March of the Fossil Penguins

Fossil penguin discoveries and research

Baby Penguins in the Fossil Record

with 13 comments

Penguin bones are common in the fossil record.  Trillions of penguins have lived over course of the Cenozoic, and a tiny portion of these died in environments favorable to fossil preservation.  Some fossil penguins are giant and others tiny, some are complete skeletons and others single bones, some pristine and others badly damaged by erosion or chewed on by sharks.  However, almost all of them are bones of adult birds.  This is actually not too surprising when you think about penguin life cycles.  Adults spend most of their time in the water, so it is easier for animals that die and sink to the bottom to be covered by sediments and have a chance at fossilization.  Hatchling and juvenile penguins stay on land though, and if they don’t make it to adulthood it often means they were gobbled up by a predator and leave no trace in the fossil record.

Hatchling penguin fossils can be really informative, because they provide unequivacal evidence that a breeding colony existed in the area.  Usually, this is very hard to prove in the fossil record, because modern penguins are infamous drifters.  Some travel more than a thousand miles over the course of a normal year before returning to their breeding grounds, and a few random individuals always end up on the wrong continent annually (like New Zealand’s stray Emperor Penguin).  Because of these penguin proclivities, it is hard to be sure whether adult fossil penguin bones we find at some sites belong to penguins that bred there, or instead belong to a bird that was just passing through.

Unfledged birds are those that haven’t yet left the nest.  In dramatic cases, fledging occurs when a baby bird is pushed out of the nest by its parent, and instinctively takes its first flight. For penguins, fledging involves a trip into the ocean instead.   That’s why hatchling penguin bones can be so informative to paleontologists.  If we find a fossil from an unfledged bird, we know with certainty that bird was hatched in the area because it was too young to have started swimming.

Fossil leg bones from a hatchling of the extinct species Inguza predemersus.

Part of the story in my recent paper with Dr. Daniel Thomas is based on tiny fossils from hatchling penguins.  There are quite a few fossils of juvenile animals in the South African records from Langebaanweg. These bones show a very spongy texture because they have not completely ossified yet and parts remain cartilaginous (just like our own bones when we are children).  There are also fossil parts of compound bones that remain separate in hatchlings but fuse together in adults. For example, the three small bones on the right side of the photo are parts of the foot that join completely together in fully grown penguins.  In order to figure out how old these penguins were when they perished, we looked at modern skeletons of hatchling, juvenile and adult penguins in museums.  Based on the patterns we observed, we aged the bones in the photo to a very young bird, which would not yet have started moulting into its adult feathers (and therefor wouldn’t be ready to take its first plunge).  It’s sad to think these birds never had a chance to enter the marine realm, but studying their fossil remains pins down the location of their species breeding ground pretty precisely.  That’s a rare and valuable peek into a vanished ecosystem.

Written by Dan Ksepka

September 21, 2011 at 10:26 am

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  1. I know the modern-day African Penguin nests in burrows, and it seems like their unfledged offspring would be more likely to enter the fossil record than species that nest on the surface. That is, nests could be buried when burrows collapsed. Is there evidence that the ancient penguins from Africa would nest in burrows, and could that be why you and your colleagues were lucky enough to discover these hatchling specimens?


    September 21, 2011 at 10:50 am

    • Blackfooted Penguins, as well as many South American species, prefer burrows to nests made of vegetation. Part of the reason is that this helps them shelter their young from the hot sun. A collapsing burrow is a great hypothesis for how these baby penguins ended up in the fossil record. However, in this particular case the bones are scattered and were found in deposits that formed underwater. Most likely they were swept out to sea in a storm, or maybe captured by predators that dropped the remains in the sea. A collapsed burrow, which we haven’t found yet in the fossil record, would be very interesting because there would be a higher chance of complete skeletons being preserved in articulation, and maybe even some fossil eggshell as a bonus!

      Dan Ksepka

      September 21, 2011 at 10:58 am

  2. Since baby penguins bones look very different than adult pengion bones, how can you tell what species they are from? I am doing a report on extinct penguins for school.


