USING DENTAL MICROWEAR ANALYSIS FOR ...hardness and size available to a predator (Budney et al. 2006). Presence of a cementum-covered root situated in a deep socket and presence of

USING DENTAL MICROWEAR ANALYSIS TO PREDICT FEEDING

TYPES IN MESOZOIC MARINE REPTILES

A THESES PRESENTED TO THE DEPARTMENT OF BIOLOGY

IN CANDIDACY FOR THE DEGREE OF MASTER OF SCIENCE

By

JEREMY MARK POYNTER

NORTHWEST MISSOURI STATE UNIVERSITY MARYVILLE, MISSOURI

AUGUST 2011

Running Head: DENTAL MICROWEAR IN MESOZOIC MARINE REPTILES

Using Dental Microwear Analysis to Predict Feeding

Types in Mesozoic Marine Reptiles

Jeremy Mark Poynter

Northwest Missouri State University

THESIS APPROVED Thesis Advisor Date Dean of Graduate School Date

iii

TABLE OF CONTENTS Page

LIST OF FIGURES ................................................................................................ iv LIST OF TABLES .................................................................................................. v ABSTRACT ............................................................................................................ vi CHAPTER I – INTRODUCTION .......................................................................... 1 CHAPTER II – MATERIALS and METHODS ..................................................... 17 CHAPTER III – RESULTS .................................................................................... 37 CHAPTER IV – DISCUSSION.............................................................................. 46 LITERATURE CITED ........................................................................................... 54 ACKNOWLEDGEMENTS .................................................................................... 61

iv

LIST OF FIGURES Page

FIGURE 1. Tooth of Mosasaurus sp. from Caldwell (2007) ............................. 4 FIGURE 2. Figure of tooth of Mosasaurus sp. (USNM 437998) showing measurements of crown height and basal width used to calculate height:base ratio .............................................................................. 21 FIGURE 3. Tooth of Mosasaurus sp. (USNM 437998) showing position of the apex (shown is sharply pointed apex) ............................................. 24 FIGURE 4. Tooth of Mosasaurus sp. (USNM 437998) showing typical pre-mortom apical wear .................................................................. 25 FIGURE 5. Teeth of (A) Mosasaurus sp. (USNM 437998) and (B) Mosasaurus

sp. (USNM 481126) showing shape of a cutting edge under low (A) and high (B) magnification ............................................................. 26

FIGURE 6. Injection of polyvinyl siloxane molding material into custom ring 27 FIGURE 7. Diekeen stone poured into tooth mold ............................................ 29 FIGURE 8. Tooth cast made of Diekeen cast material. Specimen shown is of Tylosaurus sp. (VP 7262) ............................................................... 30 FIGURE 9. Keyence VHX-600 Digital Reflective Microscope ........................ 31 FIGURE 10. Lingual surface of Tylosaurus sp. (VP 7262) showing a typical pit microwear feature ........................................................................... 33 FIGURE 11. Lingual surface of Globidens sp. (VP 13830) showing a typical

scratch microwear feature ............................................................... 34 FIGURE 12. Lingual surface of Platecarpus sp. (VP 13910) showing a typical

gouge microwear feature ................................................................. 35

v

LIST OF TABLES Page

TABLE 1. Inventory of specimens sorted by museum accession numbers ...... 18 TABLE 2. Tooth morphology characteristics as related to three feeding types predicted for Mesozoic marine reptiles ........................................... 22 TABLE 3. Taxonomic summary of specimens ................................................ 38 TABLE 4. Summary of means and standard errors for crown:base ratios and microwear counts ............................................................................ 40 TABLE 5. Summary statistics of total objects, pits, scratches, gouges, and crown height to basal diameter ratio described by feeding type ..... 41 TABLE 6. Kruskal-Wallis one-way analysis of variance results comparing microwear features among feeding types ....................................... 42 TABLE 7. Mann-Whitney U test results of paired feeding type differences in microwear features .......................................................................... 43

vi

ABSTRACT

Extinct predatory marine reptiles constitute a paraphyletic group that includes

ichthyosaurs, plesiosaurs, placodonts, and mososaurs. These animals evolved numerous

feeding strategies to exploit a diverse prey base that included heavily armored ammonites

and belemnoids, and softer-bodied bony fishes, sharks, squid, and other marine reptiles.

Judy Massare's seminal work correlating tooth form and prey preference of Mesozoic

marine reptiles suggests morphologic analysis of teeth has significant utility in inferring

predator-prey dynamics. Three extreme feeding types within predatory marine Mesozoic

reptiles include crush-type, cut-type, and pierce-type feeders.

This project was aimed at establishing (for the first time) if differences in dental

microwear patterns are correlated to extreme feeding types in the predatory marine

Mesozoic reptiles. I observed that total numbers of microwear objects, pitting, and

gouging all correlated well with diet as predicted by tooth shape. Taxa with crush-type

dentition (e.g., Globidens) had significantly more overall wear, pitting, and gouging than

cut- and pierce-type feeders. Similarly, cut-type feeders had more wear than pierce-type

feeders. These results are consistent with wear that would be expected from consuming

prey with hard armoring (crush-type feeders), flesh and bone (cut-type feeders), and soft

bodies (pierce-type feeders). Scratch microwear patterns were poor at predicting diet and

feeding type.

Dental Microwear 1

INTRODUCTION

Extinct predatory marine reptiles constitute a paraphyletic group that includes

ichthyosaurs, plesiosaurs, placodonts, and mososaurs. These fast swimming predators

dominated many ecological niches in Mesozoic oceans 65 – 250 million years ago (Ma).

They evolved numerous feeding strategies to exploit a diverse prey base that included

heavily armored ammonites and belemnoids, and softer-bodied bony fishes, sharks,

squid, and marine reptiles. Judy Massare’s (1987) seminal work correlating tooth form

and prey preference in Mesozoic marine reptiles suggests morphologic analysis of teeth

has significant utility in inferring predator-prey dynamics in this group. Three extreme

feeding types observed among predatory marine Mesozoic reptiles include crush-type,

cut-type, and pierce-type (Massare 1987).

Dental microwear analysis (DMA) is the study of microscopic scratches and pits

on tooth surfaces as a result of tooth-tooth or tooth-food interactions (e.g., Walker et al.

1978; Scott et al. 2006). Different types of microwear patterns among taxa suggest

variable feeding strategies and diet and is independent of predictions of diet based on

tooth form (Ungar 1996). DMA has been used to study dentition interactions in taxa as

divergent as conodonts, dinosaurs, ungulates, and primates (Fraser et al. 2009). Analysis

of microwear features provides a way of testing hypotheses about tooth-tooth and tooth-

food interaction (Williams et al. 2009). To date, there have been no analyses on the dental

microwear of Mesozoic marine reptiles.

My research is aimed at determining if differences in dental microwear patterns

are correlated to feeding types predicted for various predatory marine Mesozoic reptiles.

The working hypothesis of this research project is that Massare’s (1987) tooth form and

Dental Microwear 2

function paradigm, originally used to predict foraged prey, will also correlate well with

characteristics of dental microwear. Pierce-feeders foraging on soft prey should have

little wear; cut-feeders should have medium wear; and crush-feeders should have

substantial wear.

Mesozoic marine reptiles represent a paraphyletic group of predatory carnivores

of ancient seas. These aquatic predators occupied an ecological niches similar to and as

diverse as Cenozoic marine mammals and birds. Fossil evidence suggests that several

terrestrial reptile groups began to adapt to aquatic life in the Late Permian (Stearn and

Carroll 1989). Low body temperatures, high tolerance of anoxia, and low metabolic rates

provided ancestors of aquatic Mesozoic reptiles good physiological capacities for

secondary aquatic adaptation (Carroll 1988). Aquatic reptilian radiations in the Mesozoic

did not originate from a single ancestor but rather from several terrestrial clades;

however, despite their genealogical diversity, there is surprising anatomical homogeneity

and potential behavioral-functional similarities for interesting comparative work across

aquatic reptiles (Carroll 1997). Most fauna from this paraphyletic assemblage are extinct

marine Mesozoic reptiles.

According to Root (1967: 346), a guild is defined as “a group of species that

exploit the same class of environmental resources in a similar way.” Mesozoic marine

reptiles foraged on fauna from the water column or benthos (e.g., the mosasaur Globidens

and placodonts), preying on animals such as bony fish, sharks, cephlapods, gastropods,

and belemnoids (Massare 1987). These creatures did not chew prey but likely swallowed

prey whole (Massare 1987). Some reptilian clades from the larger predatory guild

Dental Microwear 3

exploiting marine prey in the Mesozoic oceans include Crocodylia, Ichthyosauria,

Mosasauria, Nothosauria, Phytosauria, Placodontia, and Plesiosauria (Mazin 2001).

