Holly Woodward Ballard

• Ph.D.
• Professor at Oklahoma State University - Center for Health Sciences

At the end of the Cretaceous, a bolide impact wiped out ~75% of life on Earth, but turtles show minimal gross anatomical changes. Herein, we examine the shell histology from trionychid turtles 2 million years before and 8 million years after the extinction event. We collected over 25,000 semi‐quantitative and quantitative measurements and statistic...

All paleohistological observations should be contextualized with modern taxa, and although the importance of variables like latitude, body size, and age are broadly acknowledged for all animals, quantification of the importance of these variables has not been undertaken for many groups, including soft‐shelled turtles. In an effort to both better un...

Saurophaganax maximus is the designation of material attributed to a massive theropod dino-saur recovered from the Kenton 1 Quarry in the Kenton Member of the Upper Jurassic Morrison Formation of Oklahoma. The theropod was originally given the name Saurophagus maximus, but was later revised to Saurophaganax maximus because the former did not confor...

In the context of an increasing interest for Pseudosuchia, we have compiled a Special Issue, comprising 14 collaborative studies that deepen our understanding of pseudosuchian evolution. These contributions range from the description of a new taxon to exhaustive reviews of thermometabolism, morphological adaptation, systematics, and detailed invest...

Identifying sex in extinct archosaurs has proven difficult due, in part, to low sample sizes, preservation biases, and methodology. While previous studies have largely focused on morphological traits, here we investigate intracortical signals of egg‐shelling in extant alligators. Egg‐shelling requires large mobilizations of calcium reserves. Aves u...

The clade Pseudosuchia appeared 250 million years ago. The exclusively semi‐aquatic Crocodylia, which includes crocodiles, alligators, caimans, and gharials is the only surviving subgroup. Investigating Crocodylia biology is pivotal for inferring traits of extinct pseudosuchians. Alligator femur length is widely used for modeling pseudosuchian body...

A recent study showed evidence that endothermy was ancestral for amniotes using a variety of proxies and a large sample of taxa. However, it did not include numerous crucial taxa. We reevaluated this hypothesis using a large sample of early amniotes and tetrapodomorphs. We inferred the probability of endothermy for each taxon using a model construc...

Caenagnathidae is a clade of derived, Late Cretaceous oviraptorosaurian theropods from Asia and North America. Because their remains are rare and often fragmentary, caenagnathid diversity is poorly understood. Anzu wyliei is the only caenagnathid species currently described from the late Maastrichtian Hell Creek Formation of the USA and is also amo...

Cranial bony projections (“headgear”) have diverse forms and functions, such as defense, species recognition, mate selection, and thermoregulation. Most commonly, they are associated with the artiodactyl infraorder, Pecora. All pecoran headgear—antlers, horns, ossicones, and pronghorns—are osseous protrusions of the frontal or parietal bone with an...

Fossil bones were once living tissues that demanded internal blood perfusion in proportion to their metabolic requirements. Metabolic rates were primarily associated with bone growth (modeling) in the juvenile stages and with alteration and repair of existing bone affected by weight bearing and locomotion (remodeling) in later stages. This study es...

Modern crocodylians—crocodiles, alligators, caiman (Central and South America), and gharials (India)—have evolved over 250 million years from a fully terrestrial, bipedal ancestor. Along with birds, crocodylians are the only living members of Archosauria, the group including nonavian dinosaurs. Ruling Reptiles features contributions on a broad ran...

Ostriches and emus are among the largest extant birds and are frequently used as modern analogs for the growth dynamics of non-avian theropod dinosaurs. These ratites quickly reach adult size in under 1 year, and as such do not typically exhibit annually deposited growth marks. Growth marks, commonly classified as annuli or lines of arrested growth...

The paucity of early Pleistocene hominin fossils in Eurasia hinders an in-depth discussion on their paleobiology and paleoecology. Here we report on the earliest large-bodied hominin remains from the Levantine corridor: a juvenile vertebra (UB 10749) from the early Pleistocene site of ‘Ubeidiya, Israel, discovered during a reanalysis of the faunal...

The whole‐body (tachymetabolic) endothermy seen in modern birds and mammals is long held to have evolved independently in each group, a reasonable assumption when it was believed that its earliest appearances in birds and mammals arose many millions of years apart. That assumption is consistent with current acceptance that the non‐shivering thermog...

Bone histology of crown-group birds is a research topic of great interest, permitting insight into the evolution of remarkably high growth rates in this clade and variation across the altricial-precocial spectrum. In this study, we describe microanatomical characteristics of the humerus and femur in partial growth series from 14 crown group birds r...

