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5 Terrestrial Invertebrates

Anthony J. Martin Indiana University Press PDF

5

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

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8 Terrestrial Vertebrates, Part II: Birds and Mammals

Anthony J. Martin Indiana University Press PDF

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

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2 History of the Georgia Coast and Its Ichnology

Anthony J. Martin Indiana University Press PDF

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.

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

Anthony J. Martin Indiana University Press PDF

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

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4 Marginal-Marine and Terrestrial Plants

Anthony J. Martin Indiana University Press PDF

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.

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