Cursorial

Horses can be considered cursorial grazers.

Cursorial is a biological term that describes an organism as being adapted specifically to run. It is typically used in conjunction with an animal's feeding habits or another important adaptation. For example, a horse can be considered a "cursorial grazer", while a wolf may be considered a "cursorial predator". The term is typically applied to animals adapted to long-distance running at high speeds, rather than animals with high acceleration over short distances - a cheetah is considered cursorial, while a leopard is not. Within vertebrates, the term is rarely applied to animals under 1 kg of mass, as such organisms typically move in a series of short bursts rather than at a constant speed. All extant curosial vertebrates are endothermic, allowing high metabolic rates and high endurance, though it is possible some extinct species were ectothermic.

Some species of spiders are also considered cursorial, as they walk much of the day, looking for prey. The oldest fossils of jumping spiders are from Baltic amber dated at 54 to 42 million years ago.

Cursorial Adaptions

Locomotion of terrestrial vertebrates

Adaptions for cursorial locomotion include:

• Increased stride length by:
  • Increased limb bone length
  • Adoption of digitigrade or unguligrade stance
  • Loss of clavicle in mammals, which allows the scapula to move forwards and backwards with the limb and thereby increase stride length.
  • Increased spinal flexion during galloping
• Decreased distal limb weight (in order to minimize moment of inertia:
  • Increase in mass of proximal muscles with decrease in mass of distal muscles
  • Increase in length of distal limb bones (the manus and pes) rather than proximal ones (the brachium or thigh).
  • Longer tendons in distal limb
• Decreased ability to move limbs outside of the saggital plane, which increases stability.
• Loss of digits.
• Loss of ability to pronate and supinate the forearm
• Hooves, hoof-like claws, or blunt claws for traction (as opposed to sharp claws for prey-capture or climbing)

Locomotion of spiders

A spider at take-off when jumping. It fixes a silk dragline (safety line) just before jumping.

Spiders maintain balance when walking, so that legs 1 and 3 on one side and 2 and 4 on the other side are moving, while the other four legs are on the surface. To run faster, spiders increase their stride frequency.^[1] Jumping spiders can also jump up to 50 times their own length by powerfully extending the third or fourth pairs of legs.^[2]

Cursorial taxa

Several notable taxa are cursorial, including some mammals (such as wolves, cheetahs, ungulates, agoutis, and kangaroos) and birds (such as the ostrich), as well as some dinosaurs (such as theropods, and Heterodontosauridae). Several extinct archosaurs were also cursorial, including the crocodylomorphs Pristichampsus, Hesperosuchus, and several genera within Notosuchia.

Jumping spiders and other non-web based spiders generally walk throughout the day, so that they maximize their chances of a catch,^[3] and web-based spiders run away if threatened.^[4]

In evolutionary theory

The cursorial (or Ground-Up) theory of the evolution of flight is the theory that birds evolved from ground-living theropods, as opposed to arboreal species. This refers to the presumed cursorial nature of theropod dinosaurs, and that the flight apparatus may have been adapted to improve hunting by lengthening leaps and improving maneuverability.

The evolution of the horse is one of the most widely-known sequences of transitional fossils, depicting all stages of evolution between a small, unspecialized grazer to a large, cursorial mammal capable of extremely high speeds.

Several Carboniferous spiders were members of the Mesothelae, a primitive group now represented only by the Liphistiidae.^[5] The mesothelid Paleothele montceauensis, from the Late Carboniferous over 299 million years ago, had five spinnerets.^[6] Attercopus fimbriunguis, from 386 million years ago in the Devonian period, bears the earliest known silk-producing spigots, and was therefore hailed as a spider.^[5] However, this may not have been a true spider as it shows no sign of having spinnerets, whose mobility is important in the building of webs, and Attercopus probably used silk for lining nests or producing egg-cases rather than for building webs.^[7] The oldest fossils of jumping spiders are from Baltic amber dated at 54 to 42 million years ago, in the Eocene epoch.^[8]

References

1. ^ Anderson, D.T. (1998). "The Chelicerata". In D.T. Anderson. Invertebrate Zoology (1 ed.). Oxford University Press Australia. p. 328. ISBN 0915539419. 
2. ^ Ruppert, E.E., Fox, R.S., and Barnes, R.D. (2004). "Chelicerata: Araneae". Invertebrate Zoology (7 ed.). Brooks / Cole. p. 578. ISBN 0030259827. 
3. ^ Forster, Lyn M. (Nov 1977). "Some factors affecting feeding behaviour in young Trite auricoma spiderlings (Araneae: Salticidae)". New Zealand Journal of Zoology (The Royal Society of New Zealand) 4 (4): 435–442. doi:10.1080/03014223.1977.9517967. http://books.google.com/?id=WWznrYjY53cC&pg=PA435&dq=%22Phidippus+clarus%22#v=onepage&q=%22Phidippus%20clarus%22&f=false. Retrieved 24 April 2011. 
4. ^ Wilcox, R. Stimson; Robert R. Jackson (1998). "Cognitive Abilities of Araneophagic Jumping Spiders". In Russell P. Balda, Irene Maxine Pepperberg, Alan C. Kamil. Animal cognition in nature: the convergence of psychology and biology in laboratory and field. Academic Press. p. 418. ISBN 9780120770304. http://books.google.com/?id=504iRS01AK0C&pg=PA411&dq=%22portia+fimbriata%22+%22sri+lanka%22+#v=onepage&q=%22portia%20fimbriata%22%20%22sri%20lanka%22&f=false. Retrieved 23 May 2011. 
5. ^ ^{a b} Vollrath, F., and Selden, P.A. (December 2007). "The Role of Behavior in the Evolution of Spiders, Silks, and Webs" (PDF). Annual Review of Ecology, Evolution, and Systematics 38: 819–846. doi:10.1146/annurev.ecolsys.37.091305.110221. http://homepage.mac.com/paulselden/Sites/Website/ARES.pdf. Retrieved 2008-10-12. 
6. ^ Selden, P.A. (February 1996). "Fossil mesothele spiders". Nature 379 (6565): 498–499. doi:10.1038/379498b0. 
7. ^ Selden, P.A., and Shear, W.A. (July 2008). "Fossil evidence for the origin of spider spinnerets" (PDF). Nature Precedings. http://precedings.nature.com/documents/2088/version/1/files/npre20082088-1.pdf. Retrieved 2008-10-12. 
8. ^ Hill, David Edwin (October 7, 2009). "Salticidae of the Antarctic land bridge". Peckhamia. http://www.peckhamia.com/peckhamia/PECKHAMIA%2076.1.pdf. 

See also

• Arboreal
• Fossorial