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Triassic pterosaurs
Abstract
Pterosaurs are a clade of highly specialized, volant archosauromorphs recorded from
the Upper Triassic to the uppermost Cretaceous. Problematic remains referred to the Pterosauria
are reported from the Triassic of Europe and both North and South America, but unequivocal
pterosaur specimens are only known from the Alps (Italy, Austria and Switzerland: Preondactylus
buffarinii, Austriadactylus cristatus, Peteinosaurus zambellii, Eudimorphodon ranzii, Carniadactylus
rosenfeldi, Caviramus schesaplanensis and Raeticodactylus filisurensis) and Greenland
(‘Eudimorphodon’ cromptonellus). Pterosaurs are diagnosed mostly by features associated with
the advent of powered flight. They are generally considered to be archosaurians more closely
related to dinosaurs than to crocodilians, but non-archosaurian positions have also been proposed.
There is a lack of general agreement about ingroup relationships, particularly among the basal
pterosaurs. Triassic pterosaurs differ from other non-pterodactyloid pterosaurs in features of the
dentition and caudal vertebral column. A ‘Big Bang’ model for their early history fits better
with the fossil record: the earliest unequivocal pterosaurs show a sudden and geographically
limited appearance in the fossil record, as well as a relatively high burst of diversity and considerable
morphologic disparity. Absence of pterosaur remains from deposits where they are expected to
be found suggests that they had not yet evolved in pre-Norian times.
... Carnivory interpretations are based on comparative anatomy and functional morphology (Fig. 3). Rapid jaw closure, suggested by adductor muscle reconstructions, may have helped in the capture of small vertebrates (Ősi, 2011;Dalla Vecchia, 2013). Morphological reassessments of Dimorphodon forelimbs and pectoral girdle suggest an erect posture which would have facilitated terrestrial foraging for small vertebrates (Witton, 2015b). ...
... These pterosaurs exhibit 0.7-1.8 m wingspans and some form of heterodont and/or multi-cusped dentition (Fig. 1C) (Wild, 1978;Padian, 2008a;Ősi, 2011;Dalla Vecchia, 2013). Campylognathoidids are most commonly interpreted as pisciviorous, with insectivory, carnivory, durophagy, herbivory/frugivory and generalism also suggested (Fig. 3). ...
... Eudimorphodon exhibits serrated, monocuspid, tricuspid and pentacuspid teeth (Wild, 1978;Stecher, 2008), which could have assisted in cutting through fish scales (Ősi, 2011). Reconstructions of Eudimorphodon adductor muscles suggest high quadrate mobility and rapid jaw closure when fishing (Ősi, 2011;Dalla Vecchia, 2013). ...
Pterosaurs are an extinct group of Mesozoic flying reptiles, whose fossil record extends from approximately 210 to 66 million years ago. They were integral components of continental and marginal marine ecosystems, yet their diets remain poorly constrained. Numerous dietary hypotheses have been proposed for different pterosaur groups, including insectivory, piscivory, carnivory, durophagy, herbivory/frugivory, filter‐feeding and generalism. These hypotheses, and subsequent interpretations of pterosaur diet, are supported by qualitative (content fossils, associations, ichnology, comparative anatomy) and/or quantitative (functional morphology, stable isotope analysis) evidence. Pterosaur dietary interpretations are scattered throughout the literature with little attention paid to the supporting evidence. Reaching a robustly supported consensus on pterosaur diets is important for understanding their dietary evolution, and their roles in Mesozoic ecosystems. A comprehensive examination of the pterosaur literature identified 314 dietary interpretations (dietary statement plus supporting evidence) from 126 published studies. Multiple alternative diets have been hypothesised for most principal taxonomic pterosaur groups. Some groups exhibit a high degree of consensus, supported by multiple lines of evidence, while others exhibit less consensus. Qualitative evidence supports 87.3% of dietary interpretations, with comparative anatomy most common (62.1% of total). More speciose groups of pterosaur tend to have a greater range of hypothesised diets. Consideration of dietary interpretations within alternative phylogenetic contexts reveals high levels of consensus between equivalent monofenestratan groups, and lower levels of consensus between equivalent non‐monofenestratan groups. Evaluating the possible non‐biological controls on apparent patterns of dietary diversity reveals that numbers of dietary interpretations through time exhibit no correlation with patterns of publication (number of peer‐reviewed publications through time). 73.8% of dietary interpretations were published in the 21st century. Overall, consensus interpretations of pterosaur diets are better accounted for by non‐biological signals, such as the impact of the respective quality of the fossil record of different pterosaur groups on research levels. That many interpretations are based on qualitative, often untestable lines of evidence adds significant noise to the data. More experiment‐led pterosaur dietary research, with greater consideration of pterosaurs as organisms with independent evolutionary histories, will lead to more robust conclusions drawn from repeatable results. This will allow greater understanding of pterosaur dietary diversity, disparity and evolution and facilitate reconstructions of Mesozoic ecosystems.
