Jingmai O'Connor

Field Museum of Natural History · Geology

Important transformations of the pectoral girdle are related to the appearance of flight capabilities in the Dinosauria. Previous studies on this topic focused mainly on paravians yet recent data suggests flight evolved in dinosaurs several times, including at least once among non-avialan paravians. Thus, to fully explore the evolution of flight-re...

As a fundamental ecological aspect of most organisms, locomotor function significantly constrains morphology. At the same time, the evolution of novel locomotor abilities has produced dramatic morphological transformations, initiating some of the most significant diversifications in life history. Despite significant new fossil evidence, it remains...

Some birds intentionally ingest stones to facilitate digestion of hard foodstuffs, a behaviour inherited from non‐avian dinosaurs and present in some of the earliest birds, as evidenced by clusters of gastroliths preserved within the abdominal cavity of a wide range of dinosaurs and Cretaceous birds. For the first time, high‐resolution computed lam...

Study of the holotype and only known material of the purportedly extinct corvid species ‘Corvus fangshannus’ from the late Middle or Late Pleistocene locality 3 of the UNESCO Zhoukoudian ‘Peking Man’ site in Beijing, China, documents its identification instead as a member of the sedentary Northern Raven (Corvus corax) lineage. Shared features of th...

Feathers are a primitive trait among pennaraptoran dinosaurs, which today are represented by crown birds (Neornithes), the only clade of dinosaurs to survive the end Cretaceous mass extinction. Feathers are central to many important functions and therefore, maintaining plumage function is of great importance for survival. Thus, molt – by which new...

This year marks the 100th anniversary of the discovery of Velociraptor. In this contribution, our aim is to trace the history of the discoveries related to this fascinating non-avian theropod and to examine how it has been depicted by palaeoartists over the past century. The first Velociraptor fossil was discovered on August 11th, 1923 by the staff...

Although it is commonly considered that, in birds, there is a trend towards reduced dentition, teeth persisted in birds for 90 Ma and numerous macroscopic morphologies are observed. However, the extent to which the microstructure of bird teeth differs from other lineages is poorly understood. To explore the microstructural differences of the teeth...

The Longipterygidae are a unique clade among the enantiornithines in that they exhibit elongate rostra (≥60% total skull length) with dentition restricted to the distal tip of the rostrum, and pedal morphologies suited for an arboreal lifestyle (as in other enantiornithines). This suite of features has made interpretations of this group’s diet and...

The independent movements and flexibility of various parts of the skull, called cranial kinesis, are an evolutionary innovation that is found in living vertebrates only in some squamates and crown birds and is considered to be a major factor underpinning much of the enormous phenotypic and ecological diversity of living birds, the most diverse grou...

Jeholornis is a representative of the earliest-diverging bird lineages, providing important evidence of anatomical transitions involved in bird origins. Although ~100 specimens have been reported, its cranial morphology remains poorly documented owing to poor two-dimensional preservation, limiting our understanding of the morphology and ecology of...

If you find a bird bone in deposits from the Cretaceous period (145–66 million years ago), chances are it will belong to an enantiornithine bird. This extinct group of birds was mostly arboreal and dominated terrestrial environments from 130 to 66 million years ago. With approximately 90 known genera, they account for more than half of the known di...

Many tyrannosaurid specimens preserve unusual pathologies in the caudal half of the mandible that are of uncertain origin. The two main hypotheses put forth to date both suggest these pathologies are lesions resultant from infection either due to bacteria or protozoans. In light of this controversy, we provide a comparative anatomical study to char...

The Early Cretaceous diversification of birds was a major event in the history of terrestrial ecosystems, occurring during the earliest phase of the Cretaceous Terrestrial Revolution, long before the origin of the bird crown-group. Frugivorous birds play an important role in seed dispersal today. However, evidence of fruit consumption in early bird...

The independent movements and flexibility of various parts of the skull, called cranial kinesis, is an evolutionary innovation that is found in living vertebrates only in some squamates and crown birds, and considered to be a major factor underpinning much of the enormous phenotypic and ecological diversity of living birds, the most diverse group o...

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...

