Mark A Norell

American Museum of Natural History · Paleontology

The evolution of flight is a rare event in vertebrate history, and one that demands functional integration across multiple anatomical/physiological systems. The neuroanatomical basis for such integration and the role that brain evolution assumes in behavioural transformations remain poorly understood. We make progress by (i) generating a positron e...

Tooth-marked bones provide important evidence for feeding choices made by extinct carnivorous animals. In the case of the dinosaurs, most bite traces are attributed to the large and robust osteophagous tyrannosaurs, but those of other large carnivores remain underreported. Here we report on an extensive survey of the literature and some fossil coll...

Intraspecific variation in growth trajectories provides a fundamental source of variation upon which natural selection acts. Recent work hints that early dinosaurs possessed elevated levels of such variation compared to other archosaurs, but comprehensive data uniting body size, bone histology, and morphological variation from a stratigraphically c...

Significant evolutionary shifts in locomotor behaviour often involve comparatively subtle anatomical transitions. For dinosaurian and avian evolution, medial overhang of the proximal femur has been central to discussions. However, there is an apparent conflict with regard to the evolutionary origin of the dinosaurian femoral head, with neontologica...

Living birds (Aves) have bodies substantially modified from the ancestral reptilian condition. The avian pelvis in particular experienced major changes during the transition from early archosaurs to living birds1,2. This stepwise transformation is well documented by an excellent fossil record2–4; however, the ontogenetic alterations that underly it...

David et al . claim that vestibular shape does not reflect function and that we did not use phylogenetic inference methods in our primary analyses. We show that their claims are countered by comparative and direct experimental evidence from across Vertebrata and that their models are empirically unverified. We did use phylogenetic methods to test o...

The latest Cretaceous kogaionid multituberculates from Transylvania (western Romania) were part of an endemic European clade of mammals that underwent an insular radiation at the end of the Cretaceous and then survived the end-Cretaceous mass extinction that extinguished many groups of contemporary therians. Transylvanian kogaionids lived on what w...

Birds and mammals independently evolved the highest metabolic rates among living animals¹. Their metabolism generates heat that enables active thermoregulation¹, shaping the ecological niches they can occupy and their adaptability to environmental change². The metabolic performance of birds, which exceeds that of mammals, is thought to have evolved...

Myhrvold et al. suggest that our inference of subaqueous foraging among spinosaurids is undermined by selective bone sampling, inadequate statistical procedures, and use of inaccurate ecological categorizations. Myhrvold et al. ignore major details of our analyses and results, and instead choose to portray our inferences as if they were based on qu...

Living birds (Aves) have bodies dramatically modified from the ancestral reptilian condition. The avian pelvis in particular experienced dramatic changes during the transition from early archosaurs to living birds. This stepwise transformation is well documented by an excellent fossil record; however, the ontogenetic alterations that underly it are...

Secondary aquatic adaptations evolved independently more than 30 times from terrestrial vertebrate ancestors1,2. For decades, non-avian dinosaurs were believed to be an exception to this pattern. Only a few species have been hypothesized to be partly or predominantly aquatic3–11. However, these hypotheses remain controversial12,13, largely owing to...

Eudromaeosauria is a clade of derived dromaeosaurids that typifies the common perception of ‘raptor’ dinosaurs. The evolutionary history of this clade has been controversial due to conflicting views of taxonomic identity, and because, due to taphonomic bias, several species were diagnosed primarily or solely by the maxilla. The maxilla is therefore...

Recently, deep learning has reached significant advancements in various image-related tasks, particularly in medical sciences. Deep neural networks have been used to facilitate diagnosing medical images generated from various observation techniques including CT (computed tomography) scans. As a non-destructive 3D imaging technique, CT scan has also...

The construction of morphological character matrices is central to paleontological systematic study, which extracts paleontological information from fossils. Although the word information has been repeatedly mentioned in a wide array of paleontological systematic studies, its meaning has rarely been clarified nor specifically defined. It is importa...

