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)


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,
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


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

    Project has no matrices defined.

    Project views

    type number of views Individual items viewed (where applicable)
    Total project views67323
    Project overview4217
    Media views42537Media search (5092 views); M323732 (779 views); M324167 (661 views); M324177 (682 views); M324163 (701 views); M323836 (684 views); M324173 (668 views); M324183 (688 views); M323832 (668 views); M323886 (666 views); M323829 (676 views); M324166 (677 views); M324176 (720 views); M324162 (704 views); M323835 (702 views); M324172 (710 views); M324182 (665 views); M324159 (673 views); M324169 (641 views); M323831 (668 views); M324179 (646 views); M323828 (784 views); M324165 (871 views); M323838 (735 views); M324175 (732 views); M324161 (755 views); M323834 (687 views); M324171 (659 views); M324181 (686 views); M324168 (657 views); M323830 (713 views); M324178 (638 views); M324164 (676 views); M323837 (709 views); M324174 (681 views); M324184 (663 views); M324160 (670 views); M323833 (660 views); M324170 (689 views); M324180 (676 views); M326244 (631 views); M324185 (661 views); M326214 (664 views); M326238 (633 views); M326239 (640 views); M326243 (606 views); M326245 (638 views); M326246 (645 views); M326247 (601 views); M326248 (622 views); M326249 (585 views); M326250 (562 views); M326287 (582 views); M326288 (589 views); M326289 (570 views); M326290 (598 views); M326291 (598 views);
    Documents list1672
    Taxon list6200
    Views for media list1594
    Specimen list9977

    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);