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:1-20.
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: 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 views40945
    Project overview3004
    Media views25584Media search (3439 views); M323732 (500 views); M324167 (388 views); M324177 (413 views); M324163 (385 views); M323836 (412 views); M324173 (376 views); M324183 (423 views); M323832 (391 views); M323886 (393 views); M323829 (401 views); M324166 (401 views); M324176 (444 views); M324162 (413 views); M323835 (420 views); M324172 (411 views); M324182 (379 views); M324159 (389 views); M324169 (371 views); M323831 (405 views); M324179 (385 views); M323828 (496 views); M324165 (504 views); M323838 (441 views); M324175 (410 views); M324161 (379 views); M323834 (408 views); M324171 (409 views); M324181 (403 views); M324168 (393 views); M323830 (445 views); M324178 (376 views); M324164 (376 views); M323837 (418 views); M324174 (395 views); M324184 (387 views); M324160 (393 views); M323833 (379 views); M324170 (403 views); M324180 (385 views); M326244 (367 views); M324185 (406 views); M326214 (352 views); M326238 (363 views); M326239 (378 views); M326243 (374 views); M326245 (376 views); M326246 (387 views); M326247 (357 views); M326248 (366 views); M326249 (381 views); M326250 (341 views); M326287 (363 views); M326288 (351 views); M326289 (348 views); M326290 (372 views); M326291 (363 views);
    Documents list1179
    Taxon list4100
    Views for media list947
    Specimen list5446

    Project downloads

    type number of downloads Individual items downloaded (where applicable)
    Total downloads from project256
    Document downloads3Smithsonian Copyright Permission (3 downloads);
    Project downloads250
    Media downloads3M323732 (1 download); M324163 (1 download); M323886 (1 download);