How do large and unique brains evolve? Historically, comparative neuroanatomical studies have attributed the evolutionary genesis of highly encephalized brains to deviations along, as well as from, conserved scaling relationships among brain regions. However, the relative contributions of these concerted (integrated) and mosaic (modular) processes...

Birds today are the most diverse clade of terrestrial vertebrates, and understanding why extant birds (Aves) alone among dinosaurs survived the Cretaceous-Paleogene mass extinction is crucial to reconstructing the history of life. Hypotheses proposed to explain this pattern demand identification of traits unique to Aves. However, this identificatio...

The construction of morphological character matrices is central to paleontological systematic study, which extracts paleontological information from fossils. Although the word information has been repeatedly mentioned in a wide array of paleontological systematic studies, its meaning has rarely been clarified and there has not been a standard to me...

The construction of morphological character matrices is central to paleontological systematic study, which extracts paleontological information from fossils. Although the word information has been repeatedly mentioned in a wide array of paleontological systematic studies, its meaning has rarely been clarified and there has not been a standard to me...

Revealing behavioral secrets in extinct species Extinct species had complex behaviors, just like modern species, but fossils generally reveal little of these details. New approaches that allow for the study of structures that relate directly to behavior are greatly improving our understanding of the lifestyles of extinct animals (see the Perspectiv...

Revealing behavioral secrets in extinct species Extinct species had complex behaviors, just like modern species, but fossils generally reveal little of these details. New approaches that allow for the study of structures that relate directly to behavior are greatly improving our understanding of the lifestyles of extinct animals (see the Perspectiv...

How do large and unique brains evolve? Historically, comparative neuroanatomical studies have attributed the evolutionary genesis of highly encephalized brains to deviations along, as well as from, conserved scaling relationships among brain regions. However, the relative contributions of these concerted (integrated) and mosaic (modular) processes...

In the recent study in Current Biology by Pei and colleagues¹, we used two proxies — wing loading and specific lift — to reconstruct powered flight potential across the vaned feathered fossil pennaraptorans. The results recovered multiple origins of powered flight. We respectfully disagree with the criticism raised by Serrano and Chiappe² that wing...

Haya griva is an early-diverging neornithischian (“hypsilophodontid”) dinosaur known from several well-preserved skulls and articulated postcranial skeletons, in addition to dozens of partial or isolated finds from the Upper Cretaceous Khugenetslavkant and Zos Canyon localities (Javkhlant Formation and equivalent beds) in the Gobi Desert of Mongoli...

A new dromaeosaurid dinosaur, Shri devi, from the Late Cretaceous deposit of the Barun Goyot Formation at Khulsan, Mongolia, is described here. The Barun Goyot Formation (herein referred to as the Barun Goyot) is stratigraphically intermediate between the overlying Nemegt Formation and the underlying Djadokhta Formation, where much of the dromaeosa...

Caimaninae is one of the few crocodylian lineages that still has living representatives. Today, most of its six extant species are restricted to South and Central America. However, recent discoveries have revealed a more complex evolutionary history, with a fossil record richer than previously thought and a possible North American origin. Among the...

Ceratopsia is a diverse dinosaur clade from the Middle Jurassic to Late Cretaceous with early diversification in East Asia. However, the phylogeny of basal ceratopsians remains unclear. Here we report a new basal neoceratopsian dinosaur Beg tse based on a partial skull from Baruunbayan, Ömnögovi aimag, Mongolia. Beg is diagnosed by a unique combina...

An unabated surge of new and important discoveries continues to transform knowledge of pen-naraptoran biology and evolution amassed over the last 150+ years. This chapter summarizes progress made thus far in sampling the pennaraptoran fossil record of the Mesozoic and Paleocene and proposes priority areas of attention moving forward. Oviraptorosaur...

