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Life Traces of the Georgia Coast: Revealing the Unseen Lives of Plants and Animals

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Have you ever wondered what left behind those prints and tracks on the seashore, or what made those marks or dug those holes in the dunes? Life Traces of the Georgia Coast is an up-close look at these traces of life and the animals and plants that made them. It tells about the how the tracemakers lived and how they interacted with their environments. This is a book about ichnology (the study of such traces), a wonderful way to learn about the behavior of organisms, living and long extinct. Life Traces presents an overview of the traces left by modern animals and plants in this biologically rich region; shows how life traces relate to the environments, natural history, and behaviors of their tracemakers; and applies that knowledge toward a better understanding of the fossilized traces that ancient life left in the geologic record. Augmented by numerous illustrations of traces made by both ancient and modern organisms, the book shows how ancient trace fossils directly relate to modern traces and tracemakers, among them, insects, grasses, crabs, shorebirds, alligators, and sea turtles. The result is an aesthetically appealing and scientifically accurate book that will serve as both a source book for scientists and for anyone interested in the natural history of the Georgia coast.

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1 Introduction to Ichnology of the Georgia Coast

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I n troduction to Ich nology of th e Georgi a Coa st   3

aged about 10 cm (4 in) between each step, and decreased as it approached the bivalve. In these tracks, its digits pointed slightly toward the midline of the body, giving the trackway a pigeon-toed appearance. Its feet came together again and just to one side, followed by much shuffling in the same small area. The tracks were about 5 cm (2 in) long and almost as wide. These indicated feet with three narrow digits, widely spaced but all pointing forward, and a thin, curved line denoted webbing toward the ends of these forward-facing toes. A nub of a toe, its mark rarely seen, was at the rear of the tracks, and faint claw marks accented each digit.

I expanded the search for more clues. Spiraling outward from the shell remains, I looked for other indentations made by the clam bouncing on the sand flat, and found two more. One of these marks was near a shallow excavation, a vertically oriented hole in the sand that matched the external profile of the entire bivalve. This is where the clam had started its airborne exploits. Within a meter (3.3 ft) of the bivalve resting trace were the paired tracks of the same bipedal animal seen at the scene of the bivalve’s demise.

 

2 History of the Georgia Coast and Its Ichnology

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2

H ISTORY OF T H E GEORGI A COAST

A N D I TS ICH NOLOGY

A R ISI NG SEA, A ND L IF E T R ACES ON T HE MOV E

About 55,000 years ago, as the earth warmed and glaciers melted, the barrier island moved across the landscape in synch with the rising sea. Its oceanward side shifted to the west toward the coastal plain, and its resident biota adjusted and adapted to new locales. Laterally adjacent environments began to succeed one another vertically, and in this instance, the sands of offshore environments piled onto new surfaces scoured out of formerly onshore environments. Salt marsh mud also swelled in area and volume, spreading throughout low-lying areas, as forests and other terrestrial environments were displaced and replaced. Life in all of these environments—maritime forests, dunes, back-dune meadows, freshwater swamps, salt marshes, tidal creeks, beaches, and shallow subtidal sandy bottoms—flowed and ebbed like the tides, and all attendant traces of plant and animal behavior were transplanted with their substrates.

 

3 Tracemaker Habitats and Substrates

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3

T R ACEM A K ER H A BI TATS

A N D SU B ST R AT ES

CH A NGE I N A F EW EASY ST EPS

I nearly stepped on the snake, mistaking it for a stick on the trail leading into maritime forest. My oversight was understandable, as the trail was cluttered with branches, leaves, and pine needles, and the snake was relatively small, only about 50 cm (20 in) long. It was also stiff and torpid from the cool shade cast by the long shadows of late afternoon, helping it to blend in with other nearby twigs. Sensing a learning opportunity that could not be ignored, I reached down to pick it up, and it responded by writhing slowly and gently along my forearm. Nonetheless, a few students behind me screamed when they realized what I held. I was amused that my Moses impression had provoked such a response, and I waited a few seconds until their anxiety lessened before talking about snakes, their tracemaking, their habitats, and the substrates of those habitats.

The trail was well known to me because of many field trips led along it, and that day was another one. I was accompanied on this trip by a large group of students and my friend and colleague, Steve Henderson from

 

4 Marginal-Marine and Terrestrial Plants

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4

M A RGI NA L -M A R I N E A N D

T ER R EST R I A L PL A N TS

T HE PR ESERVAT ION OF ROOT EDNESS:

A TALE OF T WO ISL A NDS

It was July 2001, and two full days of fieldwork on Sapelo Island had nearly exhausted our small band of five ichnologists and three eager undergraduate assistants, but in a good way. During those days, we had perused two extensive beaches—Nannygoat and Cabretta, both among my favorite beaches in the world—and looked at these and their dunes for invertebrate and vertebrate traces. So far, we had been rewarded with many ichnological observations and insights. Moreover, the second day was highlighted by a visit to a relict marsh at the north end of Cabretta Beach. Relict marshes, mentioned earlier (Chapter 3; Figure 3.12), are neither fossil nor modern marshes, inhabiting a nether world in between. Because of their relatively recent entry into the geologic record, they present rare opportunities for ichnologists to witness an ecosystem shift from one fully breathing and recycling its nutrients to an inert, stony vestige of its former self. A few of my ichnologist colleagues had read about this one on Sapelo but had never seen it, and they eagerly anticipated the enhanced learning that inevitably stems from direct experience.