The study of Mesozoic marine reptiles has made important contributions and

advances to our understanding of vertebrate paleontology. This discipline was in its

infancy when the discovery of a fossilized crocodile in 1758 on the coast of southern

England (Taylor 1997) and mosasaur skeletons harvested near Maaschrict, the

Netherlands harbingered Georges Cuvier’s transformative thesis of extinction (Schulp et

al. 2005). Contemporary explication of these fossilized Mesozoic marine reptiles

provided science with a unique window into both evolutionary and ecological

transformation.

Most vertebrates have toothed jaws, and Mesozoic marine reptiles are no

exception. Caldwell (2007; Fig. 1) and Budney et al. (2006) described mosasaur tooth

structure as being divided into crown and root. The crown is that portion of a tooth

visible in the oral cavity that is covered with enamel. The root is that portion of tooth

embedded in the alveolus and is covered by cementum (Berkovitz et al., 2002). Crown-

root borders are delineated by the cementum-enamel junction (CEJ).

Most known Mesozoic marine reptiles are polyphyodont, where teeth are replaced

continually throughout life (Russell 1967; Peyer 1968). Situated in the dental groove of

maxillary and dentary bones lay multiple replacement teeth within the dental laminae.

There may be multiple teeth in this space for any one tooth position. Developmentally

advanced replacement teeth enter the functional dentition space at varying patterns and

rates (Caldwell 2007).

Dental Microwear 4

Figure 1. Tooth of Mosasaurus sp. from Caldwell (2007).

Cemento-enamel junction (CEJ)

Dental Microwear 5

A common theme of most predatory aquatic tetrapods is development of simple,

homodont teeth used to seize prey prior to swallowing (Taylor 1987). Dental tissue

formation is best understood ontogenically. Odontoblasts form dentine tissue and

ameloblasts create enamel. Differentiation of odontoblasts from neural crest cells situated

below the basal lamina is controlled by ameloblasts found in the internal epidermis of the

enamel organ. Dentine is formed in a soft tooth bud pattern. Enamel is superficially laid

over dentine construction. Dentine and enamel developmentally arise from the

mineralization of an organic matrix (Rieppel and Kearney 2005).

Tooth form is a function of soft tooth bud pattern. Shape of dentine and enamel

reflects the organization of this soft tooth bud. Small modifications to the arrangement of

epithelial cells on the outer bud surface can translate to significant changes in tooth

morphology (De Vree and Gans 1994). Therefore, only slight changes in dental

developmental tissue arrangement can generate significant morphological diversity in

tooth form. Morphological differences, in turn, typically correspond to tooth function.

The form of amniote teeth and dental tissue organization and structure is directly

influenced by composition and physical properties of food (Green 2009). Differences in

tooth size among species often reflect differences in the external characteristics of food

(e.g., size, shape, and abrasiveness). Variation in tooth shape indicates differences in the

internal characteristics of food (e.g., strength, toughness, and deformability; De Vree and

Gans 1994).

Most Mesozoic marine reptile teeth have striations on the crown-enamel surface

originating a few millimeters from the tooth base and extending towards the apex. Some

striae are muted at the apex from wear or as part of inherent form (Storrs 1997).

Dental Microwear 6

Longitudinal striae function to increase grip and bite pressure (Schulp 2005; Lingham-

Soliar 1999). Additionally, many teeth also have anterior and posterior carinae, which are

often serrated for cutting. Carinae were used for capturing prey (Massare 1987) and

perhaps for tearing apart large prey.

Caldwell (2007) published important anatomical and histological observations on

mosasaur dentition. Careful histological examination can inform researchers about how

teeth attach to jaw bone, and this can be used to predict morphological limitations on prey

hardness and size available to a predator (Budney et al. 2006). Presence of a cementum-

covered root situated in a deep socket and presence of ligamentous attachments between

root and alveoleor bone suggests thecodont attachment of mosasaur dentition (Caldwell

2007). Thecodont implantation provides teeth with a robust attachment to surrounding

bone for withstanding large masticating forces from consuming hard prey. Most

ichthyosaur teeth attached to alveolar bone by aulacodontic or subthecodontic

attachment. Both types of implantation situate teeth in longitudinal dental grooves of

maxillary and dentary bones (Motani 1997). Aulacodontic and subthecodontic

attachments lack supportive alveolar bone collar provided by thecodont attachment.

Mesozoic aquatic predators generally had homogenous, conical teeth (Peyer 1968;

Caldwell 2007) with various crown morphologies specialized for hunting particular prey.

Tooth form is closely related to tooth function and prey preference (Massare 1987).

Pollard (1990) explains that piercing-type teeth are generally cone-shaped; cutting-type

teeth possess carinae; and crushing-type teeth have a blunt apex.

Diet is key to understanding the paleoecological condition of ancient organisms

(Fleagle 1999). Detailed examinations of particular dietary items that organisms forage

Dental Microwear 7

upon and the feeding processes by which those items are consumed are often derived

from direct observation of closely related extant species. However, Adam and Berta

(2002) described methods for dietary reconstruction of extinct vertebrates with no close

relatives. Methods described for dietary study included: 1) stomach content analysis; 2)

potential prey situated in the same stratigraphic biozone as the species in question; 3)

isotope analysis; 4) dental microwear analysis; and 5) form-function comparisons with

extant species.

Of these methods, preserved stomach contents associated with particular

fossilized skeletons and coprolites provide direct evidence of diet in extinct vertebrates.

For examples, coprolites harvested from Mesozoic chalk beds contained partially

digested bones, teeth, and fragments of squid pens (Everhart 2005). The crescent-shaped

nicks found in fossilized bivalve shells purportedly made by an Early Mesozoic

placodont (Bishop 1975) are examples of indirect evidence of diet. Correlating direct and

indirect evidence of diet has helped construct models of prey preference and feeding

strategies. Each analytical method potentially provides important paleodietary

information, but individually, each method is burdened with limitations. The best

approach to diet reconstruction is likely that which uses multiple lines of evidence.

Relationships between tooth morphology and diet for fossilized species are well

established in mammals (e.g., Owen, 1845; Gregory 1922; Kay and Hylander 1978;

Ungar 2004). Massare (1987) used tooth form, stomach content analysis, and

examination of analogous extant marine mammal diets to predict prey of Mesozoic

marine reptiles. Correlating diet to dental form in Mesozoic reptiles is difficult because of

several confounding factors: 1) there are scant extant marine reptiles for correlative form-

Dental Microwear 8

function study (Massare 1987; Taylor 1987); 2) fossils of prey may not show predation

marks (Schwenk 2000); and 3) reptilian predators may alter their prey selection due to

changes in abundance or scarcity (Williams et al. 2009).

Judy Massare’s (1987) seminal work correlating tooth form and prey preference

of Mesozoic marine reptiles suggests morphologic analysis of teeth has great utility for

inferring predator preferences for prey. Her work relates tooth form and function, and

provides great insight into the uses of marine reptile dentition (Motani 2005). The

paradigm of my research project is that Massare’s (1987) tooth form-function work,

originally used to predict foraged prey, will also correlate well with characteristics of

dental microwear.

Based on tooth shape, Massare (1987, 1997) recognized three extremes of dental

morphology: pierce-, cut-, and crush-type teeth. Representatives from all three feeding

types are found in predatory marine Mesozoic reptiles. Pierce-feeding species likely

consumed soft-bodied prey (e.g., squid and octopus). Crush-feeding species had dentition

well formed for feeding on hard-bodied, armored fauna (e.g., ammonites, belemnites, and

clams). Cut-type feeders had teeth specialized for foraging on bony prey (e.g., large fish

and smaller marine reptiles). Given the differences in hardness of prey, I predict that

feeding types will also differ in tooth microwear (Poynter and Adam 2011a, 2011b).

Pierce-feeders foraging on soft prey should have little wear; cut-feeders should have

medium wear; and crush-feeders should have substantial wear owing to their preference

for hard-bodied prey.

Dental microwear analysis is likely to be a good independent test of diet as

predicted from tooth morphology. Feeding mechanisms and diet reconstruction of

Dental Microwear 9

fossilized mammals from tooth morphologies, stable isotope geochemistry, and dental

microwear analysis is well documented in the literature (reviewed by Green 2009).

Microwear features are a product of complex interactions involving food properties, jaw

mechanics, and taphonomic effects (Beatty 2005; Goswami et al. 2005).

Material wear is a product of surface interaction – forces of action and effect –

between two solid objects. Object interaction includes the surface removal of material

from one object as it interacts with a second object. Rabinowicz (1965) explicated four

forms of material wear: 1) adhesive wear; 2) abrasive wear; 3) corrosive wear; and 4)

surface fatigue wear. Dental microwear is a form of abrasive wear in that the enameled

tooth crown interacts with some other material. Microwear forming material might

include occluding teeth, ingested food material, or environmental substrate.