... Late Triassic (Norian) pterosaurs are the oldest ones found to date (Dalla Vecchia, 2013). They are represented by about 30 unequivocal remains, including fragmentary specimens and single isolated bones and teeth (Dalla Vecchia, 2013. ...
... Late Triassic (Norian) pterosaurs are the oldest ones found to date (Dalla Vecchia, 2013). They are represented by about 30 unequivocal remains, including fragmentary specimens and single isolated bones and teeth (Dalla Vecchia, 2013. Their record is rather sparse and each new find has therefore an impact upon our understanding of early pterosaur history and phylogenetic relationships. ...
A new non-monofenestratan pterosaur with multicusped dentition, Seazzadactylus venieri, is described from the Upper Triassic (middle-upper Norian) of the Carnian Prealps (northeastern Italy). The holotype of S. venieri preserves a complete mandibular and maxillary dentition, along with a nearly complete premaxillary one, showing unique features. Furthermore, the arrangement of the premaxillary teeth and the shape of jugal, pterygoid, ectopterygoid, scapula and pteroid are unique within non-monofenestratan pterosaurs. S. venieri is similar and closely related to Carniadactylus rosenfeldi and Austriadraco dallavecchiai, which are also from the Alpine middle-upper Norian of Italy and Austria, respectively. In a parsimony-based phylogenetic analysis, S. venieri is found to nest within a clade of Triassic pterosaurs composed of Arcticodactylus cromptonellus, Austriadraco dallavecchiai, Carniadactylus rosenfeldi and a trichotomy of Raeticodactylus filisurensis, Caviramus schesaplanensis and MCSNB 8950. This unnamed clade is basal within the Pterosauria, but is not the basalmost clade. Eudimorphodon ranzii lies outside this clade and is more derived, making the Eudimorphodontidae paraphyletic. S. venieri increases the diversity of Triassic pterosaurs and brings the number of pterosaur genera and species in the Dolomia di Forni Formation to four.
... Their origin remained a mystery until, in 1801, George Cuvier discovered that the fossils belonged to a flying reptile. Katsufumi Sato, a Japanese scientist, did calculations using modern birds and concluded that it was impossible for a pterosaur to stay aloft [1]. Most of the many studies on pterosaurs describe the fossil remains, and discuss how a new specimen updates the current knowledge base. ...
... The wing kinematics and wing sections are illustrated in Fig. 3. For a root flapping motion with no spanwise bending, the plunging motion is given by ht; y yγt Γy cosωt (1) where γ represents the section's dihedral (flapping) angle, Γ represents its amplitude, and ω is the flapping frequency. The dynamic twist is linearly proportional to the span according to the following relation: ...
There has been a recent interest to explore the shape and kinematics parameters of distinct pterosaurs from their fossil records. Clearly, far more evidence is needed to understand the nuances of dinosaurs flight. A multiobjective aerodynamic optimization problem of the wing kinematics and planform of a pterosaur replica ornithopter designed by Aerovironment is performed. Objective functions include minimization of the required cycle-averaged aerodynamic power and maximization of the propulsive efficiency. It is found that inclusion of the inertial power requirements is necessary for a physical and proper formulation of the optimization problem. Furthermore, the mere addition of the inertial power requirements is not enough to obtain reasonable results. Rather, one has to consider a partial (or even zero) elastic energy storage. The minimum power kinematic parameters closely match those of the previously designed pterosaur replica. Nevertheless, the obtained efficiency for such a design (minimum power) is 10%, which is considerably lower than the maximum possible efficiency for the used planform (40%). Furthermore, the optimized planform for maximum efficiency of the pterosaur yields to an increase in the propulsive efficiency by 6%.