The origin of bird and avian flight is one of the most controversial debates since the fossil of Archaeopteryx was found in Germany. With the continuous discoveries of relative fossils of dinosaurs from all over the world, scientists have reached a consensus that the ancestors of bird might be small sized non-avian theropod dinosaurs. However, the...

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...

The Early Cretaceous diversification of birds was a major event in the history of terrestrial ecosystems, occurring during the earliest phase of the Cretaceous Terrestrial Revolution. Frugivorous birds play an important role in seed dispersal today, and may have done so since their origins. However, evidence of this has been lacking. Jeholornis is...

Modern birds are typified by the presence of feathers, complex evolutionary innovations that were already widespread in the group of theropod dinosaurs (Maniraptoriformes) that include crown Aves. Squamous or scaly reptilian-like skin is, however, considered the plesiomorphic condition for theropods and dinosaurs more broadly. Here, we review the m...

We describe six specimens consisting of cranial remains and associated partial presacral axial series belonging to ornithuromorph birds from the Changma locality of the Lower Cretaceous Xiagou Formation of northwestern Gansu Province, China. Comparison among specimens is limited by the paucity of overlapping elements, their differing exposed views,...

This study seeks to better quantify the parameters that drove the evolution of flight from non-volant winged dinosaurs to modern birds. In order to explore this issue, we used fossil data to model the feathered forelimbs of Caudipteryx, the most basal non-volant maniraptoran dinosaur with elongated pennaceous feathers that could be described as for...

Enantiornithes are the most successful group of Mesozoic birds, arguably representing the first global avian radiation,1, 2, 3, 4 and commonly resolved as the sister to the Ornithuromorpha, the clade within which all living birds are nested.1,3 The wealth of fossils makes it feasible to comparatively test evolutionary hypotheses about the pattern a...

A new enantiornithine bird is described on the basis of a well preserved partial skeleton from the Upper Cretaceous Qiupa Formation of Henan Province (central China). It provides new evidence about the osteology of Late Cretaceous enantiornithines, which are mainly known from isolated bones; in contrast, Early Cretaceous forms are often represented...

Many studies of the limb bones from birds of the major clades reveal a mosaic evolution in morphological characters. From this, we assume that uninterrupted compact bone evolved independently multiple times outside of the crown group. We hypothesise that there are key intraskeletal changes in the osteohistological features, such as the organisation...

Recently, ∼100 Ma amber from Myanmar has become an important source of information regarding the morphology of Late Cretaceous enantiornithines. Two specimens consisting of partial hindlimbs exhibit unusual morphologies when compared to both extant avian taxa and other Cretaceous enantiornithines. Pedal morphology is extremely ecologically informat...

While the morphology and evolution of the quadrate among early birds and through the evolutionary origin of birds is not well known, we add to knowledge about that past diversity through description of the morphology of the quadrate in the unusually elongate skull of the Cretaceous enantiornithine bird Longipteryx chaoyangensis. The lateral and cau...

The early evolution of flight is one of the most studied topics in vertebrate paleontology. Living birds have evolved to utilize a variety of flight styles, but studies focused on inferring flight strategies in Mesozoic birds are often contradictory and without a clear consensus, making it necessary to find additional informative characteristics th...

As key components of the tetrapod pectoral girdle, the scapula and coracoid have played a significant role in the evolution of forelimb locomotion among terrestrial vertebrates. The transition from a rigid fused scapulocoracoid in ancestral non-avian theropods to a presumably more flexible separated scapula-coracoid in early birds is considered to...

Most crown-birds experience rapid growth, reaching adult size within a year. Rapid growth strategies evolved within Aves multiple times during the Cretaceous, documented in the Confuciusornithiformes and the Ornithuromorpha. In contrast, osteohistological data suggest the Enantiornithes, the dominant clade of Cretaceous terrestrial birds, were char...

Gastroliths, where preserved, can provide indirect evidence regarding diet in extinct avian and non-avian dinosaurs. Masses of gastroliths consistent with the presence of a gastric mill are preserved in many Early Cretaceous Jehol birds mostly belonging to the Ornithuromorpha. Gastroliths are also present in basal birds Sapeornis and Jeholornis in...

The early evolution of flight is one of the most studied topics in vertebrate paleontology. Living birds have evolved to utilize a variety of flight styles, but studies focused on inferring flight strategies in Mesozoic birds are often contradictory and without a clear consensus, making it necessary to find additional informative characteristics th...

