Biology of Sharks and Their Relatives

Jeffrey C. Carrier, Colin A. Simpfendorfer, Michael R. Heithaus, Kara E. Yopak, Jeffrey C. Carrier, Colin A. Simpfendorfer, Michael R. Heithaus, Kara E. Yopak

• Publisher: CRC Press
• Year: 2022
• ISBN:
  9781000542097
• Edition: 3
• Topic: Biological Sciences
• Subtopic: Zoology
• Index: Biological Sciences

Biology of Sharks and Their Relatives is an award-winning and groundbreaking exploration of the fundamental elements of the taxonomy, systematics, physiology, and ecology of sharks, skates, rays, and chimera. This edition presents current research as well as traditional models, to provide future researchers with solid historical foundations in shark research as well as presenting current trends from which to develop new frontiers in their own work.

Traditional areas of study such as age and growth, reproduction, taxonomy and systematics, sensory biology, and ecology are updated with contemporary research that incorporates emerging techniques including molecular genetics, exploratory techniques in artificial insemination, and the rapidly expanding fields of satellite tracking, remote sensing, accelerometry, and imaging.

With two new editors and 90 contributors from the US, UK, South Africa, Portugal, France, Canada, New Zealand, Australia, India, Palau, United Arab Emirates, Micronesia, Sweden, Argentina, Indonesia, Cameroon, and the Netherlands, this third edition is the most global and comprehensive yet. It adds six new chapters representing extensive studies of health, stress, disease and pathology, and social structure, and continues to explore elasmobranch ecological roles and interactions with their habitats. The book concludes with a comprehensive review of conservation policies, management, and strategies, as well as consideration of the potential effects of impending climate change.

Presenting cohesive and integrated coverage of key topics and discussing technological advances used in modern shark research, this revised edition offers a well-rounded picture for students and researchers.

1 Bridging the Gap Between Chondrichthyan Paleobiology and Biology

Lisa B. Whitenack, Sora L. Kim, and Elizabeth C. Sibert

CONTENTS

Abstract

1.1 Introduction

1.2 The Nature of the Chondrichthyan Fossil Record

1.3 Evolutionary History

1.3.1 Relationships of Early Chondrichthyans

1.3.2 Paleozoic Chondrichthyans (Reign of the Holocephali)

1.3.3 Mesozoic and Cenozoic Chondrichthyans (Reign of the Elasmobranchii)

1.3.4 Chondrichthyan Diversity Patterns in the Phanerozoic

1.3.5 Implications of Fossil Chondrichthyan Diversity Patterns for Today’s Chondrichthyans

1.4 Fossil Chondrichthyan Biology

1.4.1 Macroecology Trends

1.4.2 Functional Diversity

1.4.3 Where Did Sharks Live?

1.4.4 What Did Sharks Eat?

1.4.5 How Do Sharks Work?

1.5 Leveraging the Fossil Record for Conservation

1.6 Conclusion: Bridging the Gap Between Paleobiology and Biology

Acknowledgments

References

ABSTRACT

Chondrichthyans have a long evolutionary history, reaching back over 450 million years. Despite the longevity of the chondrichthyan fossil record, it is remarkably incomplete. This chapter focuses on chondrichthyan paleobiology, which, as the name suggests, applies techniques from both biology and geology to understand the biological processes and ecology of the once-living organism. Paleobiology is highly interdisciplinary, employing tools from mathematics, computer science, physics, chemistry, and engineering. The chapter begins with an overview of chondrichthyan evolutionary history, from the relationships of early chondrichthyans through the implications of fossil chondrichthyan diversity patterns on today’s chondrichthyans. The chapter then discusses what scientists know about fossil chondrichthyan biology in areas such as macroevolutionary trends, functional diversity, ecology, and biomechanics. Finally, the chapter discusses how the fossil record can be leveraged for conservation efforts. Knowledge of how organisms responded to and recovered from times of environmental disturbance or higher extinction rates can help us understand how contemporary organisms are responding to the current mass extinction crisis and how negative impacts might be mitigated. Integration across biology and paleobiology will further our collective knowledge of chondrichthyan ecology and evolutionary history to inform our conservation and management policies, as well as to mitigate anthropogenic impacts.

