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: 233 MB

Download Project SDD File
Currently Viewing:
MorphoBank Project 1111

    This research
    supported by


    member name taxa specimens media
    Daniel Ksepka
    Project Administrator
    Last logged in 09/16/15
    MorphoBank Curator
    Full membership
    Last logged in 09/18/15
    Sarah Werning
    Full membership
    Last logged in 09/16/15

    Project has no matrices defined.

    Project views

    type number of views Individual items viewed (where applicable)
    Total project views28473
    Project overview2148
    Media views18786Media search (2567 views); M323732 (381 views); M324167 (277 views); M324177 (304 views); M324163 (271 views); M323836 (300 views); M324173 (264 views); M324183 (314 views); M323832 (277 views); M323886 (280 views); M323829 (281 views); M324166 (284 views); M324176 (336 views); M324162 (283 views); M323835 (311 views); M324172 (295 views); M324182 (274 views); M324159 (275 views); M324169 (258 views); M323831 (288 views); M324179 (280 views); M323828 (369 views); M324165 (388 views); M323838 (306 views); M324175 (300 views); M324161 (278 views); M323834 (291 views); M324171 (300 views); M324181 (305 views); M324168 (280 views); M323830 (322 views); M324178 (270 views); M324164 (251 views); M323837 (300 views); M324174 (289 views); M324184 (280 views); M324160 (281 views); M323833 (250 views); M324170 (286 views); M324180 (273 views); M326244 (280 views); M324185 (295 views); M326214 (236 views); M326238 (272 views); M326239 (293 views); M326243 (283 views); M326245 (289 views); M326246 (298 views); M326247 (274 views); M326248 (286 views); M326249 (301 views); M326250 (256 views); M326287 (288 views); M326288 (274 views); M326289 (262 views); M326290 (292 views); M326291 (288 views);
    Documents list918
    Taxon list2087
    Views for media list665
    Specimen list3393

    Project downloads

    type number of downloads Individual items downloaded (where applicable)
    Total downloads from project151
    Document downloads3Smithsonian Copyright Permission (3 downloads);
    Project downloads146
    Media downloads2M323732 (1 download); M324163 (1 download);