John Whitlock | Mount Aloysius College (original) (raw)

Papers by John Whitlock

Huang/Stem Cells in Craniofacial Development and Regeneration, 2013

ABSTRACT

PLoS ONE, 2007

Fossils of the Early Cretaceous dinosaur, Nigersaurus taqueti, document for the first time the cr... more Fossils of the Early Cretaceous dinosaur, Nigersaurus taqueti, document for the first time the cranial anatomy of a rebbachisaurid sauropod. Its extreme adaptations for herbivory at ground-level challenge current hypotheses regarding feeding function and feeding strategy among diplodocoids, the larger clade of sauropods that includes Nigersaurus. We used high resolution computed tomography, stereolithography, and standard molding and casting techniques to reassemble the extremely fragile skull. Computed tomography also allowed us to render the first endocast for a sauropod preserving portions of the olfactory bulbs, cerebrum and inner ear, the latter permitting us to establish habitual head posture. To elucidate evidence of tooth wear and tooth replacement rate, we used photographic-casting techniques and crown thin sections, respectively. To reconstruct its 9-meter postcranial skeleton, we combined and size-adjusted multiple partial skeletons. Finally, we used maximum parsimony algorithms on character data to obtain the best estimate of phylogenetic relationships among diplodocoid sauropods. Nigersaurus taqueti shows extreme adaptations for a dinosaurian herbivore including a skull of extremely light construction, tooth batteries located at the distal end of the jaws, tooth replacement as fast as one per month, an expanded muzzle that faces directly toward the ground, and hollow presacral vertebral centra with more air sac space than bone by volume. A cranial endocast provides the first reasonably complete view of a sauropod brain including its small olfactory bulbs and cerebrum. Skeletal and dental evidence suggests that Nigersaurus was a ground-level herbivore that gathered and sliced relatively soft vegetation, the culmination of a low-browsing feeding strategy first established among diplodocoids during the Jurassic.

Naturwissenschaften, 2010

Sauropod dinosaur bones are common in Mesozoic terrestrial sediments, but sauropod skulls are exc... more Sauropod dinosaur bones are common in Mesozoic terrestrial sediments, but sauropod skulls are exceedingly rare—cranial materials are known for less than one third of sauropod genera and even fewer are known from complete skulls. Here we describe the first complete sauropod skull from the Cretaceous of the Americas, Abydosaurus mcintoshi, n. gen., n. sp., known from 104.46 ± 0.95 Ma (megannum) sediments from Dinosaur National Monument, USA. Abydosaurus shares close ancestry with Brachiosaurus, which appeared in the fossil record ca. 45 million years earlier and had substantially broader teeth. A survey of tooth shape in sauropodomorphs demonstrates that sauropods evolved broad crowns during the Early Jurassic but did not evolve narrow crowns until the Late Jurassic, when they occupied their greatest range of crown breadths. During the Cretaceous, brachiosaurids and other lineages independently underwent a marked diminution in tooth breadth, and before the latest Cretaceous broad-crowned sauropods were extinct on all continental landmasses. Differential survival and diversification of narrow-crowned sauropods in the Late Cretaceous appears to be a directed trend that was not correlated with changes in plant diversity or abundance, but may signal a shift towards elevated tooth replacement rates and high-wear dentition. Sauropods lacked many of the complex herbivorous adaptations present within contemporaneous ornithischian herbivores, such as beaks, cheeks, kinesis, and heterodonty. The spartan design of sauropod skulls may be related to their remarkably small size—sauropod skulls account for only 1/200th of total body volume compared to 1/30th body volume in ornithopod dinosaurs.

