Wednesday, August 21, 2013

A Pastiche of Turtles

Turtles, turtles, turtles.  It’s been a glorious summer for encounters with turtles . . . but, despite a lifelong love affair with them, it’s also been a time for discovering how little I know about these reptiles.  There is no “clever” hook for this post, no point larger than the fact that familiarity does not lead to understanding.  It is simply a pastiche of turtle encounters and lessons begun to be learned.  (Not much for the 200th post on this blog.)

In July, when an Eastern box turtle (Terrapene carolina carolina) crossed the yard of my summer cottage, it prompted a post about the scientific debate over the origin of turtles (land or sea).  A question I’d never considered.

Later this summer, while hiking in the Quogue Wildlife Refuge on the South Fork of Long Island, New York, I chanced upon more chelonians (turtles constitute the order Chelonia).  The refuge offers a wonderful 300 acres or so of diverse environments, from a large pond (the Old Ice Pond where ice was harvested in the 19th and early 20th centuries) to marshes and wetlands to very dry, deeply scented Pine Barrens.  As I crossed a footbridge over one extension of the pond, there in the water below I spotted several Eastern painted turtles (Chrysemys picta picta) lazily swimming and drifting amid the vegetation.

Then, on the edge of a section of the Quogue Pine Barrens, an Eastern box turtle emerged from the underbrush, contemplating a mad “dash” across the trail.

On that particular day, I felt I had met with an abundance of turtles.  But abundance certainly is not the collective noun, not the term of venery, for turtles.  I turned to James Lipton’s marvelous book An Exaltation of Larks, and learned that the word I wanted was bale – it’s a bale of turtles.  Lipton, when discussing the possible source for this term, concluded that the “origin remains as well concealed as the turtle.”  (p. 62)

The purchase of a small turtle fossil this summer taught me something else about turtles.  A fundamental element of the shell anatomy of most chelonians – made clear by this fossil – had escaped me all these years:  the shell is composed of layers, a layer of bony plates overlain by a layer of scutes.  Scutes are pieces of keratin that, in the species that do not shed them, build up over time.  The preferred adjective to describe turtle scutes in the scientific literature is horny (Oliver Perry Hay, The Fossil Turtles of North America, 1908, p. 4; Alfred Sherwood Romer, Vertebrate Paleontology, 1966, p.112), which makes sense since keratin is the stuff of animal horns and hoofs (and our fingernails and hair).  Scutes are arranged atop the series of bony plates of both the carapace (the top or dorsal element of the shell) and the plastron (the bottom or ventral element).  The so-called bridge, which joins the carapace and plastron together, is the third major component of the shell.  The pattern of intersections of the scutes only marginally overlaps that of the underlying bony plates; impressions (sulci) of the scute pattern are left on the bony plates.  (Scott F. Gilbert, et al., How the Turtle Gets Its Shell, in Jeanette Wyneken, et al., eds., Biology of Turtles:  From Structures to Strategies of Life, 2008, p. 2; Richard E. Nicholls, The Running Press Book of Turtles, 1977, p. 18-19.)

Shown below are the fossil remains of a tortoise, Stylemys nebrascensis, which were found in the Nebraska badlands, specifically in the Brule Formation on the Shalimar Ranch in Sioux County, Nebraska.  This fossil is from the Oligocene epoch, early in that epoch, making it roughly 32 million years old.  The anterior of the shell is facing up in this photo.

Trying to comprehend what’s missing and what’s present in this fossil shell helped me gain a slight sense of the turtle’s shell.  Most of the carapace is missing, with a few bony plates clinging to the periphery; all, or nearly all, of the bony plates that make up the plastron are present.  What of the scutes?  They’re gone, separated in death.  As paleontologist Alfred Sherwood Romer noted about turtle fossils, “The scutes are not, of course, preserved in fossils, although the outlines are often indicated by grooves in the bones which lay beneath them.” (p. 112)  Yet, I suspect there may be fossil turtle shells with the scutes still present.  One study of what happens to turtle shells post-mortem showed that, though a significant percentage of scutes loosen and detach relatively early in the decay process, that still takes, on average, more than a month.  I would think that specimens quickly “entombed” should still retain scutes and possibly fossilize with them.  (C. Kenneth Dodd, Jr., Disarticulation of Turtle Shells in North-central Florida:  How Long Does a Shell Remain in the Woods?, The American Midland Naturalist, Volume 134, Number 2, 1995.)  I’m also beginning to think that there is some confusion on the web, outside of the scientific literature, about the distinction between turtles’ bony plates and scutes.

One thing that isn’t evident from casual encounters with turtle, but which is a fundamental aspect of the carapace, is that the ribs and vertebrae that lie beneath certain of the bony plates are fused to them.  Other skeletal features of the reptile are contained within the animal’s ribcage.

