Pelvic spur

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External view of anal spurs on a male, albino burmese python Anal spurs.jpg
External view of anal spurs on a male, albino burmese python
Skeleton of a Boelens python showing the bones inside the anal spurs Boelens python anal spurs.jpg
Skeleton of a Boelens python showing the bones inside the anal spurs

Pelvic spurs (also known as vestigial legs) are external protrusions found around the cloaca in certain superfamilies of snakes belonging to the greater infraorder Alethinophidia . [1] These spurs are made up of the remnants of the femur bone, which is then covered by a corneal spur, or claw-like structure. [1] This femur derives from ancestral hind limbs found in the most recent common ancestor of modern snakes and the other reptiles of the clade Toxicofera , many of which have fully functional front and hind limbs. [2] Due to the fact that the spurs derive from the ancestral state of functional legs, but are no longer functional for locomotion specifically, these structures do meet the criteria for being considered vestigial. [3] Nonetheless, uses for the structures have been thoroughly documented. Species that have external spurs have corresponding muscles, neurological structures, and vascularization to allow for independent movement. [3] The spurs are more pronounced and visible in male specimens and have been observed in use during courtship behavior. [4] The spurs are specifically used in the clasping and stimulation of females by males during courtship and mating. In certain species, males will also use their spurs to engage in combat with one another. [3]

Contents

Fossil Record

The fossil record of snakes is not expansive. [5] Nonetheless, multiple fossilized specimens document the progression of the development of leglessness within the suborder Serpentes. The species of extinct snake Najash rionegrina was first described in 2006, and has been proposed as the earliest branching taxa of the suborder Serpentes. [6] The fossils were found in the Patagonia region of Argentina, and were dated to the Upper Cretaceous period. Najash rionegrina exhibited a sacrum, pelvic girdle, and robust hind limb structures outside of the ribcage, all of which led researchers to the conclusion that these hind limbs were functional for locomotion. [6] The significance of this finding is great, as there were three other known species of legged snakes from this time period, Pachyrhachis problematicus, Haasiophis terrasanctus and Eupodophis descouensi, but all were predicted to have been marine species, and all of them lacked the sacrum region found in N. rionegrina. [7] [6] The paleontologists thus concluded via phylogenetic analysis that N. rionegrina is the most ancient taxa within Serpentes, and the three extinct species previously described were more closely related to modern-day snakes belonging to Alethinophidia . [6]

Recent analysis of numerous fossil records supported these findings and further demonstrated the reduction of pelvic and hind limb structures within these lineages. [5] [2] Further evidence for these structures being plesiomorphic of can be found in the pelvis of some living taxa such as Candoia carinata or Eunectes murinus. These taxa possess a triradiate pelvis, which can also be observed in the skeletons of modern lizards. [2]

Distribution

The presence of pelvic spurs in extant species of Serpentes is limited. Within Alethinophidia , two superfamilies are known to possess spurs: Booidea and Pythonoidea . [8] These two superfamilies are sometimes referred to as primitive snakes, as they are considered to be the earliest diverging taxa of Macrostomata, the clade which includes the majority of described living snake species, and whose only other constituent beyond Booidea and Pythonoidea is Caenophidia . [9] While species of Caenophidia lack spurs, the presence and use of spurs across Booidea and Pythonoidea is well documented. In these superfamilies, spurs can be observed as tools for courtship and competition between males, and are sexually dimorphic. [3]

While these are the most well-known taxa to possess spurs, evidence does exist for the presence of ossified vestigial structures in other taxa. A 2019 publication provided evidence for similarly ossified structures in the species Liotyphlops beui of the infraorder Scolecophidia . [2] Members of this sister group of Scolecophidia are poorly understood due to their cryptic nature and are typically small in size, fossorial, and worm-like. [8] This 2019 study is the first described occurrence of these structures within the family Anomalepididae , which is one of three families within Scolecophidia. [2]

Importance to Social Behavior

Numerous studies have been conducted on the use of pelvic spurs by males in the superfamilies Booidea and Pythonoidea. The sexually dimorphic nature of the spurs was formally described by William H. Stickel and Luccille F. Stickel in 1946 in the genus Enygrus (more commonly known today as Candoia ). [10] The authors of this study noted that others in the field had made similar observations before, but had not formally researched the topic specifically. Spurs were found to be significantly larger in males, while in females spurs were much shorter, and were sometimes externally absent. [10]

