Project 1111: D. T. Ksepka, S. Werning, M. Sclafani, Z. M. Boles. 2015. Bone histology in extant and fossil penguins (Aves: Sphenisciformes). Journal of Anatomy. 227 (5):611-630.
Specimen: † "Large" Eocene stem penguin (USNM:404477)

Abstract

Substantial changes in bone histology accompany the secondary adaptation to life in the water. This transition is well documented in several lineages of mammals and non-avian reptiles, but has received relatively little attention in birds. This study presents new observations on the long bone microstructure of penguins, based on histological sections from two extant taxa (Spheniscus and Aptenodytes) and eight fossil specimens belonging to stem lineages (†Palaeospheniscus and several indeterminate Eocene taxa). High bone density in penguins results from compaction of the internal cortical tissues, and thus penguin bones are best considered osteosclerotic rather than pachyostotic. Although the oldest specimens sampled in this study represent stages of penguin evolution that occurred at least 25 million years after the loss of flight, major differences in humeral structure were observed between these Eocene stem taxa and extant taxa. This indicates that the modification of flipper bone microstructure continued long after the initial loss of flight in penguins. It is proposed that two key transitions occurred during the shift from the typical hollow avian humerus to the dense osteosclerotic humerus in penguins. First, a reduction of the medullary cavity occurred due to a decrease in the amount of perimedullary osteoclastic activity. Second, a more solid cortex was achieved by compaction. In extant penguins and †Palaeospheniscus, most of the inner cortex is formed by rapid osteogenesis, resulting an initial latticework of woven-fibered bone. Subsequently, open spaces are filled by slower, centripetal deposition of parallel-fibered bone. Eocene stem penguins formed the initial latticework, but the subsequent round of compaction was less complete, and thus open spaces remained in the adult bone. In contrast to the humerus, hindlimb bones from Eocene stem penguins had smaller medullary cavities and thus higher compactness values compared with extant taxa. Although cortical lines of arrested growth have been observed in extant penguins, none was observed in any of the current sampled specimens. Therefore, it is likely that even these ‘giant’ penguin taxa completed their growth cycle without a major pause in bone deposition, implying that they did not undergo a prolonged fasting interval before reaching adult size.


Read the article »

Article DOI: 10.1111/joa.12367

Project DOI: 10.7934/P1111, http://dx.doi.org/10.7934/P1111
This project contains
  • 56 Media
  • 1 Document
  • 5 Taxa
  • 11 Specimens
Total size of project's media files: 200.23M

Download Project SDD File
Currently Viewing:
MorphoBank Project 1111

    This research
    supported by

    Authors' Institutions

    • National Museum of Natural History, Smithsonian Institution

    • Bruce Museum

    • Des Moines University

    • Drexel University

    • Stony Brook University

    • North Carolina Department of Environment and Natural Resources



    Members

    member name taxa specimens media
    Daniel Ksepka
    Project Administrator
    1244
    MorphoBank Curator
    Full membership
    000
    Sarah Werning
    Full membership
    4912


    Project has no matrices defined.



    Project views

    type number of views Individual items viewed (where applicable)
    Total project views65003
    Project overview4138
    Media views41005Media search (4939 views); M323732 (754 views); M324167 (637 views); M324177 (659 views); M324163 (674 views); M323836 (657 views); M324173 (642 views); M324183 (665 views); M323832 (642 views); M323886 (642 views); M323829 (657 views); M324166 (652 views); M324176 (693 views); M324162 (679 views); M323835 (676 views); M324172 (683 views); M324182 (638 views); M324159 (651 views); M324169 (616 views); M323831 (644 views); M324179 (623 views); M323828 (762 views); M324165 (840 views); M323838 (708 views); M324175 (708 views); M324161 (725 views); M323834 (661 views); M324171 (635 views); M324181 (663 views); M324168 (634 views); M323830 (689 views); M324178 (613 views); M324164 (654 views); M323837 (684 views); M324174 (657 views); M324184 (640 views); M324160 (640 views); M323833 (634 views); M324170 (664 views); M324180 (651 views); M326244 (607 views); M324185 (635 views); M326214 (640 views); M326238 (607 views); M326239 (614 views); M326243 (581 views); M326245 (613 views); M326246 (625 views); M326247 (574 views); M326248 (598 views); M326249 (563 views); M326250 (541 views); M326287 (556 views); M326288 (565 views); M326289 (548 views); M326290 (576 views); M326291 (577 views);
    Documents list1629
    Taxon list6027
    Views for media list1539
    Specimen list9579
    Bibliography1086




    Project downloads

    type number of downloads Individual items downloaded (where applicable)
    Total downloads from project341
    Document downloads4Smithsonian Copyright Permission (4 downloads);
    Project downloads327
    Media downloads10M323732 (1 download); M324163 (1 download); M323886 (1 download); M326291 (1 download); M324166 (1 download); M324165 (3 downloads); M324164 (1 download); M324161 (1 download);