Different types (i.e., pits, scratches, and gouges) and densities of microwear

features reveal additional information about diet. Walker and Teaford (1989) described

how microwear features on molars of adult primates can be used to differentiate diets of

hard fruit eaters from leaves, stems, and flowers. Williams et al. (2009) and Fiorillo

(1998) employed dental microwear techniques to understand hadrosaurid and sauropod

jaw mechanics. Van Valkenburgh et al. (1990) used microwear density and orientation to

distinguish features produced from tooth-tooth contact and feeding mechanics from wear

objects produced by food and substrate.

Enamel scratches in other research has been used to identify tooth-tooth attrition

interactions (Teaford 1988; Schubert and Ungar 2005), stripping of leaves from branches

by primates (Ang et al. 2006), and tooth-tongue movements in walruses (Gordon 1984).

Scratch-to-pit densities are considered diagnostic of dietary type in primates. Teeth of

Dental Microwear 10

primate folivores have more scratches than those of frugivores that eat hard material

(Teaford and Ungar 2000).

Although most microwear studies have been conducted on extant mammalian

systems, Fiorillo (1998), Goswami et al. (2005), and Williams et al. (2009) have

substantially utilized dental microwear analysis to document paleodietary and

paleoecological characteristics of dinosaurs in the Mesozoic. Scratches were the

dominant microwear feature in all three studies. Goswami et al. (2005) and Williams et

al. (2009) used scratch length and orientation as independent evidence for assessing

physical properties of consumed food items in these herbivores. All Mesozoic reptiles in

these studies were terrestrial and not aquatic; nevertheless, these studies demonstrate

three important points relevant for microwear research on Mesozoic marine reptiles: 1)

microwear study has utility for suggesting broad feeding type of fossilized specimens; 2)

microwear study can be used for dietary distinctions among fossilized fauna lacking

extant descendents; 3) microwear study can be used for analysis of non-mammalian

systems – i.e., Mesozoic marine reptiles.

DMA involves qualitative and quantitative assessment of individual features

found on the surface of teeth (Scott et al. 2006). These features include pits, scratches,

and gouges (Solounias and Semprebon 2002). DMA employs various tools and

techniques that include the use of stereoscopic light microscopy and scanning electron

microscopy (SEM) (Fraser et al. 2009). Many tooth microwear studies have examined

enamel surfaces at high magnification. Pioneering scanning electron microscope studies

by Alan Walker and colleagues (1978) were expanded by scientists such as Mark Teaford

and Peter Ungar to understand various aspects of primate, rodent, and ungulate dietary

Dental Microwear 11

adaptations (Solounias and Semprebon 2002). However, several factors inherent to SEM

analysis necessitated other methods of dental microwear assessment. For example, SEM

analysis is costly (for training and effective operation) and unrepeatable (Fraser et al.

2009). SEM also creates two-dimensional micropictographs from three-dimensional

objects, making good feature recognition highly dependent on instrument settings and

specimen orientation (Scott et al. 2006).

Solounias and Semprebon’s (2002) and Semprebon et al. (2004) seminal work

introduced a new low-magnification method using a stereoscopic light microscope for

DMA. They compared the efficacy of traditional high-magnification SEM against low-

magnification stereoscopic light microscopy DMA to predict ungulate diets and found

results to be equivalent. They found that low-magnification methods had similar

predictive power of feeding type as the traditional SEM methods. Additionally, they

determined that object area and depth measurements were not necessary for determining

feeding types. Observational methods and objectives are different for each type of

microscopy: stereoscopic light microscopy examines a larger area of tooth at lower

magnification (usually < 50 times magnification) while SEM observes a smaller tooth

area at higher magnification (usually > 100 times magnification). Regardless of method,

the purpose of DMA is the same: to observe the effects of attrition (tooth-tooth contact)

and abrasion (tooth-food or tooth-substrate interaction) on dentition and to describe how

patterns of wear might characterize the feeding of examined specimens (Beatty 2005).

Both SEM and light microscopy DMA present challenges for accurate

measurement of observed microwear features on Mesozoic marine reptile teeth, because

these teeth are generally conical and lack complex occlusion geometry (e.g., facets)

Dental Microwear 12

traditionally examined in DMA of mammals. Measurements made along the surface

curvature of these ancient teeth also require complex algorithms for accurate

measurement of microwear features.

Another challenge for DMA is distinguishing between pre-mortem and post-

mortem taphonomic features. Taphonomy is the science of fossil preservation concerned

with dynamics of information loss and information gain available from individual fossils

(Martin 1999). One taphonomic effect on fossil dentition is breakage. From direct

observation of Mesozoic marine reptile teeth, there is obvious and apparent post-mortem

breakage of teeth. If breakage were pre-mortem, fragments would scatter never to be

assembled again. Post-mortem breakage must be accounted for in microwear analysis.

Macroscopic breakage is easy to detect and avoid in analysis, but what about post-

mortem microwear features? One potential source of post-mortem wear is from physical

movement of the object in the taphonomic pathway (Martin 1999). Argast et al. (1987)

tested dinosaur teeth to see if movement of teeth in rock matrix affected teeth surface and

found that the process created little to no macroscopic wear. Potential microwear effects

from taphonomic processes (e.g., sedimentation in matrix and movement) are generally

unknown.

A second potential source of taphonomic wear could result from weathering

effects before deposition or after exposure. King et al. (1999) and Goswami et al. (2005)

found that physical and chemical weathering obliterates microwear features rather than

creating microwear artifacts. While weathering might shift overall counts of microwear

densities, the ratio of densities among feeding types should not be affected, assuming

weathering affects teeth from all three feeding types equally.

Dental Microwear 13

Diet variability within taxonomic and morphological contrived groups affects

microwear analysis. Several factors affect foraging behavior even within a particular

species. Seasonal changes of available food items, dietary resources available within an

occupied microhabitat, and fall-back food items in times of resource scarcity all

potentially contribute to dentition microwear variability (Scott et al. 2005, Galbany et al.

2009). Additionally, microwear patterns can change because of shifts among prey

species, for example in response to climate changes (Rivals and Solounias 2007).

Mesozoic marine reptiles are represented by approximately 20 lineages that

independently and secondarily adapted to marine life (Carroll 1997). Given this great

diversity, comprehensive taxonomic sampling is costly and inherently limited to those

species exposed and discovered. Research suggests variability in microwear patterns is

more related to differences in diet and ecological conditions than to taxonomy (Galbany

et al. 2009). Microwear analysis, therefore, would be a good independent test of

Massare’s (1987) predicted prey preference defined by feeding type. This taxon-

independent analysis is supported by the work of Villier and Korn (2004) who examined

changes in ammonite morphology across extinction events. Their results suggested that

when basing comparative work on form differences, “morphological disparity is

relatively independent of taxonomy” and thereby allows for “the comparison of samples

in which a variable proportion of taxa are preserved or sampled” (Villier and Korn 2004:

264).

Kaiser and Rössner (2007) employ a taxon-independent method of microwear

analysis to examine and compare diversity of ruminant feeding types in adjacent Miocene

communities. Microwear dentition analysis was used to detect and quantify different

Dental Microwear 14

ruminant feeding types within the two bio-communities; this information was not

discernable by other metric analysis (e.g., tooth crown height). Therefore, Kaiser and

Rössner (2007) assert that microwear analysis contributes unique information about the

ecological milieu of extinct and extant biomes and that “using the dietary interface as a

taxon-independent pathway may allow a more precise comparison of two biomes more

independent from species historical circumstances.” (Kaiser and Rössner 2007: 425).

Most analyses of tooth wear are based on mammalian taxa. These animals have

one or two generations of teeth (monophyodont) and precise occlusion. Most fish

(Purnell et al. 2006) and Mesozoic marine reptiles (Caldwell 2007) are polyphyodont,

where developmentally advanced replacement teeth enter the functional dentition space at

varying patterns and rates. This creates potential experimental anomalies when

examining limited numbers of teeth from small sample groups. For instance, a tooth

examined with few microwear features might reflect a diet of soft-bodied prey, or it

might reflect that the tooth was newly formed and functional.