Background: Tooth replacement rate can be calculated in extinct animals by counting incremental l... more Background: Tooth replacement rate can be calculated in extinct animals by counting incremental lines of deposition in tooth dentin. Calculating this rate in several taxa allows for the study of the evolution of tooth replacement rate. Sauropod dinosaurs, the largest terrestrial animals that ever evolved, exhibited a diversity of tooth sizes and shapes, but little is known about their tooth replacement rates.
Methodology/Principal Findings: We present tooth replacement rate, formation time, crown volume, total dentition volume, and enamel thickness for two coexisting but distantly related and morphologically disparate sauropod dinosaurs Camarasaurus and Diplodocus. Individual tooth formation time was determined by counting daily incremental lines in dentin. Tooth replacement rate is calculated as the difference between the number of days recorded in successive replacement teeth. Each tooth family in Camarasaurus has a maximum of three replacement teeth, whereas each Diplodocus tooth family has up to five. Tooth formation times are about 1.7 times longer in Camarasaurus than in Diplodocus (315 vs. 185 days). Average tooth replacement rate in Camarasaurus is about one tooth every 62 days versus about one tooth every 35 days in Diplodocus. Despite slower tooth replacement rates in Camarasaurus, the volumetric rate of Camarasaurus tooth replacement is 10 times faster than in Diplodocus because of its substantially greater tooth volumes. A novel method to estimate replacement rate was developed and applied to several other sauropodomorphs that we were not able to thin section.
Conclusions/Significance: Differences in tooth replacement rate among sauropodomorphs likely reflect disparate feeding strategies and/or food choices, which would have facilitated the coexistence of these gigantic herbivores in one ecosystem. Early neosauropods are characterized by high tooth replacement rates (despite their large tooth size), and derived titanosaurs and diplodocoids independently evolved the highest known tooth replacement rates among archosaurs.

Stem cells in craniofacial development, regeneration and repair.

Regeneration of reptile teeth

International Journal of Oral Science

Tooth replacement is a common trait to most vertebrates, including mammals. Mammals, however, hav... more Tooth replacement is a common trait to most vertebrates, including mammals. Mammals, however, have lost the capacity for continuous tooth renewal seen in most other vertebrates, and typically have only 1–2 generations of teeth. Here, we review the mechanisms of tooth replacement in reptiles and mammals, and discuss in detail the current and historical theories on control of timing and pattern of tooth replacement and development.

Background As gigantic herbivores, sauropod dinosaurs were among the most important members of Me... more Background As gigantic herbivores, sauropod dinosaurs were among the most important members of Mesozoic communities. Understanding their ecology is fundamental to developing a complete picture of Jurassic and Cretaceous food webs. One group of sauropods in particular, Diplodocoidea, has long been a source of debate with regard to what and how they ate.

The rise of computational methods and widespread availability of phylogenetic software packages h... more The rise of computational methods and widespread availability of phylogenetic software packages has resulted in a dramatic increase in the number of phylogenetic analyses published each year. We anticipate that as the number of workers and the number of analyses continues to increase, interest in so-called 'meta-analyses’ that compare not just the resultant trees, but the data themselves, will also increase. Here, we demonstrate a simple method for authors to facilitate such comparisons by visually representing the character data included in their analyses, the Character Distribution Map (CDM).

UMI. ProQuest® Dissertations & Theses The world's most comprehensive collection ... more UMI. ProQuest® Dissertations & Theses The world's most comprehensive collection of dissertations and theses. Learn more... ProQuest. Paleoecology and Systematics of the Diplodocoid Sauropods. by Whitlock, John Andrew ...

Palaeogeography, Palaeoclimatology, Palaeoecology, Jan 1, 2011

The Late Jurassic sauropod Australodocus bohetii was originally assigned to Diplodocidae, primari... more The Late Jurassic sauropod Australodocus bohetii was originally assigned to Diplodocidae, primarily on the basis of bifurcate neural spines. The holotype and paratype materials of A. bohetii are re-examined and found to have closer affinities with Brachiosaurus and relatives than with any diplodocoid. The presence of a second titanosauriform sauropod in the Tanzanian fauna is important for understanding the palaeoecology of the region. Comparisons between Tendaguru and three other contemporaneous sauropod faunas (Morrison Formation, USA; Lourinhã and Alcobaça formations, Portugal; Cañadón Calcáreo, Argentina) are also made. The revised Tendaguru fauna, with its high diversity of high-browsing Macronarians, now more closely matches the conifer-forest dominated landscape inferred from palaeobotanical evidence. The Morrison Formation, dominated by low-browse, is once again the only formation containing multiple diplodocids.

