why do reptiles lay fewer eggs than amphibians?
100844
Basically, because the investment made in the eggs is different, according to their reproductive strategy.\n\nThe eggs of amphibians are oligolecithal, that is, they have only a small quantity of vitellum (nutritive substance). Amphibian development includes a larval stage (the tadpole) that is able to feed for itself before becoming an adult; therefore vitellum is only needed during the short period of embryo development inside the egg and during the first stages of the tadpole life, when its mouth is not yet developed. \nThe female produces hundreds of eggs, very few of which will eventually become adults. Most amphibians do not exhibit parental care either, thus the reproductive strategy is focused on producing larger amounts of eggs, rather than protecting each one. \nIn contrast, reptiles (and birds, i.e. all sauropsid amniotes) have macrolecithal eggs, with a large proportion of nutritive vitellum (vitellum is the yellow part of hen's eggs). This large amount of vitellum is necessary because all amniotes undergo direct development, and it represents the entire food source for the reptile embryo (except for the viviparous forms). Although most reptiles (with the exception of crocodiles) do not have parental care either, the formation of these eggs, which provide food and protection from environmental factors, is a greater investment. If more energy is spent in producing each egg, there will be less of them, but with higher survival probabilities.
390773
It's an example of a transition between lobe-finned fish and AMPHIBIAN vertebrates, not reptiles.  \n\n(Well, it is a reptile transition in the sense that it's part of the spectrum between fish and reptiles, but it's also part of the spectrum between fish and birds or fish and mammals, it just seems a bit forced to call it a fish/mammal transition to me.)\n\nMore importantly, it shows exactly the type of features scientists predicted it should have, confirming the most common theory about how vertebrates moved onto land.
911397
Reptiles were laying shelled eggs for millions of years before some of them evolved into birds - and chickens came even later than that. So, by the time the first chicken laid the first chicken egg, eggs were already ancient. If your question is supposed to pertain only to chicken eggs, then obviously a species and its reproductive cells evolve simultaneously. Neither of them can exist before the other.
475647
This question is a bit misleading... only SOME species of spider die soon after laying their eggs. Many will live on for years and can reproduce several times.\n\nAs to those few which do die; reproduction is a very costly endeavor for any organism and this could diminish the spider's resources. Evolutionarily speaking, the only goal it to get one's genetic material to the next generation, that done, the organism is simply taking up habitat.
40335
Some reptile species are parthenogenetic (from Greek: virgin + originate, generate). That is, the development of the ovum can be triggered without sperm intervention.\nAs a consequence, these populations are only formed by females and all the offspring are genetically identical to their mothers (unless there is some recombination at cross-over, which I'm not sure about). \nThere are only a few lizards and snakes that present this mechanism; see the links below for the best known parthenogenetic snake species (there are probably others that have not been studied yet). \nHere in Argentina we have some parthenogenetic lizards! :)
897987
Because they develop similarly. Read this: http://www.ucmp.berkeley.edu/chordata/chordata.html
387546
Snakes, like other reptiles, are built around moisture conservation. Most snakes and lizards don't even pee, let alone sweat! They excrete their uric acid in a solid pellet. If they sweated, they would have to top up on moisture, which would be difficult and dangerous for many species. By not having to drink free-standing water, reptiles are able to occupy some of the driest environments on earth. As has been pointed out, most reptiles are what are called "shuttling heliotherms", moving in and out of the sun to maintain a constant body temperature. Sankes, having a large surface area in relation to their mass, tend to heat up more quickly than lizards. They can absorb heat through the ground as well, which is called being "thigmothermic" -which makes one wonder if they get warm by beating up other reptiles they would be "thugmothermic" ;-). \n\nSnakes shed their skin periodically and for a variety of reasons- not only to allow them to grow, but also if they have any sort of parasites. It is only the outermost layer of the skin that is shed, but there is usually a little bit of pigment in the shed skin and this often allows the  pattern, although not the colour of the snake that shed the skin to be ascertained. Humans shed their skin too, we call it dandruff. Most household dust is shed skin of people.