Purnell et al. (2006) emphasize that mammalian microwear features are the result

of tooth-tooth and tooth-food-tooth interactions during mastication. They also raise

concern that the feeding processes of many fish (suction or ram feeding) have little use of

teeth, and seemingly less microwear. However, fish do not chew; therefore, the

mechanism of microwear feature production in aquatic animals is different than that of

terrestrial organisms. Adam and Berta (2002) found that microwear analysis was not

useful in paleodietary reconstruction of pinnipeds. One reason they believed microwear

was analytically impotent was because pinnipeds do not masticate their homogenous food

(Adam and Berta 2002). Research work of Taylor (1987) and Massare (1987) suggest

Dental Microwear 15

most Mesozoic marine reptiles did not masticate either. However, the benefit of using

Mesozoic aquatic vertebrates is that variation in dietary hardness had extremes: soft-

bodied prey (e.g., squid and octopus); bony prey (e.g., large fish and smaller marine

reptiles); and hard-bodied, armored fauna (e.g., ammonites, belemnites, and clams).

Despite some additional limitations, DMA studies of some aquatic fauna have met

with success. Wear analysis was used to determine patterns of tongue movement of

walrus during feeding (Gordon 1984); walruses forage benthic shelled prey and in

captivity these animals have been observed using a suction feeding mechanism to extract

bivalve feet and/or siphons and to cast out the valves (Gordon 1984). Domning and

Beatty (2007) demonstrated that correlating functional and morphological change is

difficult, but showed how microwear helped unravel the Gordian knot of detecting form-

function changes of dugong tusks, and how these changes related to diet. Purnell et al.

(2007) showed that differences in microwear pattern and density of fossil stickleback

correlated with different feeding types (e.g., benthic feeding vs. limnetic feeding).

Because sticklebacks provide high spatial and temporal resolution, feeding type

differences were used to examine changes in paleoecology and food resources.

Methods for DMA developed by Solounis and Semprebon (2002) provide a good

means for distinguishing between broadly defined feeding types (Grine et al. 2002).

There is a common theme in the discussion of many microwear study papers (Gosawami

et al. 2005; Purnell et al. 2007; Teaford 2007; Townsend and Croft 2008) that across

different microwear analysis methods and experimental designs, microwear analysis

provides a good test for gross dietary observations of fossilized assemblages and their

feeding type assessment.

Dental Microwear 16

This is the first attempt to examine dental microwear of Mesozoic marine reptiles.

Work from this study correlates tooth wear patterns to predicted diet. Pierce-feeders

foraging on soft prey should have little wear; cut-feeders should have medium wear; and

crush-feeders should have substantial wear.

Dental Microwear 17

MATERIALS AND METHODS

Sampled taxa included representatives of three feeding types (i.e., crush-, cut-,

and pierce-type) as classified by Massare (1987). Taxa were selected to maximize

representation of these feeding types from specimens available at the visited museums.

There is a paucity of Mesozoic marine reptile specimens with teeth attached to the skull.

Most of the specimens examined were made from isolated teeth.

Replicas of selected Mesozoic marine reptile specimen were collected from: Fort

Hays Sternberg Museum of Natural History, Fort Hays, Kansas (FHSM); Kansas

University Natural History Museum, Lawrence, Kansas (KU); United States National

Museum of Natural History, Washington, D.C. (USNM); University of Oklahoma Sam

Noble Museum of National History Norman, Oklahoma (OMNH); Southern Methodist

University Shuler Museum, Dallas, Texas (SMU); and the Royal Ontario Museum

Toronto, Ontario, Canada (ROM).

Museum collection catalogs were examined to identify potential Mesozoic marine

reptile specimens with teeth (Table 1). On-site physical examination of each potential

specimen was necessary to assess the condition of each tooth and to eliminate specimens

with obvious taphonomic breakage and wear that would disrupt the molding process and

obscure microscopic examination.

Teeth suitable for molding were measured using Westward digital calipers to the

nearest 0.01 mm. Crown height and basal diameter of each tooth were measured and

recorded (Fig. 2 and Table 2). Specimens were photographed using a Canon PowerShot

with lens and flash adaptors specific for dental photography, or with a Nikon D90 with a

Speedlight SB-600 flash. Additional notes on crown morphology were made

Dental Microwear 18

Table 1. Inventory of specimens sorted by museum accession numbers.

MUSEUM ID ORDER FAMILY GENUS Feeding Type

KU uncatalogued Sauria Mosasauridae Tylosaurus CUT

KU 1178 Sauria Mosasauridae indet PIERCE

KU 118936 Plesiosauria indet indet PIERCE

KU 1300 Plesiosauria Polycotylidae Trinacromerum PIERCE

KU 40001 Plesiosauria Polycotylidae Dolichorhynchops PIERCE

KU 85502 Sauria Mosasauridae Platecarpus CUT

KU 85585 Sauria Mosasauridae Platecarpus PIERCE

KU 950 Sauria Mosasauridae Prognathodon CUT

OHNH 1059 Sauria Mosasauridae indet PIERCE

OMNH 01046 Sauria Mosasauridae Platecarpus PIERCE


OMNH 1011 Crocodylia indet indet PIERCE






OMNH 35410 Sauria Mosasauridae indet PIERCE

OMNH 35410 Sauria Mosasauridae indet CUT

OMNH 35410 Sauria Mosasauridae indet CUT


ROM uncatalogued Ichthyopterygia Ichthyosauridae Ichthyosarus PIERCE

ROM 00310 Placodontia Placohelyidae Placodus CRUSH

ROM 00363 Nothosauria Nothosauridae Nothosaurus PIERCE



ROM 00956 Ichthyopterygia Ichtyosauridae Ichthyosaurus PIERCE

ROM 01860 Ichthyopterygia Ichthyosauridae Ichthyosarus PIERCE

ROM 01872 Plesiosauria Pliosauridae Polyptycodon PIERCE

ROM 05596 Plesiosauria Pliosauridae indet CUT

ROM 11692 Phytosauria Phytosauridae Phytosaur PIERCE

ROM 11692 Phytosauria Phytosauridae Phytosaur CUT




ROM 28549 Plesiosauria Pliosauridae Polyptycodon PIERCE



(continued on next page)

Dental Microwear 19

Table 1. (continued)


