Differential Limb Scaling in the American Alligator (<i>Alligator mississippiensis</i>) and Its Implications for Archosaur Locomotor Evolution

Livingston, Victoria J.; Bonnan, Matthew F.; Elsey, Ruth M.; Sandrik, Jennifer L.; Wilhite, D. Ray

doi:10.1002/ar.20912

Cited by 19 publications

(36 citation statements)

References 38 publications

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“…This may represent a shift in relative importance between these two heads of caudofemoralis, with the short head becoming more important for locomotion in adult alligators. Similar ontogenetic increases of the moment arm for the pectoralis (PEC) due to a distal shift of its insertion on the deltopectoral crest (Livingston et al. 2009) are also correlated with positive allometry in fascicle length, although isometry is observed for the mass and PCSA of the PEC (Fig.…”

Section: Discussionmentioning

confidence: 87%

“…Through alligator ontogeny, the limbs become relatively shorter. In particular, distal limb segments became increasingly shorter relative to proximal segments (Dodson, 1975; Livingston et al. 2009).…”

Section: Introductionmentioning

confidence: 98%

“…The fourth trochanter, a feature of the femoral shaft that marks the insertion of the massive caudofemoral muscles, and the deltopectoral crest, an analogous feature of the humeral shaft that marks the insertion of the large pectoralis and deltoideus muscles, were both found to migrate distally through ontogeny (Dodson, 1975; Livingston et al. 2009).…”

Section: Introductionmentioning

confidence: 99%

“…To investigate this hypothesis our study builds on Dodson’s (1975) and Livingston et al.’s (2009) skeletal scaling analyses through quantification of the architectural properties of muscles relevant to limb function in A. mississippiensis . We use regression analysis to determine the relationship of muscle architectural properties with body mass in an ontogenetic series of specimens, leading to a re‐examination of the anatomical implications for significant ontogenetic alteration of terrestrial locomotor patterns in crocodylians.…”

Section: Introductionmentioning

confidence: 99%

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Functional specialization and ontogenetic scaling of limb anatomy in Alligator mississippiensis

et al. 2010

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Crocodylians exhibit a fascinating diversity of terrestrial gaits and limb motions that remain poorly described and are of great importance to understanding their natural history and evolution. Their musculoskeletal anatomy is pivotal to this diversity and yet only qualitative studies of muscle-tendon unit anatomy exist. The relative masses and internal architecture (fascicle lengths and physiological cross-sectional areas) of muscles of the pectoral and pelvic limbs of American alligators (Alligator mississippiensis Daudin 1801) were recorded for an ontogenetic series of wild specimens (n = 15, body masses from 0.5 to 60 kg). The data were analysed by reduced major axis regression to determine scaling relationships with body mass. Physiological cross-sectional areas and therefore muscle force-generating capacity were found to be greater in the extensor (anti-gravity) muscles of the pelvic limb than in the pectoral limb, reflecting how crocodylians differ from mammals in having greater loading of the hindlimbs than the forelimbs. Muscle masses and architecture were generally found to scale isometrically with body mass, suggesting an ontogenetic decrease in terrestrial athleticism. This concurs with the findings of previous studies showing ontogenetic decreases in limb bone length and the general scaling principle of a decline of strength : weight ratios with increasing size in animals. Exceptions to isometric scaling found included positive allometry in fascicle length for extensor musculature of both limbs, suggesting an ontogenetic increase in working range interpreted as increasing postural variability -in particular the major hip extensorsthe interpretation of which is complicated by previous described ontogenetic increase of moment arms for these muscles.

