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category: Paleontology
Secrets of the Shoreline Revealed by Tracks in the Sands of Time
Life Traces of the Georgia Coast: Revealing the Unseen Lives of Plants and Animals, by Anthony J. Martin, 2013, Indiana University Press, Bloomington, Indiana, 670 pp., ISBN 978-0-253-00602-9

Secrets of the Shoreline Revealed by Tracks in the Sands of Time

Post: May 15, 2013 2:31 pm
Author: Sally Walker         Source: TVOL Exclusive

Life Traces of the Georgia Coast: Revealing the Unseen Lives of Plants and Animals, by Anthony Martin, is a paean to the diversity of barrier island life that is underfoot and often overlooked in our fast-paced adventures through life. But Dr. Martin asks you to stoop and marvel at the astounding antics of the ant lion, the carnivorous peregrinations of predatory snails, and the willful wallowing of pigs or birds. If you thought a barrier island was just sand and surf, once you gleefully wade through the watery and terrestrial recesses of every barrier-island habitat presented in this book, you will be astounded at the teaming life forms and their graffiti that encodes their behavior in the sands of time.

Martin's book is about how to read animal or plant behavior from their traces, such as footprints, burrows or other forensic evidence left in sand, soil, mud, shells or plants. The fossilized equivalents of this behavior are known as trace fossils (ichnofossils) that are essential for reconstructing ancient ecologies and environments. Martin also provides behind-the-scenes musings of what it is like to be an ichnologist (a trace-fossil scientist) and details his discoveries concerning crayfish burrows, for example, and the process that led to his interpretation. In a way, his book reads like a field trip, filled with his friends, colleagues and students, gesticulating and arguing over what a trace may be, providing minute detail on the size of the burrow or track, followed by an elaborate reconstruction of the behavior of the trace maker.

My favorite part of the book details the lives of bees and wasps and other insects. Bees leave traces of their activity as burrows in soil or wood while parasitoid wasps have complex brooding chambers large enough for their larvae and the parasitized prey upon with the larvae feed. Ant lions, noted for their circumnavigations just under the sand that look like doodles, hence the apt name, "doodle bugs", are ravenous for ants and other insects. They make funnel-like holes in the sand that are excellent pit traps for the unsuspecting prey. After seeing Teshigahara's movie, "Women in the Dunes," I have a deep respect for ant lions. Martin gives them serious treatment, down to the last drop of juices sucked out of the unfortunate prey.

Life Traces is organized into sections based on plants, invertebrate and vertebrate trace makers. The last chapters provide a foray into trace-fossil science focusing on ichnofacies analysis (using traces as environmental guides) and suggestions for future studies on unsolved ichnological issues. The organization of the book was sometimes difficult to follow. It would be helpful to have the book divided into two sections based on environment such as, Part I: Terrestrial and freshwater habitats and Part II: Beach and intertidal habitats. Within those subsections would be chapters on the groups of organisms (invertebrates, vertebrates). I found myself more than once flipping between chapters and pages to track down information. If one has more time, the book is an enjoyable read, but if one is pressed for time, the page flipping can be a bit frustrating. Fortunately, there is an excellent and comprehensive index that facilitates retrieval of information sprinkled among the chapters. The following provides a brief chapter-by-chapter overview of the topics covered in this hefty and comprehensive tome to traces:

Chapter 1 introduces the reader to the study of ichnology and clearly separates body fossil traces (i.e., leaf impressions) from those studied in the ichnological realm (e.g., tracks, trails, burrows, predation marks). It introduces the reader to the three pillars of ichnological wisdom: substrate, behavior and anatomy that affect the nature and cohesiveness of the trace. A figure illustrating different traces found in Georgia barrier islands (Fig. 1.3) was wonderful, but I wish it were larger so that the surface and subsurface of the landscape can be clearly delineated and the traces labeled. This would be especially helpful for people who are not familiar with organismal traces and whet their appetite for what is to follow in the rest of the chapters.

Chapter 2 discusses the formation of the Georgia barrier islands, the early history of human occupation, and the development of using modern traces in marine ecosystems to interpret the rock record. Martin's Ph.D. professor, Robert Frey, along with his colleagues, James Howard and George Pemberton, revealed the importance of studying modern traces from Sapelo Island, a beautiful Spanish-moss and live-oak covered barrier island of Georgia. A wonderful picture of Robert Frey, taken by Steve Henderson another of Dr. Frey's Ph.D students, shows Frey in his element, the tidal flats of Sapelo Island where he discovered and documented much of what we know about barrier island traces. The fossil equivalent of modern traces, ichnofossils, are instrumental for oil prospecting, parameterizing geochemical cycling and for documenting past ecosystems and environments.

Chapter 3 provides an overview on the diversity of barrier island habitats and their associated traces. Traces that can be seen on the surface of the sediment and those that occur below the sediment are discussed for terrestrial, freshwater, dune, beach and tidal flat habitats. Included in this section is a relatively unique habitat, a relict marsh. At one time a healthy marsh was buried by sand that killed the marsh occupants. When exposed years later, the subfossil marsh is reinvaded by living plants and animals that rework the older deposit. Thus, the relict marshes become a palimpsest surface, although unlike the true derivation of the term, the old marsh's biotic record was not scraped clean, just overprinted with modern organisms. This is a welcome addition as it shows that trace fossils can also be time-averaged, with overprinting by successive generations of trace makers.