The turtle’s shell is truly an amazing structure with long term consequences for its possessor.  But, I am struck by the fact that some of the scientists who study them assume that the rest of us have become blasé about them.   Biologists Carl H. Ernst and Jeffrey E. Lovich (Turtles of the United States and Canada, 2009) put it this way, “The single feature that most defines living turtles is their bony shell. . . . Our familiarity with turtles trivializes this fantastic architecture.” (p. 3)  In this regard, they quote Romer who concluded, “The chelonians are the most bizarre, and yet in many respects the most conservative, of reptilian groups.  Because they are still living, turtles are commonplace objects to us; were they entirely extinct, their shells – the most remarkable defensive armor ever assumed by a tetrapod – would be a cause for wonder.”  (p. 112)

I think they have it wrong.  Familiarity, in this case, doesn’t lead us to accept turtles as commonplace, or make us experience a loss of wonder over their presence.  On the contrary, we are deeply attracted to turtles, approaching them with a mixture of wonder and affection, tempered with a touch of disbelief.  Familiarity also, at least in my case, hasn't led to understanding.

Tuesday, August 6, 2013

Museums Telling a New Natural History Story

My intention to write a post about the blog that the Paleobiology Department in the Smithsonian’s National Museum of Natural History (NMNH) launched several months ago was reinforced when I came across Edward Rothstein’s review of the multi-million dollar “transformation” or “refashioning” of the Natural History Museum of Los Angeles County (NHM) (Beyond Dioramas:  Nature’s New Story, New York Times, August 3, 2013).  It struck me that both efforts – one a very expensive investment in the remaking of a museum and the other a low-cost digital activity with minimal financial outlay – present (to varying degrees) a critical element of the story that natural history museums are now sharing with their visitors, whether those visitors come to a physical structure or a website.  These museum are telling how scientists in the natural history fields do their work.

Rothstein, cultural critic of the New York Times, asserts that the natural history museum, in general, has been a lumbering beast, resistant to change, that is, until recently.  The beast’s evolution, he posits, is “quickening.”  So, what has changed for the NHM?  The essence of his somewhat rambling review seems to be that NHM chose to go “local” (read, Los Angeles) and focus on the “history of human interaction with nature.”  The tried and true elements of the natural history museum remain in the NHM – the dioramas from the 1920s and 1930s have their place along with the fossils.  But these are just a part of this museum’s landscape which now features local artifacts – to wit, the shoes and clothes Charlie Chaplin wore in City Lights, or a 1902 Tourist, a wooden car – topped off by the exhibit titled Becoming Los Angeles which presents the history of the peopling of the area.  Apparently, where this new approach most reveals its promise is in the Nature Lab in which children (and their parents) learn about the local Los Angeles fauna and are drawn into “citizen science” activities.  Rothstein labels the Nature Lab’s exhibits “among the most successful I have seen for children in a science museum.”

I must admit that I initially thought that the LA museum might have wandered too far afield in its efforts to remake itself (and appeal to a broader audience), but I have to remember the sweeping nature of what’s included in that term natural history.  Wooden cars and movie costumes are not a stretch.

In drawing visitors into a greater understanding of the “history of human interaction with nature,” the NHM appears to have embraced two disparate aspects of that objective.  The first centers on humans reshaping their natural environment (e.g., the Becoming Los Angeles exhibit).  Interesting and important, to be sure.  The second – how we humans learn about nature – is, for me, the more critical element.  This should be part of the heart and soul of the story that natural history museums are telling – how paleontologists, botanists, entomologists, and the other scientists in the natural history fields do their work.

Rothstein writes that the NHM’s Mammal and Dinosaur Halls now “hint” at this.  They seek to present the “interpretations” and “uncertainties” of the work.  Further, and more to the point, in some of these NHM exhibits,
[t]he emphasis is on how paleontologists learn and on how our understanding has changed.  Scientists appears in videos and panels, outlining arguments and demonstrating procedures.
I'll have to see them for myself to know whether hint is the appropriate verb.  Based on the description of the new Dinosaur Hall on the NHM's website, I come away feeling that the NHM is doing more than just hinting.  Of the three questions purportedly addressed by new Dinosaur Hall, one is "How do scientists know what they know?"  Luis Chiappe, Director of the NHM's Dinosaur Institute, is quoted as saying, “The new Dinosaur Hall has the potential of inspiring new generations of scientists, since this exhibition highlights discovery-based fieldwork, the experience of going outdoors and finding treasures, and then understanding how they fit within current scientific record.”

Amen to that.