Dominance Displays

Research has since found the use of pelvic spurs in dominance displays in numerous species. The use of spurs alongside biting was observed in displays between males in a captive group of Indian pythons (Python molurus), which subsequently formed a linear dominance hierarchy. The position in this hierarchy was directly correlated with a male’s number of successful instances of mating. [11] Another study found the use of spurs in madagascan boas ( Sanzinia madagascariensis ), an arboreal species. In this species, researchers did not observe biting. [12] In fact, the authors observed that the heads of combating males were frequently out of sight of one another. In its place, observed males would tightly grip on to each other using the posterior regions of their bodies, orienting their spurs to be perpendicular to their body while doing so. [12] The authors postulate that this form of spur-based combat is adaptive to the species’ arboreal habitat. [12] It is also worth noting that combat between males in species that lack spurs, such as species of Caenophidia, relies on a distinct repertoire of behaviors that differs from species possessing spurs. [13]

Courtship Behaviors

Similar to the described observations of sexual dimorphism prior to their publication, William H. Stickel and Luccille F. Stickel also noted that observations had been made by others of pelvic spur use by males on females during mating. [10] These observations have since been formally investigated and published in multiple species.

One such study found dynamic use of spurs by males during different phases of courtship and mating in Burmese pythons (Python molurus bivittatus), with anterior to posterior spur movements varying in speed of undulation by phase. [14] Furthermore, the males exhibited use of the spurs to better position or adjust the female’s cloaca for mating. The authors note that spur use for combat can also be observed in this species between males. [14] A separate study found similar results in diamond pythons (Morelia spilota), a species that does not exhibit any bouts of combat between males. [15] In this species, multiple males were observed mating with the same female simultaneously, and males did not engage in combat. Instead, it was observed that spurs were used by males to manipulate the tail of the female. [15] Corroborating these results in a New World species, a study in 2023 documented the use of spurs in mating by red-tailed boas, Boa constrictor . [3] It was observed that males repeatedly alternated the orientation of the spurs between horizontal and vertical positions, which the authors suggest stimulated muscle contractions in the female, which would allow for better alignment between the individuals for mating. [3]

Related Research Articles

<span class="mw-page-title-main">Snake</span> Limbless, scaly, elongate reptile

Snakes are elongated, limbless, carnivorous reptiles of the suborder Serpentes. Like all other squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales. Many species of snakes have skulls with several more joints than their lizard ancestors, enabling them to swallow prey much larger than their heads. To accommodate their narrow bodies, snakes' paired organs appear one in front of the other instead of side by side, and most have only one functional lung. Some species retain a pelvic girdle with a pair of vestigial claws on either side of the cloaca. Lizards have independently evolved elongate bodies without limbs or with greatly reduced limbs at least twenty-five times via convergent evolution, leading to many lineages of legless lizards. These resemble snakes, but several common groups of legless lizards have eyelids and external ears, which snakes lack, although this rule is not universal.

<span class="mw-page-title-main">Boidae</span> Family of snakes

The Boidae, commonly known as boas or boids, are a family of nonvenomous snakes primarily found in the Americas, as well as Africa, Europe, Asia, and some Pacific islands. Boas include some of the world's largest snakes, with the green anaconda of South America being the heaviest and second-longest snake known; in general, adults are medium to large in size, with females usually larger than the males. Six subfamilies comprising 15 genera and 54 species are currently recognized.

<span class="mw-page-title-main">Ball python</span> Species of constricting snake

The ball python, also called the royal python, is a python species native to West and Central Africa, where it lives in grasslands, shrublands and open forests. This nonvenomous constrictor is the smallest of the African pythons, growing to a maximum length of 182 cm (72 in). The name "ball python" refers to its tendency to curl into a ball when stressed or frightened.

<span class="mw-page-title-main">Ophidia</span> Group of squamate reptiles

Ophidia is a group of squamate reptiles including modern snakes and reptiles more closely related to snakes than to other living groups of lizards.

<i>Loxocemus</i> Genus of snakes

Loxocemus bicolor, the sole member of the monotypic family Loxocemidae and commonly known as the Mexican python, Mexican burrowing python and Mexican burrowing snake, is a species of python-like snake found in Mexico and Central America. No subspecies are currently recognized. Analyses of DNA show that Loxocemus is most closely related to the true pythons and the sunbeam snakes.

<span class="mw-page-title-main">Henophidia</span> Group of snakes

Henophidia is a former superfamily of the suborder Serpentes (snakes) that contains boas, pythons and numerous other less-well-known snakes.

<span class="mw-page-title-main">Green anaconda</span> Species of snake

The green anaconda, also known as the giant anaconda, emerald anaconda, common anaconda, or common water boa, is a boa species found in South America and the Caribbean island of Trinidad. It is the largest, heaviest and the second longest snake in the world. No subspecies are currently recognized. Like all boas, it is a non-venomous constrictor.

