22-31 January 2005

Installment #255---Visitor #blog analyzer

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Back in the 1970's, Jack Klugman gained a cult-like television following as "Quincy, M.E.," the initials standing for Los Angeles "Medical Examiner." Ever-curious Quincy solved crimes by finding some shred of evidence everyone else missed--ofttimes by looking at an unusual anatomical or physiological feature of the deceased--and the show added the word "forensics" to the Nation's vocabulary. In the past few years, interest in forensic science has been rekindled on television, witness the highly popular theme of "CSI" (Crime Scene Investigation) that seems to play out almost every night via "CSI: New York," "CSI: Miami," and re-runs of just plain "CSI." We were pondering such things this week, mostly because we knew that Newberry College, our undergraduate alma mater, was about to announce it would become the first school in the Carolinas and Georgia to offer a degree in Forensic Chemistry. Partnering with SLED (South Carolina Law Enforcement Division), Newberry will graduate students who can go directly into the crime-solving work force without additional training--something the "little school on the hill" can honestly brag about. With all this in mind, it was only appropriate on our first excursion to the woods since our latest retinal surgery that we stumbled upon a mysterious clue along the path. Was it an indication of murder or mayhem? A turbulent act of nature? An extraterrestrial invasion? To solve the mystery, we called on "CSI: Hilton Pond" to get to the bottom of things.

All text & photos © Hilton Pond Center

As we walked around Hilton Pond Center that afternoon of 31 January, we noticed a light-colored object a few feet off a trail bordering a small meadow. We had passed this spot dozens of times in recent months without seeing the item in the grass, so at first we suspected it had just arrived. When we bent to examine the two-inch long object (above), we noticed it had settled slightly into the soil, so it must have been there for some time. Pondering this, we recollected there had been a mild ice storm earlier in the week, so perhaps the weight of frozen precipitation had flattened out the grass enough to reveal the object. At first glance the artifact appeared to be a skull, bleached by sunlight and weather, with what seemed to be two eye sockets and a nostril hole. We occasionally find small animal skulls around the Center, usually Eastern Gray Squirrels or Cotton Rats or sometimes a Virginia Opossum or Raccoon; all these have pointed snouts and are rounded in back, but the object at hand was just the opposite. What would be the "nose end" was rounded, while the posterior had a pointy projection that made the whole thing look like one of those new-fangled aerodynamic bicycle helmets. What's more, there was something missing that is always obvious in mammal skulls we've encountered--they have teeth, or at least tooth sockets where teeth used to be--but the new-found object had no signs of either. If this was a skull, it was toothless, and what kind of animal this big has no teeth?

All text & photos © Hilton Pond Center

One answer is "birds"--such as the Green Heron (above)--which have traded calcified teeth and heavy jaws for lightweight bills and hollow bones that facilitate flight. But when we looked at the anterior end of our artifact there was no sign of an avian bill, and the skull itself was much too dense to have come from a bird. There WAS a hint of an overhanging beak, however, and that was the clue that led us to know the creature from which the object had come. A toothless vertebrate with a heavy, beaked skull? But, of course! It had to be a turtle!

Turtles are pretty common in and around Hilton Pond. We sometimes see terrestrial Eastern Box Turtles as they meander about looking for Blackberries, and several kinds of turtles live in the pond itself. Even the typically aquatic species must leave the water to nest, so in late spring we encounter gravid females seeking suitable spots to lay their eggs. An aquatic turtle out of water is almost like a fish in the same predicament; it's designed more for swimming than for navigating on land. Perhaps the turtle that left its skull where we could find it was a female looking for a nest site but finding a predator instead, or maybe she gave her all for her progeny and simply died from ambulatory exhaustion after laying her eggs. In any case, we suspected more should remain of this turtle than just its skull, so we looked around in the grass for other artifacts. It didn't take long. About 15 feet away near the base of an Eastern Red Cedar was a belly-up turtle shell half-buried in dead leaves.

All text & photos © Hilton Pond Center

Now that the vegetation around it was dead or flattened out by the ice storm, the 9-inch-long shell (above) was pretty obvious. And based on its color and size, we knew it had come from one of the larger turtle species, in this case a Yellowbelly Slider, Trachemys s. scripta. We observe this species frequently from spring through fall, either sunning on the muddy banks of Hilton Pond or floating lazily just below the water surface. We've also spotted them laying eggs nearly a quarter mile from the pond itself, so our current vantage point--about 50 yards from the dam--was well within turtle-walking range. The big question was whether this turtle met a violent death or died of natural causes, so we started thinking like Quincy and looking for more clues.

