Luis M. Chiappe

Natural History Museum of Los Angeles County · Research & Collections

The Alvarezsauridae comprises a group of enigmatic maniraptoran theropods from the Upper Cretaceous of South America, North America, Europe, and Asia. Among their most distinctive features are their short, robust forelimbs, and manus with an enlarged digit I bearing a massive claw and lateral digits highly reduced or absent. Among the Gondwanan alv...

A dearth of Mesozoic-aged, three-dimensional fossils hinders understanding of the origin of the distinctive skull and brain of modern (crown) birds¹. Here we report Navaornis hestiae gen. et sp. nov., an exquisitely preserved fossil species from the Late Cretaceous of Brazil. The skull of Navaornis is toothless and large-eyed, with a vaulted craniu...

The study of the Cretaceous birds closest to the living euornithine species has mainly focused on the evolutionary patterns leading to the modern group. Yet, the morphological and ecological diversity of the euornithine branches not directly ancestral to the crown-group is probably underestimated. A new euornithine bird, Shuilingornis angelai gen....

Aucasaurus garridoi is an abelisaurid theropod from the Anacleto Formation (lower Campanian, Upper Cretaceous) of Patagonia, Argentina. The holotype of Aucasaurus garridoi includes cranial material, axial elements, and almost complete fore- and hind limbs. Here we present a detailed description of the axial skeleton of this taxon, along with some p...

The Chinese early Cretaceous Confuciusornis sanctus is the most abundant Mesozoic bird and a model species for studies of early avian evolution. While previous investigations were largely focused on aspects of the anatomy, taxonomy and systematics, and life history and ecology of this bird, there has been minimal research on its flight properties....

The Lower Cretaceous fossil site of Las Hoyas (Cuenca, Spain) has yielded the richest Cretaceous avifauna of the European continent. We describe a new fossil (MUPA-LH-33333) of an enantiornithine bird from this locality. This specimen consists of a partially articulated skeleton preserving portions of the vertebral column, both girdles and limbs, r...

Feathers are epidermal structures with different degrees of complexity (e.g., filamentous, pennaceous, and vaned feathers) that are present in avian dinosaurs (birds) and some non-avian dinosaurs, and contentiously in pterosaurs. They are composed of fibrous corneous β-proteins and their microstructure is formed by medulla, cortex, and inner and ou...

Extant terrestrial vertebrates, including birds, have a panoply of symbiotic relationships with many insects and arachnids, such as parasitism or mutualism. Yet, identifying arthropod-vertebrate symbioses in the fossil record has been based largely on indirect evidence; findings of direct association between arthropod guests and dinosaur host remai...

Integration of the world's natural history collections can provide a resource for decision-makers.

Over the past three centuries, people have collected objects and specimens and placed them in natural history museums throughout the world. Taken as a whole, this global collection is the physical basis for our understanding of the natural world and our place in it, an unparalleled source of information that is directly relevant to issues as divers...

The forelimb of Patagonian alvarezsaurids is known from a partially complete appendicular element of Patagonykus puertai (MCF-PVPH-37, Museo Cármen Fúnes) and from an I-2 ungueal phalanx (currently lost) of Alvarezsaurus calvoi (MUCPv-54, Museo Universidad del Comahue). New material of A. calvoi from the Fm. Bajo de la Carpa was recently collected...

The Early Cretaceous (129-125 Mya) Las Hoyas wetland in Cuenca (Spain) contains the richest Cretaceous avifauna in the European continent. More than 30 years of paleontological excavations at this site have resulted in the discovery of many relevant enantiornithine fossils. Among these, Iberomesornis romerali, Concornis lacustris, Eoalulavis hoyasi...

Among terrestrial vertebrates, only crown birds (Neornithes) rival mammals in terms of relative brain size and behavioural complexity. Relatedly, the anatomy of the avian central nervous system and associated sensory structures, such as the vestibular system of the inner ear, are highly modified with respect to those of other extant reptile lineage...