Response by Jingmai O'Connor for the presentation of the 2019 Schuchert Award of the Paleontological Society - Volume 94 Issue 5 - Jingmai O'Connor

The keratinous beak is inferred to have evolved multiple times in the Archosauria and in Aves. Unfortunately, this feature rarely preserves in the fossil record. Here we examine a collection of 603 specimens belonging to the Confuciusornithiformes, a clade of edentulous basal avians, only two of which preserve visible traces of the rhamphotheca. Pr...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

New and important pennaraptoran specimens continue to be discovered on a regular basis. Yet, with these discoveries the number of viable phylogenetic hypotheses has increased, including ones that challenge the traditional grouping of dromaeosaurids and troodontids within a monophyletic Deinonychosauria. This chapter will cover recent efforts to add...

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 Coelurosauria are a group of mostly feathered theropods that gave rise to birds, the only dinosaurians that survived the Cretaceous-Paleogene extinction event and are still found today. Between their first appearance in the Middle Jurassic up to the end Cretaceous, coelurosaurians were party to dramatic geographic changes on the Earth's surface...

The Coelurosauria are a group of mostly feathered theropods that gave rise to birds, the only dinosaurians that survived the Cretaceous-Paleogene extinction event and are still found today. Between their first appearance in the Middle Jurassic up to the end Cretaceous, coelurosaurians were party to dramatic geographic changes on the Earth’s surface...

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...

New and important pennaraptoran specimens continue to be discovered on a regular basis. Yet, with these discoveries the number of viable phylogenetic hypotheses has increased, including ones that challenge the traditional grouping of dromaeosaurids and troodontids within a monophy-letic Deinonychosauria. This chapter will cover recent efforts to ad...

Many specimens of the basal bird Jeholornis from the Early Cretaceous Jehol Biota of northeast China include one or two distinctive paddle-shaped skeletal elements preserved in the thoracic region. These ossifications have generally been identified as lateral trabeculae, paired processes of the sternum that are common within the derived avian clade...

The remains of ovarian follicles reported in nine specimens of basal birds represents one of the most remarkable examples of soft-tissue preservation in the Early Cretaceous Jehol Biota. This discovery was immediately contested and the structures alternatively interpreted as ingested seeds. Fragments of the purported follicles preserved in an enant...

Recent discoveries of enantiornithine birds trapped in amber have decreased the lower size limit of members of this clade, increased their morphological diversity, and provided significant new data regarding their plumage. Here, we describe a new specimen that consists of the distal extremities of both forelimbs and hindlimbs. Size and morphology s...

Feather molt is an important life-history process in birds, but little is known about its evolutionary history. Here, we report on the first fossilized evidence of sequential wing feather molt, a common strategy among extant birds, identified in the Early Cretaceous four-winged dromaeosaurid Microraptor. Analysis of wing feather molt patterns and e...

Protopteryx fengningensis is from the 130.7 Ma Huajiying Formation making it one of the oldest known enantiornithines. Contributing to its significance, this taxon is also commonly resolved as the basal-most enantiornithine in phylogenetic analyses. Protopteryx preserves several unusual morphologies that are otherwise absent in the Enantiornithes b...

We welcome any new interpretation or alternative hypothesis regarding the taxonomic affinity of the enigmatic Oculudentavis khaungraae. However, here we demonstrate that Li et al. have failed to provide conclusive evidence for the reidentification of HPG-15-3 as a squamate. We analyse this specimen in a matrix that includes a broad sample of diapsi...

The Lower Cretaceous Huajiying Formation of the Sichakou Basin in northern Hebei Province, northern China contains key vertebrate taxa of the early Jehol Biota, e.g., Protopteryx fengningensis , Archaeornithura meemannae , Peipiaosteus fengningensis , and Eoconfuciusornis zhengi . This formation arguably documents the second-oldest bird-bearing hor...

Living birds are unique among vertebrates in the formation of a female-specific bone tissue called medullary bone (MB) that is strictly associated with reproductive activity. MB is a rapidly mobilized source of calcium and phosphorus for the production of eggshell. Among living taxa, its skeletal distribution can be highly extensive such that it ev...

