how many mammals lay eggs and which ones?
367609
There are three living genera of Monotremes, which are the group of mammals that lay eggs:\n\nThe Platypus (Ornithorhyncus) of Australia\nThe Short-nosed Echidna (Tachyglossus) of Australia\nThe Long-nosed Echidna (Zaglossus) of Australia and New Guinea\n\nThere used to be a lot more species of egg-laying mammals, but these are the only ones that survive today.
811443
The above answer is right; the record litter size among wild mammals goes to the tailless tenrec, but according to the sources I found, the maximum record is 31 (of which 30 survived), not 32. However, the average nº of young is approx. 15.\n\nThe next largest litters correspond to some opossums (20 young), the ermine (a carnivore) with 18 kits, and the rest are rodents (with a maximum of 15 pups for some rat species).  \n\n\nAmong domestic breeds (many of which have been selected to be prolific) the record belongs to a domestic mouse with 34 pups (33 of them survived.)\n\nSee the sources :-)
33261
Dogs.  Canine.  Canariensis.\n\nAllegedly, there are still wild dogs to this day there.
409350
HENS, they first have animals, then came eggs.
264541
I read recently in a weekly magazine that there are 230,000 oceanic and 1.5 million non oceanic (land + air + lakes + river) classified species. According to the same article there would be around 1.5  to 2 millions not classified species in the oceans alone.\nI don't consider this magazine very higly and it did not state its sources.\nBut anyways, I would guess less than 3 million in all.
711473
other animals ....of course.\n\nDo you know about plate tectonics?
330982
I think so! Visit: http://www.bbc.co.uk/nature/animals/mammals/
660801
Actually, they are Ovoviviparous, meaning they lay eggs, but they are retained inside the mother's body until they hatch.  The young get nutrition only from the egg "yolk," unlike the mammals' viviparous "live birth," where the embryo gets its nutrition directly from its mother during its development.  It looks like they are giving live birth, but it is not quite the same.
682062
Warm-blooded Vertebrate Animals belonging To the Class Mammalia, including all that Possess Hair and Suckle their Young. It includes Three Major groups: Placentals and Marsupials, which are vivparous, and Monotremes, which are Oviparous.
910323
Humans are not the only ones. Primates do and yes dogs and cats do as well. Other sexually reproducing species go through oestrous cycle. Very similar to menstrual cycle, except it isn't always seasonal. Some rodents for example ovulate every 4-5 days; while others are induced ovulators meaning they only ovulate after sex. Both types have cyclical endocrine changes that lead to ovarian changes and ovulation. Interesting tidbit though is that humans are the rare ones...other species only have sex to procreate...humans have sex whether they can have kids or not (while they are pregnant or elderly, for example).
429981
They are hermaphrodites.  Each delivers sperm to the other.  Each later lays eggs.
442999
older ones. younger ones lay smaller eggs. (not kidding)
1027119
The EGG... Reptiles came first, then birds, then mammals.... And reptiles LAY eggs!! Therefore the EGG came before the birds (in this case the chicken).
159981
There are about 56 species, so which one do you want?\nI'll say "Rattus adustus," and let you look at the source below for the other 55.
436565
There are actually quite a few "other animals" that don't lay eggs -- some sharks have a version of live birth, as do many vipers.  Boa constrictor females retain their eggs (they don't actually "lay" them) until they hatch, so the young come out live.  \n\nThere are egg-laying mammals; they're called Monotremes -- the only ones alive today are the duck-billed platypus & the short- and long-beaked echidna.   \n\nAs for the rest of us mammals, we all still come from eggs, but we've developed an awesome internal incubation system -- just think, now we don't have to worry about eggs rolling out of nests, dehydrating, getting too cold, or being carried away by predators!
380846
The largest egg ever discovered was laid by the now extinct, flightless elephant bird. This 13- by 9.5-inch (33- by 24.1- centimeter) egg held over 2 gallons (9 liters) of liquid. That's eight times as much as an ostrich egg.\n\nThe ostrich egg is the largest egg in the world today.\n\nThe kiwi bird lays the largest egg in proportion to its body size. It would be as if a human gave birth to a 43-pound (19.5-kilogram) baby. No wonder the female lays the egg, and the male has to sit on it.
318800
The mammals are the class of vertebrate animals characterized by the presence of mammary glands, which in females produce milk for the nourishment of young; the presence of hair or fur; and endothermic or "warm-blooded" bodies. The brain regulates endothermic and circulatory systems, including a four-chambered heart. Mammals encompass some 5,500 species, distributed in about 1,200 genera, 152 families and up to 46 orders, though this varies with the classification scheme.\n\nPhylogenetically, Mammalia is defined as all descendants of the most recent common ancestor of monotremes (e.g., echidnas and platypuses) and therian mammals (marsupials and placentals).