PloS one, Jan 1, 2011

Background: The axial skeleton of extinct saurischian dinosaurs (i.e., theropods, sauropodomorphs... more Background: The axial skeleton of extinct saurischian dinosaurs (i.e., theropods, sauropodomorphs), like living birds, was pneumatized by epithelial outpocketings of the respiratory system. Pneumatic signatures in the vertebral column of fossil saurischians include complex branching chambers within the bone (internal pneumaticity) and large chambers visible externally that are bounded by neural arch laminae (external pneumaticity). Although general aspects of internal pneumaticity are synapomorphic for saurischian subgroups, the individual internal pneumatic spaces cannot be homologized across species or even along the vertebral column, due to their variability and absence of topographical landmarks. External pneumatic structures, in contrast, are defined by ready topological landmarks (vertebral laminae), but no consistent nomenclatural system exists. This deficiency has fostered confusion and limited their use as character data in phylogenetic analysis.

Palaeontology, Jan 1, 2011

The recent description of an anterior caudal vertebra purportedly belonging to a diplodocid sauro... more The recent description of an anterior caudal vertebra purportedly belonging to a diplodocid sauropod from the Early Cretaceous of China has the potential to drastically alter our interpretation of the evolution and timing of geographical dispersal of a major dinosaur lineage. However, comparison with a wider taxonomic sample points more strongly towards titanosauriform affinities for this specimen, which is in keeping with the affinities of all other sauropods known from the Cretaceous of Asia. We explain the disparity in phylogenetic interpretation of this isolated vertebra as a by-product of scoring differences and analysis of fragmentary material using repurposed data matrices. Rescoring the isolated vertebra based on our interpretation of the anatomy and rerunning the original analyses removes the specimen from Diplodocoidea but does not place it within Titanosauriformes, because of inadequacy in taxon and character sam-pling inherited from the repurposed data matrices. We suggest that phylogenetic analysis must begin with an initial hypothesis of affinity, based on comparative anatomy and spatiotemporal distributions, that must be adequately tested by the data matrix employed -i.e. data matrices should be tailored to sample anatomically, geographically and temporally relevant clades, and new characters should be added in tandem with new taxa so that the potential synapomorphy pool is not diluted. This is especially important for analyses of fragmentary specimens, which are likely to return coarse phylogenetic results with general evolutionary and palaeobiogeographical implications.

Journal of Vertebrate Paleontology, Jan 1, 2010

Zoological Journal of the Linnean Society

Diplodocoidea includes some of the first well-known sauropod dinosaurs, including such late 19 th... more Diplodocoidea includes some of the first well-known sauropod dinosaurs, including such late 19 th century and early 20 th century discoveries as Apatosaurus, Diplodocus, and Dicraeosaurus. As a consequence of their long history of study, the basic set of suprageneric diplodocoid interrelationships is well resolved, and the diagnostic features of each genus are well established. However, intergeneric relationships are less resolved, including the relationships of putatively basal taxa like Amphicoelias and Haplocanthosaurus, the flagellicaudatan Suuwassea, and the highly specialized rebbachisaurids. For the rebbachisaurids, this uncertainty is coupled with a recent surge in the discovery of new taxa. Comparative cladistic methods demonstrate that character and taxon sampling need to be improved before greater phylogenetic resolution can be expected. Here, I present a new phylogenetic analysis that resolves many of the outstanding questions regarding the relationships within Diplodocoidea and examines palaeobiogeographical trends within the group. Suuwassea is recovered as a basal dicraeosaurid (the only Laurasian member of the group), and two distinct clades of rebbachisaurids are identified: a group closely allied with Nigersaurus and a clade associated with Limaysaurus. Amphicoelias, Amazonsaurus, and Haplocanthosaurus are provisionally placed as successively less-derived taxa at the base of Diplodocoidea. A North American origin for Diplodocoidea and Flagellicaudata is hypothesized based on the geographical and temporal distribution of those taxa. Rebbachisaurid taxa demonstrate a South American/African vicariance pattern, but the timing of the event pre-dates the proposed final rifting of those continents by c. 40 million years; the meaning of this discrepancy is uncertain.

