• We are sorry, but NCBI web applications do not support your browser and may not function properly. More information
Logo of transbhomepageaboutsubmitalertseditorial board
Philos Trans R Soc Lond B Biol Sci. Sep 29, 2003; 358(1437): 1525–1533.
PMCID: PMC1693243

Bipedalism in lizards: whole-body modelling reveals a possible spandrel.

Abstract

This paper illustrates how simple mechanical models based on morphological, ethological, ecological and phylogenetic data can add to discussions in evolutionary biology. Bipedal locomotion has evolved on numerous occasions in lizards. Traits that appear repeatedly in independent evolutionary lines are often considered adaptive, but the exact advantages of bipedal locomotion in lizards remain debated. Earlier claims that bipedalism would increase maximal running speed or would be energetically advantageous have been questioned. Here, we use 'whole body' mechanical modelling to provide an alternative solution to the riddle. The starting point is the intermittent running style combined with the need for a high manoeuvrability characterizing many small lizard species. Manoeuvrability benefits from a caudal shift of the centre of mass of the body (body-COM), because forces to change the heading and to align the body to this new heading do not conflict with each other. The caudally situated body-COM, however, might result in a lift of the front part of the body when accelerating (intermittent style), thus resulting in bipedal running bouts. Based on a momentum-impulse approach the effect of acceleration is quantified for a mechanical model, a virtual lizard (three segments) based on the morphometrics of Acanthodactylus erythrurus (a small lacertid lizard). Biologically relevant input (dimensions, inertial properties, step cycle information, etc.) results in an important lift of the front part of the body and observable distances passively covered bipedally as a consequence of the acceleration. In this way, no functional explanation of the phenomenon of lizard bipedalism is required and bipedalism can probably be considered non-adaptive in many cases. This does not exclude, however, some species that may have turned this consequence to their benefit. For instance, instantaneous manipulation of the position of the centre of the body-COM allows stable, persisting bipedal running. Once this was achieved, the bipedal spandrel could be exploited further.

Full Text

The Full Text of this article is available as a PDF (292K).

Selected References

These references are in PubMed. This may not be the complete list of references from this article.
  • Farley CT, Ko TC. Mechanics of locomotion in lizards. J Exp Biol. 1997 Aug;200(Pt 16):2177–2188. [PubMed]
  • Fedak MA, Seeherman HJ. Reappraisal of energetics of locomotion shows identical cost in bipeds and quadrupeds including ostrich and horse. Nature. 1979 Dec 13;282(5740):713–716. [PubMed]
  • Gould SJ, Lewontin RC. The spandrels of San Marco and the Panglossian paradigm: a critique of the adaptationist programme. Proc R Soc Lond B Biol Sci. 1979 Sep 21;205(1161):581–598. [PubMed]
  • Irschick DJ, Jayne BC. Effects of incline on speed, acceleration, body posture and hindlimb kinematics in two species of lizard Callisaurus draconoides and Uma scoparia. J Exp Biol. 1998 Jan;201(Pt 2):273–287. [PubMed]
  • Irschick DJ, Jayne BC. Comparative three-dimensional kinematics of the hindlimb for high-speed bipedal and quadrupedal locomotion of lizards . J Exp Biol. 1999 May;202(Pt 9):1047–1065. [PubMed]
  • Jindrich DL, Full RJ. Many-legged maneuverability: dynamics of turning in hexapods . J Exp Biol. 1999 Jun;202(Pt 12):1603–1623. [PubMed]
  • Roberts TJ, Kram R, Weyand PG, Taylor CR. Energetics of bipedal running. I. Metabolic cost of generating force. J Exp Biol. 1998 Oct;201(Pt 19):2745–2751. [PubMed]
  • SNYDER RC. The anatomy and function of the pelvic girdle and hindlimb in lizard locomotion. Am J Anat. 1954 Jul;95(1):1–45. [PubMed]
  • Taylor CR, Rowntree VJ. Running on two or on four legs: which consumes more energy? Science. 1973 Jan 12;179(4069):186–187. [PubMed]

Articles from Philosophical Transactions of the Royal Society B: Biological Sciences are provided here courtesy of The Royal Society

Formats:

Related citations in PubMed

See reviews...See all...

Cited by other articles in PMC

See all...

Links

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...