Snout-vent length

Morphometric measurement used in herpetology

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.[1]

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.[2] 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.[3]

AdvantagesEdit

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.[4]

MethodsEdit

The scientist or other person can measure snout-vent length with dial calipers or digital calipers.

The scientist can use other tools to hold the animal still. For example, snake tubes, "Mander Mashers,"[5] or a "Salamander Stick."[6]

LimitationsEdit

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.

ReferencesEdit

  1. "direct line distance from tip of snout to posterior margin of vent" Watters, Jessa L.; Cummings, Sean T.; Flanagan, Rachel L.; Siler, Cameron D. (2016). "Review of morphometric measurements used in anuran species descriptions and recommendations for a standardized approach". Zootaxa. 4072 (4): 477–495. doi:10.11646/zootaxa.4072.4.6. ISSN 1175-5334. PMID 27395941.
  2. Vitt, Laurie J.; Zug, George R. (2012). Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. p. 34. ISBN 978-0127826202.
  3. Kupfer, A. (2007). "Sexual size dimorphism in amphibians: an overview". In Fairbairn, D. J.; Blanckenhorn, W. U.; Székely, T. (eds.). Sex, Size, and Gender Roles: Evolutionary Studies of Sexual Size Dimorphis. New York: Oxford University Press. pp. 50–59. ISBN 978-0-19-920878-4.
  4. Bolton, Melvin (1989). "7. Capture, Transport, Marking and Measuring of Young Crocodiles". The management of crocodiles in captivity. FAO.
  5. Wise, S. E.; Buchanan, S.W. (1992). "An efficient method for measuring salamanders". Herpetological Review. 23: 56–57.
  6. Walston, L. J.; Mullin, S. J. (2005). "Evaluation of a new method for measuring salamanders". Herpetological Review. 36: 290–292.

Further readingEdit