Journal of Vertebrate …, Jan 1, 2010

More than any other sauropod dinosaur group, the long-necked herbivores belonging to Diplodocoide... more More than any other sauropod dinosaur group, the long-necked herbivores belonging to Diplodocoidea have been defined by their skulls. Their unique skull shape, which is extremely elongate antorbitally, with a transversely broad, square snout packed at its anterior extreme with narrow-crowned, pencil-like teeth, has served as a touchstone for describing the biology of these animals ever since the discovery of the first skull in the late 19th century. In particular, the unusual diplodocoid skull has been discussed frequently in the context of examining feeding behavior, spawning hypotheses ranging from branch stripping, propalinal shearing, and aquatic plant 'grazing.' Here, we describe a juvenile skull of Diplodocus (Carnegie Museum 11255) that does not share the unusually blunted snout and anteriorly sequestered teeth seen in adult specimens, suggesting that adults and juveniles may have differed greatly in their feeding behavior, an ontogenetic distinction that may be unique among sauropodomorphs.

Journal of Vertebrate Paleontology, Jan 1, 2010

The early Eocene great lakes of the Green River system preserved a rich fauna, allowing detailed ... more The early Eocene great lakes of the Green River system preserved a rich fauna, allowing detailed study of the paleoecology of the area. Two genera, †Priscacara and †Mioplosus, are interesting because they are among the earliest well-known representatives of Percoidei sensu lato, and so offer a chance to explore the evolution of the North American fish fauna. A phylogenetic analysis including †Priscacara, †Mioplosus, and representatives of some 'basal' percoid families suggests that †Priscacara is a member of Moronidae, and that †Mioplosus has affinities with Lateolabrax, Siniperca, and Lates. †Priscacara is recovered as paraphyletic relative to the rest of Moronidae, primarily on the basis of meristic characters; in the absence of more robust evidence, both †P. serrata and †P. liops are retained within †Priscacara. The phylogenetic position of †Priscacara suggests a trans-Atlantic connection, because Moronidae contain genera from eastern North America and Europe. †Mioplosus is suggestive of an Asian link to the Eocene Green River system, due to its relationship with the Western Pacific Lateolabrax, the Asian Siniperca, and the African/Asian Lates.

Huang/Stem Cells in Craniofacial Development and Regeneration, 2013

ABSTRACT

PLoS ONE, 2007

Naturwissenschaften, 2010

Stem cells in craniofacial development, regeneration and repair.

Regeneration of reptile teeth

International Journal of Oral Science

Palaeogeography, Palaeoclimatology, Palaeoecology, Jan 1, 2011

PloS one, Jan 1, 2011

Palaeontology, Jan 1, 2011

Journal of Vertebrate Paleontology, Jan 1, 2010

Zoological Journal of the Linnean Society

Journal of Vertebrate …, Jan 1, 2010

Journal of Vertebrate Paleontology, Jan 1, 2010

Incremental lines of von Ebner are microstructural features that demarcate the daily apposition o... more Incremental lines of von Ebner are microstructural features that demarcate the daily apposition of dentin, such that the total number of incremental lines in a tooth serves as a measure of that tooth’s age. Differences in incremental line counts between successive replacement teeth within an alveolus provide a quantitative estimate of tooth replacement rate. Tooth formation times and rates have been shown to vary substantially among amniotes. We examined tooth replacement rates in two contemporaneous sauropod dinosaurs from western North America: Diplodocus and Camarasaurus. CT data reveal that each alveolus in Diplodocus has up to 5 replacement teeth, whereas Camarasaurus has a maximum of 3. Incremental lines of von Ebner are on average ~14 microns apart in Diplodocus and ~23 microns apart in Camarasaurus. Tooth formation times are about twice as long in Camarasaurus as in Diplodocus. Average tooth replacement rate in Diplodocus is ~35 days, similar to the replacement time of ~30 days found in Nigersaurus, which possessed a tooth battery. Tooth replacement rates in diplodocoid sauropods appear to be faster than those in any other dinosaurs, including derived ornithischian herbivores with tooth batteries. Preliminary data for Camarasaurus indicate a much slower rate of replacement. In the absence of incremental line counts from thin-sections in other sauropods, successive replacement tooth size was used as a proxy for replacement rate (i.e., a larger size discrepancy between successive replacement teeth indicates a slower replacement rate). Basal sauropods have fewer (1–2) replacement teeth per alveolus, and successive replacement teeth show a larger size difference than in Camarasaurus. In derived titanosaurs, which had narrow-crowned teeth, there are a high number of teeth per alveolus and small size discrepancies between successive replacement teeth. Our data suggest that neosauropods are characterized by faster tooth replacement rates than basal sauropods, and that derived titanosaurs and diplodocoids independently evolved very fast tooth replacement rates.