1081876
Eptiles do not use water to flush nitrogenous wastes from the body as urine, like mammals do, but convert them to a form which can be dumped as solid dung.\n\nDiverse lizards of Oz\nNext to birds, lizards are among the most commonly encountered vertebrate animals in the savannas. Indeed, the diversity of lizards in the tropical savannas is particularly rich, exploiting numerous habitats, from woodlands to sandstone escarpments, rainforests and semi-arid zones, many endemic to just small areas.\n\nEvolution of lizards\nThe combination of poor soils and dry climate is believed to have led to the evolution of plants with tough, thick, chemical-laden leaves—and relatively few plant-eaters. Instead, the vegetation is broken down by termites, which thrive in Australia—providing an abundant food source for reptiles. Just as mangroves don’t need salt but have developed strategies for living where no other plants can compete, so too have reptiles exploited an environment largely uninhabitable for other animals.\n\nThe great diversity of reptile species may be due to the long-term stability, and great size, of the Australian continent. Those animals which cope well with conditions have had plenty of time to evolve into different species exploiting different ecological niches. This diversity may even be fostered by shortages. This may favour large numbers of specialist species which have adapted to localised conditions over fewer, more widely distributed, species which might have evolved in a more benign environment.\n\nEfficiency of lizards\nExcepting Antarctica, Australia is the driest continent on earth; 75 per cent of it is arid or semi-arid. The climate is erratic, with long, irregular dry and wet cycles determined by the effects of El Nino and La Nina. Successful animals must cope with unreliable rainfall and prolonged periods of shortages, but take advantage of unpredictable times of plenty. In addition, Australia’s soils are also nutrient-poor, with low productivity, and fires are frequent. Energy-efficiency is thus the key to long-term survival.\n\nMammals and birds generate their own heat from food, using up to 90 per cent of their energy intake for this purpose. However most lizards, instead of consuming food to generate energy, use solar power, basking in sunshine or sleeping in a warm spot to power up their ‘batteries’ for the day’s (or night’s) activities.\n\nSome lizards, such as dragons, are able to raise their ribs and angle their bodies to increase the body surface exposed and can become darker to absorb more heat. This strategy, known as thermoregulating, is not an option for some lizards which live in closed forests. Instead, they thermoregulate passively, or ‘thermoconform’, their body temperature simply conforming to that of the air around them.\n\nLizards are also efficient users of water. Their dry scaly skin reduces moisture loss, those living in the hottest areas tending to have compact bodies to minimise loss and/or restricting most activities to hours of darkness. In addition, reptiles do not use water to flush nitrogenous wastes from the body as urine, like mammals do, but convert them to a form which can be dumped as solid dung.\n\nGetting away from predators\nGeckos, legless lizards and skinks will readily drop their tails when threatened, the wriggling appendage serving as a distraction while the owner makes its getaway. Fracture planes between certain vertebrae at the top of the tail allow it to detach easily when pulled apart by special muscles. This sacrificial offering is easily regrown. Tails of dragons and goannas can also break off, but do not do so as readily and tend not to regrow. All dragons, goannas and Australian geckos lay eggs but some skinks give birth to live young. Experiments with skink eggs suggested that those kept at ‘maternal’ temperatures were larger and fitter than those kept at normal nest temperatures. This may be an important factor in cool, or dry, clima
195288
There is a flaw to the wording of your question, technically, yes Mammal's burn more calories than reptiles due to higher metabolic requirements, however, their efficiency at burning calories is the same-- the flaw is in your wording.\n\nFor instance, all car engines have the same efficiency for burning fuel ;) The difference in car engines is how well they utilize the energy harnassed from burning the fuel. If you were to compare the bodies of reptiles and mammals to car engines, then a mammal would have a gas guzzling engine that goes very fast but for only short trips, whereas a reptile would have a much more optimized engine for longer endurance and low fuel usage.
1031791
Ovoviviparous animals develop within eggs that remain within the mother's body up until they hatch or are about to. This strategy of birth is known as ovoviviparity. It is similar to vivipary in that the embryo develops within the mother's body. Unlike the embryos of viviparous species, ovoviviparous embryos are nourished by the egg yolk rather than by the mother's body. However, the mother's body also provides for gas exchange.\n\nOvoviviparity is employed by many fish (including sharks), reptiles, and invertebrates. The young of ovoviviparous amphibians are sometimes born as larvae, and undergo metamorphosis outside the body of the mother.
64165
according to the geographic history. we have lots of dinosaurs laying eggs on earth even before the chickens arrive and laye their own eggs. therefore eggs come first before chickens.. hehehe...