All text & photos © Hilton Pond Center

When we picked up the shell it was pretty obvious the turtle had been dead a long time. There was no odor except for that of the moist earth on which it sat, and the shell was so empty we could easily see through it from front end to rear (above). We carefully examined the carapace (top shell) for scratch marks that would have been left by a predator's teeth and found none, so the violent death hypothesis was becoming less plausible. We did note the bony plates of the shell were beginning to separate at their sutures, another sign that the turtle likely had been dead for quite a while (below right). These sutures were amazing in themselves; tiny, sharp projections of bone from one plate meshed perfectly with its adjoining member and helped explain how a turtle's shell can be so rigid even though it's made of many parts.

When we tipped the shell to look inside, several bones fell out, and what looked like a layer of brownish-black humus was stuck to the inside of the carapace. We could see a few more bones imbedded in this dark matter, so rather than lose any of them we placed the shell top-down on the ground. Then we examined more closely the earth beneath the spot where we first found the shell and, sure enough, there were even more bones there. We carefully sifted through the soil with our fingertips and came up with several undecomposed skeletal parts that we carefully placed in our jacket pocket. Then it was back to the old farmhouse to examine the find in our very own "CSI: Hilton Pond" Turtle Forensics Laboratory.

Our first task was to lay out all the large bones that had fallen from within the shell or that we had scavenged from the ground beneath it. This wasn't difficult because there were surprisingly few bones (below left). A few of them were similar to those in the human body: a lower jaw, some neck vertebrae, and what looked like paired pelvic bones and two heavy femurs. There were two bones with flattened ends that we thought were scapulas, but two others were unlike anything we'd seen in mammalian skeletons; each was "L-shaped," and formed a perfect right angle. We suspected they somehow served as leverage points for the front limbs. What was missing from the group was smaller arm and leg bones, and the many phalangial bones that make up turtle feet and toes. Aside from the neck bones, we weren't expecting to find any vertebrae, since those of the back are fused into the shell itself.

We were especially curious about the two "L-shaped" bones, so to find their function we spent some time Googling for "turtle skeleton" references on the Internet. Several sites--usually those created by university professors who teach comparative anatomy--had word descriptions, but not many had illustrations that showed just how many bones a turtle has or how they articulate. We finally found a photo of a mounted box turtle with its bones in place (below right), and from it learned that our guess about the function of the "L-shaped" bone was correct. The short leg of this bone, however, was the true scapula--the longer part is the "acromion"--and the flattened bone we thought was the scapula was actually the "coracoid." Together, these bones make up the pectoral girdle and--with the carapace--provide a strong skeletal frame to which foreleg muscles are attached. The strength of the hind limbs comes in part from the heavily fused bones of the pelvic girdle.

We were still a little perplexed about the absence of additional leg bones, however, and began to think that after our turtle had died some scavenger had come along and eaten all its appendages. That also might explain why we found the turtle's skull 15 feet away from the shell.

At this point we decided to remove the brownish-black material caked inside the turtle's carapace; holding the shell over a piece of newspaper, we gently scraped it out with a butter knife and a bottle brush--two important tools in the forensic science trade. Although the dark matter looked like humus, in retrospect it probably was rotten turtle parts, but it was so well-decomposed it had a clean, earthy odor. Out with this "dirt" came a few more larger skeletal parts--a humerus and three of the four lower leg bones--and, at long last, a whole bunch of phalanges from the turtle's various toes. There were even a few small tail vertebrae and three pointed, decurved claws, so maybe this turtle didn't get its parts eaten by a predator or scavenger after all.

While we were cleaning the shell of any remaining dirt and bones, we noticed that several paper-thin scutes covering bony plates of the shell were beginning to curl--likely because they were drying out in relatively low humidity of the old farmhouse. In a live turtle, these scutes--made of the same material as fingernails and animal horn--continue to grow and help protect underlying bone from disease and abrasion; you can rightly guess that the bottom scutes are especially important in a turtle called "Yellowbelly Slider." The edge of each scute closely follows the suture of the bone beneath it, so where the bony plates were separating in our empty turtle shell the scutes were also peeling away. When we held one of the carapace scutes up against the sky (below left), we could see it was translucent and that light passed through easily--revealing a pattern of brown lines and spots that are just as distinctive for a turtle as our fingerprints are for us. Scutes, by the way, are so impervious to rot that when a turtle dies they sometimes outlast the bony shell itself.