An unabated surge of new and important discoveries continues to transform knowledge of pen-naraptoran biology and evolution amassed over the last 150+ years. This chapter summarizes progress made thus far in sampling the pennaraptoran fossil record of the Mesozoic and Paleocene and proposes priority areas of attention moving forward. Oviraptorosaur...

The evolutionary radiation of birds has produced incredible morphological variation, including a huge range of skull form and function. Investigating how this variation arose with respect to non-avian dinosaurs is key to understanding how birds achieved their remarkable success after the Cretaceous–Paleogene extinction event. Using a high-dimension...

Uncertainties in the phylogeny of birds (Avialae) and their closest relatives have impeded deeper understanding of early theropod flight. To help address this, we produced an updated evolutionary hypothesis through an automated analysis of the Theropod Working Group (TWiG) coelurosaurian phylogenetic data matrix. Our larger, more resolved, and bett...

In 1934, Barnum Brown of the American Museum of Natural History in New York (AMNH) led a large-scale dinosaur excavation in northern Wyoming, where he had found bones two years earlier. Initially, Brown expected to excavate two skeletons of sauropod dino- saurs, but soon after opening the quarry, the team realized that the site far exceeded their e...

Calcified eggshells protect developing embryos against environmental stress and contribute to reproductive success¹. As modern crocodilians and birds lay hard-shelled eggs, this eggshell type has been inferred for non-avian dinosaurs. Known dinosaur eggshells are characterized by an innermost membrane, an overlying protein matrix containing calcite...

The fossil record provides compelling examples of heterochrony at macroevolutionary scales such as the peramorphic giant antlers of the Irish elk. Heterochrony has also been invoked in the evolution of the distinctive cranial frill of ceratopsian dinosaurs such as Triceratops. Although ceratopsian frills vary in size, shape, and ornamentation, quan...

Evolution of birds from non-flying theropod dinosaurs is a classic evolutionary transition, but a deeper understanding of early flight has been frustrated by disagreement on the relationships between birds (Avialae) and their closest theropod relatives. We address this through a larger, more resolved evolutionary hypothesis produced by a novel auto...

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...

The Upper Jurassic Morrison Formation of the western United States preserves one of the best-known Mesozoic paleoecosystems worldwide. The formation crops out over an area from New Mexico and Oklahoma to Montana and Utah and encompasses a time span of approximately eight million years. Recent studies indicate a high diversity of gigantic, herbivoro...

Understanding of the Asian early Paleogene avifauna is limited relative to that of North American and European avifauna of the same period. While major patterns of mammalian faunal exchange among these three regions across the Paleocene/Eocene boundary have been described, much less is known about the dynamics of bird diversity over the same time i...

Lithornithids are volant stem palaeognaths from the Paleocene‐Eocene. Except for these taxa and the extant neotropical tinamous, all other known extinct and extant palaeognaths are flightless. Investigation of properties of the lithornithid wing and its implications for inference of flight style informs understood locomotor diversity within Palaeog...

Mamenchisauridae, a sauropod group named after the largest known proto-Asian sauropod Mamen-chisaurus, is generally believed to range from the Early to the Late Jurassic in age. Fossil remains of Mamenchisaurus are primarily found in the Upper Shaximiao Formation and less frequently in the overlying Suining Formation in the Sichuan Basin. An accura...

Fossils were thought to lack original organic molecules, but chemical analyses show that some can survive. Dinosaur bone has been proposed to preserve collagen, osteocytes, and blood vessels. However, proteins and labile lipids are diagenetically unstable, and bone is a porous open system, allowing microbial/molecular flux. These 'soft tissues' hav...

Fossils were thought to lack original organic molecules, but chemical analyses show that some can survive. Dinosaur bone has been proposed to preserve collagen, osteocytes, and blood vessels. However, proteins and labile lipids are diagenetically unstable, and bone is a porous open system, allowing microbial/molecular flux. These ‘soft tissues’ hav...