Osteohistology, the study of bone microstructure, provides an important avenue for assessing extinct and extant vertebrate growth and life history. Cortical vascularity and collagen fibre organization are direct reflections of growth rate, while bone growth marks are indicative of absolute age. However, each skeletal element has its own ontogenetic...

Despite the general perception that crocodilians exhibit indeterminate growth, recent long‐term field studies and laboratory investigations have independently suggested that growth in these animals is determinate. In this study, we had the unique opportunity to examine skeletal growth in a wild adult American alligator (Alligator mississippiensis)...

Ancient fossils give clues as to when features of modern tetrapod bones emerged.

Histological examination of bone microstructure provides insight into extant and extinct vertebrate physiology. Fossil specimens sampled for histological examination are typically first embedded in an inexpensive polyester resin and then cut into thin sections, mounted on slides, and polished for viewing. Modern undecalcified bone is chemically pro...

The avian transition from long to short, distally fused tails during the Mesozoic ushered in the Pygostylian group, which includes modern birds. The avian tail embodies a bipartite anatomy, with the proximal separate caudal vertebrae region, and the distal pygostyle, formed by vertebral fusion. This study investigates developmental features of the...

Dinosaurs are frequently used as ambassadors of science for children and adults, garnering major attention at museums and within popular culture. A new mentorship opportunity at Oklahoma State University Center for Health Sciences (OSU‐CHS) utilizes the association of dinosaurs and science learning to provide research experience as well as educatio...

The developmental and functional advantages of vertebrate metaplastic hard tissue is still relatively unclear. Metaplastic tissue forms from the direct transformation of one cell type to another. Specifically, mineralization of preformed dense connective tissue results in intratendinous metaplastic tissue, and has been described in a variety of tax...

Despite its iconic status as the king of dinosaurs, Tyrannosaurus rex biology is incompletely understood. Here, we examine femur and tibia bone microstructure from two half-grown T. rex specimens, permitting the assessments of age, growth rate, and maturity necessary for investigating the early life history of this giant theropod. Osteo-histology r...

Analysis of ontogenetic changes in long bone microstructure aid in vertebrate life history reconstructions. Specifically, osteohistological examination of common fauna can be used to infer growth strategies of biologically uncommon, threatened, or extinct vertebrates. Although nine-banded armadillo biology has been studied extensively, work on grow...

Transverse sections of sampled femora under linearly polarized light. (A) UTCM 802, (B) UTCM 801, (C) OMNH 39188, (D) UTCM 1557, (E) OMNH 40173, and (F) OMNH 40175. All sections are stained with toluidine blue. FL—femur length. Note–some sections were flipped along the horizontal axis to allow for easier comparisons. (TIF)

Transverse sections of sampled tibiae under linearly polarized light. (A) UTCM 802, (B) UTCM 801, (C) OMNH 39188, (D) UTCM 1557, (E) OMNH 40173, (F) OMNH 40175. All sections stained with toluidine blue. TL = tibia length. Note–some sections were flipped along the horizontal axis to allow for easier comparisons. (TIF)

Transverse sections of sampled femora under circularly polarized light. (A) UTCM 802, (B) UTCM 801, (C) OMNH 39188, (D) UTCM 1557, (E) OMNH 40173, and (F) OMNH 40175. All sections are stained with toluidine blue. FL—femur length. Note–some sections were flipped along the horizontal axis to allow for easier comparisons. (TIF)

Transverse sections of sampled tibiae under circularly polarized light. (A) UTCM 802, (B) UTCM 801, (C) OMNH 39188, (D) UTCM 1557, (E) OMNH 40173, (F) OMNH 40175. All sections stained with toluidine blue. TL = tibia length. Note–some sections were flipped along the horizontal axis to allow for easier comparisons. (TIF)

Annually, tetrapod vertebrate bone apposition is briefly interrupted, which typically coincides with the yearly environmental nadir. The temporary appositional hiatus is histologically recorded in bone cortex as a hypermineralized ring termed a line of arrested growth (LAG). One paleohistology study used this known LAG periodicity to quantify ontog...

High-latitude (i.e., "polar") Mesozoic fauna endured months of twilight and relatively low mean annual temperatures. Yet non-avian dinosaurs flourished in this taxing environment. Fossils of basal ornithopod dinosaurs ("hypsilophodontids") are common in the Early Cretaceous high-latitude sediments of Victoria, Australia, and four taxa have been des...

