Lindsay Zanno

North Carolina Museum of Natural Sciences · Research & Collections

Interpreting key ecological parameters, such as diet, of extinct organisms without the benefit of direct observation or explicit fossil evidence poses a formidable challenge for paleobiological studies. To date, dietary categorizations of extinct taxa are largely generated by means of modern analogs; however, for many species the method is subject...

Exaggerated cranial structures such as crests and horns, hereafter referred to collectively as ornaments, are pervasive across animal species. These structures perform vital roles in visual communication and physical interactions within and between species. Yet the origin and influence of ornamentation on speciation and ecology across macroevolutio...

Allosauroid theropods were a diverse and widespread radiation of Jurassic-Cretaceous megapredators. Achieving some of the largest body sizes among theropod dinosaurs, these colossal hunters dominated terrestrial ecosystems until a faunal turnover redefined apex predator guild occupancy during the final 20 million years of the Cretaceous. Here we de...

The correlation between large body size and digestive efficiency has been hypothesized to have driven trends of increasing mass in herbivorous clades by means of directional selection. Yet, to date, few studies have investigated this relationship from a phylogenetic perspective, and none, to our knowledge, with regard to trophic shifts. Here, we re...

Triassic predatory guild evolution reflects a period of ecological flux spurred by the catastrophic end-Permian mass extinction and terminating with the global ecological dominance of dinosaurs in the early Jurassic. In responding to this dynamic ecospace, terrestrial predator diversity attained new levels, prompting unique trophic webs with a seem...

Ankylosaurid dinosaurs were heavily armoured herbivores with tails modified into club-like weapons. These tail clubs have widely been considered defensive adaptations wielded against predatory theropod dinosaurs. Here we argue instead that ankylosaurid tail clubs were sexually selected structures used primarily for intraspecific combat. We found pa...

Paleopathological diagnoses provide key information on the macroevolutionary origin of disease as well as behavioral and physiological inferences that are inaccessible via direct observation of extinct organisms. Here we describe the external gross morphology and internal architecture of a pathologic right second metatarsal (MMNS VP‐6332) of a larg...

The Late Cretaceous dinosaur Tyrannosaurus rex was recently split into three species based on the premise that variation in the T. rex hypodigm is exceptional, indicating cryptic species and “robust” and “gracile” morphs. The morphs are based on proportional ratios throughout the skeleton. The species are claimed to be stratigraphically separate, w...

The geographic ranges in which species live is a function of many factors underlying ecological and evolutionary contingencies. Observing the geographic range of an individual species provides valuable information about these historical contingencies for a lineage, determining the distribution of many distantly related species in tandem provides in...

Although intensified work on the volcaniclastic-rich sediments of the fossil-bearing Mussentuchit Member (uppermost Cedar Mountain Formation, Utah) has provided a refined chronostratigraphic framework, paleoenvironmental interpretations remain cryptic. To resolve this, we performed facies analysis and architectural reconstruction on exposed Mussent...

The diversity of mid-Cretaceous tyrannosauroids is poorly understood. We describe a partial tyrannosauroid femur from the Albian–Cenomanian Wayan Formation of eastern Idaho that helps to fill in an important spatiotemporal gap in the North American record of tyrannosaurs. This specimen, consisting of the proximal half of the bone, is morphologicall...

We describe the sedimentology, geochronology, and geochemistry of the Early Cretaceus Sao Khua Formation of the Khorat Basin, northeastern Thailand, and report a temporal range adjustment for its dinosaurian assemblage. Facies analysis and architectural studies reveal that sedimentation occurred within a floodplain setting fed by large meandering b...

Double tooth pathologies are important indicators of trauma, disease, diet, and feeding biomechanics, and are widely documented in mammals. However, diagnosis of double tooth pathologies in extinct non-mammalian vertebrates is complicated by several compounding factors including: a lack of shared terminology reflecting shared etiology, inconsistenc...

Reconstructing the evolution, diversity, and paleobiogeography of North America’s Late Cretaceous dinosaur assemblages requires spatiotemporally contiguous data; however, there remains a spatial and temporal disparity in dinosaur data on the continent. The rarity of vertebrate-bearing sedimentary deposits representing Turonian–Santonian ecosystems,...

