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Article: Unusual histology and morphology of the ribs of mosasaurs (Squamata)

Publication: Palaeontology
Volume: 58
Part: 3
Publication Date: May 2015
Page(s): 511 520
Author(s): Michael D. D'Emic, Kathlyn M. Smith and Zachary T. Ansley
Addition Information

How to Cite

D'EMIC, M.D., SMITH, K.M., ANSLEY, Z.T. 2015. Unusual histology and morphology of the ribs of mosasaurs (Squamata). Palaeontology, 58, 3, 511-520.

Author Information

  • Michael D. D'Emic - Anatomical Sciences Department, Health Sciences Center, Stony Brook University, Stony Brook, NY, USA (email:
  • Michael D. D'Emic - Burpee Museum of Natural History, Rockford, IL, USA
  • Kathlyn M. Smith - Georgia Southern University Museum, Georgia Southern University, Statesboro, GA, USA (email:
  • Kathlyn M. Smith - Department of Geology and Geography, Georgia Southern University, Statesboro, GA, USA
  • Zachary T. Ansley - Department of Geology and Geography, Georgia Southern University, Statesboro, GA, USA (email:

Publication History

  • Issue published online: 21 APR 2015
  • Article first published online: 5 MAR 2015
  • Manuscript Accepted: 3 FEB 2015
  • Manuscript Received: 15 SEP 2014

Online Version Hosted By

Wiley Online Library
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We report the presence of two previously unrecognized features in the dorsal ribs of mosasaurs: first, the presence of extremely dense, pervasive extrinsic fibres (anchoring soft tissue to bone, sometimes called Sharpey's fibres); and second, high intraspecific variation in costal bone compactness. Extensive extrinsic fibres are developed in the dorsal ribs of the mosasaurs Tylosaurus proriger and Eonatator sternbergi. The dorsal ribs of these mosasaurs are also characterized by a longitudinally ridged texture that almost completely covers the bone. Pervasive extrinsic fibres and ridged textures are absent in the mosasaur Selmasaurus russelli as well as the dorsal ribs of extant semi-aquatic reptiles (e.g. crocodyliforms) and mosasaurs' close extant relatives and analogues (e.g. snakes and varanids). Similar ridged textures characterize the dorsal ribs of several other mosasaur taxa but are developed to a lesser extent (e.g. Mosasaurus, Clidastes, Platecarpus and Ectenosaurus), but in no other taxa have pervasive extrinsic fibres been reported. We interpret these osteohistological features in T. proriger and E. sternbergi as evidence of tendinous attachment of extensive and highly differentiated axial musculature capable of producing great stresses, most likely related to stabilization of the trunk relative to contralateral movements of the tail during carangiform locomotion. We also report the compactness indices (percentage of space occupied by bone rather than cavities) for these large mosasaur ribs, which are much higher than previously reported. This suggests high intraspecific variation in bone compactness that complicates its use in reconstructing mosasaur palaeoecology.

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