    September 21, 2011 at 3:19 pm

    • That’s a good point. Its not possible to say with 100% certainty which species these bones come from, but we speculate they belong to Inguza predemersus because that species it by far the most common at the site where the bones were found. At this early a stage in development, we would probably need to find an adult skeleton and baby skeleton side by side in a burrow to remove all doubt.

      Dan Ksepka

      September 22, 2011 at 11:19 am

  3. Very interesting! That first sentence made me think of the following questions. Are penguin bones more common in the fossil record than those of other marine birds? If so, is it because they are osteosclerotic?


    September 22, 2011 at 1:58 pm

    • Penguin bones are among the most abundant avian fossils, and their osteosclerotic structure is a major reason for that. A hollow bird bone can be destroyed pretty easily by erosion, abrasion, damage from predators, etc. A solid penguin bone holds up better.

      Dan Ksepka

      September 22, 2011 at 2:15 pm

  4. It would be interesting to hear more about the ecology of the Langebaanweg fossil site, and the role that ancient fossil penguins played in this ecosystem. Since the Langebaanweg site preserves such a rich and diverse fossil record, do we know what animals the penguins might have competed with for food, territory and other resources?


    October 1, 2011 at 8:16 pm

    • Sounds like a good topic. There were some interesting animals mixing with the penguins, including whales. I’ll make sure to keep this in mind for a future post.

      Dan Ksepka

      October 1, 2011 at 9:00 pm

  5. Hi Dan,

    I’m a little late on commenting here, but – to play devil’s advocate: how reasonably sure can you be that these juvenile individuals were not washed out to sea? Even a penguin chick is large enough to bloat and float for enough time to drift pretty far out to sea if the currents are in the right direction.

    I don’t know much about the Langebaanweg locality taphonomy and stratigraphy – but I’d hesitate to use the occurrence of juvenile penguin bones on its own as evidence of a rookery (i.e. in the vacuum of a robust taphonomic and sedimentologic context for the locality). You mention above that you do think that these bones are from individuals swept out to sea; is the inference then based not on the absolute presence of juvenile bones, but the more common occurrence of them at this locality?

    I’ve observed in the marine mammal fossil record of California that certain formations yield a wide array of juvenile fur seal bones, and I’ve given some cursory thought about some possible ways to test hypotheses regarding deposition near a fur seal rookery versus “normal” juvenile mortality rates. Interesting stuff! When does the paper come out? Or is it out already?


    October 20, 2011 at 4:52 am

    • Hello Bobby,
      The main point we make regarding colonies in the paper is that penguins were certainly breeding in South Africa during the Pliocene. These bones belong to juveniles too young to have left the nest and entered the sea on their own, so they certainly hatched locally. There is no chance a juvenile penguin skeleton could drift in from another major landmass like South America, so we know these penguins bred in Africa (rather than just passing through). Also, because these delicate bones are in such good condition and show no predation marks, they were probably transported from someplace very close – probably a few kilometers at most. We did not imply that Langebaanweg itself was a “fossil rookery” because there have not been any instances of eggshell and the deposits are estruarine and shallow marine, not terrestrial.

      Our paper is not published in print form yet, but the article is available in PDF at the Proceedings B website:

      And let me wish you good results on your own studies of pinnipeds!

      Dan Ksepka

      October 20, 2011 at 3:58 pm

      • Certainly that is substantial evidence for penguins having rookeries in South Africa! Floating from South America is definitely a bit much. I think that given a large sample size along a coastline with multiple fossiliferous localities at various latitudes, juvenile specimens of rookery-breeding taxa (some pinnipeds, penguins, and some alcids) might be able to pinpoint with some low level of precision the position of a paleo-rookery – i.e. one formation might have a much higher proportion of juveniles in shallow deposits than those to the north or south, and a rookery may have been present near that basin.

        I’ve got the pdf – great stuff! As a marine mammal worker, I’ve got to read up more on penguins because of some of the interesting applications you guys have done with their fossil record in terms of paleoecology, macroevolution, etc.


        October 20, 2011 at 6:19 pm

  6. Your article is so good I’ve bookmarked it already.

    Bill Dane

    December 19, 2011 at 2:29 am

  7. My kids love penguins and I will tell this story to them.

    Mom of Toddlers

    January 4, 2012 at 9:30 pm

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