1.1 INTRODUCTION

Scientific studies of living (extant) chondrichthyans cover almost every imaginable subfield of biology, whether they are the particular subject of interest or are being used as a model organism. The table of contents of this book reflects the former, covering everything from molecular (e.g., biochemistry and genetics) to broad ecosystem studies and considering the past, present, and future of chondrichthyans on Earth. Here we focus on chondrichthyan paleobiology, which, as a discipline, is different from paleontology. Paleontology focuses on taxonomy; it treats chondrichthyan fossils as sediments in an effort to better understand depositional environments. Paleobiology, as the name suggests, applies techniques from both biology and geology to understand the biological processes and ecology of the once-living organism.

Chondrichthyans have a long evolutionary history, reaching back over 450 million years (Ma) (Andreev et al. 2015; Burrow et al. 2019; Ginter 2004; Sansom et al. 2012; Turner 2004). Throughout their time on the planet, these charismatic vertebrates have repeatedly filled a wide variety of ecological niches, ranging far beyond the pelagic predators of today’s best known shark communities. Despite the longevity of the chondrichthyan fossil record, it is remarkably incomplete. This is not a phenomenon that is unique to chondrichthyans; most paleontologists have heard some variant of the statement “less than 1% of all organisms that have lived on Earth have been preserved in the fossil record.”

A recent study by Shiffman et al. (2020) examined the over 30-year history of abstracts submitted to the American Elasmobranch Society (AES) and found that the most common research areas for members of this society, such as reproductive biology, movement/telemetry, age and growth, and population genetics, are linked to conservation and fisheries management. If we take a broader view beyond AES and search Google Scholar for “Chondrichthyes,” limiting our search to “2019 through 2021,” we come up with about 3400 results. A similar search for “shark” yields about 17,000 results. In addition to many of the themes identified by Shiffman et al. (2020), we also see studies on micro- to macroevolutionary processes (e.g., Fonseca et al. 2019; Jambura et al. 2020), genomics (e.g., Weber et al. 2020), developmental biology (e.g., Pears et al. 2020; Smith et al. 2020), parasitology (e.g., Schaeffner and Smit 2019), and even the production of biodiesel from shark liver oil (Al Hatrooshi et al. 2020). This is also where we see the studies that fall under the category of paleontology. Most of those papers describe new species or genera from various times during the last 450 Ma (e.g., Brito et al. 2019; Sokolskyi and Guinot 2021; Stumpf and Kriwet 2019; Villalobos-Segura et al. 2019).

Like many other fields of biology, paleobiology is highly interdisciplinary and employs tools from mathematics, computer science, physics, chemistry, and engineering (Figure 1.1). In fact, if we compare the description of the journal Paleobiology to the sections of this book, we find many of the same themes: evolution, morphology, molecular biology, ecology, adaptation, and extinction. There are numerous similarities in what these two groups of scientists are studying; however, the language and scope, both temporal and spatial, can be barriers to collaboration (Table 1.1). For example, marine conservationists and conservation paleobiologists agree on conservation goals, such as establishing baselines, and that long-term data should be used for these goals. However, the definition of “long-term” differs, with conservation paleobiologists operating on the geological time scale, considering thousands or millions of years at a time, and marine conservation scientists operating on the order of decades (Smith et al. 2018).

FIGURE 1.1 Disciplines and subdisciplines that are used in the field of paleobiology.