ROM 28964 Ichthyopterygia Ichtyosauridae Ichthyosaurus PIERCE

ROM 3180 Ichthyopterygia Ichthyosauridae Stenoptergius PIERCE

ROM 45694 Sauria Mosasauridae indet CUT

ROM 47690 Plesiosauria Elasmosauridea indet PIERCE

ROM 47690 Plesiosauria Elasmosauridea indet PIERCE

ROM 47698 Ichthyopterygia Ichthyosauridae Leptonectes PIERCE

ROM 52043 Crocodylia Dyrosauridae indet PIERCE

ROM 52043 Crocodylia Dyrosauridae indet PIERCE

ROM 52550 Sauria Mosasauridae Mosasaurus CUT

ROM 52573 Sauria Mosasauridae Platecarpus CUT







ROM 54516 Sauria Mosasauridae Globidens CRUSH


ROM 54526 Plesiosauria indet Plesiosaurus PIERCE

ROM 54527 Plesiosauria indet indet PIERCE

ROM 54527 Plesiosauria indet Plesiosaurus PIERCE


ROM 54551 Sauria Mosasauridae Mosasaurus CUT

ROM54552 Sauria Mosasauridae Mosasaurus CUT

SMU uncatalogued Sauria Mosasauridae Liodon CUT

SMU 61113 Sauria Mosasauridae Tylosaurus CUT

SMU 62410 Sauria indet Elasmobranch PIERCE

SMU 69120 Plesiosauria Elasmosauridae Libonectes PIERCE

SMU 72206 Sauria Mosasauridae indet PIERCE

SMU 75374 Sauria Mosasauridae Tylosaurus CUT

SMU 75586 Sauria Mosasauridae indet CUT

SMU 76398 Sauria Mosasauridae Globidens CRUSH




SMU 75586 Sauria Mosasauridae indet PIERCE

SMU 60314 Plesiosauria Elasmosauridae Polyptycodon PIERCE

USNM uncatalogued Ichthysauria indet indet PIERCE


Dental Microwear 20



USNM 1 Sauria Mosasauridae Mosasaurus PIERCE

USNM 10540 Sauria Mosasauridae Mosasaurus CUT

USNM 11647 Sauria Mosasauridae Clidastes PIERCE

USNM 11655 Sauria Mosasauridae Platecarpus PIERCE

USNM 12287 Sauria Mosasauridae Tylosaurus CUT

USNM 16153 Plesiosauria Polycotylidae Polyptycodon PIERCE

USNM 16154 Plesiosauria Polycotylidae Polyptycodon PIERCE



USNM 25444 Plesiosauria Pliosauridae Pliosaurus PIERCE




USNM 418456 Sauria Mosasauridae indet PIERCE

USNM 419635 Plesiosauria Pliosauridae Pliosaurus PIERCE

USNM 421698 (cast) Placodontia Placohelyidae Macroplacus CRUSH

USNM 421699 (cast) Placodontia Placohelyidae Cynamdus CRUSH

USNM 421700 (cast) Placodontia Placohelyidae Placochelys CRUSH

USNM 437572 Plesiosauria Polycotylidae Cimoliasaurus PIERCE



USNM 437998 Sauria Mosasauridae Clidastes CUT


USNM 4992 Sauria Mosasauridae Tylosaurus PIERCE

USNM 535507 Plesiosauria indet indet PIERCE


USNM 6527 (cast) Sauria Mosasauridae Globidens CRUSH

USNM 76 Sauria Mosasauridae Lestosaurus PIERCE


VP uncatalogued Sauria Mosasauridae Ectenosaurus PIERCE

VP 13830 Sauria Mosasauridae Globidens CRUSH

VP 13910 Sauria Mosasauridae Platecarpus CUT

VP 15631 Sauria Mosasauridae Tylosaurus CUT

VP 17017 Sauria Mosasauridae Platecarpus PIERCE

VP 17314 Sauria Mosasauridae Platecarpus CUT

VP 17576 Sauria Mosasauridae Clidastes PIERCE

VP 7262 Sauria Mosasauridae Tylosaurus CUT

Dental Microwear 21

Figure 2. Figure of tooth of Mosasaurus sp. (USNM 437998) showing measurements of crown height and basal width used to calculate height:base ratio.

Dental Microwear 22

Table 2. Tooth morphology characteristics as related to three feeding types predicted for Mesozoic marine reptiles.

Morphological Character CRUSH CUT PIERCE

Apex Shape very blunt Pointed pointed

Apex Wear coronal abrasions breakage common some breakage

Cutting Edges none usually two occasional

Crown-Basal Ratio < 1.0 1.3 – 2.5 1.3 – 4.3

Dental Microwear 23

from specimens, including apex shape, apical wear, and presence or absence of distinct

cutting edges (Fig. 3-5 and Table 2).

Teeth were examined and cleaned with a soft brush or cloth to remove dust and

debris. 3M Impression II polyvinyl siloxane impression material was injected into custom

split ring polyvinyl chloride (PVC) coupling connectors of varying diameters (17, 20, 26,

and 34 mm) corresponding to tooth basal diameter (Fig. 6) PVC rings provided a form for

the molding material and allowed preservation of three-dimensional tooth structure. Each

ring had unique index marks created with a Foredom series TX drill for aligning cured

molding material into the ring for storage.

For teeth still associated with skulls or embedded in rock medium, PVC forms

could not be used and impression peel molds were made from these teeth using polyvinyl

siloxane impression material. Polyvinyl siloxane is a two-part syringeable paste that

automixes as it is extruded through an application tip. This combined product was applied

directly to the fossilized tooth. The advantage of polyvinyl siloxane product over

traditional silicone molding materials is reduced mixing, working, and curing times

(Leiggi and May 1994). Polyvinyl siloxane product cures in approximately ten minutes,

in contrast to many hours, without losing resolving detail.

When molding material had dried, specimens were extracted. The split PVC rings

were opened and an incision was made into the polyvinyl siloxane mold approximately

0.25 mm from the labial tooth surface. Impression molds were stored at room

temperature according to manufacturer specifications. Each study specimen was encased

in the labeled PVC ring used in the molding process. Peel molds were stored in plastic

bags.

Dental Microwear 24

Figure 3. Tooth of Mosasaurus sp. (USNM 437998) showing position of the apex (shown is sharply pointed apex).

Dental Microwear 25

Figure 4. Tooth of Mosasaurus sp. (USNM 437998) showing typical pre-mortem apical wear.

Dental Microwear 26

A B Figure 5. Teeth of (A) Mosasaurus sp. (USNM 437998) and (B) Mosasaurus sp. (USNM 481126) showing shape of a cutting edge under low (A) and high (B) magnification.

Dental Microwear 27

Figure 6. Injection of polyvinyl siloxane molding material into custom ring.

Dental Microwear 28

Leiggi and May (1994) found dental gypsum plaster to be a good casting

compound for use in paleontological studies. Diekeen stone (Modern Materials

Manufacturing Company: Saint Louis, Missouri) was used to create study casts from

polyvinyl siloxane tooth molds. Compatibility of polyvinyl siloxane and Diekeen stone

has been tested by the American National Standards Institute (ANSI) and the American

Dental Association (ADA), who found that Diekeen cast material accurately reproduced

20 µm scratches from polyvinyl siloxane molding material (Schelb et al., 1987).

Therefore, I prepared casting material in the same manner: gypsum stone powder was

added to water at a ratio of 100 mg of Diekeen powder to 21 ml of water. Diekeen

powder was added to the water and hand-spatulated in a vacuum canister for 10 seconds.

This mixture was then vacuum-spatulated using a Vac U Vestor Power Mixer (General

Electric: Louisville, Kentucky) pressurized to 36,200 Torr and stirred at 1725 rpm.

Specimens were placed at an angle on a vibrating plate and the Diekeen mixture was

loaded from the vacuum canister using a chemical spatula.

Polyvinyl siloxane molds loaded with the Diekeen casting stone (Fig. 7) were

placed at ambient room temperature and allowed to cure overnight. Replica teeth were

removed from the polyvinyl siloxane mold, and casts were stored for microscopic

examination (Fig. 8). Molds were placed back into the PVC ring for archiving.

Casts were examined using a Keyence VHX-600 progressive scan digital

reflective microscope (Fig. 9). A 1628 x 1236 charged-coupled device sensor on this

scope provides a 2.11 million-pixel resolution image (Keyence 2007). Casts were

illuminated using a unidirectional light with a 12 V, 100 W halogen lamp. Lingual

surfaces of teeth (Smith and Dodson 2003) were examined and photographed with

Dental Microwear 29

Figure 7. Diekeen stone poured into tooth mold.

Dental Microwear 30

Figure 8. Tooth cast made of Diekeen cast material. Specimen shown is of Tylosaurus sp. (VP 7262).

Dental Microwear 31

Figure 9. Keyence VHX-600 Digital Reflective Microscope.

Dental Microwear 32

the microscope at 50X. Alpha chromatic and sharpening adjustments of virtual

micropictographs produced greater definition of microwear object boundaries for more

accurate visualization and identification. Analytical software embedded into the Keyence

microscope also allowed for generation of a working graphics layer to overlay the

micropictograph. Keyence graphic tools were used to create a virtual 24 square-grid

comprised of 1 mm x 1 mm cells overlayed on tooth images.

Microwear features were classified as in Solounias and Semprebon (2002). Using

parameters established by Grine (1987), microwear objects with a length-to-width ratio

less than or equal to 4:1 were classified as pits. Pits are circular in nature and regular in

appearance with sharp, discrete boundaries, and appear relatively bright (Fig. 10). Wear

features with regular edges and a length to width ratio greater than 4:1 were categorized

as scratches (Walker and Teaford 1989; Solounias and Semprebon 2002) (Fig. 11).

Gouges are discrete microwear features with jagged, irregular edges; gouges are typically

larger and deeper than pits (Fig. 12).

Scratches, pits, and gouges were identified, counted, and digitally recorded from

real-time images of positive casts. Observations were made from ten randomly selected 1

mm squares represented by the 24-cell grid superimposed over the lingual surface of the

tooth. Random grid cell selections were made using a random number generator in

Microsoft Excel. Cells containing obvious taphonomic artifacts such as post-mortem

breakage were avoided and another grid was selected. Microwear features encroaching

upon right or bottom gridlines were not included in wear counts. The total number of pits

Dental Microwear 33

Figure 10. Lingual surface of Tylosaurus sp. (VP 7262) showing a typical pit microwear feature.

Dental Microwear 34

Figure 11. Lingual surface of Globidens sp. (VP 13830) showing a typical scratch microwear feature.

Dental Microwear 35

Figure 12. Lingual surface of Platecarpus sp. (VP 13910) showing a typical gouge microwear feature.

Dental Microwear 36

and scratches were counted using the multiple selection tool from the Keyence graphics

elements utility.

Absolute numbers of pits, gouges and scratches for individuals per feeding type

and taxon were recorded in each of the ten selected cells. Counts from the ten squares

were then averaged to obtain a mean number of pits and scratches per cast. These means

were then averaged for all individuals per taxon to obtain a final average number of pits

and scratches per taxon.

All data sets were tested for normality and homogeneity of variance using the

Shapiro-Wilks W normality test. Kruskal-Wallis non-parametric analysis of variance was

used to assess differences among feeding types. Difference in: 1) pit densities; 2) scratch

densities; 3) gouge densities; and 4) total microwear features were all tested. Mann-

Whitney U tests were employed to test for differences between feeding type pairs.