A less significant but still an important contribution toward this refocusing of the natural history museum and its story is the blog launched by the Paleobiology Department at the Smithsonian's NMNH.  Getting beyond the “punny” title – Digging the Fossil Record:  Paleobiology at the Smithsonian – is well worth the effort because typically the content is very interesting and the blog’s authors successfully explicate the complicated.  (Unfortunately and rather puzzling, the identity of the writers of individual posts isn’t always provided.) The tone is light and engaging.  Altogether, it’s a fun blog to monitor.

In its initial post, the blog sought to entice readers:
If you have ever wondered what paleontologists do in the field or wished you could see Smithsonian fossils that aren’t on display, subscribe to this blog for behind-the-scenes photos, field reports from our scientists, research news, archival images, paleo art, and many other stories about our collection and our work, past and present.
So, far in its brief existence, Digging the Fossil Record has lived up to its own PR, offering a fairly wide mix of content, though, to date, it’s been largely dominated by accounts of Smithsonian scientists doing field work.  Among these posts have been a multipart series about collecting plant fossils at a Permian site in north-central Texas, a two-part series focused on core drilling in Tanzania in order to collect the fossil shells of marine microorganisms, and, most recently, a five-parter on a collecting trip to the North Dakota badlands (more on that one in a moment).

Though other kinds of offerings have been on the menu, they’ve been a bit sparser.  The blog has explored, among other subjects, some of the prep work being done by volunteers in the Museum’s FossiLab on material brought back from the field, the background of the new T. rex skeleton coming to the Smithsonian (just in time for the disruption of the complete remodeling of all of the paleontological offerings at the NMNH, including the Dinosaur Hall), and the life’s work of a premier, though largely forgotten, dinosaur hunter, Charles W. Gilmore, a curator at the NMNH for a couple of decades in the first half of the 20th Century.

The North Dakota badlands series, titled From the Field:  Putting Dinosaurs in Their Place, is a good example of what the blog has to offer (besides titles with puns).  The collecting trip is placed firmly in context.  In preparation for an exhibit opening next year that will “flesh out” the natural environment in which the Triceratops and Tyrannosaurus rex lived, the NMNH team went in search of fossils of “small vertebrates, mollusks, plants, and, of course, dinosaurs . . . ” in the Late Cretaceous Hell Creek Formation.  It was eye opening to this amateur collector that the objective of the trip was that clear cut – gather the material needed for an exhibit on a Late Cretaceous ecosystem.  For me, setting out with such a definitive goal would be a certain recipe for disappointment.  But that’s where experience and expertise enter the equation.  The team included paleobotanist Kirk Johnson (also the Director of the NMNH) who has often collected plants in this area.  He led the team to favorite and productive spots.

Methods employed in the field are on display in these posts.  Small quarries are dug, rocks are moved and split, revealing the impressions of plants within.

(The photo of the multiple leaf impressions was taken by Diana Marsh; that of the palm leaf was taken by Kirk Johnson.  These pictures and one below were downloaded from the blog under the terms of use specified by the Smithsonian.)

Ancient river channels are crawled through in search of tiny fossil teeth and bones lying on the surface.  Matrix is shoveled into bags for more thorough searching back in the Museum’s FossiLab.  GPS devices are used to record precise locations of finds.  Sketches are made of the landscape, attending to the locations of different sedimentary layers.  Layers are measured with a Jacob’s staff (had to look that one up since the post in question offers no explanation).

(I could not find a credit for this photograph.)

One post describes a “bone walk” or biostratigraphic survey in which every visible fossil is collected, with its location noted, from one specific sedimentary layer.

These posts make it abundantly clear that this work, in general, is not one string of wonderful fossil discoveries; they well capture the painstaking nature of the work and the challenge of collecting under the hot North Dakota sun.

Perhaps most important to me is that any attentive reader of this series will learn that the field work is but one step in the process.  These badlands posts repeatedly emphasize that lab work awaits these finds – sifting through matrix for more vertebrate fossils, carefully exposing more of the leaves from the split rocks.  I hope that the blog will follow these fossils from the field through the lab, onto the curation process, and, finally, to display in the new exhibit opening in 2014 (or, if we're being really honest, sometimes to storage in plaster jackets or in drawers in some cabinets).  Now, that would certainly capture some of how the work of natural history is done.

Sadly, the small effort by the National Museum of Natural History’s Digging the Fossil Record blog is blunted because the blog is rather hidden (I originally wrote “buried”) on the Smithsonian’s busy website. Yes, there are some other offerings on the NMNH website that feature the processes of science, but these are too little and too secreted away.

Yet, hope springs eternal.  I look forward to seeing, in several years' time (possibly by 2019), the NMNH's totally remade paleontological offerings fully expressing this new story of natural history.

[Note:  As originally uploaded, this post perpetuated the misconception that the NMNH was renovating just its Dinosaur Hall.  All of its paleontological offerings are being redone as outlined in a Washington Post article from last year.]
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