Chapter 4 reveals the astonishing ichnological traces associated with barrier island plants, concentrating on root traces from terrestrial trees (pines, oaks), dune plants (sea oats) to saltmarsh grasses (glasswort, cord grass). Insect galls and herbivory on leaves are also discussed, with the chapter suggesting topics for further research in plant: sediment interactions.

Chapter 5 plunges into the hidden world of freshwater and terrestrial invertebrate traces, starting first with crayfishes, one of Dr. Martin's favorite creatures, then moving to scorpions, insects, earthworms, snails and millipedes. What is wonderful about this chapter is that it goes into more detail about the fossil record of these traces, showing that many of the modern traces have a deep fossil record, often extending to the Paleozoic Era.

Chapter 6 wades into the frothy sea foam region of the intertidal zone to explain the myriad invertebrate traces found in beach and tidal flats. This chapter unfolds in systematic order, starting with bioeroding sponges and ending with our nearest relatives, the acorn worms (hemichordates such as Balanoglossus). Recycling of carbonate by shell-chipping sponges and shell-drilling or shell-prying predatory snails are discussed in lively detail, as are the shell-dragging antics of hermit crabs and the burrowing expertise of mole crabs. Wood- and bone-boring bivalves are also on display here. Unusual squiggles resulting from a sea star stranded by the receding tide are also illustrated, along with the squeezed toothpaste-like mass of Balanoglossus fecal strings. Unlike the previous chapter, less is discussed about the antiquity of these traces in the fossil record.

Chapter 7 is a wonderful foray into terrestrial and freshwater vertebrate traces focused on fish, reptiles and amphibians. A basic guide to tracking is also proffered in this chapter. Fish swimming trails, alligator tail scrapes, mud turtle trackways, along with dragging frog feet and remarks on salamanders are characterized along with wonderful depictions of freshwater and non-freshwater turtle and tortoise, respectfully, nesting sites. Sharing tortoise burrows are often snakes, such as rattlesnakes. Martin points out at the end of the chapter that little is known about how seasons affect the diversity and distribution of vertebrate traces.

Chapter 8 starts off with a dead, bloody opossum and their buddies in death, the vultures and their morbid totentanz. The evisceration of the former is documented in gory detail--down to plucking the eyes out-- to illustrate the fact that scavenging organisms can greatly decrease what gets preserved in the fossil record. The majority of the chapter, however, is about bird and mammal feeding traces, nests or burrows, tracks and other traces. No chapter on this topic would be complete without armadillos, the wily armored and leprosy-carrying placentals that are slowly making their way up the east coast of the United States from their ancestral homeland in South America. The nine-banded armadillo, as Martin expounds, produces the most ubiquitous and abundant mammalian traces on the Georgia coast. Their burrows are often lined with leaf debris, which may make them recognizable in the fossil record, and their digging traces are distinct. Martin also gives us, forgive me Karen Chin, the scoop on mammalian barrier island poop, albeit, thankfully short and not in complete scatological detail.

Chapter 9 takes us to the dune and beaches to look for sea turtle traces, and along the way, telling us about the importance of barrier islands for nesting sea turtles. In tidal flats, stingray traces abound but Martin doesn't stop there, as he lists the many toothy sharks that occur in the seawaters offshore of the tidal flats and the fossil shark tooth marks reported from Pliocene whalebones and Cretaceous dinosaur bones preserved in the southeastern United States. Nothing is more
reaffirming than to see alligator trackways on the beach right after you emerge from an invigorating swim. Martin calms us by telling us about other's observations that alligators voraciously gulp down horseshoe crabs in the surf zone of barrier islands. Just when you thought it was safe to go into the water…fortunately, after discussing alligators, birds are treated in great detail right down to their beak marks, feces and footprints. Carcasses of bird prey and bird vomit are also depicted, and thankfully I wrote this after lunch. Traces from mammals, like mice and manatees, are also discussed.

Chapter 10 takes us from the modern wind-and-wave swept beaches and billowing maritime forests of barrier islands to give us a heuristic introduction to fossil ichnology. After detailing a project Martin was involved in, he then discusses how trace fossils are named and outlines how trace fossils affect the layering of sediments in the rock record by discussing the study of ichnofacies and ichnofabric analysis. He then summarizes the variety of potential ichnofacies found on Georgia's barrier islands. This chapter is aimed more for the student and worker in the field of ichnology, but is intriguing for anyone curious about how trace fossils are classified and used in paleoenvironmental analysis.

The last chapter, Chapter 11, enlightens us about how technology is revolutionizing the study of ichnology. Importantly, Martin outlines how traces can be used to document the behavior of invasive species and summarizes areas where research is still needed in ichnological studies.

Life Traces appears to be written for master naturalists, upper-level students, or scientists with knowledge of biological, geological and ecological terms and concepts. For a teacher who takes students to beaches or barrier islands, this is an excellent comprehensive guide that reveals the surface and depths of traces found in maritime forests, dunes, beaches and tidal flats. Martin's book is not just a low country boil, it is a feast salted with humor and insights. The book's cover is a beautiful and bright watercolor by acclaimed artist Alan Campbell, and the photos and illustrations are mostly by Dr. Martin or his wife, Ruth Schowalter. The best way to enjoy this book is to take it to a beach or barrier island near you and explore the diversity of traces!



Sally Walker is a professor in the Geology Department at the University of Georgia. She works in the field of fossil forensics (taphonomy). She is a Fellow of the American Association for the Advancement of Science and enjoys the southeastern barrier islands, among the most beautiful and fragile ecosystems of the world.