<span class="mw-page-title-main">Indian python</span> Species of snake

The Indian python is a large python species native to tropical and subtropical regions of the Indian subcontinent and Southeast Asia. It is also known by the common names black-tailed python, Indian rock python, and Asian rock python. Although smaller than its close relative the Burmese python, it is still among the largest snakes in the world. It is generally lighter colored than the Burmese python and reaches usually 3 m. Like all pythons, it is nonvenomous.

Pachyrhachis is an extinct genus of snake with well developed hind legs known from fossils discovered in Ein Yabrud, near Ramallah, in the central West Bank. It is a relatively small snake, measuring more than 1.5 metres (4.9 ft) long at maximum. Pachyrhachis appears to have been an ancient marine snake; the fossils occur in a marine limestone deposit, and the thickened bone of the ribs and vertebrae would have functioned as ballast to decrease the buoyancy of the animal, allowing it to dive beneath the ancient Cretaceous seas that it once inhabited.

<i>Python</i> (genus) Genus of snakes

Python is a genus of constricting snakes in the Pythonidae family native to the tropics and subtropics of the Eastern Hemisphere.

<span class="mw-page-title-main">Madtsoiidae</span> Extinct family of snakes

Madtsoiidae is an extinct family of mostly Gondwanan snakes with a fossil record extending from early Cenomanian to late Pleistocene strata located in South America, Africa, India, Australia and Southern Europe. Madtsoiidae include very primitive snakes, which like extant boas and pythons would likely dispatch their prey by constriction. Genera include Madtsoia, one of the longest snakes known, at an estimated 10 metres (33 ft), and the Australian Wonambi and Yurlunggur. As a grouping of basal forms the composition and even the validity of Madtsoiidae is in a state of flux as new pertinent finds are described, with more recent evidence suggesting that it is paraphyletic as previously defined.

<span class="mw-page-title-main">Alethinophidia</span> Clade of snakes

The Alethinophidia are an infraorder of snakes that includes all snakes other than blind snakes and thread snakes. Snakes have long been grouped into families within Alethinophidia based on their morphology, especially that of their teeth. More modern phylogenetic hypotheses using genetic data support the recognition of 19 extant families, although the taxonomy of alethinophidian snakes has long been debated, and ultimately the decision whether to assign a particular clade to a particular Linnaean rank is arbitrary.

The Pythonoidea, also known as pythonoid snakes, are a superfamily of snakes that contains pythons and other closely related python-like snakes. As of 2022, Pythonoidea contains 39 species, including the eponymous genus Python and 10 other genera of pythons, all in the family Pythonidae, as well as two lesser-known families, Loxocemidae and Xenopeltidae.

<i>Eunectes</i> Genus of snakes

Eunectes is a genus of boas found in tropical South America commonly called anacondas. They are a semiaquatic group of snakes and include one of the largest snakes in the world, E. murinus, the green anaconda. Four species are currently recognized.

<span class="mw-page-title-main">Boa constrictor</span> Species of snake

The boa constrictor, also known as the common boa, is a species of large, non-venomous, heavy-bodied snake that is frequently kept and bred in captivity. The boa constrictor is a member of the family Boidae. The species is native to tropical South America. A staple of private collections and public displays, its color pattern is highly variable yet distinctive. Four subspecies are recognized. This article focuses on the species Boa constrictor as a whole, and on the nominate subspecies B. c. constrictor.

<span class="mw-page-title-main">Spur (zoology)</span> Anatomical term for an outgrowth of bone covered in a sheath of horn

A spur is an outgrowth of bone covered in a sheath of horn found in various anatomical locations in some animals. Unlike claws or nails, which grow from the tip of the toes, spurs form from other parts of the foot, usually in connection with joints where the toes meet the foot or the foot meets the long bones. Spurs are most commonly found on the hindfeet, though some birds possess spurs at the leading edge of the wings.

<i>Malayopython</i> Genus of snakes

Malayopython is a genus of constricting snakes in the family Pythonidae. The genus is native to India and Southeast Asia. It contains two species, both of which were previously classified within the genus Python. However, multiple studies recovered these species as distinct. Known as the "reticulatus clade", it was eventually found to be a sister lineage to a lineage giving rise to the Indo-Australian pythons rather than the genus Python.

