A Different Way to See Fossil Skeleton Mounts

Memorandum
To:  Myself
Subject:  Fossil Skeleton Mounts

Next time you are in a natural history museum (one with its fossil halls not undergoing renovation, so, forget the Smithsonian’s National Museum of Natural History), approach a fossil skeleton mount (that sine qua non of natural history museums), and try your damnedest to get beyond that initial awe-inspiring view.  Move as close as you’re allowed and look for those telltale signs of how that skeleton is being held together, how it’s holding its pose.  Look for the armature, that construct of metal that keeps the bones in place.  Yes, some armatures are internal, but a glimpse of a bit of metal sneaking through joints, from inside one bone into another, might be had (unless the joints are filled in with plaster).  An external armature might be as obvious as that holding up the neck and torso of the Apatosaurus skeleton dominating the Peabody Museum of Natural History’s Great Hall,

or it might be mostly hidden on the backside of the bones.

Look carefully at the bones.  Try to identify which of the skeleton’s bones are real fossils and which are casts.  Museums seem to be doing a better job these days of ensuring that fossil bones and casts can be distinguished from each other.  On older mounts this may not be so easy given that fossils and casts were often painted the same color.

If fossil bones can be distinguished from casts, consider the fate of those real fossil bones in such a mount.


It’s not clear when I’ll be able to follow the guidance in this memo.  [Later edit:  I will be able to follow the memo a lot sooner than I thought.  In the original version of this post, I wrote that "there are no fossil skeleton mounts on display, at the moment, at the NMNH (my natural history museum home)."  That's wrong.  There's at least one on display in the Sant Ocean Hall, a Basilosaurus, which is an ancient whale.  See Addendum at end.]  “Hatcher,” the cast of a Triceratops, which had been the sole dinosaur standing publicly in the museum after the Fossil Halls shuttered their doors earlier this year, is now behind temporary walls on the third floor as a new Late Cretaceous display takes shape around it and “Stan,” the museum’s T. rex cast.  When it opens in late November, this display will be up for five years as the Fossil Halls undergo their total makeover.

It’s not a coincidence that my interest in the process and consequences of including real fossils in skeleton mounts has taken flight just when the NMNH Fossil Halls are off-limits.  Most folks would be interested in the construction of the new NMNH displays, but, in my contrarian (perhaps better read “perverse”) fashion, I have become focused on the flipside of that, that is, on the dismantling of the myriad mounts that graced the Fossil Halls for the past century.

Some wonderful pictures of aspects of this deconstruction can be found in various postings in the Smithsonian blog Digging the Fossil Record:  Paleobiology at the Smithsonian.  To date, primarily featured in these posts is the taking apart and moving of the casts of “Hatcher” and “Stan” (cast mounts really aren't my concern here).

Visitors to the NMNH can witness some of that fossil mount deconstruction if they visit the museum’s FossiLab on the second floor and look in through the windows and watch the volunteers at work.  A recent entry in the Digging the Fossil Record blog highlighted the reopening of the FossiLab (which had briefly been shielded from public view in its previous location down in the Fossil Halls) and noted that some volunteers in the lab will be engaged in taking mounts apart and creating storage containers for the disarticulated bones.  The blogger (sadly, anonymous) comments that:

Dismantling skeletons is challenging.   Some of the mounts were built a long time ago and, since mounting techniques have changed a lot over time, nearly every mount was constructed in a different way.  Add in the problem that some of the bones are extremely fragile, and it can take some puzzling to figure out how to tease the mounts apart safely.  Once the bones are free of the armature they are photographed, logged into our collections database, and placed in archival storage where they will be preserved for scientific study and, perhaps, remounting for a future exhibit.

What happens to fossil bones when they are included in such mounts, particularly those “built a long time ago”?  There is literature out there about that.  A particularly depressing account comes from Robert L. Evander, senior principal preparator at the American Museum of Natural History, in a 2009 piece titled Armature Damage to a Mounted Specimen (this full-text link is listed on the Society of Vertebrate Paleontology’s Preparator’s Resources site).

