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
    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 views38640
    Project overview2876
    Media views24069Media search (3283 views); M323732 (474 views); M324167 (364 views); M324177 (392 views); M324163 (358 views); M323836 (386 views); M324173 (351 views); M324183 (396 views); M323832 (365 views); M323886 (369 views); M323829 (374 views); M324166 (375 views); M324176 (423 views); M324162 (387 views); M323835 (397 views); M324172 (384 views); M324182 (355 views); M324159 (362 views); M324169 (345 views); M323831 (377 views); M324179 (359 views); M323828 (473 views); M324165 (481 views); M323838 (417 views); M324175 (385 views); M324161 (356 views); M323834 (379 views); M324171 (383 views); M324181 (378 views); M324168 (367 views); M323830 (421 views); M324178 (353 views); M324164 (350 views); M323837 (396 views); M324174 (375 views); M324184 (362 views); M324160 (370 views); M323833 (354 views); M324170 (378 views); M324180 (360 views); M326244 (344 views); M324185 (382 views); M326214 (327 views); M326238 (338 views); M326239 (354 views); M326243 (350 views); M326245 (352 views); M326246 (364 views); M326247 (335 views); M326248 (342 views); M326249 (358 views); M326250 (316 views); M326287 (341 views); M326288 (332 views); M326289 (327 views); M326290 (350 views); M326291 (343 views);
    Documents list1134
    Taxon list3918
    Views for media list897
    Specimen list5092

    Project downloads

    type number of downloads Individual items downloaded (where applicable)
    Total downloads from project242
    Document downloads3Smithsonian Copyright Permission (3 downloads);
    Project downloads236
    Media downloads3M323732 (1 download); M324163 (1 download); M323886 (1 download);