Allometric growth of limb and body proportions in crocodylians. (20th July 2019)

• Record Type: Journal Article
• Authors: Iijima, M.; Kubo, T.
• Is Part Of: Journal of zoology. Volume 309:Number 3(2019)
• Page Start: 200
• Page End: 211
• Publication Date: 2019-07-20
• Subjects: Crocodylia -- forelimb -- hindlimb -- presacral length -- midshaft circumference -- ontogeny -- allometric growth -- body size; Zoology -- Periodicals; Zoologie -- Périodiques; 590.5
• DOI: 10.1111/jzo.12714
• Languages: English
• ISSNs: 0952-8369

Abstract

Abstract: Crocodylia is the sole extant remnant of quadrupedal archosaurs playing a pivotal role in understanding the evolution of growth allometry in the archosaur locomotor apparatus. However, among crocodylians, the postnatal growth of the postcranial skeleton has almost exclusively been examined in Alligator mississippiensis, and whether other species share the same growth pattern is unknown. Here, we tested whether the following allometric trends are conserved across Crocodylia: (1) forelimb length grows isometrically relative to hindlimb length; (2) fore‐ and hindlimb lengths become relatively shorter with increasing body size; and (3) long bone cross‐sectional geometry becomes more robust relative to body size. We examined the relationships of limb lengths, stylopodial circumferences and presacral length (body size proxy) in extant crocodylians using reduced major axis regressions and compared the slopes among species. The result revealed non‐uniform growth patterns of limb architecture among living crocodylians. Generally, the hindlimb grows with negative allometry against the forelimb in non‐gavialid crocodylians, whereas two gavialids ( Gavialis gangeticus and Tomistoma schlegelii ) showed isometry in hind‐ vs. forelimb length scaling, potentially reflecting their unique locomotor ecology. Femur circumference scales negatively against humerus circumference in most of the species examined, which may be related to the anterior shift of the center of mass during growth. Stylopodial circumferences scale variously against stylopodial lengths and presacral length in crocodylians, lending little support to hypotheses that these allometries correlate with adult body size or metabolism (i.e. ectothermic or endothermic) in tetrapods. Abstract : Crocodylia is the sole remnant of quadrupedal archosaurs playing a significant role in understanding the evolution of archosaur locomotor ontogeny. However, the postcranial growth has almost exclusively been examined in Alligator mississippiensis, and whether other species share the same growth pattern is unknown. In this paper, we provide the first comprehensive interspecific comparisons of the limb and body proportion ontogeny among extant crocodylian species. The result showed that the fore‐ vs. hindlimb length scaling patterns are different between non‐gavialids and gavialids ( Gavialis gangeticus and Tomistoma schlegelii ), probably reflecting the unique locomotor ecology in gavialids. The growth of humeral midshaft circumference is faster than that of femur in most of the species, suggesting that the ontogenetic anterior shift of the center of mass might be the shared characteristic in Crocodylia.