Analysis of the presence of metaplastic tissue in selected limb bones of the nine-banded armadillo.

Analysis of ontogenetic changes in long bone microstructure aid in vertebrate life history reconstructions. Specifically, osteohistological examination of common fauna can be used to infer growth strategies of biologically uncommon, threatened, or extinct vertebrates. Although armadillo biology has been studied extensively, work on growth history i...

Increasing importance has been placed on bone microstructure studies of extant organisms to better interpret the fossil record. For instance, studies examining extant crocodylians, aves, and mammals help describe and interpret extinct tetrapod growth. Nine-banded armadillos (Dasypus novemcinctus) are common taxa throughout the southern United State...

Fossil bone microanalyses reveal the ontogenetic histories of extinct tetrapods, but incomplete fossil records often result in small sample sets lacking statistical strength. In contrast, a histological sample of 50 tibiae of the hadrosaurid dinosaur Maiasaura peeblesorum allows predictions of annual growth and ecological interpretations based on m...

Predator confrontation or predator evasion frequently produces bone fractures in potential prey in the wild. Although there are reports of healed bone injuries and pathologies in non-avian dinosaurs, no previously published instances of biomechanically adaptive bone modeling exist. Two tibiae from an ontogenetic sample of fifty specimens of the her...

Evolutionary biologists define “metaplasia” as the permanent transformation of a cell identity, and there are many examples of such transformations in living vertebrates (e.g., chondrocytes transforming directly into osteoblasts). These metaplasias have been observed during the mineralization of “ossified” tendons of living birds. In the present st...

Bone microanalyses of extant vertebrates provide a necessary framework from which to form hypotheses regarding the growth and skeletochronology of extinct taxa. Here, we describe the bone microstructure and quantify the histovariability of appendicular elements and osteoderms from three juvenile American alligators (Alligator mississippiensis) to a...

The bones in a skeleton grow at different rates. A single bone changes its growth rate through time, and even parts of the same bone grow at different rates over an individual’s lifetime. Nonetheless, animals have a single growth trajectory and this chapter discusses how to estimate the age of the body as a whole. It discusses the marks of growth;...

This chapter discusses the advantages and disadvantages of various types of growth measurements including mass, length, time, and osteohistological texture. It explains the intensity of measurement, and how sampling intensity can limit the types of questions addressed by growth data but can also clarify longstanding misconceptions such as “indeterm...

Figures are in a separate folder of 45,000 KB WHAT BONE IS This chapter examines the topic that, with elegant simplicity, Hancox (1972) called "Biology of Bone." Whereas cartilage may be found in vertebrates and in many invertebrates, bone is a unique, vascularized skeletal tissue found only in vertebrate animals (Hall, 2005). In this section, we d...

An external fundamental system (EFS) is a form of bone microstructure present in the outermost cortex of long bones in animals that have attained skeletal maturity. It indicates an effective cessation of any significant periosteal growth (i.e., growth in circumference or girth). Although an EFS has been noted in several reptile taxa, the idea that...

Analysis of bone microstructure in ornithopod and theropod dinosaurs from Victoria, Australia, documents ontogenetic changes, providing insight into the dinosaurs' successful habitation of Cretaceous Antarctic environments. Woven-fibered bone tissue in the smallest specimens indicates rapid growth rates during early ontogeny. Later ontogeny is mark...

The carnivorous Tyrannosauridae are among the most iconic dinosaurs: typified by large body size, tiny forelimbs, and massive robust skulls with laterally thickened teeth. The recently described small-bodied tyrannosaurid Raptorex kreigsteini is exceptional as its discovery proposes that many of the distinctive anatomical traits of derived tyrannos...

Bones of Alamosaurus sanjuanensis were collected from the Upper Cretaceous Javelina and Black Peaks formations in Big Bend National Park, Texas, for use in the first extensive histological study of a titanosaurian sauropod dinosaur. Samples include cervical, dorsal, and caudal vertebrae; ribs; a scapula; humeri; an ulna; a metacarpal; an ischium; f...

Sauropod dinosaurs were the largest terrestrial animals and their growth rates remain a subject of debate. By counting growth lines in histologic sections and relating bone length to body mass, it has been estimated that Apatosaurus attained its adult body mass of about 25,000 kg in as little as 15 years, with a maximum growth rate over 5000 kg/yr....

of a paper presented at Microscopy and Microanalysis 2007 in Ft. Lauderdale, Florida, USA, August 5 – August 9, 2007

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