Statistical analyses were run using SYSTAT 11.0 (SYSTAT Software Inc.: Richmond,

California) with significance set at p ≤ 0.05.

Dental Microwear 37

RESULTS

This microwear study examined 16 crush-type teeth, 32 cut-type teeth, and 68

pierce-type teeth (Table 1) representing 7 orders, 9 families, and 25 genera (Table 3).

Feeding type was determined using four tooth crown characteristics: 1) shape of apex; 2)

apex wear; 3) presence or absence of cutting edges; and 4) ratio of crown height to basal

diameter. Parameters of tooth crown characteristics used to determine feeding type are

found in Table 2. There were more total microwear objects in crush-type teeth than cut-

type and pierce-type teeth. There was an average of 111 (standard error, SE = 9.74) total

microwear objects per crush-type tooth, 58 (SE = 7.86) average total objects per cut-type

tooth, and an average of 20 (SE = 4.61) total microwear objects per pierce-type tooth

(Table 4). Mean values of total microwear objects per tooth were not normally

distributed, as indicated by a Shapiro-Wilk test for cut-type (p = 0.02) and pierce-type (p

= 0.00) teeth (Table 5) thereby requiring non-parametric testing of mean differences.

Therefore, Kruskal-Wallis one-way analysis of variance was used to test for equality

between feeding types. Results of this test suggested that there were significant

differences (χ2 = 43.31, degrees of freedom, DF = 2, p = 0.000) in the number of total

microwear objects among the three feeding types (Table 6).

Follow-up Mann-Whitney U tests were employed to compare total microwear

object densities among feeding types. Three of these tests (i.e., crush- v. cut-type; crush-

v. pierce-type; and cut- v. pierce-type) revealed statistically significant mean differences

between all treatment group pairs (χ2 = 11.73, 33.92, and 16.21, respectively; DF = 1; p =

0.001, p = 0.000, p = 0.000, respectively; Table 7).

Dental Microwear 38

TABLE 3. Taxonomic summary of specimens.

Taxa CRUSH CUT PIERCE AGGREGATE

Total Teeth 16 32 68 116

ORDER (2) (3) (6) (7)

Crocodylia 0 0 7 7

Ichthyosauria 0 0 11 11

Nothosauria 0 0 3 3

Phytosauria 0 3 4 7

Placodontia 6 0 0 6

Plesiosauria 0 1 18 19

Sauria 10 28 25 63

FAMILY (3) (3) (8) (9)

Dyrosauridae 0 0 2 2

Elasmosauridae 0 0 4 4

Ichthyosauridae 0 0 10 10

Mosasauridae 9 28 24 61

Nothosauridae 0 0 3 3

Phytosauridae 0 3 4 7

Placochelyidae 5 0 0 5

Placodontidae 1 0 0 0

Pliosauridae 0 1 4 5

Polycotylidae 0 0 5 5

Indet 1 0 12 14

GENUS (5) (6) (19) 25

Cimoliasaurus 0 0 1 1

Clidastes 0 1 4 5

Cynamdus 1 0 0 1

Dolichorhynchops 0 0 1 1

Ectenosaurus 0 0 1 1

Elasmobranch 0 0 1 1

Globidens 10 0 0 10

Ichthyosaurus 0 0 8 8

Leptonectes 0 0 1 1

Lestosaurus 0 0 1 1

Libonectes 0 0 1 1

Macroplacus 2 0 0 2


Dental Microwear 39


Taxa CRUSH CUT PIERCE AGGREGATE

Mosasaurus 0 7 4 11

Nothosaurus 0 0 3 3

Phytosaur 0 3 4 7

Placochelys 1 0 0 1

Placodus 2 0 0 2

Platecarpus 0 6 6 12

Plesiosaurus 0 0 2 2

Pliosaurus 0 0 2 2

Polyptycodon 0 0 5 5

Prognathodon 0 1 0 1

Stenoptergius 0 0 1 1

Trinacromerum 0 0 1 1

Tylosaurus 0 8 1 9

Indet 0 6 16 22

Dental Microwear 40

Table 4. Summary of means and standard errors for crown:base ratios and microwear counts.

CRUSH CUT PIERCE

Independent Variable

AVG SE AVG SE AVG SE

Crown-Basal Ratio

0.62 0.09 1.78 0.06 2.30 0.08

Total Microwear Features

111 9.74 58 7.86 20 4.61

Pits 102 9.91 52 7.48 18 4.61

Scratches 4 1.83 4 1.14 2 0.43

Gouges 5 1.27 1 0.35 0 0.10

Dental M

icrowear 41

Table 5. S

umm

ary statistics of total objects, pits, scratches, gouges, and crown height to basal diam

eter ratio described by feeding type. A

bbreviations: CI =

confidence interval; SW

= S

hapiro Wilk; D

ev = deviation.

C

RU

SH

CU

T

PIE

RC

E

Total

microw

ear objects

Pits

Scratches

Gouges

Total

microw

ear objects

Pits

Scratches

Gouges

Total

microw

ear objects

Pits

Scratches

Gouges

N of cases

16 -

- -

32 -

- -

68 -

- -

Minim

um

50 50

0 0

0 0

0 0

0 0

0 0

Maxim

um

190 178

27 18

199 199

45 12

281 281

18 6

Range

140 128

27 18

199 199

45 12

281 281

18 6

Sum

1772.5

1626 71

75.5 1914.5

1734 133

47.5 1385

1241 129

15

Mean

110.781 101.63

4.438 4.719

59.828 54.188

4.156 1.484

20.368 18.25

1.897 0.221

95% C

I U

pper 131.547

122.75 8.329

7.432 77.874

71.733 7.205

2.607 29.572

27.451 2.753

0.425

95% C

I L

ower

90.016 80.502

0.546 2.005

41.783 36.642

1.108 0.361

11.163 9.049

1.041 0.016

Std. E

rror 9.742

9.91 1.826

1.273 8.848

8.603 1.495

0.551 4.611

4.609 0.429

0.102

Standard D

ev 38.97

39.642 7.303

5.092 50.051

48.664 8.455

3.115 38.026

38.011 3.537

0.844

Variance

1518.632 1571.5

53.329 25.932

2505.139 2368.22

71.491 9.701

1445.96 1444.8

12.512 0.712

Skew

ness 0.305

0.36 2.245

1.201 0.841

1.093 3.942

2.483 5.359

5.509 2.733

5.395

Kurtosis

-0.387 -0.927

5.647 1.561

0.687 1.376

18.221 5.694

34.081 35.396

8.279 33.815

SW

Statistic

0.98 0.947

0.673 0.858

0.92 0.898

0.521 0.554

0.447 0.417

0.604 0.288

SW P-

Value

0.963 0.442

0 0.018

0.021 0.006

0 0

0 0

0 0

Dental Microwear 42

Table 6. Kruskal-Wallis one-way analysis of variance results comparing microwear features among feeding types.

Total Objects Pits Scratches Gouges

Kruskal-Wallis one-way ANOVA

test Significant Significant

Not Significant

Significant

p value (p = 0.000) (p = 0.000) (p = .309) (p = 0.000)

Dental Microwear 43

Table 7. Mann-Whitney U test results of paired feeding type differences in microwear features.

Mann-Whitney U Total Objects Pits Gouges

Pierce v. Cut p value

Significant Significant Significant

(p = 0.000) (p = 0.000) (p = 0.006)

Pierce v. Crush p value


(p = 0.000) (p = 0.000) (p = 0.000)

Cut v. Crush p value


(p = 0.001) (p = 0.001) (p = 0.007)

Dental Microwear 44

In addition to total microwear objects, there were differences in the number of

pits, gouges, and scratches. Pitting density trends between the three feeding types

followed the same pattern as total microwear objects. There was an average of 102 (SE =

9.91) pits per crush-type tooth, 52 (SE = 7.48) per cut-type tooth, and an average of 18

(SE = 4.61) per pierce-type tooth (Table 4). Mean pit values of cut-type (p = 0.00) and

pierce-type (p = 0.00) teeth failed a Shapiro-Wilk test (Table 5) of normality; therefore, a

Kruskal-Wallis test was used to evaluate differences in pit density. Results suggested a

significant difference (χ2 = 42.87, DF = 2, p = 0.000; Table 6).

Mean pit density differences were tested among feeding type pairs. Statistically

significant differences were detected using Mann-Whitney U tests (i.e., crush- v. cut-

type, χ2 = 11.06; DF = 1, p = 0.001; crush- v. pierce-type, χ2 = 33.92; DF = 1, p = 0.000;

cut v. pierce, χ2 = 16.21; DF = 1, p = 0.000); (Table 7).