TABLE 1.1 Concepts and Areas of Study Common to Neontology and Paleobiology and Data Used in Each Field

	Data Type
Concept	Neontology	Paleobiology
Taxonomy and systematics	Molecular data and morphology	Morphology (mostly tooth shape)
Evolution and phylogeny	Molecular data and morphology	Morphology (mostly tooth shape)
Reproductive biology	Physiology	Morphology of reproductive anatomy when preserved, fossilized egg cases, fossilized fetal material
Age and growth, life history	Embryology, vertebral rings	Vertebral rings, tooth size
Biomechanics and functional morphology	Anatomy, morphology, performance testing, models	Anatomy, morphology, performance testing, models
Diet and feeding ecology	Behavioral data, stomach contents, stable isotopes, food web mapping and dynamics	Stable isotopes (geochemistry), trace fossils, concurrent fossils as potential prey (assemblage descriptions), tooth morphology
Community ecology	Biodiversity indices	Assemblage description, community structure, biodiversity indices
Population biology	Population dynamics	Body size distribution, latitudinal gradients
Biogeography and distribution	Movement and telemetry data, population genetics, latitudinal gradients	Body size distribution, latitudinal gradients, data from the Paleobiology Database
Conservation and management	Population assessments, movement and telemetry data, ecological data	Extinction and speciation rates
Note: This concept list is based on the contents of this volume and Shiffman et al. (2020).

The overlap in research themes suggests an opportunity to bring two groups of researchers together. With this in mind, we have written this chapter to serve as a resource for those who are new to the chondrichthyan fossil record, those who are interested in how to apply techniques from neontology (biology of living organisms) to extinct chondrichthyans, and those who are interested in how to leverage the extensive chondrichthyan evolutionary history (over 450 Ma, which includes surviving several mass extinction events) for their research on extant chondrichthyans. We begin with a synopsis of the chondrichthyan fossil record, followed by an overview of chondrichthyan paleobiology. We end by examining the ways in which the chondrichthyan fossil record can be leveraged to provide new insights into chondrichthyan conservation biology.

1.2 THE NATURE OF THE CHONDRICHTHYAN FOSSIL RECORD

A number of factors determine an organism’s likelihood of fossilization, including the supply and durability of remains, nature of the pre-burial environment, rate and permanence of burial, diagenetic (fossilization) conditions, and the fate of the larger sedimentary body that remains are buried in (Behrensmeyer et al. 2000). The factors determining fossilization outside of supply are largely determined by the physical, chemical, and biological components of the environment in which the organism dies (or where teeth are shed, in the case of sharks) (Behrensmeyer et al. 2000). Burial is the first hurdle to overcome. Without rapid burial, remains are exposed to environmental conditions that may cause too much damage, and tissues are not subject to the chemical processes necessary for fossilization. Biological agents largely determine whether remains are buried or remain buried before they are destroyed by exposure to destructive forces; the actions of bioturbators, bioeroders, and scavengers tend to decrease the likelihood of fossilization, whereas organisms that form dens or burrows may increase the likelihood of fossilization if they bury remains as part of the burrow-building process (Behrensmeyer et al. 2000; Feichtinger et al. 2020a; Maisch et al. 2019; Underwood et al. 1999). Physical reworking from storm events or wave action can also prevent remains from staying buried. Provided that remains stay buried, chemical alteration is the next step. This process can occur through physical means, such as seawater infiltration, or can be aided by microbes (Carpenter 2005; Hedges 2002; Nemliher et al. 2004; Wang and Cerling 1994). In the ideal scenario, the remains are made more stable or durable through the replacement of materials with harder minerals, although replacement is not required for preservation in the fossil record, and some chondrichthyan remains retain their original bioapatite. Finally, the rocks and sediments that encase these altered remains must remain intact. Geologic processes, such as structural deformation and erosion from glaciers, water, or wind, can remove rock strata and their fossils from the geographic record entirely.

Many chondrichthyans fare well in terms of their input into the potential fossil record, although some parts of the skeleton are far less likely to fossilize than others (Figures 1.2 and 1.3). Whole-body fossils of chondrichthyans are quite rare (but see Ehret et al. 2009; Grogan et al. 2012; Marramà et al. 2018; Williams 2001), because most skeletal cartilage is poorly mineralized. Teeth, on the other hand, are the most common chondrichthyan fossil (Cappetta 1987; Cappetta and Schultze 2012; Ginter et al. 2010). Teeth in elasmobranchs and other extinct groups are constantly shed throughout their lifetimes and at a fairly high rate (Moss 1967; Luer et al. 1990; Reif et al. 1978; Wass 1973). Teeth are extremely durable, thanks ...