Ask A Scientist
How can platypuses be mammals when they lay eggs?
School: Jennie F. Snapp Middle School, Union-Endicott
Teacher: Kimberly Coury
Hobbies/Interests: Kimberly Coury
Career Interest: Teacher, state trooper
Answer from Debbie Dittrich
Research Support Specialist, Binghamton University
Research area: Teardown analysis of electronic packages
Interests/hobbies: Docent at the Binghamton Zoo, nature photography and gardening
Believe it or not, platypuses are not the only mammals that lay eggs. Mammals that lay eggs are called monotremes and include platypuses and echidnas, both of which live in Australia. Like all mammals, monotremes are warm-blooded, covered with fur and nurse their young. Animals are so interesting because they don’t always follow the rules. Some mammals lay eggs; some snakes give birth to live young. Birds are in fact the only class of vertebrates that reproduce solely by laying eggs.
Platypuses are certainly funny looking, with duck-like bills, tails like a beaver and webbed feet. Their legs come out on the sides like a reptile rather than from underneath. Nocturnal and semi-aquatic, platypuses inhabit small rivers and streams. They swim by rowing with their front legs and steering with their back legs and tail. Using bills that are very sensitive to changes in electrical fields, they hunt underwater for worms, insects and freshwater shrimp. Monotremes, and some dolphins, are the only mammals known to use electrical fields to locate prey. Unlike duck bills, the platypus’ mouth is located underneath. When not in the water, platypuses rest in burrows that they dig in stream banks.
Female platypuses have more extensive burrows than males because that is where they rear their young. Eggs develop in the mother’s body for about 28 days. The eggs (1-3) are then laid in the burrow, and the female curls around them to provide warmth. After 10 more days, they hatch into lima bean-sized, helpless infants. Mother platypuses do not have nipples, but instead their milk comes from pores in their skin and collects in grooves on their stomach. Babies lap the milk rather than suck. After about four months, the babies are ready to come out of the burrow and learn to swim.
If all this isn’t unusual enough, male platypuses have venomous spurs on their back legs called ankle spurs (very few mammals are venomous). Platypus venom is strong enough to kill a small animal like a dog. Although not potent enough to kill a human, it causes extreme pain, which can last for days or even months. The venom is thought to be used during mating season, when males compete for females. Maybe someday you will be lucky enough to see a platypus. Just remember, they are not cuddly!
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