Gouge density patterns were also significantly different for feeding types;

however, gouge density trends are different than trends observed in total microwear or

pitting. There was an average of 5 (SE = 1.27) gouges per crush-type tooth, 1 (SE = 0.35)

gouge per cut-type tooth, and 0 (SE = 0.10) gouges per pierce-type tooth (Table 4). Mean

gouge values of cut- (p = 0.000) and pierce-type (p = 0.000) teeth were not normally

distributed according to a Shapiro-Wilk W test (Table 5). Kruskal-Wallis results

indicated a significant difference among feeding types (χ2 = 29.38, DF= 2, p = 0.000);

(Table 6).

Differences in gouge density were tested among feeding type pairs. All three

Mann-Whitney U tests confirmed significant difference due to feeding type (i.e., crush- v.

Dental Microwear 45

cut-type, χ2 = 7.239; DF = 1, p = 0.007; crush- v. pierce-type, χ2 = 30.09; DF = 1, p =

0.000; cut- v. pierce-type, χ2 = 7.795; DF= 1, p = 0.006); (Table 7).

Scratch density proved less capable of differentiating feeding type. There was an

average of 4 (SE = 1.83) scratches per crush-type tooth, 4 (SE = 1.14) per cut-type tooth,

and 2 (SE = 0.43) per pierce-type tooth (Table 4). Mean scratch values of cut- (p = 0.00)

and pierce-type (p = 0.00) teeth were not normally distributed (Shapiro-Wilk W test;

Table 5). Kruskal-Wallis one-way analysis of variance, however, did not indicate

significant mean differences (χ2 = 2.35; DF = 2, p = 0.31) between feeding types (Table

6).

In sum, data suggest that there are significant differences between total number of

microwear objects, pitting, and gouging densities. No statistical difference between

scratch densities in crush-, cut-, and piece-type teeth was detected.

Dental Microwear 46

DISCUSSION

Feeding type had a statistically significant effect on the total microwear object

density in Mesozoic marine reptile teeth (χ2 = 43.31, DF = 2, p = 0.000; Table 6). Results

were consistent with predictions derived from Massare’s (1987) tooth form and function

paradigm used to predict prey foraged and consequent correlation with dental microwear.

Predictions derived from Massare’s (1987) work include that pierce feeding specimens

consumed soft-bodied prey (e.g., squid and octopus), thus creating minimal dental

microwear objects. Crush-type teeth were optimal for feeding on hard-bodied, armored

fauna (e.g., ammonites, belemnites, and clams) and were predicted to have heavy wear.

Cut-type feeders had teeth specialized for foraging bony prey (e.g., large fish and smaller

marine reptiles) creating microwear densities between the two extreme feeding types of

pierce- and crush-types.

Crush-type teeth had higher average microwear objects per tooth (111) than cut-

(58) or pierce-type (20) teeth (Table 4). Dental microwear is a form of abrasive and

attritional wear in that the enameled, hardened tooth crown surface interacts with some

other material. Microwear-forming material might include occluding teeth, ingested food

material, or environmental substrate. Abrasional (formed by tooth-food and tooth-

substrate interactions) and attritional (formed by tooth-tooth interactions) microwear

features are formed by these interactions (Beatty 2005; Green 2009). Increased total

microwear densities suggest that these teeth had more interaction with wear-forming

material bearing sufficient force for formation of microwear.

Massare (1987) used tooth crown morphology, stomach content analysis, and diet

correlation of extant specimens with similar tooth form to predict prey resources

Dental Microwear 47

available to and eaten by animals in each feeding type. She used observations on skull

structure and tooth morphology of crush feeders to infer a hard, armored prey diet. No

stomach content observations of crush feeders were available to Massare, but others

found bivalves in the stomach contents of Globidens skeletons (Martin 1994; Martin and

Fox 2004). I found abundant microwear (avg = 114) on Globidens teeth. No extant taxa

comparison was made by Massare (1987) for crush-type feeding. Taylor (1987) explains

that some extant aquatic tetrapods – like freshwater turtles and walruses – feed on hard-

bodied invertebrates. Stomach content analyses of walruses show they consume bivalves

(Gordon 1984) as did benthic predators such as Globidens and placadonts included in my

microwear study. Walruses have molariform teeth with flat or bulbous occlussial surfaces

specialized for crushing prey (Taylor 1987). Although not molariform per se, molars

have a low crown height to basal diameter ratio similar to Globidens and placadont teeth.

Bivalves, gastropods, and armored cephalopods provided Mesozoic marine

reptiles with hard-bodied prey that would have inflicted significant tooth-food abrasion.

Significant tooth-to-hard-bodied food interaction likely produces more microwear

features in dental tissue compared with soft-bodied prey foraged upon by other feeding

types. Having established a significant difference between total microwear object

densities of crush, cut, and pierce teeth – what kind of features (e.g., pits, scratches, and

gouges) might interaction with hard-bodied prey produce on teeth of these three types?

Crushing teeth were the most pitted and most gouged, but the three tooth types

had similar numbers of scratches. Mean pitting and gouge densities between feeding

types had significant mean variances (χ2 = 42.87, DF = 2, p = 0.000 and χ2 = 29.38, DF =

2, p = 0.000, respectively). My results show crush-type teeth averaged 48.39% more

Dental Microwear 48

pitting than cut-type teeth and 82.04% more pits than pierce-type feeders (Table 4).

These differences are likely attributable to varying interactions with hard food items (e.g.,

shells and bones). Average crush-type teeth had 76.77% more gouges than cut feeders

and averaged 95.67% more gouges than pierce-type teeth (Table 4).

These observations are paralleled in terrestrial vertebrates. Microwear analysis of

hyraxes and primates has shown a relationship between food properties and scratch

densities (Walker and Teaford 1989). Animals that consumed food items like hard fruit

had more microwear pits than herbivorous foragers (Calandra et al. 2010). Van

Valkenburgh et al. (1990) compared hyena (bone-consuming) with cheetah (non-bone

consuming) microwear and found a high pit-to-scratch ratio in hyenas. Among the

Mesozoic marine reptiles of my study, highest pit:scratch ratios were found in crush- and

cut-type teeth.

Mesozoic marine reptiles formed part of a predatory guild partitioning food

resources from the water column and benthos (Massare 1987). Pitting is the predominant

microwear feature found on the surface of carnivore teeth (Goswami et al. 2005). My

study confirmed this: there were significantly more pits (102) than gouges (5) or

scratches (4) (Table 5) found on the surface of crush-type teeth of Mesozoic marine

reptiles. The pit-to-scratch ratio of crush feeders is approximately 25:1. This high pitting

ratio is also consistent with a carnivorous diet in terrestrial predator guilds eating hard

prey (Teaford 1988; Van Valkenburgh et al. 1990). High pit-to-scratch ratios likely

reflect ingestion of harder food items.

Scratch wear features were not abundant on examined Mesozoic marine reptile

teeth (4 scratches per examined area on crush-type teeth; 4 scratches per examined area

Dental Microwear 49

on cut-type teeth; 2 scratches per examined area on pierce-type teeth). Additionally, mean

scratch densities were not found to be statistically different between feeding types (χ2 =

2.35, p = 0.31; Table 6). There was less than a 4% difference between the average

number of scratches on crush- and cut-type teeth. The difference between scratches of

crush- and pierce-type feeders, however, was 57.11% (Table 4).

If all Mesozoic marine reptiles in this study were ancient carnivores and

carnivores usually have high pitting densities, then why is there such a paucity of pitting

scribed on the enamel surface of pierce-type teeth? In fact, tooth surfaces examined

suggest there is significantly less pitting on pierce-type teeth (18) than crush- (102) or

cut-type teeth (52) (Table 4). However, just because pierce feeders have a carnivorous

diet does not necessarily translate to the presence of microwear pitting, as microwear pit

formation occurs from tooth interaction with hard food or substrate material. Pierce-type

feeders had a tooth morphology specialized for preying upon soft-bodied fauna. They had

a pointed tooth apex with varying degrees of apical breakage and abrasive wear (Massare

1987). Most soft-bodied cephalopods like squid and octopus do not have hard food parts

with which teeth can interact; therefore, although pierce feeders were likely carnivorous,

it is plausible that their foraging likely did not usually produce microwear. However,

there were significant microwear features observed on the surface of some pierce teeth

(e.g., ROM 52695 Phytosaur with 281 total microwear objects – the most objects found

on a tooth from any feeding type; ROM 28549 Pleisosaur with 123 total microwear

objects; OMNH 01046 Platecarpus with 99 total microwear objects; and OMNH 1011

Crocodylia with 28 total microwear objects). There are several possible reasons for this

observed variation in microwear among pierce-type feeders. Some of these teeth (i.e.,

Dental Microwear 50

OMNH 1011) were difficult to assign to a single feeding category. Their tooth

morphology seemed to rule out cut- and crush-type feeding because there are no cutting

edges. Further difficulty in classifying teeth was caused by an unusual crown-

height:diameter ratio.

