Hypaxial Motor Patterns and the Function of Epipubic Bones in Primitive Mammals

  title={Hypaxial Motor Patterns and the Function of Epipubic Bones in Primitive Mammals},
  author={Stephen M. Reilly and Thomas D. White},
  pages={400 - 402}
Since the first description of epipubic bones in 1698, their functions and those of the associated abdominal muscles of monotremes and marsupial mammals have remained unresolved. We show that each epipubic bone is part of a kinetic linkage extending from the femur, by way of the pectineus muscle, to the epipubic bone, through the pyramidalis and rectus abdominis muscles on one side of the abdomen, and through the contralateral external and internal oblique muscles to the vertebrae and ribs of… 

Abdominal muscle and epipubic bone function during locomotion in Australian possums: Insights to basal mammalian conditions and eutherian‐like tendencies in Trichosurus

Several novelties discovered in Trichosurus reveal that it exhibits an evolutionary transition to intermediate eutherian‐like morphological and motor patterns paralleling many other unique features of this species.

Abdominal muscle function in ventilation and locomotion in new world opossums and basal eutherians: Breathing and running with and without epipubic bones

It is revealed that continuous abdominal muscle tonus during resting ventilation and a 1:1 breath to step cycle during locomotion appear to be the basal condition for mammals, and that hypaxial function in generalized eutherians is more similar to marsupials than cursorial mammals.

Musculoskeletal anatomy and nomenclature of the mammalian epipubic bones

This work analyzed the epipubic bones of 302 skeletons comprising American and Australian marsupials, as well as 27 monotreme skeletons, and dissected 10 mars upials for myological attachments analysis and suggested the following nomenclature for the epIPubic bone structures: crest for the cranial end, shaft for the body of the bone, lateral tubercle and the medial articular process.

Sagittal spine movements of small therian mammals during asymmetrical gaits

Intervertebral joint movements were studied in two metatherian and three eutherian species during the gallop and halfbound and the observed timing of dorsoventral oscillations of the spine are in accordance with that observed in other mammals and with activity data of respiratory and epaxial back muscles.

Femoral loading mechanics in the Virginia opossum, Didelphis virginiana: torsion and mediolateral bending in mammalian locomotion

Femoral safety factors were as high as those of non-avian reptiles and greater than those of upright, cursorial mammals, primarily because the load magnitudes experienced by opossums are lower than thoseof most mammals.

Formation, structure, and function of extra‐skeletal bones in mammals

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  • Biology
    Biological reviews of the Cambridge Philosophical Society
  • 2020
This review provides the first extensive comparative description of the skeletal and integumentary systems of AHOOOs in a variety of mammals.

In vivo strains in the femur of the Virginia opossum (Didelphis virginiana) during terrestrial locomotion: testing hypotheses of evolutionary shifts in mammalian bone loading and design

Loading patterns of opossum limb bones appear intermediate in some respects between those of eutherian mammals and non-avian reptiles, providing further support for hypotheses that high torsion and elevated limb bone safety factors may represent persistent ancestral conditions in the evolution of tetrapod limb bone loading and design.

A Reevaluation of the Unusual Abdominal Musculature of Squamate Reptiles (Reptilia: Squamata)

The abdominal muscles of lizards and snakes (Squamata) have been the subject of periodic attention from anatomists, embryologists, and systematists. Until now, the presence of a superficial portion



Epipubic bones in eutherian mammals from the Late Cretaceous of Mongolia

The occurrence of epipubic bones in two Cretaceous eutherians suggests that the dramatic modifications connected with typical placental reproduction, may have been later events in the evolution of the Eutheria.

Activity of the hypaxial muscles during walking in the lizard Iguana iguana.

  • D. Carrier
  • Biology
    The Journal of experimental biology
  • 1990
The demands of locomotion may provide a functional explanation for the basic organization of the hypaxial muscles of tetrapods and support the hypothesis that the hypAXial muscles act to stabilize the trunk during locomotion.

Twisting and bending: the functional role of salamander lateral hypaxial musculature during locomotion.

The presence of asynchronous, relatively high-intensity alpha-bursts indicates that the lateral hypaxial muscles generate torsional moments during terrestrial locomotion, but it is possible that the balance of forces from both alpha- and beta-Bursts may allow the lateral Hypaxial muscle coactivation to contribute to lateral bending of the body as well.

Function of the oblique hypaxial muscles in trotting dogs.

It is suggested that the oblique hypaxial muscles of trotting dogs act to stabilize the trunk against sagittal shearing torques induced by limb retraction (Fore-aft acceleration) and protraction (fore-aft deceleration).


Activity of the hypaxial muscles during walking and swimming was measured in the salamander Dicamptodon ensatus. During walking, there was activity on both sides of the trunk simultaneously. The

Axial muscle function during lizard locomotion

  • Ritter
  • Biology
    The Journal of experimental biology
  • 1996
The timing of epaxial muscle activity in Iguana iguana relative to the kinematics of limb support and lateral trunk bending is similar to that observed in Varanus salvator, a finding that supports the hypothesis that the epaxIAL muscles stabilize the trunk during locomotion in lizards and that this stabilizing role is a basal feature of lizards.

Sprawling Locomotion in the Lizard Sceloporus clarkii: Speed Modulation of Motor Patterns in a Walking Trot

  • S. Reilly
  • Biology
    Brain, Behavior and Evolution
  • 1998
Differences in axial function and differences among lizards in postures of the foot and crus during locomotion indicate that there are different ways that lizards run and that the functional and anatomical diversity of modes of locomotion in lizards is greater than is recognized at present.


  • F. Jenkins
  • Biology
    Evolution; international journal of organic evolution
  • 1970
This paper uses a functional interpretation of the postcranial anatomy of certain advanced mammal-like reptiles and the phylogenetic implications of monotreme biology to evaluate the question of the kind of biological organization that characterized the transitional forms on or near the reptilemammal boundary.

Analysis of Asymmetrical Gaits

Asymmetrical gaits (that is, gallops and bounds) have the footfalls of a pair of feet unevenly spaced in time and probably evolved, in amphibians and several times in reptiles, to benefit escape.