595645
It is my understanding that rolling a bird egg equalizes the heat generated by the nesting mother, while for the reptile, the nest of decaying vegetation provides a pretty equal heating.\n\nThe bits before about the embryo attachment are true- and it would be interesting to researh the differing pathways these species took. Obviously, being able to heat your eggs on your own means you can and must protect them, which seems to logically flow into raising them at least a little. \n\nThis also means your young can be less developed at birth- unable to feed or care for themselves... it all sort of flows together, doesn't it?
675764
The simple answer is no, they don't produce more sperm & just because they're bigger than average, doesn't mean that they are any less fertile.
261210
Perhaps, the time of birthing and mating is in the spring.  They can not lay their eggs on land.  So, if they do not have water to deposit them in, then new frogs can not be born.  Hence, the population declines.  What do you think?
1164186
because they don't have ovaries, which produce estrogen and progesterone, which causes the ovaries to develop eggs for possible fertilization.
1099085
I don't think you mean development of the zygote....that is a fertilized egg.  Do you mean all the embryological stages after fertilization? There are similarities and differences in all three of these organisms' embryology.\n\nThe starfish zygote and amphibian zygote are both slimy-jelly coated and are vulnerable to fungus-bacterial infections in the water they are laid in, and vulnerable to being eaten by misc hungry aquatic organisms. These eggs are laid and fertilized as a result of external fertilization in the water.  Starfish just release the gametes in the water at a specific time in breeding season without a mating act per se.  If you are standing on a hill above a tidepool while groups of male and female starfish shed their gametes you can see the cloudiness in the water from the huge quantities of sperm and egg they release quasi-synchronistically. \n\nFrogs and other amphibians actually have a mating act called amplexus. The male does all the ribbiting to audition for the job of dna donor.  If she is ok with it, he jumps on the back of the female and he squeezes her eggs out while he releases his sperm on them. Starfish zygotes go thru many many larval stages-metamorphoses (they are part of zooplankton) and eventually mature to the adult on the tidepool rocks.  The bipinnaria larva of echinoderms are famous for their DEUTEROSTOMATE development like other vertebrates-chordates (see below)!\n\nAmphibian zygotes eventually turn into ONE aquatic tadpole larval stage which uses gills and then grow appendages-lungs to be eventually become more terrestrial.  \n\nAmphibians do not have an amnion in their eggs and are therefore anamniotes. Birds and reptiles produce "land eggs" that can resist dessication pretty well and are therefore called AMNIOTES, those who have the amniotic sac to help protect the developing embryo from the drying air on land. The amniotic fluid is in the amniotic sac. Mammals can lay eggs (monotremes) but most are placental mammals who have the amniotic sac in the uterus, but amnion and amniotic fluid with the fetus is not inside a shelled egg like the birds and reptiles.So placental mammals are the most advanced amniotes\n\nOne way these three embryo types do NOT differ: starfish and amphibian and bird are all "deuterostomate" animals.  . All animals you listed on your question are deuterostomate. Most invertebrates are "protostomes. So it is said to be an evolutionary LINK, that the echinoderm-starfish bipinnaria larva shows deuterostomate embryology! "Proto means "first," deutero means "last" and stom means "mouth." Again, both echinoderm bipinnaria larva and chordates-vertebrates (amphibians and birds) are deuterostomate. \n\nWhen embryos change from blastulas to gastrulas, there is an early indentation-invagination process of the tissue to begin the formation of endoderm and the future GI tract from MOUTH to ANUS.  In protostomates, most invertebrates except the echinoderm-starfish group, the mouth is formed first at the first indentation or invagination of blastula to become gastrula, and the anus is formed last.  \n\nIn the deuterostomates, the mouth is formed last and the anus is formed first.  The Echinoderms which includes the starfish, are deuterosomates like the chordates (bird and amphibian), including us humans. Aren't you glad you now know that your anus formed before your mouth?
328647
It would have laid eggs.  If you think of marsupials as being the simpliest form of mammal and the dimetrodon as being a more distant ancestor we can conclude as platypus, echindna etc as laying eggs so did dimetrodon.\nThis is just going by logic and evolutionary theory, I cannot prove it laid eggs.  We don't know for certain as (as far as I can discover) no eggs have been found - although one of the maxims of archaeology is that absence of evidence is not evidence of absence!