Morphological characters were based on Massare (1987); however, these

characters are in gradients and some diagnostic values overlap. For example, the ratio of

pierce-type crown height to basal diameter ranges from 1.3 – 4.3, while cut-type ranges

from 1.3 – 2.5 (Table 2). Most Phytosaur and Platecarpus teeth examined from the

pierce-type feeders had two cutting edges suggesting some analogy with cutting-type

teeth. Therefore, some teeth designated as pierce-type have some characteristics (e.g.,

robust base and cutting edges) to process bony prey. Predation on bony prey creates

microwear not formed from soft-bodied animal consumption.

There are other possible causes for dental microwear variability. Diet variability

within phylogenetically and morphologically contrived groups affects potential

microwear formation. Several factors affect foraging behavior and prey selection even

within a particular species. For example, seasonal changes of food item availability,

dietary resources available within an occupied microhabitat, and fall-back food items in

times of resource scarcity all potentially contribute to dentition microwear variability

(Scott et al. 2005, Galbany et al. 2009). Nonetheless, the general picture is clear:

crushing-type teeth tend to be more damaged than the other types.

Cut-type feeders had less pitting (52) than crush-type feeders (102) but more than

pierce-type feeders (18) (Table 4). These differences suggest cut-type feeders had less

hard material in their diet than did crushers; however, observed pitting in cut-type feeders

Dental Microwear 51

suggests there was significant interaction with hard food items. Paleodietary and tooth

form analysis suggests cut-type feeders had prey resources not utilized by pierce-type

feeders. Stomach contents of one Tylosaurus contained bones from a bird, bones of a

smaller Clidastes mosasaur, and shark teeth (Everhart 2005). Additionally, members of

the cutting class preyed on large fish (Williston 1898; Massare 1987), smaller

Platecarpus (Everhart 2008), and plesiosaurs (Everhart 2004). These food items

contained substantial amounts of bone for tooth. Functional studies indicate that

craniokinetic joints between tooth-bearing bones of cut-type feeders allowed initial

puncture of large prey and then back-and-forth ratcheting of prey as they were processed

and swallowed (Taylor 1987; Everhart 2005). Tooth-bone abrasion that occurred as prey

were processed in the mouth likely formed microwear pits.

Some teeth categorized as cut-type feeders showed little to no microwear objects

on the examined tooth surface (i.e., USNM 4910 Mosasaurus, ROM 52574 Platecarpus,

and SMU 75586 Mosasauridae had no microwear features). Although cut-type feeders

had a tooth morphology specialized for consuming bony prey, food resources available to

the individual might not reflect the fauna available to it as suggested by tooth form. For

example, it is possible that Mesozoic marine reptiles with cut-type teeth forged in

biozones with abundant soft-bodied prey. In these instances, dentition may not

significantly interact with the microwear-forming prey materials. Another possible reason

for less wear than predicted is weathering effects when a fossil becomes exposed in

sedimentary rock. King et al. (1999) and Goswami et al. (2005) found that physical and

chemical weathering tends to obliterate microwear features rather than creating new

microwear artifacts

Dental Microwear 52

Despite some problems, (e.g., different analysis methods and experimental

designs) microwear analysis allows inference of gross dietary observations of fossilized

predators (Gosawami et al. 2005; Purnell et al. 2007; Teaford 2007; Townsend and Croft

2008).

Experimental results from my study show significant differences in dental

microwear densities between crush-, cut- and pierce-type feeders of Mesozoic marine

reptiles (Tables 6 and 7). An important source of microwear is interaction with hard food

items in the diet. This study provides strong support for using dental microwear as an

independent test of diet as predicted from tooth morphology in Mesozoic marine reptiles.

Good methods for paleoecological and paleodietary reconstruction are limited.

Future research examining dental microwear of Mesozoic marine reptiles might consider

biostratigraphical relationships of specimens for greater understanding of the

paleoecological context of these ancient marine reptiles. This higher resolution

examination might indicate shifts in available prey resources through time. Additionally,

future work might examine microwear variation within abundantly recovered species to

assess within-species range of diet. For example, while most Tylosaurus teeth have a

significant number of microwear objects, some Tylosaurus teeth (i.e., VP 15631) lack

significant numbers of microwear features. Wear of anterior-posterior striae likely is not

reduced by consumption of a soft-bodied prey diet; however, weathering likely mutes

attrition microwear and striae alike. Correlating microwear density with striae wear might

help clarify the source of reduced microwear objects in teeth with specialized crown

morphology for processing hard or bony prey. Finally, these teeth could be re-examined

using a confocal microscope to create a three-dimensional map of a tooth surface.

Dental Microwear 53

Geographical Information System (GIS) tools could then be used to quantify feature

dimensions and then analyzed to see if more information about the diet of these Mesozoic

marine reptiles may be gleaned.

Dental Microwear 54

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ACKNOWLEDGEMENTS

I returned to Northwest Missouri State University to work on a Master’s degree

in preparation for dental school which I begin the fall 2011. I sought a research project

that afforded me the opportunity to think about teeth and work with dental materials and

tools. A journey that started for me in the study of ancient teeth has culminated in an

appreciation for what these teeth might be able to tell us about the story of aquatic life in

the Mesozoic.

I am thankful for many people helping to make this journey possible. First and

foremost I give thanks to my thesis advisor, Peter J. Adam. He was instrumental in my

achievement of two goals. The first was to gain admittance to dental school. The second

was to leave the graduate program a more educated scientist and a more effective

communicator. Adam understood that being a good advisor is a delicate balance of

knowing when to listen and encourage and when to be the adversary and critic. I am

thankful for both his academic expertise and professionalism as well as his friendship.

I am thankful for the many people at the museums where I did research for

allowing me to study and make molds of the Mesozoic marine reptile teeth: Larry Martin

and David Burnham at the University of Kansas Natural History Museum; Michael

Everhart at the Sternberg Museum of Natural History at the Ft. Hayes State University;

Michael Brett-Surman and Steve Jabo at the Smithsonian United States National Museum

of Natural History; Richard Cifelli and Jennifer Larsen at the Sam Noble Museum of

Natural History at the University of Oklahoma; Louis Jacobs, Dale Winkler, and Mike

Polcyn at the Shuler Museum at Southern Methodist University; and to Kevin Seymour

and Brian Iwama at the Royal Ontario Museum.

Dental Microwear 62

I gratefully acknowledge the funding sources that made my thesis work possible:

Dean Gregory Haddock and the NWMSU Graduate School; Gregg Dieringer and the

Department of Biology; Dean Charles McAdam and the College of Arts and Sciences at

NWMSU. My father, Phil Poynter, provided dental molding and casting material used for

this research work and allowed me to use laboratory space for specimen casting.

For this thesis I would like to thank my committee members: Peter Adam, Kurt

Haberyan, and John Pope for their time and interest toward this thesis and for their

insightful questions during my oral defense. Additionally, I thank Peter Adam, Erick

Bourassa, and Rafiq Islam for challenging me with rigorous comprehensive exam

questions.

I thank Phil Lucido for conversation and support that resulted in my return to

graduate school at NWMSU and serving as the biology graduate student advisor. I give

thanks to Lisa Crater for support and friendship. My appreciation goes to Michelle Allen

for suggesting I consider using the digital reflective microscope for this microwear

research. My friend Loren Baxter provided valuable editorial assistance in formatting the

thesis. My time at NWMSU was enriched by colleagues and friends in the Adam lab

reading group including Clint Coffey, Aaron Welch, and Ginger Fleer. Additionally, I am

grateful for the excellent preparation and support I received from the faculty of the

biology and chemistry departments at NWMSU.

Lastly, I’d like to thank my family for their love and encouragement. My parents

raised me to be curious and supported me in all pursuits. My father was crucial in

creating the successful molding techniques of teeth, was my research colleague on trips to

museums in Kansas and Washington, D.C., and guided my comparison of the teeth of

Dental Microwear 63

Mesozoic marine reptiles and humans. My grandparents, uncles and aunts, and in-laws

supported us in numerous ways from research consultation and brainstorming to cooked

meals and childcare. My wife Wendy and children Julia and Miles are the loves of my

life and the reason for making cross-country moves and career changes. My deep

gratitude goes to them for their steadfast love and support. The journey is worth walking

with them beside me.

Documents

USING DENTAL MICROWEAR ANALYSIS FOR ...hardness and size available to a predator (Budney et al. 2006). Presence of a cementum-covered root situated in a deep socket and presence of