|The Simple English Wiktionary has a definition for: svl.|
Snout–vent length (SVL) is the length of an animal's body. It is measured from the tip of its snout to its rear end. The snout is the part of the face at the front. The tail (if any) is not counted, nor is any protruding teeth or tusks.
So, in a frog, it is the length of the frog's body but not the frog's legs. For turtles, carapace length (CL, the length of the shell) and plastral length (PL) are used.
The SVL can change depending on whether the animal is alive, dead, moving, or still. It can change if scientists have used chemicals to preserve its dead body. Scientists also try to determine snout-vent length in fossils using an osteological correlate such as precaudal length. A scientist can look at the animal's SVL, weight, and body and may be able to tell if it is male or female or how old it is.
Scientists use snout-vent length instead of the animal's whole body length because it does not change much. In some animals, young ones do not have tails or do not have large tails.
The term is really useful for mammals. It's not so useful for animals where the tail is an important continuation of the body, and not just a fly-whisk. Bipedal dinosaurs come to mind as an example. It took a long time for palaeontologists to appreciate this, as one look at the Crystal Palace dinosaurs will show. Tails of snakes are also longer than the position of their vent. The tails of fish are integral to their body, and absolutely necessary. In other words, "snout-vent length" is best used for mammals, and has to be re-interpreted for other kinds of animals.
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