Pygoscelis tyreei and Aptenodytes ridgeni – you can find a fossil penguin!

Pygoscelis tyreei is a fossil penguin species from the South Island of New Zealand known only from a single specimen.  This specimen represents one of the best amateur fossil discoveries ever for fossil birds – a roughly 70% complete penguin and a species new to science.  Its not too uncommon for local rock hounds to report scientifically important fossils to museums and (hopefully) donate them for study.  However, such complete skeletons are rarely found even by professional expeditions.  The specimen unfortunately lacks the head, even though the neck is still articulated, and is also missing the feet – almost as if it has chopped into three sections and only the middle survived.  It may not look too impressive to the layman, but to a penguin paleontologist it is a beautiful sight.

Peter Tyree was only 11 years old when he discovered a boulder with the Pygoscelis tyreei bones in it on Montunau Beach on Christmas Day, 1967. Recognizing the importance of this find, Peter donated the specimen to the Canterbury Museum in Christchurch.  All present and future penguin paleontologists should be grateful for this act, which made the specimen perpetually available for study.  In less generous circumstances, the penguin could easily have moldered on a shelf in someone’s garage or basement while all geological context slipped away.   Peter Tyree is not alone amongst amateur collectors who have made fossil penguin discoveries on Montunau Beach.  In July of the following year Alan Ridgen, also age 11 at the time, found another penguin fossil, this time some of the leg bones from a much larger but less complete skeleton.  Likewise civic-minded, Alan also donated his find to the Canterbury Museum.

These noble acts were not unrewarded. American paleontologist George Gaylord Simpson, a famous mammal paleontologist who also wrote extensively on penguins, wrote a scientific paper formally describing both of these fossils in 1972.  In honor of the finders, he named them Pygoscelis tyreei and Aptenodytes ridgeni.  The origin of the species name should be obvious, but the choice of genus names has more scientific significance. By assigning these species to living genera (Pygoscelis and Aptenodytes), Simpson made an important statement about their inferred relationships to living penguins.

Pygoscelis is the genus that includes the three “stiff-tailed” penguin species.  These species – the Adélie Penguin (Pygoscelis adeliae), Gentoo Penguin (Pygoscelis papua) and Chinstrap Penguin (Pygoscelis antarctica) – are some of the most cold-adapted penguins to have evolved.  None of them spends much time outside the sub-Antarctic, and show up in New Zealand today only when a wayward bird arrives by accident. Pygoscelis tyreei would represent the most northern occurrence for the Pygoscelis group, indicating fossil members of the lineage could thrive in more mild climates that the living species.

But is Pygoscelis really a member of the stiff-tailed penguin group? Some of the key features of the skeleton that help identify Pygoscelis penguins include a shallow depression for the muscles that close the jaw (possibly related to a typically krill-heavy diet), fusion of the vertebrae and hip bones and a particular arrangement of the openings for the blood vessels of the foot.  Unfortunately, these parts of the skeleton are not preserved in our only specimen of  Pygoscelis tyreei. So, this fossil may indicate that stiff-tailed penguins with habits much different from the living species invaded lower latitudes during the Miocene – or nothing of the sort.  In science, we often simply cannot answer a question with the data at hand.  That’s why new experiments and observations are carried out.  In paleontology, the data we need are often new specimens.  In the case of Pygoscelis tyreei new specimens are precisely what is needed to reveal exactly what was going on.  The penguin may belong to a different genus than Pygoscelis, perhaps even one that is now extinct.

Partial articulated skeleton of Pygoscelis tyreei. Some other bones were also found and have been separated from the main skeletal block, but are not shown here.

Aptenodytes ridgeni is generally accepted as a member of the genus Aptenodytes, which includes two living species – the King and Emperor Penguins.  Only a few bones from the hindlimb are known though, so a close phylogenetic (evolutionary) relationship to living Kings and Emperors remains likely but not conclusive.  The type specimen of this penguin includes all the major bones of the leg: the femora, tibiotarsi, tarsometatarsi and even the patella (knee cap).  The only elements missing are the phalanges (toe bones).  In particular, the tarsometatarsus looks like that of living Aptenodytes penguins – even more square than other penguin species and with a similar arrangement of the blood vessel openings and trochlea for attachment of the toes.  Just like Pygoscelis, Aptenodytes is today restricted to high latitude, cold areas, so this fossil if proven conclusively to belong to the genus would greatly expand its past geographical range. Regardless of relationships, Aptenodytes ridgeni is important because it was the last penguin larger than the Emperor penguin to have lived.  If the hindlimb scales to the rest of the skeleton the same way as in living Emperors, the fossil species would have been about 10% larger – not a huge bird compared to the true giants of the Eocene-Oligocene, but substantial nonetheless.

Tarsometatarsus of the fossil penguin Aptenodytes ridgeni (left) and the Emperor Penguin Aptenodytes forsteri (right)

Important amateur fossil discoveries continue today. Just three years ago, New Zealand school children on a fossil collecting trip with the Hamilton Junior Naturalist Club discovered a nearly complete giant penguin – a spectacular articulated skeleton missing only the head and feet (see story here).  This specimen is still undescribed, so it remains uncertain whether it belongs to one of the penguin species known from the South Island or a new species.  So the lesson should be clear – share your penguin discoveries with the world and you may be rewarded with a small slice of immortality as a species honorific.