The Hesperornithiformes (sometimes referred to as Hesperornithes) are the first known birds to have adapted to a fully aquatic lifestyle, appearing in the fossil record as flightless, foot-propelled divers in the early Late Cretaceous. Their known fossil record—broadly distributed across the Northern Hemisphere—shows a relatively rapid diversificat...

Paleontological evidence reveals that the rapid growth characteristic of living birds evolved close to the origin of the crown-group Neornithes, as more stemward birds experienced protracted growth until becoming fully grown.1 Research on Mesozoic confuciusornithids, the earliest divergence of fully beaked birds, has revealed a complex life cycle i...

Background Dinosaurs dominated terrestrial environments for over 100 million years due in part to innovative feeding strategies. Although a range of dental adaptations was present in Late Jurassic dinosaurs, it is unclear whether dinosaur ecosystems exhibited patterns of tooth disparity and dietary correlation similar to those of modern amniotes, i...

Polyphyodonty—multiple tooth generations—in Mesozoic birds has been confirmed since the nineteenth century. Their dental cycle had been assessed through sparse data from tooth roots revealed through broken jawbones and disattached teeth. However, detailed descriptions of their tooth cycling are lacking, and the specifics of their replacement patter...

Despite the abundant number of enantiornithine fossils from the Jehol Biota, the cranial anatomy of these birds remains only superficially known. Similarly, data on dental replacement within this clade, and among toothed birds in general, is largely lacking. Here we describe a new and exquisitely preserved specimen of a bohaiornithid enantiornithin...

Birds are one of the most diverse clades of extant terrestrial vertebrates, a diversity that first arose during the Mesozoic as a multitude of lineages of pre-neornithine (stem) birds appeared but did not survive into the Cenozoic Era. Modern birds (Neornithes) inhabit an extensive array of ecologically distinct habitats and have specific and varie...

Feathered dinosaurs discovered during the last decades have illuminated the transition from land to air in these animals, underscoring a significant degree of experimentation in wing-assisted locomotion around the origin of birds. Such evolutionary experimentation led to lineages achieving either wing-assisted running, four-winged gliding, or membr...

Birds are living dinosaurs, an evolutionary transition increasingly well documented in the abundant fossil record of Mesozoic birds. The avian fossil record begins 150 Ma (million years ago) in the late Jurassic, and for the next 85 million years, birds experienced an evolutionary radiation resulting in a wide range of body forms and lifestyles, oc...

Presentation of the 2019 Schuchert Award of the Paleontological Society to Jingmai O'Connor - Volume 94 Issue 5 - Luis M. Chiappe

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

Multiple factors involved in the evolutionary transformation of the manus across the maniraptoran radiation, including its current morphology in modern birds, remain unexplored. Specifically, the morphological disparity of the manus has never been studied quantitatively, and there are no hypotheses about the possible mechanisms and constraints unde...

Unseen and difficult-to-see soft tissues of fossil birds revealed by laser-stimulated fluorescence (LSF) shed light on their functional morphology. Here we study a well-preserved specimen of the early pygostylian Sapeornis chaoyangensis under LSF and use the newly observed soft-tissue data to refine previous modeling of its aerial performance and t...

The first dinosaur embryos found inside megaloolithid eggs from Auca Mahuevo, Patagonia, were assigned to sauropod dinosaurs that lived approximately 80 million years ago. Discovered some 25 years ago, these considerably flattened specimens still remain the only unquestionable embryonic remains of a sauropod dinosaur providing an initial glimpse in...

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 Hesperornithiformes constitute the first known avian lineage to secondarily lose flight in exchange for the evolution of a highly derived foot-propelled diving lifestyle, thus representing the first lineage of truly aquatic birds. First unearthed in the 19th century, and today known from numerous Late Cretaceous (Cenomanian-Maastrichtian) sites...

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 environments1–3. Among a diversity of vertebrates, seven specimens that preserve the skeletal remains of enantiornithin...

