Whence Brontosaurus?

22 03 2012

Paleontologists, like everyone else, make their share of mistakes.  Unfortunately, paleontological mistakes become incorporated into scientific literature and sometimes (as in this case) also into the collective consciousness of the general public, reverberating through decades and centuries, long after they are left behind by the science that spawned them.

Such is the case with Brontosaurus.  Long the icon of the dinosaur world, this genus of herbivorous sauropods whose name means “thunder lizard” was a mistake.  An Apatosaurus that had an inaccurate reconstruction of its head added to the original display (because the specimen being used was missing its head when it was discovered), it now exists in science only as a casebook example of phylogenetic inference run amok.  It is also a casebook example both of how we sometimes let our prejudices guide our decisions and how scientific competition is not always a good thing.

The original specimen, still in the great hall of the Peabody Museum of Natural History, at Yale University, in New Haven, Connecticut (USA), went on display in 1905, some six years after Marsh’s death.  It remains in its original pose, based on the early twentieth belief that the animal walked with its head drooping and its tail dragging the ground behind it.  It has, however, had its head replaced with the correct one for the species.  By contrast, the specimen in the American Museum of Natural History shows what is referred to as the “modern posture”, with  its head sticking forward just higher than its body and its tail raised to body level, to demonstrate how scientists currently believe the animal actually looked in life.

Apatosaurus excelsus formerly Brontosaurus excelsus

The original conception of how Brontosaurus excelsus, now Apatosaurus excelsus looked, with its head drooping and its tail being dragged behind.
Image Credit: Image is from Wikipedia Commons and is in the public domain.

So, how did all of this happen?  The story goes something like this… From the late 1860s onward, two American paleontologists, Othniel Charles Marsh and Edward Drinker Cope were engaged in an open feud over the discovery of dinosaur fossils in the American West.  The feud began “back east” as they use to say in the West, when Cope accused Marsh of paying quarrymen in New Jersey to divert to himself fossils that had been paid for by and promised to Cope.  Soon, the two men were engaged snipping at each other’s fossil finds, feuding over fossil hunting rights in the western territories, and in general name calling and accusations.  They tried to out-do each other by finding and naming the largest number of fossils and the biggest specimens they could find.

In the midst of this feud, in 1879, Marsh discovered a very large specimen of a sauropod dinosaur at Como Bluff, in southeastern Wyoming (USA).  It was larger and much more complete than anything that had been found up to then, but it had one little problem.  It was missing its head.  Marsh was convinced that it was an entirely new genus and species, which he named Brontosaurus excelsus. The species name (excelsus) means “highest or sublime” and is intended to refer to the fact that it had the greatest number of sacral vertebrae of any sauropod known at the time.

Scientists started preparing the specimen for display.  Missing bones were replaced using known examples from close relatives of Brontosaurus.  The specimen was missing its feet, so sauropod feet that had been found at the same quarry were used.  But, the head was still a problem.  What to do?  What would the head of such a beast look like?  Marsh, being a thorough nineteenth century man, dismissed many of the proposal as being too effete for such a large animal.  Surely its head would be robust, virile (one at the time might have been tempted to say manly).  So, Marsh had a head constructed from bones of similar species that looked the way Marsh thought Brontosaurus‘ head should look.  This composite skull (which we now know to be mostly made of Brachiosaur bones) was duly created and fitted to the mounted skeleton.  Thus, it was not the (relatively) delicate skull of Apatosaurus excelsus, that would eventually be deemed to be the true appearance of the creature.

Othniel Charles (O.C.) Marsh

Othniel Charles (O.C.) Marsh, who found and named Brontosaurus.
Image Credits: Image is from Wikipedia Commons and is in the public domain.

Marsh, who died in 1899, never lived to see his specimen on display.  Cope had already died in 1897, and their great feud, now known as the Bone War, had died with them.

When it went on display, Brontosaurus was the first sauropod to be seen by the public, and it created a sensation.  It captured the public’s imagination and became a cultural icon of the science of paleontology.  And there it remained through most of the twentieth century, captured in a million images ranging from hollywood renditions in movies to corporate images for oil companies, to a thousand and one cartoon creations and magazine images.

But, even before Brontosaurus went on display, its name and identity were being challenged.  In 1903, paleontologist Elmer Riggs took another look at the fossils.  He agreed with Marsh that B. excelsus was likely its own species, but decided that it had too much in common with Apatosaurus to be a distinct genus.  Riggs reclassified the specimen as Apatosaurus excelsus, where it has remained to this day.  Most scientists over the years have agreed with him.  Yet, in the eyes of the public, it was always Brontosaurus.

Why, you might ask, didn’t Riggs reclassify Apatosaurus into Brontosaurus, since the latter was clearly the better known and more popular name?  The reason for that is the rules surrounding the naming and renaming of animals in biology.  This is governed by rules set down by the International Commission on Zoological Nomenclature (ICZN).  According to those rules, if two genera are determined to be the same, then the one that was named first has priority and the animal(s) in the one named later are reclassified into the older one.  It should be noted here that the same rule applies at all levels of scientific nomenclature (family, genera, species, etc.).  Since Apatosaurus had been named in 1877 (ironically by Marsh himself), Apatosaurus won, and Brontosaurus became what is known as a “junior synonym” and was discarded from formal use.

It might have remained that way, with the general public knowing Brontosaurus and scientists knowing Apatosaurus, but for the U.S. Postal Service.  In 1989, they issues a series of four dinosaur stamps, one of which was of Brontosaurus.  A number of paleontologists went ballistic, accusing the post office of promoting inaccurate science.  From that hoopla, the general public first became aware of the whole Brontosaurus fiasco and the fact that their “beloved” Brontosaurus was actually something else.  In the eyes of some in the public, it called into question the reputation that paleontologists had worked so hard to established.  It seemed that the Bone War had done more harm to paleontology, nearly a century after it had ended.