 

5 Terrestrial Invertebrates

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T ER R EST R I A L

I N V ERT EBR AT ES

T HE CR AY F ISH OF JEK YLL ISL A ND

I was surprised, yet not surprised, to find out I was wrong. This feeling of humility is a common one among scientists, especially natural scientists who go outside to test what they learned indoors, whether this knowledge was gained through books, journal articles, Web sites, hearsay, or Web sites repeating hearsay. The habit of correction becomes even more acute among ichnologists, particularly when we practice actualism: What are the traces being made by modern organisms, and where are these traces?

Traces, as the products of behavior that form whether humans witness it or not, also often point toward an animal presence in places that defies our expectations. In this particular instance, the traces were burrows, the animals were freshwater crayfish, and the place was Jekyll Island on the

Georgia coast.

Although Web pages, just like books (yes, this one too), are never to be trusted completely, the brief item I encountered while reading one—stating that Jekyll Island had freshwater crayfish—was intriguing news. For the previous several years, I had assumed that none of the Georgia barrier islands should have these animals. My reasoning was based largely on

 

6 Marginal-Marine Invertebrates

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M A RGI NA L -M A R I N E

I N V ERT EBR AT ES

T HE DEAT H SPIR AL T H AT ONLY SPIR A LED

No matter how many times I visit the beaches of Sapelo Island, its sediments always hold surprising traces. On this particular morning in June

2008, my wife, Ruth, found the wonder-inducing trace of the day and directed me to it, just before she left to show some of our companions a fresh sea turtle trackway further south on the beach. This was also well before my ichnologic partner in crime solving, Andy Rindsberg, of the University of

West Alabama, joined me. What could be more interesting to an ichnologist than an expectant sea turtle’s trackway and her probable nest structure, made mere hours before? Something much more primeval beckoned us, a tug that pulled me back into the Paleozoic Era instead of the mere Mesozoic. The latter was when sea turtles evolved from their land-dwelling ancestors, but the Paleozoic connected with a time before any four-legged animal walked on land. The beguiling trace of the day was made by a large adult limulid (Limulus polyphemus), popularly known as a horseshoe crab, that most archaic of marginal-marine arthropods available for us ordinary,

 

7 Terrestrial Vertebrates, Part I: Fish, Amphibians, Reptiles

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7

T ER R EST R I A L V ERT EBR AT ES,

PA RT I

Fish, Amphibians, Reptiles

T HE ALL IGATORS T H AT W EN T TO T HE BEACH

One July morning, on what promised to be another hot day, our merry group of ichnologists walked along Cabretta Beach on Sapelo Island at low tide and stared at the sand, a typical activity for those with our interests. After all, we were keenly interested in the burrows and tracks left by animals in the extensive sand flats of this beach; moreover, we could do it privately, as our footprints were the only human traces added to the assemblage. Thus we were understandably distracted enough to not notice that one member of our group—Jon Garbisch, the UGAMI education coordinator—had disappeared. This fact became apparent as soon as he popped up in front of us, his rematerialization accompanied by a grin—a sort of Cheshire cat in reverse. With this, he then announced happily, “Wait till you see what’s around the corner!” No matter how much we pleaded, he would not divulge what could possibly interest all of us so much, especially with so many other distracting traces nearby. Our curiosities thus properly provoked, we quickened our pace at the northern end of the beach and turned sharply left toward a small tidal channel dividing the beach from a salt marsh. The

 

8 Terrestrial Vertebrates, Part II: Birds and Mammals

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8

T ER R EST R I A L V ERT EBR AT ES,

PA RT I I:

Birds and Mammals

PL AY I NG ’POSSU M A ND DR. BUZZA R D

I could not help but notice the dead body of the opossum (Didelphis virginiana), a dark lump on an otherwise light brown sandy road, as I traveled through Hog Hammock (Sapelo Island) that last morning of July. Squinting through the dusty windshield of a UGA Marine Institute pickup truck,