The fossil mount in question is the skeleton of a glyptodont, a large (some were car-sized), armored, armadillo-like mammal, that dates back to at least the Miocene (23 to 5 million years ago) and which went extinct about 10,000 years ago.  Evander basically reverse-engineered the mount because the American Museum of Natural History’s Adam Hermann, who prepared the mount from the fossil bones in 1916 – 1917, left no detailed account of how that particular mount was constructed.  This was the final fossil skeleton he mounted, so, it may reflect the best of Hermann’s work.  Writes Evander,

Adam Hermann’s free mounts are deceptive.  The bones appear to be gently mounted upon cleverly-hidden external armatures closely shaped to the bones.  The few visible drill holes seem to be attaching individual bones to this external armature.

How did he achieve this deception?  Well, he drilled some 100 holes lengthwise into articulated fossil bones in order to run wires through them as part of the internal armature.  Spaces in joints were filled with plaster.  The external armature was shaped on the basis of plaster casts of the bones and was then attached to the fossil bones by more drilling through the bones, and the insertion of many more nuts and bolts.  Here’s an illustration of parts of this method from a piece Hermann wrote explaining his fossil preparation and mounting techniques; the caption tells the story (Modern Laboratory Methods in Vertebrate Palæontology, Bulletin of the American Museum of Natural History, Volume XXVI, 1909, p. 318):

Evander discovered that, because the armatures are harder than the bones, the points at which the armatures are screwed or bolted to the fossil bones are places where cracks and breaks have developed.

Conclusion?  Disaster.  Writes Evander of this fossil skeleton and others mounted by Hermann a century ago,

In some measure, Hermann’s mounting has adversely affected scientific access to these specimens, which will never be freely available to study in the disarticulated state.  Individual postcranial elements cannot be extracted easily.  Realistically, these mounts are permanent.

It is ironic (from our perspective a century later) that in the same 1909 piece of his, Hermann cautioned,

I therefore say, that a beginner in a palæontological laboratory never ought to be trusted with a delicate and rare specimen.  In my experience, I have seen irremediable damage done on account of poor judgment.  (p. 331)

Because Hermann-like treatment of fossil bones in mounted skeletons continued well into the 20th century, Evander finishes with a word for us frequenters of natural history museums:

Thus the mounted specimens seen in the museums of the world may be more fragile than they appear.

Though the doors to the NMNH’s Fossil Halls are shut, I wondered whether photographs I’d taken previously of its fossil skeleton mounts might show something about the mounting process employed.  One entry in Digging the Fossil Record includes a couple of pictures of the work on dismantling the museum’s Irish Elk with its massive antlers.  This particular mount, which went on display in 1872, was the Smithsonian’s first mount utilizing real fossil bones.  (A post on the superb blog Dinosours! [sic] discusses this skeleton mount.)  That prompted me to look at pictures I’d taken of the Irish Elk for a previous post on my blog.  The picture below (looking head on) shows the animal’s left antler and the wiring that holds up.  A couple of seemingly benign metal supports appear to cradle the antler from its ventral side.

But, the following picture (taken from behind the animal) suggests that all is not so benign.  The “cradling” arms are apparently bolted through the antler to a metal plate on the backside of the antler.  Further, part of a metal armature can be seen coming from the skeleton up onto the antler.  This too is apparently bolted to the antler.  I have marked several of these bolt heads.

I found a bit more in my collection of photos.  A set of photos of the NMNH’s Brontotherium hatcheri (taken for a blog posting about this rhinoceros-like herbivore related to horses that lived some 40 million years ago) may also be revealing.  Unfortunately, I cannot be certain when this mount was created (the fossil bones were discovered by John Bell Hatcher in 1887) nor exactly which of the bones in this skeleton are real.  But, the Smithsonian’s Collections Search Center describes this specimen as including the following fossil bones:  “skull elements, lower jaw, Axial element, thoracic vertebra, Appendicular elements, pelvic girdle, phalange.”  Here’s a picture of the rump of the specimen.  I’ve marked two places that particularly drew my attention.

The lower arrow points to part of the external armature, where it is bolted onto the skeleton.

Do these go into fossil bone?  I don’t know.  I’d love to be able to see this skeleton again.

The upper arrow points to part of the pelvic girdle (which is listed as fossilized bone but perhaps not all of it is) where a bolt head is obvious.