Others point out that it has shown paleontology as a science that learns from its mistakes and is honest and strong enough to make the necessary changes and go on.

In any case, it certainly shows that men of science can have their own issues.  Aside from the rivalry between Cope and Marsh, it shows how we are slaves to our times.  Marsh could not see that his fossil’s head was smaller and more delicate than the burly version he envisioned, largely because his society said it was supposed to be that way.

It also demonstrates the nineteenth century European fascination with naming and categorizing things, often to the exclusion of anything else, especially if that something else disagreed with the way they thought things should be.

Alas, we have our own prejudices.  Will we be able to stand the scrutiny of our successors a hundred years from now?  Only time will tell, but in any event, Brontosaurus was the dinosaur that never was, except in our own imaginations.

Imperfect Imitation is (Sometimes) the Best Form of Flattery

21 03 2012

A letter published March 21 in the online edition of the journal Nature indicates that there are evolutionary reasons why some animals that mimic other more aggressive or dangerous species do so rather imperfectly.

The study conducted by a team of Canadian researchers indicated that, at least in hoverfly populations, predators impose less selection if the mimic is smaller.  Thus, small mimic species need to have less fidelity with the species they are mimicking than do larger ones.  The team concludes that the most likely reason for this is that the mimics are less profitable prey species and are not apt to be pursued as strongly as are larger species.  So, less fidelity will do.

The team was also able to show little or no correlation of mimicry to several other theories that had been posited over the years as explanations for the imperfections.  Among these, they were able to show that human ratings of mimetic fidelity are positively correlated with both morphometric measures and avian rankings of the mimicry, indicating that variation in mimetic fidelity is not just an illusion based on human perception.

See here for the complete paper.

Scientists Trace Origin and Evolution of GPCR Kinases

20 03 2012

G protein-coupled receptor (GPCR) kinases (GRKs) are important in regulating many signaling pathways in the bodies of animals.  Both under and over regulation of GRKs has been implicated in a variety of human illnesses, including heart disease, Parkinson’s disease, and depression.

Reporting in an article published on March 19, in the online journal PLoS One (Public Library of Science One), a team of scientists from the United States has traced the origins and evolution of these kinases.  Based on their study, the team concludes that GPCRs are very old, having appeared before the rise of Metazoa and expanded rapidly among true metazoans.  They hypothesize that this rapid expansion was the result of the need for quick signalling adjustments in fast-moving animals.  They note that this “lifestyle requires the ability to reset and re-engage the environmental sensors frequently, which calls for [a] rapid shut-off mechanism.  A dedicated system for quick deactivation of GPCR may have been one of the factors profoundly determining the metazoan lifestyle.”  For the full paper, see here.

G Protein-Coupled Receptor Kinase

Crystal structure of G protein coupled receptor kinase 1 (GRK1) bound to ATP (Credit: Image is from Wikipedia Commons and is by the Jmol development team. It is used under a GNU Free License.)

Like Mice Off a Not So Sinking Ship

19 03 2012

The humble house mouse (Mus musculus), traveling the globe with man. Image is courtesy of Wikimedia Commons and is in the public domain.

An international team of researchers led by scientists at the University of York in the United Kingdom have used mitochondrial DNA to show that the timeline of house mice migration across the upper north Atlantic through Scotland and the Scottish Islands, to Iceland, Greenland, and Newfoundland closely matches that of the Viking invasion.

The Vikings, who fought, raided, and explored their way across the north Atlantic from the late eighth to the mid-tenth centuries were the scourge of most of Europe at that time, raiding, killing, and pillaging large swaths of the continent, not just the areas above, but also parts of England, Wales, the Isle of Man, and Ireland.  They established the first cities in Ireland.  They founded the duchy of Normandy, in France, and they even established a kingdom in Sicily in the Mediterranean Sea.

It seems that where they went, their house mice (scientific name Mus musculus) went with them, at least on the northern part of their journey.

According to a press release (see here) the research team, made up of members from the UK, US, Iceland, Denmark, and Sweden, used techniques designed to characterize genetic similarity, and thereby infer the relatedness of one population, or one individual, with another, in order to determine a mouse colonisation timeline.

They obtained modern samples of house mic DNA and compared them to ancient samples dating mostly from the 10th to 12th centuries.  Samples were collected from nine sites in Iceland, Narsaq in Greenland, and four sites near the Viking archaeological site, L’Anse aux Meadows, in Newfoundland.  Ancient samples came from the Eastern and Western settlements in Greenland and four archaeological sites in Iceland.

When analyzed, the samples showed that house mice traveled with the Vikings to Iceland in the early 10th century , either from Norway or the northern part of the British Isles.  From Iceland the mice continued their journey on Viking ships to settlements in Greenland.  However, while descendants of these stowaways can still be found in Iceland, the early colonizers in Greenland have become extinct and their role has been filled by Danish house mice (same species) brought much later by a second wave of European human immigrants.

Of significance is the fact that no evidence of house mice was found in the Viking settlement in Newfoundland, nor was there any evidence of ancestral Viking house mice DNA in modern house mice there.  So, it seems that if the mice made if as far as Newfoundland, they became extinct before they could contribute to the modern house mice lineage on the island.

Replica of a Viking Long Ship

Replica of a Viking long ship. Photograph by archiwum własne wikingów, Jarmeryk, from Wikimedia Commons.