I slowed the vehicle and unrolled the driver’s-side window to get a peek at its corpse. Judging from the shiny flecks of blood around part of the body, the opossum was freshly killed. Its position on the right-center side of the road implied it was walking across the road from the left, a supposition based on the location of a maritime forest (the opossum’s probable former home) to the left, or west. So the opossum probably met its demise from a motor vehicle driving north (the same direction I was heading) as it walked from west to east. I noted the time—8:25 a m—and figured that it must have been struck less than an hour beforehand. With this mixture of observations and hypotheses duly noted, I did not pause long. My foot pressed on the accelerator and the truck lurched and rumbled forward in response. Other learning opportunities awaited in the northeastern corner

 

9 Marginal-Marine and Marine Vertebrates

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M A RGI NA L -M A R I N E A N D

M A R I N E V ERT EBR AT ES

A TALE OF TURTLE T R ACKS

Sea turtle trackways are perhaps the most impressive of marginal-marine vertebrate traces anyone can stumble upon on a Georgia beach, and this one was no exception. But because my wife, Ruth, and I were infrequent visitors to the coast, we had never seen one in all of its glorious three dimensions. Its presence that June morning was enhanced by its freshness, telling us that its tracemaker had been on Nannygoat Beach of Sapelo Island only four or five hours beforehand. Other prominent traces in the area were of a turtle patrol vehicle (an all-terrain vehicle, or AT V) that abruptly decelerated just after intersecting the trackway, turned sharply to the left, and looped back to stop. Based on the driver’s tracks, she then spent much time at the end of the trackway, no doubt collecting data that would be analyzed later for its contribution to the larger scheme of understanding sea turtle nesting on the Georgia coast.

 

10 Trace Fossils and the Georgia Coast

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10

T R ACE FOS SI L S A N D

T H E GEORGI A COAST

Y ELLOW BA NKS BLUFF DECODED

Yellow Banks Bluff on St. Catherines Island is one of those places where the people who named it limited themselves to pure description and allowed for no flights of fancy. It is indeed a yellowish, banked bluff, forming an outcrop about 4 m (13.1 ft) tall and 600 m (1,970 ft) long, extending much of the length of a beach on the northeast corner of the island (Figure 10.1a).

The first time I saw it was with about 30 other people on a geology field trip in the spring of 2007. The trip was associated with and just before a regional meeting of the Geological Society of America, held in nearby Savannah,

Georgia, that year. Our group rode in ATVs, four to five people per vehicle, zooming down the beach and weaving between downed oaks and pines, the former living parts of the maritime forest just above the bluff, but now victims of sea-level rise and coastal erosion (Chapter 2). This fast-forward way of viewing was definitely not my style—too many traces on the beach were missed along the way—but was essential for us to reach a particular part of the outcrop in a timely way. Once there, the field trip leaders would educate us about its geologic significance, with plenty of time left over to eat dinner, drink adult beverages, and mentally digest what we had seen that day.

 

11 Future Studies, Future Traces

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11

F U T U R E ST U DI ES,

F U T U R E T R ACES

LOOK I NG FOR T R ACES I N ALL T HE W RONG PL ACES

A self-deprecating realization struck me in the middle of the fall of 2008, as startling as looking in a mirror and suddenly noticing a large, unsightly growth projecting from the side of my head. I had been spending too much time inside lately, devoted largely to teaching classes; grading exams (or, more likely, putting off their grading); committee meetings; reading, writing, and sending e-mails; and, once in a great while, in between all of these activities, reading about traces, trace fossils, and ichnology in general.

In contrast, too little had been devoted to fieldwork, especially tracking.

Tracking and neoichnology in general are similar to the use of another language, where skills atrophy with disuse, become tattered around the edges, and otherwise become traces themselves of knowledge and wisdom once held so keenly. Yes, some of that previous experience can be put in the bank, so to speak, but if left alone, it does not gain any interest.

 

APPENDIX

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Appendix

Modern tracemakers of the Georgia barrier islands, including recently extirpated organisms and nonnative species. List is organized alphabetically by genus and species, and sorted according to broad taxonomy (plants, invertebrates, vertebrates) and habitats (terrestrial–freshwater and marginal-marine).

Terrestrial–Freshwater Plants

Acer rubrum—red maple

Aristida stricta—wiregrass

Cladium jamaicense—giant sawgrass

Equisetum spp.—scouring rushes

Gordonia lasianthus—loblolly bay

Ilex opaca—American holly

Ilex vomitoria—yaupon holly

Magnolia grandiflora—southern magnolia

Magnolia virginiana—sweet bay

Myrica cerifera—wax myrtle

Nymphaea stellata—water lily

Peltandra virginica—green-arrow arum

Persea borbonia—red bay

Pinus echinata—short-leaf pine

Pinus elliottii—slash pine

Pinus palustris—long-leaf pine

Pinus serotina—pond pines

Pinus taeda—loblolly pine

Polypodium polypodioides— resurrection fern

Pontederia cordata—pickerel weed

Quercus laurifolia—laurel oak

Quercus virginiana—live oak

Sagittaria latifolia—arrowhead

 

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