I assume this bolt attaches to the external armature which runs behind the bone, and I believe that this bolt runs through fossil bone, not plaster.  Of interest is the crack that radiates from the bolt head.  Evander would probably not be surprised.

Despite all of this, I’m not prepared to let the other shoe drop, the one that signals opposition to inclusion of any actual fossils in free standing skeleton mounts.  That’s a major bone (pun intended) of contention in paleontological circles where there is concern, not just for the damage done in the mounting process, but the potential damage incurred by being in such a mount for the long term, subject to changes in temperature and humidity, vibrations, and other harmful stresses.  Though mounting techniques have changed for the better, I may still be heading in the direction of advocating for nothing real in free-standing mounts (I would not be alone in holding that position).

For the time being, memo writer, I will consider such mounts from that different perspective and with a great deal of concern.

ADDENDUM

Ben, author of the blog Dinosours!, commented on this posting (see below) and asked my reaction to more "gentle" mounting techniques.  In my response, I referred to Digging the Fossil Record and a post there by Matt Carrano, Smithsonian Curator of Dinosauria, in which he stated that mounts in which fossil bones were drilled into were a thing of the past.  He included a photo of some of the sternum bones of an ancient whale currently on display at the NMNH; these bones were cradled in metal supports.  When I went back to his post, I was dismayed on two counts:  first, I should have quoted Carrano in my original post (I do in my response to Ben), and, second, I had completely overlooked the fossil skeleton mount of the ancient whale in the Sant Ocean Hall (which allowed me to make the erroneous assertion that, with the closing of the Fossil Halls, there weren't any still on display - indeed, there may still be others, my search continues).  I've had a chance to take a look at that whale skeleton (which includes real bones) and, though I tried, I found it difficult to really observe how all of it was mounted (sorry, memo writer) because the whole thing floats high overhead, suspended from the ceiling (and accompanied by two cast mounts).  Clearly, the sternum bones are being supported without drilling, as apparently are the vertebrae.  Also, real bone and cast are easily distinguishable, a good practice.  But, I cannot be so sure that some bolts aren't still penetrating real bone.  Unfortunately, I cannot get close enough to be sure.  Here is a picture of a few of the ribs and a flipper (real bone is darker and rougher).  Perhaps I'm just inclined to see it, but it does look to me as though some real bone may have been drilled into.

Poetic Pursuit in the Museum: Seamus Heaney and Bogland

Twilight at the museum, though, to be honest, it’s always twilight in much of this building, never night when, as we well know, the specimens on display would come alive.  The visitors are departing, leaving in their wake faint pulses of voices and fading fragments of sentences.

On a quest, I peer into one hallway – early and middle Cenozoic mammals – too early.  The Ice Age and beyond is to my left – much more promising.  In the soft gloom, I pass a giant sloth, round a corner and stop.  As though from a mist, rises Megaloceros giganteus, the Irish Elk.

What an amazing creature, seemingly a victim of size gone wrong.  During a brief warm period, some 12,000 to 11,000 years ago, the Irish Elk bulked up and grew those monstrous antlers, spanning upwards of 12 feet and weighing 100 pounds.  But, as Stephen Jay Gould described, the animal, neither an elk (it was a deer) nor exclusively Irish (fossil remnants are found throughout Eurasia), was a battleground over which Darwinians and their naysayers long fought.  The latter at times contending that an attribute such as those grossly huge antlers showed the impotence of natural selection, once an animal started down an evolutionary path, there was no turning back even if it lead directly to the animal’s extinction.  Though the former have won this field, they remain somewhat at odds among themselves over the forces actually at work in driving up body and antler size.