Table S1. Parameters used for CT imaging of specimens.

Data S1. Procrustes aligned shape data of brains and endocasts of Alligator and Gallus specimens (plain text file).

Medullary bone is an ephemeral type of bone tissue, today found only in sexually mature female birds, that provides a calcium reservoir for eggshell formation. The presence of medullary bone-like tissues in extant birds, pterosaurs, and dinosaurs distantly related to birds shows that caution must be exercised before concluding that fossils bear med...

Cranial endocasts, or the internal molds of the braincase, are a crucial correlate for investigating the neuroanatomy of extinct vertebrates and tracking brain evolution through deep time. Nevertheless, the validity of such studies pivots on the reliability of endocasts as a proxy for brain morphology. Here, we employ micro‐computed tomography imag...

Mosasaurs were among the last marine reptiles that lived before the Cretacesous–Paleogene extinction. Little is known about the sensory evolution of mosasaurs in relation to their aquatic lifestyle. In this study, the braincase of Platecarpus was CT-scanned and virtual models were constructed showing the bony labyrinth — or the inner ear — a sensor...

Vertebrate hard tissues consist of mineral crystallites within a proteinaceous scaffold that normally degrades post-mortem. Here we show, however, that decalcification of Mesozoic hard tissues preserved in oxidative settings releases brownish stained extracellular matrix, cells, blood vessels, and nerve projections. Raman Microspectroscopy shows th...

White fibers from a Late Cretaceous dinosaur Shuvuuia deserti stained positive for β-keratin antibodies in a 1999 paper, followed by many similar immunological claims for Mesozoic protein in bones and integument. Antibodies recognize protein epitopes derived from its tertiary and quaternary structure, so such results would suggest long polypeptide...

Birds are the only living amniotes with coloured eggs1-4, which have long been considered to be an avian innovation1,3. A recent study has demonstrated the presence of both red-brown protoporphyrin IX and blue-green biliverdin5-the pigments responsible for all the variation in avian egg colour-in fossilized eggshell of a nonavian dinosaur6. This ra...

Diplodocid sauropods had a unique skull morphology, with posteriorly retracted nares, an elongated snout, and anteriorly restricted, peglike teeth. Because of the lack of extant analogs in skull structure and tooth morphology, understanding their feeding strategy and diet has been difficult. Furthermore, the general rarity of sauropod skulls and th...

Unraveling the origins of the character complexes diagnosing major crown clades is one of the greatest challenges in evolutionary biology. These origination events tend to optimize along extraordinarily long stem lineages where the comparative biology of extant lineages is relatively weak in its heuristic power. Here we add to a growing paleontolog...

Shartegosuchids are a poorly known, early-branching group of Asian and North American crocodylomorphs. Shartegosuchids have been hypothesized to have eusuchian-type secondary palates, but a paucity of described material makes assessing this difficult. Our fieldwork in western Mongolia recovered cranial material of a new Shartegosuchus specimen from...

Brain-behavior studies using 18F-FDG PET aim to reveal brain regions that become active during behavior. In standard protocols, 18F-FDG is injected, the behavior is executed during 30–60 min of tracer uptake, and then the animal is anesthetized and scanned. Hence, the uptake of 18F-FDG is not itself observed and could, in fact, be complete in very...

Adult dinosaurs preserved attending their nests in brooding positions are among the rarest vertebrate fossils. By far the most common occurrences are members of the dinosaur group Oviraptorosauria. The first finds of these were specimens recovered from the Djadokhta Formation at the Mongolian locality of Ukhaa Tolgod and the Chinese locality of Bay...

Significance Island-living animals often differ from close relatives and mainland contemporaries in unusual ways, as best demonstrated by modern and Cenozoic mammals that are dwarfed or evolved aberrant anatomical features. However, it is unclear whether mammals from the Age of Dinosaurs followed this same pattern. We describe the fossil skeleton o...