We describe the detailed cranial osteology of Sapeornis chaoyangensis based on information from previously described specimens and IVPP V19058, a specimen that was recently reported with regards to the palatal elements but not fully described. The skull in this specimen is entirely preserved in disarticulation, providing the most comprehensive glim...

Recent discoveries of enantiornithine remains in Burmese amber have provided a wealth of paleobiological data on this extinct clade of Mesozoic birds. Amber, as a unique medium of fossilization, preserves in three dimensions structures with details unmatched elsewhere in the fossil record. This provides the opportunity to combine osteological infor...

Bohaiornithidae is currently the most diverse recognized family of Early Cretaceous enantiornithines, with unique morphology of the rostrum and pedal digits. Here we describe a second specimen of the bohaiornithid Longusunguis kurochkini from the Jiufotang Formation. This specimen provides new anatomical information regarding this taxon, in particu...

Skeletal inclusions in approximately 99-million-year-old amber from northern Myanmar provide unprecedented insights into the soft tissue and skeletal anatomy of minute fauna, which are not typically preserved in other depositional environments1,2,3. Among a diversity of vertebrates, seven specimens that preserve the skeletal remains of enantiornith...

Early bird plumage is well known primarily due to numerous discoveries of specimens preserving feathers from Early Cretaceous deposits in China. Remiges and rectrices are most commonly preserved with rectrices showing the greatest variation. The long boney-tailed Jeholornis has a unique tail plumage employing two anatomically distinct rectricial pt...

All of the bird specimens previously recovered from Burmese amber have belonged to either immature specimens, or small-bodied taxa belonging to Enantiornithes. This has led to questions about whether the size bias inherent to preservation in amber has limited inclusions to smaller individuals or species, or if the avifauna of the amber-producing fo...

Molting-the process replacing one plumage with another-is a critically important biological function in Aves. This process annually replaces the feather coat, damaged by normal wear and tear, produces ontogenetic changes in feathering, and produces alternate breeding plumages associated with reproductive activity in adults. Immature, growing feathe...

Living birds are unique among vertebrates in the formation of a female-specific bone tissue called medullary bone (MB) that is strictly associated with reproductive activity. MB is a rapidly mobilized source of calcium and phosphorus for the production of eggshell. Among living taxa, its skeletal distribution can be highly extensive such that it ev...

The avian predentary is a small skeletal structure located rostral to the paired dentaries found only in Mesozoic ornithuromorphs. The evolution and function of this enigmatic element is unknown. Skeletal tissues forming the predentary and the lower jaws in the basal ornithuromorph Yanornis martini are identified using computed-tomography, scanning...

The earliest record of the Ornithuromorpha, which includes crown birds, is currently known from the Early Cretaceous Jehol Biota in north-eastern China. Here we describe a new ornithuromorph bird, Mengciusornis dentatus gen. et sp. nov., from the Jiufotang Formation of this biota. Mengciusornis preserves a suite of morphological features exclusivel...

The Confuciusornithiformes represent the most stem-ward avian occurrence of an edentulous rostrum. Although a keratinous beak is widely considered to have covered the rostrum in confuciusornithiforms, this feature is almost never preserved, having been previously reported only in the holotype of Confuciusornis dui and the holotype of Eoconfuciusorn...

The avian digestive system, like other aspects of avian biology, is highly modified relative to other reptiles. Together these modifications have imparted the great success of Neornithes, the most diverse clade of amniotes alive today. It is important to understand when and how aspects of the modern avian digestive system evolved among neornithine...

Since the first skeletal remains of avians preserved in amber were described in 2016, new avian remains trapped in Cretaceous-age Burmese amber continue to be uncovered, revealing a diversity of skeletal and feather morphologies observed nowhere else in the Mesozoic fossil record. Here we describe a foot with digital proportions unlike any previous...

In the mid-19th century, the discovery that bone microstructure in fossils could be preserved with fidelity provided a new avenue for understanding the evolution, function, and physiology of long extinct organisms. This resulted in the establishment of paleohistology as a subdiscipline of vertebrate paleontology, which has contributed greatly to ou...