... The origin of Christian Foth -Habilitationsschrift 8 Archosauria dates back to at least the Early Triassic . During their cosmopolitan Mesozoic radiation, archosaurs became extremely diverse in terms of number of species, diet spectra, and body plans, and adapted to different forms and manners of locomotion (e.g., Weishampel et al. 2004;Brusatte et al. 2008;Nesbitt 2011), including terrestrial (most archosaur groups), aquatic to semi-aquatic (e.g., phytosaurs, thalattosuchians, neosuchians) (e.g., Young et al. 2010;Stocker & Butler 2013), as well as aerial and arboreal habitats (e.g., pterosaurs, avialans) (e.g., Dalla Vecchia 2013;Brusatte et al. 2015). Today, archosaurs represent the most successful group of tetrapods with approximately 10,000 extant species, of which the vast majority are birds (Westheide & Rieger 2004). ...
Macroevolution describes the divisions of taxonomic hierarchy above the species level, and the formation of complex organ systems. In contrast, intraspecific variation summarizes discrete morphological and physiological differences in one individual or between several individuals of the same species, and can be distinguished between two main types: polymorphism (including sexual dimorphism) and ontogenetic variation. This thesis summarizes my recent work on macroevolutionary and intraspecific patterns in reptiles, focusing on two major clades, turtles (Testudinata) and archosauromorphs.
Applying morphological comparisons, bone histology, cladistics methods, and 2D geometric morphometrics, I investigated, among others, the skull disparity of turtles and archosauromorphs through time, common ontogenetic patterns in the skull of caimanine crocodylians and basal saurischian dinosaurs, ontogenetic growth patterns of crocodylian ancestors, and the evolution of pennaceous (= contour) feathers in theropod dinosaurs.
The cranial disparity of turtles shows a steady increase from the Late Triassic to the end the Late Cretaceous, followed by a period of stagnation, matching global biogeographic events, and indicating a certain resilience across the K/T extinction event. Stem-archosaurs show a previously unappreciated high skull disparity, evolving prior to the major radiation of crown archosaurs. However, disparity patterns in the Ladinian and Carnian indicate a gradual faunal replacement of stem archosaurs by the crown group, followed by an abrupt decline during the Late Triassic. Among others, the major radiation of crown archosaurs benefitted from the evolution of fast growth patterns, which occurred in both pseudosuchians and ornithodirans, and probably correlates with higher metabolic activity levels. During growth, archosaurs show some deeply conserved ontogenetic patterns in the skull, even between species that are strongly separated from each other in morphospace. Finally, while the feather plumage of basal theropod dinosaurs was filamentous, and rather conform within different body regions, the origin of planar pennaceous feathers caused a high plumage diversity in different body regions of theropod dinosaurs, especially in the tail and hindlimbs. This high diversity went hand in hand with the increase of colour patterns, indicating an original biological role of pennaceous feathers in the context of signalling rather than flight.
... The Triassic outcrops of the Santa Maria Supersequence (Middle-Late Triassic) located in the central region of the Rio Grande do Sul State of southern Brazil have historically been the site of many important finds since they were first scientifically prospected in the late 1920s (Huene, 1935(Huene, -1942(Huene, , 1942Beltrão, 1965). Efforts to explore these and new localities have continued during subsequent decades (Barberena, 1977;Barberena et al., 1985;Schultz, Scherer & Barberena, 2000;Da-Rosa, 2014;Horn et al., 2014;Müller et al., 2014) and have produced an ample record for many groups of archosaurs and non-archosaurian archosauriforms, such as aetosaurs (Desojo, Ezcurra & Kischlat, 2012;, doswellids (Desojo, Ezcurra & Schultz, 2011), early branch loricatans (Barberena, 1978;França, Ferigolo & Langer, 2011;Lacerda, Schultz & Bertoni-Machado, 2015;Roberto-Da-Silva et al., 2014), rauisuchids (Huene, 1935(Huene, -1942Lautenschlager & Rauhut, 2014), poposaurids (França et al., 2014), phytosaurs (Kischlat & Lucas, 2003), proterochampsids (Bertoni-Machado & Kischlat, 2003;Raugust, Lacerda & Schultz, 2013), aphanosaurians , a possible pterosaurs (Bonaparte, Schultz & Soares, 2010;Dalla Vecchia, 2013) and several dinosauriforms (e.g. Colbert, 1970;Bonaparte, Ferigolo & Ribeiro, 1999;Langer et al., 1999;Leal et al., 2004; Figure 1. ...