Schroeder et al. (Reports, 26 February 2021, p. 941) reported a size gap among predatory dinosaur species. We argue that the supporting dataset is skewed toward Late Cretaceous North America and that the gap was likely absent during other intervals in most geographic regions. We urge broader consideration of this hypothesis, with quantitative evalu...

Beipiaosaurus inexpectus , from the Lower Cretaceous Yixian Formation (Sihetun locality, near Beipiao), Liaoning, China, is a key taxon for understanding the early evolution of therizinosaurians. Since initial publication in 1999, only the cranial elements of this taxon have been described in detail. Here we present a detailed description of the po...

The Dinosaur Park Formation (DPF) of Alberta, Canada, has produced one of the most diverse dinosaur faunas, with the record favouring large-bodied taxa, in terms of number and completeness of skeletons. Although small theropods are well documented in the assemblage, taxonomic assessments are frequently based on isolated, fragmentary skeletal elemen...

The “mid-Cretaceous” (~125–80 Ma) was punctuated by major plate-tectonic upheavals resulting in widespread volcanism, mountain-building, eustatic sea-level changes, and climatic shifts that together had a profound impact on terrestrial biotic assemblages. Paleontological evidence suggests terrestrial ecosystems underwent a major restructuring durin...

The Upper Cretaceous Western Interior Basin of North America provides a unique laboratory for constraining the effects of spatial climate patterns on the macroevolution and spatiotemporal distribution of biological communities across geologic timescales. Previous studies suggested that Western Interior Basin terrestrial ecosystems were divided into...

A new ichnospecies, Glossifungites gingrasi n. isp., is described from multiple locations in basal sand-filled coastal plain distributary channels of the Turonian (Upper Cretaceous) Ferron Sandstone (central Utah). Glossifungites gingrasi n. isp. is attributed to the ichnogenus Glossifungites based on the presence of scratch imprints, passive fill,...

The ability to determine the sex of extinct dinosaurs by examining the bones they leave behind would revolutionize our understanding of their paleobiology; however, to date, definitive sex‐specific skeletal traits remain elusive or controversial. Although living dinosaurs (i.e., extant birds) exhibit a sex‐specific tissue called medullary bone that...

Dietary habits in extinct species cannot be directly observed; thus, in the absence of extraordinary evidence, they must be reconstructed with a combination of morphological proxies. Such proxies often include information on dental organization and function such as tooth formation time and tooth replacement rate. In extinct organisms, tooth formati...

Major evolutionary transitions, in which animals develop new body plans and adapt to dramatically new habitats and lifestyles, have punctuated the history of life. The origin of cetaceans from land-living mammals is among the most famous of these events. Much earlier, during the Mesozoic Era, many reptile groups also moved from land to water, but t...

Relative brain sizes in birds can rival those of primates, but large-scale patterns and drivers of avian brain evolution remain elusive. Here, we explore the evolution of the fundamental brain-body scaling relationship across the origin and evolution of birds. Using a comprehensive dataset sampling> 2,000 modern birds, fossil birds, and theropod di...

Medullary bone (MB) is a sex-specific tissue produced by female birds during the laying cycle, and it is hypothesized to have arisen within Avemetatarsalia, possibly outside Avialae. Over the years, researchers have attempted to define a set of criteria from which to evaluate the nature of purported MB-like tissues recovered from fossil specimens....

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...

Background Medullary bone (MB) is an estrogen-dependent, sex-specific tissue produced by female birds during lay and inferred to be present in extinct avemetatarsalians (bird-line archosaurs). Although preliminary studies suggest that MB can be deposited within most skeletal elements, these are restricted to commercial layers or hormonally treated...

The importance of adaptation [1-4] versus organizational constraints [5-7] in shaping common macroevolutionary trends remains unclear [8]. The fossil record is key to this problem, as it provides data on repetitive trait evolution between lineages [4, 8]. However, quantitative analyses investigating these dynamics with fossil data are rare [8]. Her...

