Functional morphology and biomechanics of the cynodont Trucidocynodon riograndensis from the Triassic of southern Brazil. Part I. Pectoral girdle and forelimb

Oliveira, Téo Veiga de; Schultz, César Leandro

doi:10.4202/app.00171.2015

Cited by 11 publications

(23 citation statements)

References 33 publications

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“…Kemp (1980b) reported over 90°of flexion-extension for the radius and the ulna at their respective articulations with the humerus. Oliveira and Schultz (2016) considered the radius and ulna as a functional unit, and measured over 100°of flexion-extension at the elbow. Oliveira and Schultz additionally reported 25°of mediolateral rotation at the clavo-interclavicular joint, and 15°of roll, 25°of yaw, and 30°of pitch at the acromio-clavicular joint.…”

Section: Comparison With Previous Range Of Motion Measurementsmentioning

confidence: 99%

“…In contrast to the hip articulation, where a socket-like acetabulum clearly circumscribed the range of motion (Jenkins, 1971a), the cynodont gleno-humeral joint possessed the relatively unconstrained, hemisellar architecture on which late Permian archosaurs, lepidosaurs, and synapsids converged (Jenkins, 1993)the typical mammalian ball-and-socket articulation did not appear until the Jurassic theriimorphs (Ji et al 1999;Luo, 2015). Multiple reconstructions of the cynodont pectoral limb have been advanced, drawing on skeletal morphology (Watson, 1917;K€ uhne, 1956;Bonaparte, 1963;Jenkins, 1970bJenkins, , 1971aKemp, 1980a,b;Oliveira & Schultz, 2016) as well as muscle anatomy as inferred from osteology and homology to extant taxa (Gregory & Camp, 1918;Romer, 1922).…”

Section: Introductionmentioning

confidence: 99%

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Three‐dimensional mobility and muscle attachments in the pectoral limb of the Triassic cynodontMassetognathus pascuali(Romer, 1967)

2018

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The musculoskeletal configuration of the mammalian pectoral limb has been heralded as a key anatomical feature leading to the adaptive radiation of mammals, but limb function in the non-mammaliaform cynodont outgroup remains unresolved. Conflicting reconstructions of abducted and adducted posture are based on mutually incompatible interpretations of ambiguous osteology. We reconstruct the pectoral limb of the Triassic non-mammaliaform cynodont Massetognathus pascuali in three dimensions, by combining skeletal morphology from micro-computed tomography with muscle anatomy from an extended extant phylogenetic bracket. Conservative tests of maximum range of motion suggest a degree of girdle mobility, as well as substantial freedom at the shoulder and the elbow joints. The glenoid fossa supports a neutral pose in which the distal end of the humerus points 45° posterolaterally from the body wall, intermediate between classically 'sprawling' and 'parasagittal' limb postures. Massetognathus pascuali is reconstructed as having a near-mammalian complement of shoulder muscles, including an incipient rotator cuff (m. subscapularis, m. infraspinatus, m. supraspinatus, and m. teres minor). Based on close inspection of the morphology of the glenoid fossa, we hypothesize a posture-driven scenario for the evolution of the therian ball-and-socket shoulder joint. The musculoskeletal reconstruction presented here provides the anatomical scaffolding for more detailed examination of locomotor evolution in the precursors to mammals.

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Section: Comparison With Previous Range Of Motion Measurementsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Three‐dimensional mobility and muscle attachments in the pectoral limb of the Triassic cynodontMassetognathus pascuali(Romer, 1967)

2018

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“…The striations in Thrinaxodon (NMQR 809) are less pronounced. The posterior and particularly the anterior margins of the blade are raised to form the infraspinous fossa (Oliveira & Schultz, ; Lai et al . ), which is deepest across the anterior section of the scapular blade.…”

Section: Descriptionmentioning

confidence: 99%

“…Oliveira ; Oliveira et al . , , ; Oliveira & Schultz ) and from a Laurasian traversodontid (Liu et al . ).…”

mentioning

confidence: 99%

Postcranial morphology of the Early Triassic epicynodont Galesaurus planiceps (Owen) from the Karoo Basin, South Africa

Butler

Abdala

Botha‐Brink

2018

Papers in Palaeontology

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The Early Triassic non‐mammaliaform epicynodont Galesaurus planiceps formed an important part of ecosystems following the Permo‐Triassic Mass Extinction, the greatest mass extinction in Phanerozoic history. Here, we re‐examine the postcranial skeleton of Galesaurus and present data which sheds light on the biology, ecology and possible survival strategies of this species. We find evidence for two distinct morphotypes, a gracile and a robust morph, which we interpret as stages in an ontogenetic series. The primary differences between the morphs manifest in the girdles, with further subtle differences in the fore and hind limbs. Our study also reveals postcranial differences between Galesaurus and the contemporaneous taxon Thrinaxodon liorhinus, allowing these taxa to be distinguished in the absence of cranial material. We also report the first evidence of intraspecific variation in the presence and distribution of disc‐like phalanges in a non‐mammaliaform cynodont. An analysis of the osteohistology of Galesaurus reveals rapid growth to skeletal maturity within one year, thereafter transitioning to slow intermittent growth. This growth pattern is similar to that of Thrinaxodon, which also grew rapidly and continuously to skeletal, and possibly reproductive, maturity within its first year of life. Features such as a strong, reinforced pelvis, elongated ilium, thick, robust forelimbs and stout unguals indicate that Galesaurus was capable of actively excavating burrows. The combination of rapid maturation and fossoriality may have aided its survival in the harsh, unpredictable post‐extinction Early Triassic environment.

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“…In contrast to the hip articulation, where a socket-like acetabulum clearly circumscribed range of motion (Jenkins, 1971a), the cynodont gleno-humeral joint possessed the relatively unconstrained, hemisellar architecture on which late Permian archosaurs, lepidosaurs, and synapsids converged (Jenkins, 1993)—the typical mammalian ball-and-socket articulation did not appear until the Jurassic theriimorphs (Ji et al 1999; Luo, 2015). Multiple reconstructions of the cynodont pectoral limb have been advanced, drawing on skeletal morphology (Watson, 1917; Jenkins, 1970b, 1971a; Kemp, 1980a, 1980b; Oliveira & Schultz, 2016) as well as muscle anatomy as inferred from osteology and homology to extant taxa (Gregory & Camp, 1918; Romer, 1922).…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional mobility and muscle attachments in the pectoral limb of the Triassic cynodontMassetognathus pascuali

Lai

Pierce

Biewener

2017

Preprint

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Functional morphology and biomechanics of the cynodont Trucidocynodon riograndensis from the Triassic of southern Brazil. Part I. Pectoral girdle and forelimb

Abstract: Non-mammalian cynodonts provide insights on several points about mammalian evolution, such as the postural change and locomotory advances

Cited by 11 publications

References 33 publications

Three‐dimensional mobility and muscle attachments in the pectoral limb of the Triassic cynodontMassetognathus pascuali(Romer, 1967)

Three‐dimensional mobility and muscle attachments in the pectoral limb of the Triassic cynodontMassetognathus pascuali(Romer, 1967)

Postcranial morphology of the Early Triassic epicynodont Galesaurus planiceps (Owen) from the Karoo Basin, South Africa

Three-dimensional mobility and muscle attachments in the pectoral limb of the Triassic cynodontMassetognathus pascuali

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