closes it's eyes and ears when they search for food and they have about 900 hairs per millimetre which is thicker then a polar bears! The female platypus has two ovaries but only the left one is functional.
Diagram of platypus burrow Source:http://panecoeducation.weebly.com/marvelous-monotremes-march-2013.html
Map of platypus population Source:http://designeranimals2011.wikispaces.com/Platypus
Female platypus with babies Source:http://www.ucmp.berkeley.edu/mammal/monotremelh.html
Egg with embryo source:http://sarahorsomeone.deviantart.com/art/Platypus-Egg-283606158