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Platypuses can give a low growl when disturbed, and a range of vocalisations have been reported in captivity. [16] Size varies considerably in different regions, with average weight from 0.7 to 2.4 kg (1 lb 9 oz to 5 lb 5 oz); males have average length 50 cm (20 in), while females are the smaller at 43 cm (17 in). [21]
According to the observation of embryonic cells of egg, chromosome number of the itch mite is either 17 or 18. While the cause for the disparate numbers is unknown, it may arise because of an XO sex determination mechanism, where males (2n=17) lack the sex chromosome and therefore have one less chromosome than the female (2n=18). [29] [29] 32 ...
Egg size tends to be proportional to the size of the adult bird, [citation needed] from the half gram egg of the bee hummingbird to the 1.5 kg egg of the ostrich. Kiwis have disproportionately large eggs, up to 20% of the female's body weight. [ 18 ]
The only living mammals that lay eggs are echidnas and platypuses. In the latter, the eggs develop in utero for about 28 days, with only about 10 days of external incubation (in contrast to a chicken egg, which spends about one day in tract and 21 days externally). [11] After laying her eggs, the female curls around them.
The average lifespan of an echidna in the wild is estimated at 14–16 years. Fully grown females can weigh about 4.5 kilograms (9.9 lb), the males 33% larger, at about 6 kilograms (13 lb). [ 12 ] Though the internal reproductive organs differ, both sexes possess an identical single cloaca opening for urination, defecation, and mating.
The mammals included are only viviparous (marsupials and placentals) as some mammals, which are monotremes (including platypuses and echidnas) lay their eggs. A marsupial has a short gestation period, typically shorter than placental. For more information on how these estimates were ascertained, see Wikipedia's articles on gestational age.
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However, the five species of monotreme, the platypuses and the echidnas, lay eggs. The monotremes have a sex determination system different from that of most other mammals. [ 2 ] In particular, the sex chromosomes of a platypus are more like those of a chicken than those of a therian mammal.