<span class="mw-page-title-main">Booidea</span> Superfamily of snakes

The Booidea, also known as booid snakes, are a superfamily of snakes that contains boas and other closely related boa-like snakes. As of 2017, Booidea contains 61 species, including the eponymous neotropical Boa constrictor, anacondas, and smaller tree and rainbow boas as well as several genera of booid snakes from various locations around the world: bevel-nosed boas or keel-scaled boas (Candoia) from New Guinea and Melanesia, Old World sand boas (Eryx) from Northeast Africa, the Middle East, and Southwest Asia, rubber boas (Charina) and rosy boas (Lichanura) from North America, neotropical dwarf boas (Ungaliophis) and the Oaxacan dwarf boa (Exiliboa) from Central America, Madagascan boas or Malagasy boas from Madagascar, and the Calabar python (Calabaria) from tropical West-Central Africa.

<span class="mw-page-title-main">Amerophidia</span> Clade of snakes

The Amerophidia, also known as amerophidian snakes, are a superfamily of snakes that contains two families: Aniliidae and the boa-like Tropidophiidae.

References

  1. 1 2 Pough, F. H. (Ed.). (2004). Herpetology (3rd ed). Prentice Hall.
  2. 1 2 3 4 5 Palci, A., Hutchinson, M. N., Caldwell, M. W., Smith, K. T., & Lee, M. S. Y. (2019). The homologies and evolutionary reduction of the pelvis and hindlimbs in snakes, with the first report of ossified pelvic vestiges in an anomalepidid (Liotyphlops beui). Zoological Journal of the Linnean Society, zlz098. https://doi.org/10.1093/zoolinnean/zlz098
  3. 1 2 3 4 5 6 Anzai, R. K., Eleuterio, N. F., Oliveira Lima, T. D., Manfio, R. H., & Almeida Santos, S. M. D. (2023). Pelvic spur use during courtship and mating in the red-tailed boa Boa constrictor. The Herpetological Bulletin, 163, 35–36. https://doi.org/10.33256/hb163.3536
  4. ↑ Bauchot, R. (Ed.). (1994). Snakes: A natural history. Sterling Pub.
  5. 1 2 Garberoglio, F. F., Apesteguía, S., Simões, T. R., Palci, A., Gómez, R. O., Nydam, R. L., Larsson, H. C. E., Lee, M. S. Y., & Caldwell, M. W. (2019). New skulls and skeletons of the Cretaceous legged snake Najash , and the evolution of the modern snake body plan. Science Advances, 5(11), eaax5833. https://doi.org/10.1126/sciadv.aax5833
  6. 1 2 3 4 Apesteguía, S., & Zaher, H. (2006). A Cretaceous terrestrial snake with robust hindlimbs and a sacrum. Nature, 440(7087), 1037–1040. https://doi.org/10.1038/nature04413
  7. ↑ Bellairs, A. D., & Underwood, G. (1951). The origin of snakes. Biological Reviews, 26(2), 193–237. https://doi.org/10.1111/j.1469-185X.1951.tb00646.x
  8. 1 2 Serpentes(Snakes). (n.d.). Retrieved October 10, 2023, from https://www.ucl.ac.uk/museums-static/obl4he/vertebratediversity/serpentes_snakes.html
  9. ↑ Lee, M. S. Y., Hugall, A. F., Lawson, R., & Scanlon, J. D. (2007). Phylogeny of snakes (Serpentes): Combining morphological and molecular data in likelihood, Bayesian and parsimony analyses. Systematics and Biodiversity, 5(4), 371–389. https://doi.org/10.1017/S1477200007002290
  10. 1 2 3 Stickel, W. H., & Stickel, L. F. (1946). Sexual dimorphism in the pelvic spurs of enygrus. Copeia, 1946(1), 10. https://doi.org/10.2307/1438812
  11. ↑ Barker, D. G., Murphy, J. B., & Smith, K. W. (1979). Social behavior in a captive group of indian pythons, python molurus (Serpentes, boidae) with formation of a linear social hierarchy. Copeia, 1979(3), 466. https://doi.org/10.2307/1443224
  12. 1 2 3 Carpenter, C. C., Murphy, J. B., & Mitchell, L. A. (1978). Combat bouts with spur use in the madagascan boa(Sanzinia madagascariensis). Herpetologica, 34(2), 207–212. https://www.jstor.org/stable/3891678
  13. ↑ Gillingham, J. C. (1980). Communication and combat behavior of the black rat snake(Elaphe obsoleta). Herpetologica, 36(2), 120–127. https://www.jstor.org/stable/3891474
  14. 1 2 Gillingham, J. C., & Chambers, J. A. (1982). Courtship and pelvic spur use in the burmese python, python molurus bivittatus. Copeia, 1982(1), 193. https://doi.org/10.2307/1444292
  15. 1 2 Slip, D. J., & Shine, R. (1988). The reproductive biology and mating system of diamond pythons, morelia spilota(Serpentes: Boidae). Herpetologica, 44(4), 396–404. https://www.jstor.org/stable/3892404


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