We describe a new taxon of advanced ornithuromorph bird, Khinganornis hulunbuirensis gen. et sp. nov., from the previously unreported Pigeon Hill locality of the Lower Cretaceous Longjiang Formation in the northern Greater Khingan Range area of Inner Mongolia, China. A cladistics analysis resolves K. hulunbuirensis as the sister group of a clade fo...

The Early Cretaceous (∼131 Million Years Ago) Protopteryx fengningensis is one of the oldest and most primitive enantiornithine birds; however, knowledge of its anatomy has largely been limited to the succinct description of two specimens (holotype and paratype). This study describes two new specimens of P. fengningensis preserving most of the skel...

We describe three-dimensionally preserved feathers in mid-Cretaceous Burmese amber that share macro-morphological similarities (e.g., proportionally wide rachis with a “medial stripe”) with lithic, two-dimensionally preserved rachis-dominated feathers, first recognized in the Jehol Biota. These feathers in amber reveal a unique ventrally concave an...

More than a thousand specimens of Confuciusornis sanctus have been recovered from the Early Cretaceous Jehol Group of Northeastern China. Here, we investigate the bone microstructure of 33 long bones sampled from 14 C. sanctus specimens in an attempt to assess the life history patterns of this basal pygostylian bird. Analysis of the histology of va...

Exceptionally preserved Mesozoic feathered dinosaur fossils (including birds) are famous, but recognized from only very few localities worldwide, and are especially rare in the Southern Hemisphere. Here we report an assemblage of non-avian and avian dinosaur feathers from an Early Cretaceous polar (around 70°S) environment in what is now southeaste...

During the last decade, several Bohaiornis -like enantiornithine species—and numerous specimens—have been recognized from the celebrated Jehol Biota of northwestern China. In this paper, we describe the anatomy of another “bohaiornithid” species from the 125 million-year-old Yixian Formation of Liaoning Province, China. The new taxon differs from p...

The transformation of the hand from a prensil structure to a wing component across maniraptorans (including modern birds) is a key morphological transition in tetrapod evolution. Yet, it has never been studied quantitatively at a broad macroevolutionary scale. The sustained miniaturization occurring along the lineage towards crown birds suggests th...

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...

Mocho P, Escaso F, Chiappe L. 2019. Gnatalie quarry, a window to understand the dinosaurian paleodiversity of the Late Jurassic of Southeastern Utah (Morrison Fm., USA), pp. 251-252. In: Droser M, Hughes N, Bonuso N, Bottjer D, Eernisse D, Gaines R, Hendy A, Jacobs A, Miller-Camp J, Norris R, Roy K, Sadler P, Springer M, Wang X, Vendrasco M (eds.),...

Over the last three years, Burmese amber (~99 Ma, from Myanmar) has provided a series of immature enantiornithine skeletal remains preserved in varying developmental stages and degrees of completeness. These specimens have improved our knowledge based on compression fossils in Cretaceous sedimentary rocks, adding details of three-dimensional struct...

Atmospheric conditions are critical for a range of biological functions—locomotion among others—and long-term changes in these conditions have been identified as causal for different macroevolutionary patterns. Here we examine the influence of variations in atmospheric O2 concentration (AOC), temperature (Tair), and air density (ρair) on the power...

A new Morrison bonebed (Brushy Basin Member) from San Juan County, Utah, yields abundant remains of sauropods as well as more fragmentary fossils of theropods, ornithopods, and thyreophorans. The 'Gnatalie Quarry' (locality LACM 7683; Natural History Museum of Los Angeles County) contains the remains of at least two sauropod clades: Diplodocinae an...

A new Morrison bone-bed (Brushy Basin Member) from San Juan County yields abundant remains of sauropods as well as more fragmentary fossils of theropods, ornithopods, and thyreophorans. The ‘Gnatalie quarry’ (locality LACM 7683; Natural History Museum of Los Angeles County) contains the remains of at least two sauropod clades: Diplodocinae and Macr...