The evolution and diversification of Triassic pseudosuchian lineages has been the subject of much interest and revision in the last couple of decades, fuelled by new and important discoveries, which have allowed for better-sampled phylogenetic analysis. In the present contribution, we add to this by describing a new taxon, Pagosvenator can-delariensis gen. et sp. nov., for the Middle-Late Triassic Dinodontosaurus Assemblage Zone of the Santa Maria Supersequence of southernmost Brazil. A comparative osteological analysis combined with a phylogenetic analysis supports its inclusion within the clade Erpetosuchidae and provides an insight into the phylogenetic relationship and evolutionary history of this clade, with two possibilities for the Erpetosuchidae relationship: as an early branch of pseudosuchians, being a sister group of Ornithosuchidae; or a closer relationship with the clade composed by Gracilisuchidae and Paracrodylomorpha with respect to Orntithosuchidae and Aetosauria. Additionally, the results presented and discussed here are of biostratigraphical importance, given that the taxon is from the Ladinian/Carnian age and would fill a temporal gap that exists within Erpetosuchidae between Parringtonia gracilis from the Anisian and Erpetosuchus from late the Carnian to Norian. Furthermore, it would be the first occurrence of a member of this clade in South America. ADDITIONAL KEYWORDS: Archosauria-Brazil-Erpetosuchidae-Pagosvenator-Santa Maria Supersequence-South America-Triassic.
... As new material has not been found in the meantime, the matter remains hypothetical. MPUM 6009 and MFSN 1797 were found in localities that are now about 250 km apart (see Dalla Vecchia 2013: fig. 3) and they were on that order of distance also during the latest Triassic. Both localities were located on the shallow carbonate platform along the eastern margin of Pangaea far from a continental land mass (Dalla Vecchia 2014: figs 3. 1.1-4), where the only emergent areas were probably low lying islands (Dalla Vecchia 2014). ...
Six stages (OS1-6) were identified by Kellner (2015) to establish the ontogeny of a given pterosaur fossil. These were used to support the erection of several new Triassic taxa including Bergamodactylus wildi, which is based on a single specimen (MPUM 6009) from the Norian of Lombardy, Italy. However, those ontogenetic stages are not valid because different pterosaur taxa had different tempos of skeletal development. Purported diagnostic characters of Bergamodactylus wildi are not autapomorphic or were incorrectly identified. Although minor differences do exist between MPUM 6009 and the holotype of Carniadactylus rosenfeldi, these do not warrant generic differentiation. Thus, MPUM 6009 is here retained within the taxon Carniadactylus rosenfeldi as proposed by Dalla Vecchia (2009a).
... Taxon sampling is based on a large-scale phylogenetic analysis of the pan-avian clade (Cau, in prep.) and includes representatives of all main pan-avian groups, each represented by two or more species/genus-level taxa. Although pterosaurs are usually placed among the basalmost members of the pan-avian clade (e.g., Nesbitt et al., 2017), the ancestral condition of these highly modified flying reptiles is problematic (Dalla Vecchia, 2013): pending a large-scale analysis of pterosaur relationships that accurately samples the Triassic disparity of the clade, they are provisionally excluded from the analysis of the ASL. Taxa included in this version of the analysis were chosen based on a balanced series of criteria, such as amount of skeletal completeness (preferring most complete taxa and those sampling poorly known anatomical regions instead of fragmentary taxa or those having character combinations redundant with other better preserved taxa), inferred phylogenetic position relative to other members of the same subclade (i.e., using a consensus among recently published phylogenies as reference, the earliest-diverging members were preferred over members of late-diverging subclades), and stratigraphic significance (preferring oldest taxa of a clade to the youngest members). ...