The teeth of diplodocine sauropods are often deemed undiagnostic to species or genus level. To test this hypothesis we conducted morphometric studies on the teeth of three diplodocine specimens (likely representing at least two species, one including a hypothesized juvenile) and two outgroup sauropod taxa (Camarasaurus lentus and material assigned...

The teeth of diplodocine sauropods are often deemed undiagnostic to species or genus level. To test this hypothesis we conducted morphometric studies on the teeth of three diplodocine specimens (likely representing at least two species, one including a hypothesized juvenile) and two outgroup sauropod taxa (Camarasaurus lentus and material assigned...

A partial skeleton including both dentaries and multiple isolated teeth of an early diverging iguanodontian (NCSM 29373) was excavated from the Cenomanian-aged Mussentuchit Member of the Cedar Mountain Formation in Emery County, Utah during the 2014-2016 field seasons. Due to the presence of jaw sections with unerupted teeth, we were able to calcul...

Terrestrial tetrapods use their claws to interact with their environments in a plethora of ways. Birds in particular have developed a diversity of claw shapes since they are often not bound to terrestrial locomotion and have heterogeneous body masses ranging several orders of magnitude. Numerous previous studies have hypothesized a connection betwe...

Terrestrial tetrapods use their claws to interact with their environments in a plethora of ways. Birds in particular have developed a diversity of claw shapes since they are not bound to terrestrial locomotion and have heterogeneous body masses ranging several orders of magnitude. Numerous previous studies have hypothesized a connection between ped...

The unusual clubbed tails of glyptodonts among mammals and ankylosaurines among dinosaurs most likely functioned as weapons of intraspecific combat or interspecific defense and are characterized by stiffening of the distal tail and, in some taxa, expansion of the distal tail tip. Although similarities in tail weaponry have been noted as a potential...

To date, eco-evolutionary dynamics in the ascent of tyrannosauroids to top predator roles have been obscured by a 70-million-year gap in the North American (NA) record. Here we report discovery of the oldest Cretaceous NA tyrannosauroid, extending the lineage by ~15 million years. The new taxon—Moros intrepidus gen. et sp. nov.—is represented by a...

The vertebrate fauna of the Late Cretaceous Mussentuchit Member of the Cedar Mountain Formation has been studied for nearly three decades, yet the fossil-rich unit continues to produce new information about life in western North America approximately 97 million years ago. Here we report on the composition of the Cliffs of Insanity (COI) microverteb...

Aetosaurs comprise a clade of quadrupedal, armored, omnivores to herbivores that lived across much of the supercontinent of Pangea during the Late Triassic. Their relative abundance in many units, and the rarity of other Triassic herbivores, points to them as key components of Late Triassic ecosystems. Debate persists about whether they were growin...

Von Ebner lines (VELs) are incremental growth marks of daily dentin apposition, which are widely used to calculate the: (1) age of teeth; (2) dentin deposition rate (DDR, estimated by mean VEL increment width VEIW); and (3) tooth replacement rate (TRR) in extinct taxa. However, the influence of methods used to assess TRR and mean VEIW is rarely con...

We describe a new iguanodontian ornithopod, Choyrodon barsboldi gen. et sp. nov. from the Albian-aged Khuren Dukh Formation of Mongolia based on several partial skeletons interpreted to represent a subadult growth stage based on osteohistological features. This new taxon is diagnosed by many autapomorphies of the maxilla, nasal, lacrimal, opisthoti...

Aetosauria is a clade of heavily armored, quadrupedal omnivorous to herbivorous archosaurs known from the Late Triassic across what was the supercontinent of Pangea. Their abundance in many deposits relative to the paucity of other Triassic herbivores indicates that they were key components of Late Triassic ecosystems. However, their evolutionary r...

Data matrix used for TNT analysis Complete set of character scorings for taxa used for the phylogenetic analysis in this study. Provided in .txt format for ease of editing and use in multiple programs.

Phylogenetic character descriptions List of character descriptions used in phylogenetic analysis. Characters 1–37 from Parker (2007) and characters 38–44 added by Schoch & Desojo (2016).