The unusual skulls of Diplodocus and its relatives, with their protracted, blunt snouts and anter... more The unusual skulls of Diplodocus and its relatives, with their protracted, blunt snouts and anteriorly restricted dentition have spawned a number of theories but no consensus regarding the method by which these megaherbivores gathered food. Recent work has shown a considerable variation in snout shape throughout the group, ranging from the square-snouted Nigersaurus to the more gently rounded Dicraeosaurus. These differences in snout shape are coupled with variations in dental microwear, suggesting that snout shape is related to diet. A broad snout shape and microwear patterns consistent with high dietary grit indicate that diplodocoids like Diplodocus and Nigersaurus were low-level browsers. Others, like Dicraeosaurus, were more likely to have been selective low-to mid-height browsers, based on their comparatively pointed snout and low-grit content diet. Jaw elements referred to Tornieria indicate that it was also a selective browser. In order to study the evolution of herbivory of diplodocoids, a new phylogenetic analysis of the group was conducted. This analysis attempts to resolve the interrelationships of the group by creating a new character-taxon matrix generated by first hand observation of specimens. Most interesting are the relationships of the highly specialized rebbachisaurids, the most derived members of which can be divided into two clades: a South American clade including Limaysaurus and Cathartesaura; and a more widely distributed clade including the South American Zapalasaurus as sister taxon to the African Nigersaurus and an unnamed rebbachisaurid from Europe. Of additional interest is the recovery of Suuwassea as a basal dicraeosaurid, making it the only Laurasian representative of that group. Mapping dietary information onto the best-fit cladogram indicates that feeding behavior was independent of phylogeny. Instead, it appears that herbivorous adaptations were more directly tied to regional ecology. The phenotypic plasticity expressed between taxa is on par with the variation in snout shape recognized during the ontogeny of Diplodocus, and suggests that feeding specializations may have been easier to evolve than previously recognized.

Although relatively common by sauropod dinosaur standards, few diplodocoid skulls have received t... more Although relatively common by sauropod dinosaur standards, few diplodocoid skulls have received thorough description in the post-war era. One of the first specimens to benefit from a modern treatment was Carnegie Museum (CM) specimen 11162, a large, nearly complete skull assignable to Apatosaurus louisae. With the recent resurgence in interest in diplodocoid evolution and ecology, this specimen is of great significance: it is the most complete described skull of Apatosaurus, and is a primary source of information regarding the facial skeleton of flagellicaudatans other than Diplodocus and Dicraeosaurus. Here, we revisit this specimen following additional preparation and the recent publication of several descriptions of diplodocoid skulls that have highlighted new characters and regions of interest.
We identify or confirm six size-independent cranial character states that distinguish Apatosaurus from Diplodocus. We confirm that Apatosaurus lacks a basipterygoid recess, and that the basipterygoid processes are autapomorphically flared distally, as previously published. We also confirm the presence of globose basal tubera, as opposed to the sheet-like tubera of Diplodocus; we further observe that the tubera of Apatosaurus face posteriorly, not posterolaterally as in Diplodocus. In lateral view, the squamosal and quadratojugal of Apatosaurus do not appear to closely approximate each other as they do in Diplodocus. Finally, the supraoccipital crest of Apatosaurus is massive, prominent, and flanked by deep nuchal fossae, unlike the relatively low crest and shallow fossae of Diplodocus. We are unable to confirm the absence of a sharp-lipped fossa surrounding the preantorbital fenestra; this fossa has been proposed as an autapomorphy of Diplodocus, but the poor preservation of this region of CM 11162 obscures the condition in Apatosaurus.
In addition, we document the presence in CM 11162 of two character states that were previously identified as autapomorphies of Diplodocus: no contact between the vomer and premaxillae, and pterygoid at least partially medial to ectopterygoid on transverse palatal hook. The presence of these character states in Apatosaurus suggests that they are synapomorphies of a more inclusive diplodocoid clade, probably Diplodocidae."