Birds are one of the most successful groups of vertebrates. The origin of birds from their reptilian ancestors is traditionally rooted near the Jurassic "Urvogel" Archaeopteryx, an approach that has contributed in defining the dichotomy between the "reptilian" (pre-Archaeopteryx) and "avian" (post-Archaeopteryx) phases of what is instead a single evolutionary continuum. A great and still ever increasing amount of evidence from the fossil record has filled the gaps between extinct dinosaurs, Mesozoic birds and modern avians, and led to the revision of the misleading dichotomy between pre-and post-Archaeopteryx stages in the evolution of bird biology. Herein, the progressive assembly of the modern avian body plan from the archosaurian ancestral condition is reviewed using a combination of phylogenetic methods. The stem lineage leading to modern birds is described using 38 internodes, which identity a series of progressively less inclusive ancestors of modern birds and their Mesozoic sister taxa. The 160-million-year long assembly of the avian bauplan is subdivided into three main stages on the basis of analyses of skeletal modularity, cladogenetic event timing, divergence rate inference and morphospace occupation. During the first phase ("Huxleyian stage": Early Triassic to Middle Jurassic), the earliest ancestors of birds acquired postcranial pneumatisation, an obligate bipedal and digitigrade posture, the tridactyl hand and feather-like integument. The second phase ("Ostromian stage": second half of Jurassic) is characterised by a higher evolutionary rate, the loss of hypercarnivory, the enlargement of the braincase, the dramatic reduction of the caudofemoral module, and the development of true pennaceous feathers. The transition to powered flight was achieved only in the third phase ("Marshian stage": Cretaceous), with the re-organisation of both forelimb and tail as flight-adapted organs and the full acquisition of the modern bauplan. Restricting the investigation of the avian evolution to some Jurassic paravians or to the lineages crown-ward from Archaeopteryx ignores the evolutionary causes of over 60% of the features that define the avian body. The majority of the key elements forming the third phase are exaptations of novelties that took place under the different ecological and functional regimes of the Huxleyian and Ostromian stages, and cannot be properly interpreted without making reference to their original historical context.
RIASSUNTO - [La costruzione del piano corporeo aviano: un processo lungo 160 milioni di anni] - Gli uccelli sono uno dei gruppi di vertebrati di maggiore successo. L'origine degli uccelli dai loro antenati rettiliani è tradizionalmente ancorata intorno allo "Urvogel" giurassico Archaeopteryx; questo approccio ha consolidato la distinzione tra una fase "rettiliana" (precedente Archaeopteryx) ed una "aviana" (successiva ad Archaeopteryx) in quello che è invece un singolo continuum evolutivo. Una crescente quantità di evidenze dal registro fossilifero ha colmato le lacune esistenti tra i dinosauri non-avialiani, gli uccelli mesozoici e quelli moderni, e ha portato alla revisione della fuorviante dicotomia tra fasi pre-e post-Archaeopteryx nell'evoluzione della biologia aviana. Il progressivo assemblaggio del moderno piano corporeo aviano è qui discusso usando una combinazione di metodi fi logenetici. La linea filetica che conduce agli uccelli moderni è descritta da 38 internodi, che identifi cano una serie progressiva di antenati condivisi tra gli uccelli attuali e i loro sister group mesozoici. I 160 milioni di anni di durata della costruzione del bauplan aviano sono suddivisi in tre fasi principali sulla base di analisi della modularità scheletrica, della cronologia degli eventi cladogenetici, dei tassi di divergenza, e delle regioni del morfospazio occupate. Durante la prima fase (detta "huxleyiana": dal Triassico Inferiore al Giurassico Medio), gli antenati degli uccelli svilupparono la pneumatizzazione postcraniale, una postura bipede obbligata e digitigrada, la mano tridattila e un tegumento simile al piumaggio. La seconda fase ("ostromiana": seconda metà del Giurassico) è caratterizzata da un più elevato tasso di evoluzione divergente, la perdita dell'ecologia ipercarnivora, l'espansione dell'endocranio, la drammatica riduzione del modulo caudofemorale, e lo sviluppo di piumaggio pennaceo. La transizione al volo battuto fu sviluppata solo nella terza fase ("marshiana": Cretacico), con la riorganizzazione dell'arto anteriore e della coda in organi adatti al volo, e la completa acquisizione del bauplan moderno. Restringere l'indagine sull'evoluzione aviana ad alcuni paraviani giurassici o alle linee successive ad Archaeopteryx significa ignorare la causa di oltre il 60% delle caratteristiche che definiscono il modello corporeo degli uccelli. La maggioranza degli elementi chiave che defi niscono la moderna fase dell'evoluzione aviana sono exaptation di novità occorse sotto diff erenti regimi ecologico-funzionali nelle fasi huxleyiana e ostromiana, e non possono essere propriamente interpretati senza fare riferimento al contesto storico della loro origine.