Gould, in his essay The Misnamed, Mistreated, and Misunderstood Irish Elk (in the essay collection Ever Since Darwin (1977)) offered evidence for the allometric relationship between body size and antlers (as the one increased so did the other), and concluded that selection was working on the antlers.  As selection drove an increase in antler size, body size increased along with them.  He proffered that the oversized antlers were used in ritualized combat between Irish Elk males, a process that established dominance hierarchies without inflicting fatal injuries on the vanquished, and, most importantly, ensured the reproductive success of the more robustly antlered victors.  Others argued that the key was body size and it was the antlers that were along for the ride.  The plaque below the skeleton of M. giganteus here in the Smithsonian’s National Museum of Natural History posits just that.  Extinction, Gould argued, came when the climate cooled and the flora changed with it, no longer able to support these animals.  The plaque cites as the principal cause of the beast’s extinction the impossibility of moving with their racks through the forests that arose with the changing climate.  Some have offered up a more convincing hypothesis, arguing that the nutritional requirements for animals of this size with their array of antlers could not be met by the newly available flora, and that it changed too quickly for the animals to adapt, all the while sexual selection continued to promote larger antlers. (Ron A. Moen, et al., Antler Growth and Extinction of the Irish Elk, Evolutionary Ecology Research, 1999.)  Regardless of the precise cause of the extinction, Gould concluded that all this was fully in keeping with the theory:

Darwinian evolution decrees that no animals shall actively develop a harmful structure, but it offers no guarantee that useful structures will continue to be adaptive in changed circumstances.  (p. 90)

So why my quest for the Irish Elk?  It grew out of my reading Bogland, a poem by Seamus Heaney, 1995 Nobel Laureate in Literature (awarded "for works of lyrical beauty and ethical depth, which exalt everyday miracles and the living past").  (Bogland was published in a 1969 collection titled Door into the Dark.  I am reading it in Opened Ground:  Selected Poems 1966 – 1996.)

I come late to Heaney’s poetry and have been reading mostly his earliest pieces, those that most center on the ebb and flow of rural life in Ireland and the Irish landscape.  Here a spongy, porous boundary separates past and present.  In this bogland of Ireland, this watery earth, the past is just below the surface and seemingly unchanged.  In Bogland, Heaney writes of butter buried for a hundred years reemerging “salty and white.”  And ancient trees that turn not to coal, but to “waterlogged trunks/ . . . , soft as pulp.”  In the harvesting of peat, the past is present – “Our pioneers keep striking/ Inwards and downwards,/ Every layer they strip /Seems camped on before.”

And my quest?  “They’ve taken the skeleton/ Of the Great Irish Elk/ Out of the peat, set it up,/ An astounding crate full of air.”

A striking and true image of the ribcage?  I think so.

But I am puzzled why it’s the ribcage the poet remarks on, not the massive set of antlers.  Perhaps it’s just a striking image, though I think not with this poet.  A comment on the meaning of the past?  On an effort to recreate it?

Bog-mediated preservation of the past recurs often in Heaney’s early poems.  For example, in a series of poems, including The Tollund Man, he finds a resonance between the violent troubles in his home land (Northern Ireland) and the well preserved bodies found in bogs in Denmark, victims of sacrifice 2,000 years ago.  (William Doreski, Diggings, Harvard Review, Spring 1996.)

The first of Heaney’s poems I read was Death of a Naturalist from the 1966 collection of the same name.  (Heaney was featured in a recent installment of the PBS NewsHour’s Poetry Series; the text of the poem and a video of Heaney reading it appear on the NewsHour’s website.)  The poem offers an almost maddening array of stimulations for the senses.  It demands to be read aloud and savored.  Every spring, the narrator, Heaney as a boy, I assume, gathered frogs’ eggs (“frogspawn”) in jars and watched them develop on window sills at home and shelves at school.  And, as the poem reads, every spring his teacher, Miss Walls, told the children of daddy frogs and mammy frogs.  To mark the boy’s youthfulness, the first portion of the poem ends with a delightful non sequitur about how the color of the frogs changes depending upon the weather – the prototypical young child telling all he knows about a subject, whether relevant or not.

That innocence vanishes in the second portion of the poem when the boy comes upon a gathering of croaking bullfrog – “Poised like mud grenades, their blunt heads farting.”  The would be naturalist?  “I sickened, turned, and ran.  The great slime kings/ Were gathered there for vengeance and I knew/ That if I dipped my hand the spawn would clutch it.”  Death of a naturalist.  Actually, I think not.

I am still working on this poem, considering if it’s about the death of sexual innocence (though why at that particular moment when Miss Walls had told him often about mammy and daddy frogs), if it marks the moment of the boy’s realization of the potential dangers of the natural world, if there’s some Irish folktale about vengeful frog kings, or if . . . .  Regardless, I do not, for a moment, believe that it describes the death of the naturalist in Heaney.  His poetry says otherwise.