Weekly Spotlight: Plotopterum

12 06 2010

Good tidings and well-wishes!

NOTE: Due to the scarcity of images depicting Plotopterum and its family, this post will be somewhat more “text-heavy” than usual.

Many creationists deride the paleontologist’s seemingly dubious ability to reconstruct entire organisms from solitary bones or even from fragments thereof. Granted, this practice is far from fool-proof and, consequently, the experienced student of this prehistoric study knows better than to inject an irresponsibly large amount of purely hypothetical ideas into reconstructions based on these mysterious fossils. However, what young-Earthers and other non-scientists fail to realize is that a single bone, even an incomplete one, can reveal an immense amount of information about its owner’s anatomy, lifestyle, and taxonomic relationships. A perfect example of this fact lies within the story of the plotopteridae: a family of penguin-like diving birds of the Oligocene and Miocene of Japan and North America.

In 1968, ornithologist Hildegarde Howard of the Los Angeles County Museum classified the isolated proximial end of a coracoid hailing from a mid-Tertiary deposit in the outskirts of Bakersfield. In her official scientific paper on the subject, she gave voice to her suspicion that the bone came from a pelicaniform bird such as a cormorant, gannet, booby or pelican yet was distinct enough to justify not only the creation of a new species, Plotopterum joaquinensis, but a new family as well: the Plotopteridae, the name of which literally means “the swimming winged”.

The coracoid in question.

Just what made this coracoid fragment so special as to warrant this significance in Howard’s view? In her original short communication, she writes:

“The swelling of the lower part of the triosseal canal in the fossil coracoid, the narrowness and thickness of the bone in this area and through the neck, and the anterior overhang of the head are characters found in marine birds such as the penguins and alcids. Although taxonomically unrelated, these two groups of birds are alike in the modification of the wing bones toward a flipper-like condition adapted to under water “flight.” Even in those alcids still capable of aerial flight, the coracoid has similar characters. The swelling of the lower triosseal region tends to narrow and deepen the passageway for the pectoral tendon, and presumably afforded support to the tendon so as to strengthen the upstroke of the wing in swimming. The channel is even more constricted and deeper in the alcids and penguins than in Plotopterum, suggesting that the fossil bird may not have been the equal of these other birds as a swimmer…

The modifications of the bone are entirely different from those found in the coracoid of the flightless cormorant, Nannopterum. In Nannopterum the modifying process has been one of degeneration, whereas the evidence indicates that in Plotopterum the wing had assumed a secondary function as a strong swimming organ. The fact that the modifications of the coracoid parallel those of the coracoid of penguins and auks suggests that the wing elements were shorter and more flattened in the fossil than in the cormorants and anhingas. Obviously Plotopterum represents a trend in aquatic adaptation sufficiently distinct from either of these two existing groups to warrant the designation of a separate family, to be known as the Plotopteridae.”

This conclusion was significantly less obvious to several of Howard’s colleagues. Storrs Olson, a distinguished Smithsonian ornithologist (who still resides at the institution and is considered to be one of the foremost paleo-ornithologists of our time), heavily criticized the perceived boldness of her argument and was vehemently skeptical of her decision to create an entire family on the basis of a single fossilized scrap.

However, Olson was eventually forced to concede the validity of Howard’s contentions when a near-complete bird skeleton which nearly rivaled the largest modern penguins in size was unearthed from the Oligocene of Washington in 1977 by the late, great amateur fossil collector Douglas Emlong. According to David Rains Wallace’s “Neptune’s Ark: From Ichthyosaurs To Orcas”:

“Its rigid, paddlelike wings were powerful enough to ‘fly’ through the water penguin-fashion, and its sturdy leg bones suggested that it too had waddled about on land. But it wasn’t a penguin. In fact, its wing bone turned out to be like Plotopterum‘s proving that Howard’s new family had existed, and Olson accordingly named it Tonsala hildegardae. Other skeletal aspects upheld Howard’s idea that Tonsala was a pelican and cormorant relative, although its affinities were more with freshwater anhinga, which [use] feet instead of wings for underwater propulsion. Tonsala must have been an even more efficient underwater predator than its closest living relative and, given its size, doubtless consumed vast quantities of fish, squid, and other prey.”

A reconstruction of Copepteryx, a Plotopterid from the Japanese Oligocene.

Olson has subsequently observed that the presence of these giant, penguin-like birds off the North American West Coast indicates that not only was food abundant, but that the shoreline must have contained islands upon which Plotopterum and its kin could seek refuge from any contemporaneous predatory marine mammals.

It should be noted that in addition to the  aforementioned relationship of Plotopterum and its kin to modern anhingas, Gerald Mayr has suggested that the plotopteridae may have also fact been a sister taxon to penguins as well. Regardless of the precise affiliations of this most intriguing avians, their amazing scientific history stands as a monument to what incredible academic feats the deductive reasoning of knowledgable paleontologists and anatomists can achieve.

May the fossil record continue to enchant us all!

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4 responses

17 06 2010
johannes

> but that the shoreline must have contained islands upon
> which Plotopterum and its kin could seek refuge from any
> contemporaneous predatory marine mammals.

Island nesting sites would have been protected from terrestrial predators – I dimly remember there was a bear-like beachcombing carnivore at the Pacific coast of Miocene NA, but I have forgotten the name. An island would have offered no protection from marine mammals, which could have reached it by swimming, but this was probably rather irrelevant, because even those marine mammals that are reasonably agile on land (sea lions, sea otters) rarely, if ever, hunt there. Seals frequently hunt penguins in the sea, but ignore them when on land.

18 06 2010
tanystropheus

I believe that the bear to which you’re referring is Kolponomos sp., a carnivoran whose dental and mandibular morphology indicate a diet comprised chiefly of mollusks and other marine invertebrates. Nonetheless, it’s quite likely that this marine ursid wouldn’t have passed up the opportunity to predate upon these birds if given the chance.

However, given the extensive “arsenal” of large, contemporaneous predatory whales and pinnipeds, I think that it’s fairly logical to conclude that isolated islands would have granted Plotopterids just as much safety from aquatic predators as most terrestrial threats.

22 06 2010
johannes

> I believe that the bear to which you’re referring is Kolponomos sp.

Thanks! 🙂 *Kolponomos*, desmostylians, killer walrusses, plotopterids – Miocene coastal and marine fauna is really weird and fascinating.

22 06 2010
tanystropheus

It really is! (Don’t forget osteodontornids!)

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