Diplodocid sauropods are characterized by cranial characters that may be directly related to herb... more Diplodocid sauropods are characterized by cranial characters that may be directly related to herbivory: the maxilla and premaxilla are elongated, with the teeth located far anterior of the quadrate/articular joint, and the quadrate is inclined, such that it lies beneath the orbit ventrally and posterior to the orbit dorsally, bringing the jaw joint itself forward. Preliminary investigation of the morphology of juvenile Diplodocus indicates that younger individuals do not completely share this morphology.
The present study represents an empirical approach to quantifying ontogenetic change in the skull of Diplodocus through geometric morphometrics. Individual skulls of varying size were reconstructed in lateral, dorsal, and anterior view. Landmark and semi- landmark based morphometric analyses on these reconstructions indicate allometric growth, particularly in the facial regions. Of particular significance are the changes that occur in the tooth-bearing regions. Such changes include the relative repositioning of the last tooth, which moves anteriorly relative to the rest of the face with increasing skull size. The anterior margin of the skull, formed by the premaxillary and maxillary bones, broadens, forming the truncate, flattened shape of the adult. Little relative change occurs in the region of the braincase. The observed changes represent a shift in shape from a more conventional oral morphology to the divergent shape typified by Diplodocus adults. Moreover, the largest excursions occur between the large sub-adult and adult specimens. This may be concurrent with the plateau observed at the upper range of growth rates, but a lack of definite age control hinders comparisons of growth rate and skull morphology. The nature and timing of these changes, therefore, have important consequences for interpretations of the life history and feeding mechanics of Diplodocus.

Diplodocoid sauropods are notable not only for their large average size but also for their remark... more Diplodocoid sauropods are notable not only for their large average size but also for their remarkable skulls, the use of which in gathering food has long been a source of confusion. Particularly noteworthy is the shape of the snout, which is commonly described as broad and blunted. Snout shape has been correlated with feeding behavior in mammals, both living and extinct. Blunt snouts are most often found in grazers and low-croppers, whereas rounded or pointed snouts are associated with more selective browsers: in some instances relatively small absolute differences in shape correlate with highly distinct diets. This relationship may have important consequences for determining the habits of diplodocoid sauropods. Prior work has shown that snout shape differs between adults and juveniles within at least one genus, Diplodocus; it also appears likely that this is true for other diplodocoid taxa as well. Snout shape also varies between taxa, both drastically, as in the disparate shapes of Nigersaurus and Diplodocus, as well as subtly, such as between Diplodocus, Apatosaurus and Dicraeosaurus. Snout shape can be quantified by a metric that is here termed the premaxilla-maxilla index (PMI). Comparisons of PMI and enamel microwear (an indicator of diet) in a sample of diplodocoids allow for the relationship of shape and diet to be tested. Adult skulls with blunt snouts (e.g. Diplodocus) typically have teeth with unidirectional scratch patterns and increased pitting, both indicators of low-height grazing behavior. Preliminary investigations of skulls with rounded snouts indicate an association with less regular wear patterns, which may be related to browsing rather than grazing behavior. Shape and wear data from some diplodocoid and dicraeosaurid sauropods are examined in the context of an ongoing phylogenetic analysis, building towards the development of a comprehensive hypothesis of the evolution of variability in feeding behavior in diplodocoid sauropods.

The diplodocoid sauropods have been defined in large part by their blunt, shovel-snouted skulls a... more The diplodocoid sauropods have been defined in large part by their blunt, shovel-snouted skulls and their narrow-crowned, anteriorly sequestered dentition. This arrangement of the snout and teeth has also been the focus of some controversy, and hypotheses abound to explain the function of this anatomy for feeding. Here we describe a nearly complete juvenile skull of Diplodocus (CM 11255) which does not conform to the morphology expected based upon larger specimens. Although somewhat laterally crushed, the skull is still largely intact, and CT imaging has revealed a nearly complete palate, allowing an accurate reconstruction of the lateral dimensions of the skull. In dorsal view, the reconstructed CM 11255 is narrower than would be expected and quite rounded anteriorly, in contrast to the characteristic squared-off snout of adult Diplodocus. The dentition in CM 11255 is also not restricted to the extreme anterior portion of the skull, and in fact extends posteriorly to near the preantorbital fenestra. A rounded snout in dorsal view is more typical of basal sauropods, and ontogenetic change towards a square snout is potentially related to feeding behavior and specialization in adults. Work comparing snout shapes and dental microwear features between different diplodocoid sauropod genera (including Diplodocus) suggests that snout shape is closely linked to feeding strategy. Although no microwear features have been recovered from CM 11255, the shape change suggests ontogenetic niche partitioning between adults and juveniles is suggested—smaller juveniles accessed nutrients through highly selective browsing behaviors, and large adults obtained nutrition through less selective, bulk browsing behaviors.