Weaponry, for the purpose of intraspecific combat or predator defence, is one of the most widespread animal adaptations, yet the selective pressures and constraints governing its phenotypic diversity and skeletal regionalization are not well understood. Here, we investigate the evolution of tail weaponry in amniotes, a rare form of weaponry that no...

Horizontal and inclined U-shaped trace fossils are commonly associated with the Cruziana and Glossifungites ichnofacies, but have rarely been described as a component of the Teredolites ichnofacies (xylic substrates). This study provides several examples of morphologies of Glossifungites saxicava from the Campanian Sunnyside Coal (Blackhawk Formati...

Previous investigations document functional and phylogenetic signals in the histology of dinosaur teeth. In particular, incremental lines in dentin have been used to determine tooth growth and replacement rates in several dinosaurian clades. However, to date, few studies have investigated the dental microstructure of theropods in the omnivory/herbi...

In situ Falcarius utahensis dentary teeth UMNH VP 14527 (A–C) and UMNH VP 15259 (D, E) in labial (A, D), lingual (B, E) , and occlusal (C) views. Scale bar represents 1 mm.

Computed tomographic images of Falcarius utahensis dentary teeth (A) UMNH VP 14527 in transverse (labiolingual) cross-section. (B) UMNH VP 14529 in transverse cross-section. Crowns are not completely formed until they have begun erupting from the alveolus. Root lengths that equal or exceed crown height are indicative of fully erupted functional tee...

Location of transects on sectioned teeth Digital microscopy images of therizinosaurian teeth in longitudinal thin section. (A) UMNH VP 22857 maxillary tooth. (B) UMNH VP 15231 dentary tooth. (C) Suzhousaurus tooth. Red boxes indicate location of transects sampled in Figs. 2A–2C. Scale bar represents 500 µm.

Enamel apposition rates and enamel/crown volumes in therizinosauria Enamel Apposition Rates: calculated EAR in F. utahensis and S. megatherioides. EAR decreases by 52% in Suzhousaurus and LIG count is 85% greater than in Falcarius. However, enamel volume is 2.79 percentage points greater in the more derived taxon. Crown and Enamel Volumes: Calculat...

Crown volume, body mass, and dental microstructure raw data from sampled taxa Raw data from this study as well as Erickson (1996b) and D’Emic et al., 2013 on crown volumes, body masses, and dental microstructure in Archosauria. Body mass data from Benson et al., 2014. DDR vs. Replacement: No significant correlation was found between deposition rate...

von Ebner increment widths in Therinosauria Summary: Summary statistics for von Ebner line increment widths in thin sections of F. utahensis and S. megatherioides teeth. Raw: measured increment widths from histological thin sections of therizinosaurian teeth and distribution of thin VELs from EDJ to pulp cavity. Digital microscope images were taken...

Background Eolambia caroljonesa is the most abundant dinosaur in the lower Cenomanian Mussentuchit Member of the Cedar Mountain Formation of Utah, and one of the most completely known non-hadrosaurid iguanodontians from North America. In addition to the large holotype and paratype partial skulls, copious remains of skeletally immature individuals,...

Character list, list of supplemental references, and list of synapomorphies. List of morphological characters and supplemental references used in the phylogenetic analysis, and list of synapomorphies. (DOC)

Nexus file formatted for TNT. Nexus file used in the phylogenetic analysis. (TXT)

List of specimens examined. Iguanodontian specimens examined firsthand. (XLS)

Table of measurements. Measurements of select anatomical features of FMNH PR 3847. (DOC)

Data matrix. Character-taxon matrix used in the phylogenetic analysis. (XLS)

Recent research indicates greater sophistication in the dental anatomy of the megaherbivorous dinosaur clade Sauropoda than previously appreciated, including high tooth replacement rates that range from comparable with those of hadrosaurs to much higher rates (90 to 14 days). Diplodocoid and titanosaurian sauropods convergently acquired the highest...

Supplementary Figure 1, Supplementary Tables 1-6, Supplementary Discussion, Supplementary Methods, Supplementary References

All model results from the OU analysis with the root not estimated, but instead taken from the status distribution.

All model results from the OU analysis with the root estimated.