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Section: Discussionmentioning

confidence: 87%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Functional specialization and ontogenetic scaling of limb anatomy in Alligator mississippiensis

et al. 2010

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“…Thus, the portion of the leg below the knee joint is slightly longer in the younger animal. This may differ from the condition in Alligator mississippiensis , which shows isometry over the ontogeny of the fibula relative to the femur (Livingston et al, 2009). Both Alligator and Parasaurolophus seem to maintain a consistent humerus:femur ratio over ontogeny.…”

Section: Discussionmentioning

confidence: 68%

Ontogeny in the tube-crested dinosaurParasaurolophus(Hadrosauridae) and heterochrony in hadrosaurids

Farke¹,

Chok²,

Herrero³

et al. 2013

PeerJ

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The tube-crested hadrosaurid dinosaur Parasaurolophus is remarkable for its unusual cranial ornamentation, but little is known about its growth and development, particularly relative to well-documented ontogenetic series for lambeosaurin hadrosaurids (such as Corythosaurus, Lambeosaurus, and Hypacrosaurus). The skull and skeleton of a juvenile Parasaurolophus from the late Campanian-aged (∼75.5 Ma) Kaiparowits Formation of southern Utah, USA, represents the smallest and most complete specimen yet described for this taxon. The individual was approximately 2.5 m in body length (∼25% maximum adult body length) at death, with a skull measuring 246 mm long and a femur 329 mm long. A histological section of the tibia shows well-vascularized, woven and parallel-fibered primary cortical bone typical of juvenile ornithopods. The histological section revealed no lines of arrested growth or annuli, suggesting the animal may have still been in its first year at the time of death. Impressions of the upper rhamphotheca are preserved in association with the skull, showing that the soft tissue component for the beak extended for some distance beyond the limits of the oral margin of the premaxilla. In marked contrast with the lengthy tube-like crest in adult Parasaurolophus, the crest of the juvenile specimen is low and hemicircular in profile, with an open premaxilla-nasal fontanelle. Unlike juvenile lambeosaurins, the nasal passages occupy nearly the entirety of the crest in juvenile Parasaurolophus. Furthermore, Parasaurolophus initiated development of the crest at less than 25% maximum skull size, contrasting with 50% of maximum skull size in hadrosaurs such as Corythosaurus. This early development may correspond with the larger and more derived form of the crest in Parasaurolophus, as well as the close relationship between the crest and the respiratory system. In general, ornithischian dinosaurs formed bony cranial ornamentation at a relatively younger age and smaller size than seen in extant birds. This may reflect, at least in part, that ornithischians probably reached sexual maturity prior to somatic maturity, whereas birds become reproductively mature after reaching adult size.

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Alligator appendicular architecture across an ontogenetic niche shift

Hedrick

Schachner

Dodson

2021

The Anatomical Record

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A variety of species undergo ontogenetic niche shifts in either diet, habitat, or both. As a result, multiple ontogenetic stages are able to take advantage of different resources and live in sympatry without competing with one another. The American alligator (Alligator mississippiensis) begins to undergo an ontogenetic niche shift in both diet and habitat at a length of 1.2 m. They transition from a terrestrial wetland environment to a riverine environment and take advantage of different dietary resources. At 1.8 m, A. mississippiensis reaches sexual maturity. Ontogenetic shifts in habitat have the capacity to alter morphology, especially limb morphology, as different age classes traverse different ecological systems. We evaluated shape trends in the scapulae, humeri, ilia, and femora using geometric morphometrics to test whether there were punctuated changes in limb shape, shape disparity, and integration corresponding to either the ontogenetic habitat shift or onset of sexual maturity. We found size to strongly correlate with limb shape but found a continuous size gradient rather than punctuated changes in size. Furthermore, we found that adults (total length > 1.8 m) had significantly higher limb shape disparity than juveniles or subadults, likely related to ontogenetic decreases in limb use and a reduction in limb constraints. Finally, we found that the forelimb and hindlimb acted as a single integrated unit and that neither the forelimb nor hindlimb was significantly more integrated than the other. Therefore, the ontogenetic niche shift itself did not impact limb morphology in A. mississippiensis.

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Differential Limb Scaling in the American Alligator (Alligator mississippiensis) and Its Implications for Archosaur Locomotor Evolution

Cited by 19 publications

References 38 publications

Functional specialization and ontogenetic scaling of limb anatomy in Alligator mississippiensis

Functional specialization and ontogenetic scaling of limb anatomy in Alligator mississippiensis

Ontogeny in the tube-crested dinosaurParasaurolophus(Hadrosauridae) and heterochrony in hadrosaurids

Alligator appendicular architecture across an ontogenetic niche shift

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