Sauropods evolved from small, bipedal omnivores (e.g., Panphagia). Over time these basal sauropod... more Sauropods evolved from small, bipedal omnivores (e.g., Panphagia). Over time these basal sauropodomorphs became more reliant on herbivory and achieved larger body sizes, eventually becoming obligate quadrupeds. With this increase in body size and dietary shift came an increase in tooth wear, which reduced dental effectiveness. Sauropods responded to increased tooth wear by increasing crown volume and/or increasing tooth replacement rate. Here, we present data describing both responses and place them in a temporal and phylogenetic context. Replacement rate data are based on histological study when possible. In all other cases, rate is approximated using a cross-checked proxy: the height corrected ratio (HCR), calculated by dividing the height ratio of successive teeth in a family by mature tooth height. Higher HCR scores indicate less time between tooth formation events and correspond to faster replacement rates. Basal sauropodomorphs (e.g., Plateosaurus) had low-crowned, leaf-shaped teeth and one replacement tooth per family. Spatulate tooth crowns with greatly increased volumes (~5x that of Plateosaurus) evolved in basal sauropods (e.g., Tazoudasaurus), which enabled these taxa to cope with more extensive tooth wear and resulted in slower replacement (HCR ~2.0). Replacement rate first increased in more derived eusauropod taxa on the stem leading to Neosauropoda (e.g., Mamenchisaurus). These taxa possessed up to two replacement teeth per family and higher HCRs (~4.0). A second increase in replacement rate occurred in Late Jurassic neosauropods. These taxa (e.g., Camarasaurus, Diplodocus) are observed to have three or more replacement teeth per family, which were replaced at least every 62 days. Within Neosauropoda, at least two secondary reductions in crown volume occurred, in the clades Diplodocoidea and Titanosauriformes. This reduction in volume (~14% that of spatulate crowns) was coupled with an increase in replacement rate in both instances (HCR 12.4+). Narrow-crowned taxa often have five or more replacement teeth per family; in diplodocoids (e.g., Diplodocus), replacement occurred twice as fast (30–35 days) as in spatulate-crowned neosauropods.

Character data in a phylogenetic analysis are often seen as being trapped in a ‘black box’, hidde... more Character data in a phylogenetic analysis are often seen as being trapped in a ‘black box’, hidden from outside observers. In addition to the obvious difficulties this poses for independent assessment of the results of an analysis, important patterns within the data may go unnoticed without further examination. Here, we outline a simple graphical method for displaying regional character information. These images provide a convenient visual shorthand that allows a reader to understand at a glance the proportional representation of various anatomical regions in a matrix. This information can be used to identify regions of the body that are phylogenetically important, to identify areas of data paucity, and as a companion to comparative cladistic methods as a way to compare data between different analyses. In addition, these methods can be adapted to display missing data by body region; in tandem, these images provide a simple way to examine the influence of missing data on phylogenetically problematic taxa. Applying these methods to phylogenetic analyses of Sauropoda and its subgroups reveals interesting trends. Large-scale analyses examining the evolution of Sauropoda as a whole are represented subequally by characters from each of the three main body regions (cranial, axial, and appendicular). This is not surprising, as the broad taxonomic scope of these analyses covers multiple alterations to the skull, changes in the complexity of neural spines and internal pneumaticity of vertebral centra, and important locomotor transitions. Finer scale analyses, such as those of the subgroup Diplodocoidea, reduce the importance of certain body regions, such as the appendicular skeleton, and highlight others, such as the dermal skull (20% of all characters). The relative importance of cranial characters is suggested to be a function of innovations focused on the cranial region over the limbs and girdles. Curiously, the cranial region is also the region with the most missing data (41% cells unscorable), which may have been a contributor to a lack of phylogenetic resolution in the past.

PLoS ONE, 2007