We thought for a while we would peel off all the scutes and keep the bare white turtle shell as a teaching tool, but portions of the anterior plastron (flat bottom shell) were so loose we decided to dismantle it. This turned out to be an interesting and productive activity because--as we broke away the plastron one plate at a time--we got an increasingly better view of the shell's interior. Eventually we removed all the plates to the left of the plastron's mid-line and peered at vertebrae that were fused to the inside ridge of the carapace (below). Such a configuration completely eliminated spinal flexibility for the turtle, but at least the slow-moving reptile never got backaches!

All text & photos © Hilton Pond Center

One question that arose as we marveled over the turtle's backbone was how impulses were transmitted from the animal's brain to its extremities. In humans the silvery-gray spinal cord is actually "outside" the main section of the vertebral column so that lateral nerve branching is unrestricted (right), but our turtle's thoracic and lower vertebra were plastered directly to the shell with no spaces above or between them. Peering a little closer inside the turtle shell, we found that each vertebra had a small circular hole--called a "foramen"--on each side (below left); these openings allow nerves to branch from the main spinal cord to control--and receive return signals from--a turtle's internal organs and appendages.

So that's the story of our initially mysterious turtle skull and all the things we learned by taking a close look at it. What a splendid creature the turtle is, whether viewed from outside or from within. Among the most ancient vertebrates on Earth, turtles have been around since at least the Triassic Period--more than 200 million years ago--and some species have changed very little in the last 20 million years. That's of little consequence to the turtle we found--after all, it IS dead--and despite our best efforts we still don't know if it died a peaceful death or met a violent end. It seems there just wasn't quite enough evidence for "CSI: Hilton Pond" to come to a conclusion, so we'll file this case as "unsolved."

One thing we DO know is what happened sometime AFTER the turtle died--based on one final clue we picked up as we cleaned out the contents of the turtle's dirty carapace. Among the loose bones and detritus we came across an item that most definitely did not originate from the turtle: A thin, quarter-inch oval disk with a black spot in the middle (below right). It was about the same color as old bone, but we knew from experience this was the pronotum (thoracic exoskeleton) of a familiar insect--the American Carrion Beetle--which certainly could be expected inside a dead turtle's shell. When any animal dies in nature, sooner or later "the worms crawl in and the worms crawl out," and some of those "worms" are actually the hungry larvae of carrion beetles. Again, we don't know for sure the circumstances of our turtle's death, but we DO know decomposers worked on it long enough to turn it into compost that now enriches the soil at Hilton Pond Center. We hope Quincy, M.E. and Newberry College's brand-new Forensic Chemistry program are pleased with our nature detective work.

All text & photos © Hilton Pond Center
Additional info on Newberry College's Forensic Chemistry program
Mounted turtle skeleton photo courtesy Santa Barbara City College Biology Dept.
Human spine drawing courtesy Spine University

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NOTE: Be sure to scroll down for an account of all birds banded or recaptured during the week, as well as some other interesting nature notes.

"This Week at Hilton Pond" is written & photographed
by Bill Hilton Jr., executive director of
Hilton Pond Center for Piedmont Natural History.

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22-31 January 2005

American Goldfinch--11
House Finch--3
Purple Finch--8
Northern Cardinal--2

* = New species for 2005

4 species
24 individuals

7 species
67 individuals

(since 28 June 1982)
124 species
45,374 individuals

All text & photos © Hilton Pond Center

This Week at Hilton Pond
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Nature Blog Network

(with original banding date, sex, and current age)


--A mild ice storm at mid-week brought down a few small limbs but otherwise resulted in little damage to vegetation or the old farmhouse at Hilton Pond Center. It did bring a heavy increase of feeder birds, primarily American Goldfinches, Purple Finches, and House Finches, with a few Brown-headed Nuthaches, Northern Cardinals, and Eastern Towhees to boot. Due to our recent eye surgery we weren't able to capitalize on this bad-weather bonanza, but did band 24 birds when the weather and our health improved on 30-31 Jan.


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