The avian tail played a critical role in the evolutionary transition from long- to short-tailed birds, yet its ontogeny in extant birds has largely been ignored. This deficit has hampered efforts to effectively identify intermediate species during the Mesozoic transition to short tails. Here we show that fusion of distal vertebrae into the pygostyl...

Fossils of juvenile Mesozoic birds provide insight into the early evolution of avian development, however such fossils are rare. The analysis of the ossification sequence in these early-branching birds has the potential to address important questions about their comparative developmental biology and to help understand their morphological evolution...

Cretaceous amber from Myanmar (∼99 Ma Burmese amber) has become a valuable supplement to the traditional skeletal record of small theropod dinosaurs preserved in sedimentary rocks, particularly for coelurosaurs and enantiornithines. The specimens recovered from this deposit preserve skeletal material and soft tissues in unmatched detail. This provi...

Intermittent flight through flap-gliding (alternating flapping phases and gliding phases with spread wings) or bounding (flapping and ballistic phases with wings folded against the body) are strategies to optimize aerial efficiency which are commonly used among small birds today. The broad morphological disparity of Mesozoic birds suggests that a r...

The Cretaceous Hesperornithiformes are an extinct group of aquatic birds long recognized to have practiced foot-propelled diving. This specialization is seen today in a number of modern avian families (loons, grebes, cormorants, and some ducks) that have convergently derived a diving lifestyle. Historically, hesperornithiforms have usually been com...

Here we report the associated remains of an adult sauropod specimen collected from Egg Layer 3, at the egg fossil-bearing site Auca Mahuevo, located at northern Neuquén Province. The remains were buried in coarse sandstone, and collected from a single digging site. The specimen, MCF-PVPH-335 is a fragmentary skeleton represented by an incomplete po...

The Huajiying Formation contains the earliest deposits of the Jehol Biota, representing the world's second oldest avifauna. This avifauna includes the early confuciusornithid Eoconfuciusornis zhengi, the oldest occurrence of this clade and one of the earliest divergences of pygostylian birds. Although E. zhengi shows unique traits, the holotype's i...

While environmental factors affect animal locomotion (especially among fliers), few studies have addressed the relationship between aerial function in extinct vertebrates and paleoatmospheric conditions, and none have focused on avian flight. Our study explores the impact of varying O2 concentrations, global temperatures, and air densities on the f...

We describe an exquisitely preserved new avian fossil (BMNHC-PH-919) from the Lower Cretaceous Yixian Formation of eastern Inner Mongolia, China. Although morphologically similar to Cathayornithidae and other small-sized enantiornithines from China’s Jehol Biota, many morphological features indicate that it represents a new species, here named Juno...

Abstract: We report on a diminutive pterosaur specimen (MIC-V246), from the Lower Cretaceous Lagarcito Formation, which has anatomical features and general proportions that agree with those of other juvenile specimens of the filter-feeding pterosaur Pterodaustro guinazui. MIC-V246 is nearly complete, with the majority of its bones in natural articu...

Several flight modes are thought to have evolved during the early evolution of birds. Here, we use a combination of computational modelling and morphofunctional analyses to infer the flight properties of the raven-sized, Early Cretaceous bird Sapeornis chaoyangensis—a likely candidate to have evolved soaring capabilities. Specifically, drawing info...

Burmese amber has recently provided some detailed glimpses of plumage, soft tissues, and osteology of juvenile enantiornithine birds, but these insights have been restricted to isolated wing apices. Here we describe nearly half of a hatchling individual, based on osteological and soft tissue data obtained from the skull, neck, feet, and wing, and i...

Our knowledge of the diversity, ecology, and phylogeny of Mesozoic birds has increased significantly during recent decades, yet our understanding of their flight competence remains poor. Wing loading ( WL ) and aspect ratio ( AR ) are two aerodynamically relevant parameters, as they relate to energy costs of aerial locomotion and flight maneuverabi...