Throughout history reptiles have not only had to deal with bad public relations, but a whole suite of myths and misconceptions about their origins, physiology and capabilities. In some instances, reptiles have been adorned with extra powers (e.g. the snakes "ability" to sting with its tongue). Most myths, however, are simply misconceptions about these animals due to a lack of understanding about them, the majority stemming from the belief that "cold-bloodedness" is inferior to "warm-bloodedness". With the recent dinosaur renaissance coming to an end, these misconceptions have never been more prominent. Many now believe that dinosaurs were fundamentally different from other reptiles, unaware that most of these "differences" aren't differences at all, but traits shared by others reptiles in this huge class of animals. Use the jumping links below to learn more about these commonly held myths and misconceptions about reptiles.
Myth: All reptiles lay eggs.Fact: Many reptiles are capable of giving birth to live young. This can either be through the form of simple egg retention, in which all the nutrients still come from the calcified eggs (ovoviviparity), or by having the babies actually grow inside the mother without an egg. At most the babies are covered in a membranous sack. This form of live birth is a type of viviparity, and it is commonly seen in vipers and chameleons. Still other reptiles, like the skink Chalcides chalcides give birth to live young using a placenta, just like mammals. In fact, viviparity has evolved over 100 separate times in reptiles throughout their history.
Myth: Sprawling is less efficient than erect walkingFact: Though it might seem like common sense, or even logical to assume that having the legs splayed out from under the body is less efficient than having them straight underneath, scientific studies suggest otherwise (Bakker 1972). Sprawling animals are more efficient locomotory wise, than erect walking animals. The only time this changes is when large size is reached. So the belief that there should always be a trend towards an erect stance is erroneous, with the reverse being more likely.
Myth: Mammals and birds are more advanced than reptilesFact: Evolution does not proceed anagenically (i.e. one species does not supercede another and become "better" than the former). Evolution is a process more akin to that of a bush, or dendrite system of a tree. Many branches stem from a single origin, each grows at its own pace and in its own direction. No branch is "better" than another. Though birds and mammals are considered to be better in the eyes of the public and popular science, this is far from true. Reptiles all have far more complex hearts than either mammals or birds and these hearts do a better job at conserving oxygen. The tails in reptiles are far more versatile than those of either mammals or birds. Reptiles can achieve a wider range of body sizes do to their bradymetabolisms etc. All of these are more useful to them than a mammalian or avian equivalent would be. If it weren't, then the traits wouldn't have evolved and/or lasted for as long as they have. The reptiles of today are just as advanced as the birds and mammals of today. The same thing goes for all the world's creatures.
Myth: Reptiles are incapable of aerobic endurance because they are "cold-blooded"Fact: This is one of those "just so" beliefs that came about from the fact that "cold-blooded" animals have lower resting metabolisms than "warm-blooded" ones. This statement is often made in the paleontological circles, especially when dinosaurs are mentioned.It is true that many reptiles today lack aerobic endurance, that this is caused by their "cold-bloodedness" though, is blatantly false. The lack of aerobic endurance in most reptiles is due to their anatomy. In most reptiles, locomotion follows a sigmoid (S shaped) path. This movement was inherited from the undulations of their fish ancestors. Now while gills work fine with this movement, it doesn't translate very well into terrestrial locomotion. In most reptiles, respiration is controlled by the costal (rib) muscles. Unfortunately these muscles are also used in locomotion. Furthermore this sigmoid movement alternately compresses each lung, thus making it a real chore to breath and walk at the same time. For many reptiles this means holding their breath as they move and evolving a high anaerboic capacity. This is why lizards often take breaks inbetween walking; to catch their breath. There are ways to counter this though. Chelonians, with their rigid shells, have lost the sigmoidal movement and thus, no longer face this carrier's constraint. Crocodylians use their diaphragm to breath while walking, which alleviates the pressure from their side to side movements. In many aerobically active lizards, a special form of breathing called: "gular pumping" has evolved (Owerkowicz 1999). When these lizards walk, they suck air in by pumping their throat in and out. This allows the lungs to fully fill while walking, thus removing the carrier's constraint on these animals. Other techniques are also employed, such as bipedal locomotion and holding the body stiff while running. So yes there are aerobic reptiles, and those that do lack it, don't lack it because they are "cold-blooded." Myth: Reptiles are the same temperature as their environment or lower.Fact: Very few reptiles are thermoconformers (i.e. forced to be the same temp as their environment). Those that are, are forced to be that way due to a lack of good thermoregulatory options. This is usually seen in densely forested areas, where access to sunlight is hard to come by.The majority of reptiles are thermoregulators that, by using the hottest and coldest parts of their environments, along with precise circulatory control (e.g. vasodilation and shunting of blood) are capable of keeping an almost constant, high temperature. Some reptiles even employ shivering to raise their body temperatures (e.g. monitor lizards and brooding boas). By shunting warm blood to their core, many reptiles are capable of maintaining a higher body temperature than their surroundings, even as their surroundings continue to cool down. So with a few exceptions, most reptiles are hotter than their environments, most of the time. For more on this and other thermoregulatory strategies, please see: A Question of Cold-Bloodedness.
Bakker, R.T. 1972 "Locomotor Energetics of Lizards and Mammals Compared" Physiologist vol 15:278 Owerkowicz, E.L. 1999. "Contribution of Gular Pumping to Lung Ventilation in Monitor Lizards". Science. vol. 284(5420), 1661-1662. |