Most living birds exhibit cranial kinesis—movement between the rostrum and braincase—in which force is transferred through the palatal and jugal bars. The palate alone distinguishes the Paleognathae from the Neognathae, with cranial kinesis more developed in neognaths. Most previous palatal studies were based on 2D data and rarely incorporated data...

Recent discoveries of vertebrate remains trapped in middle Cretaceous amber from northern Myanmar [1, 2] have provided insights into the morphology of soft-tissue structures in extinct animals [3-7], in particular, into the evolution and paleobiology of early birds [4, 8, 9]. So far, five bird specimens have been described from Burmese amber: two i...

Direct indicators of diet and predator-prey relationships are exceedingly rare in the fossil record [1, 2]. However, it is through such traces that we can best understand trophic interactions in ancient ecosystems [3], confirm dietary inferences derived from skeletal morphologies [4], and clarify behavioral and ecological interpretations [5]. Here,...

Change history: In this Letter, it should have been acknowledged that the silhouettes of Scansoriopterygidae in Fig. 3a were modified from a sketch by Jaime Headden. The original Letter has been corrected online.

The Coelurosauria are a group of mostly feathered theropods that gave rise to birds, the only dinosaurs that survived the Cretaceous-Paleogene extinction event and are still found today. Between their first appearance in the Middle Jurassic up to the end Cretaceous, coelurosaurs were party to dramatic geographic changes on the Earth's surface, incl...

The origin of avian flight is one of the most controversial debates in Paleontology. This paper investigates the wing performance of Caudipteryx, the most basal non-volant dinosaur with pennaceous feathered forelimbs by using modal effective mass theory. From a mechanical standpoint, the forced vibrations excited by hindlimb locomotion stimulate th...

Experiment on the Ostrich to get the lift produced by the artificial wings with the simplest plate form. (A) Force sensor. They are embedded into the wearable device to measure lift dynamically. In this experiment, each wing has one force sensor to measure the dynamic lift. (B) Embedded accelerometer and SD card on a bracket. The accelerometer reco...

Modal effective mass of Caudipteryx by means of eight excessive assumed mass distribution. (A) changes of natural frequencies with respect to the modes. (B) effective masses in Y-axis versus modes and velocities to reach to the flapping or second modes. The natural frequency decreases from 4 Hz in mass model A to 1.8 Hz in mass model I in the secon...

Fossils of Caudipteryx. (A) Caudipteryx dongi IVPP V12344 and (B) Caudipteryx sp. IVPP V12430. (TIF)

Observation on the juvenile ostrich. The forced vibrations of the wings of the young ostriches are easily found when they run on the ground. (MP4)

Experiments on the ostrich. Experiments were accomplished on the ostrich when it ran on the ground with different reconstructed wings of Caudipteryx. Collected data show that the flapping of the wings is a natural process of the forced vibrations under the actuation of running feet. (MP4)

Computer simulation on vibration modes of Caudipteryx. Computer simulations were also accomplished on reconstructed Caudipteryx with wings. Flapping motion is one of the primary modes of the Caudipteryx which is easily excited under the actuation of running feet. (MP4)

Supplementary materials. (PDF)

Reconstructed Caudipteryx robot from fossil BPM 0001. The measurements from Caudipteryx zoui BPM 0001 (Caudipteryx sp. IVPP V12430) have been used to appraise the whole body of Caudipteryx and to characterize the appropriate relationship for the robot and mathematical models of this dinosaur. Every part of the robot was fabricated with 3-D printer,...

Experiments on the test rig. Experiments were in the stationary situation when the robot flapped actively from 2.5 Hertzs to 6.3 Hertzs. Both produced positive lift and thrust forces in this case. (MP4)

Speed calculation. (XLSX)

Computer simulation for the first twenty natural frequencies. Computer simulations were executed at the finite element software of ABAQUS (S4 Video). The basic elements in the simulation were shell, linear quadrilateral with the type of S4R. The first primary mode is the rigid swaying of the wings; the second one is the flapping mode. (TIF)

Experiment on the Ostrich to obtain responses of the body and the wings in running. (A) Definition of the flapping angles of the wings. The clockwise rotation is the positive direction for the left wing while the anticlockwise rotation is the positive direction for the right wing. (B) Response of the filament feathers. The largest flapping angle of...