... Although there are some Triassic pterosaurs with fangs considerably larger than posterior crowns (e.g. Austriadactylus and Eudimorphodon), HMNS/BB 5032 lacks the multicuspid and/or serrated crowns found in these Triassic taxa (Dalla Vecchia 2013. Additionally, tooth spacing in 'campylognathoidid' Triassic forms tends to be considerably shorter than in rhamphorhynchids and HMNS/BB 5032. ...
Pterosaur fossils are rare in the Morrison Formation, and most are poorly preserved. The Breakfast Bench Facies (BBF) at Como Bluff produces incomplete but uncrushed limbs. One proximal and two distal femora match a complete femur (BYU 17214) referred to Mesadactylus. Unexpectedly, both of the BBF distal femora possess a large intercondylar pneumatopore. BYU 17214 also possesses an intercondylar pneumatopore, but it is smaller than in the BBF femora. Distal femoral pnuematicity is previously recognized only in Cretaceous azhdarchoids and pteranodontids. A peculiar BBF jaw fragment shows strongly labiolingually compressed, incurved crowns with their upper half bent backwards; associated are anterior fangs. We suspect this specimen is a previously undiagnosed pterosaur. Additional BBF material documents a diverse pterosaur fauna including a humerus with a greatly expanded ectepicondyle possibly from a non-pterodactyloid monofenestratan.
The Middle Triassic remains a poorly understood time in the evolution of land vertebrates. Here, we report a new Ladinian-age vertebrate assemblage from Miedary (southern Poland). It consists of more than 20 taxa including fish (four
species of Hybodontiformes, cf. Gyrolepis, Redfieldiiformes, ‘Thelodus’, Saurichthys, Serrolepis, Prohalecites, Ptychoceratodus), amphibians (Mastodonsaurus, Gerrothorax, Plagiosternum, chroniosuchian Bystrowiella), and reptiles (Owenettidae, Blezingeria, Nothosaurus, Tanystropheus, an additional, yet unidentified tanystropheid, the doswelliid Jaxtasuchus, and another archosauromorph, as well as eight archosauriform tooth morphotypes). Preliminary comparisons suggest biogeographic and environmental similarities with roughly contemporaneous localities known from the southwestern part of the Germanic Basin. Among differences in these two areas are the presence of a new armored archosauromorph and a surprising abundance of Tanystropheus remains in the new Polish site. Miedary is currently the richest source of three-dimensionally preserved Tanystropheus material in the world, which will be crucial for a better understanding of the preferred environment and lifestyle of this highly specialized reptile.
The transition between Early to Middle Jurassic was significant in pterosaur evolution, when these volant reptiles exploded in diversity alongside dinosaurs and other animals. It has long been thought, however, that pterosaurs did not develop large wingspans until after the Jurassic, a notion challenged by the recent discovery of Dearc sgiathanach in the Bathonian-aged Lealt Shale Formation of the Isle of Skye, Scotland, whose holotype specimen had an estimated wingspan greater than 2.5 meters. We here report the discovery of a new pterosaur specimen from the Lealt Shale Formation, comprising a tibiotarsus, metatarsal, pedal phalanges, and caudal vertebrae. The elongate tail vertebrae with ossified processes indicate the specimen is a non-pterodactyloid pterosaur, albeit its fragmentary nature makes it difficult to determine whether it belongs to a new taxon. Its metatarsal and caudal vertebrae are considerably larger than corresponding bones in the Dearc holotype, indicating that it belonged to an even larger individual, thus demonstrating that pterosaurs with broad wingspans were not anomalous in the Middle Jurassic. The growing Middle Jurassic pterosaur record of Scotland and England, although mostly represented by isolated and fragmentary fossils, reveals a high diversity of clades, long obscured by the lack of well-preserved skeletons.
Faxinalipterus minimus was originally described as a purported pterosaur from the Late Triassic (early Norian) Caturrita Formation of southern Brazil. Its holotype comprises fragmentary postcranial elements, whereas a partial maxilla was referred to the species. The assignment of Faxinalipterus minimus to Pterosauria has been questioned by some studies, but the specimen has never been accessed in detail after its original description. Here we provide a reassessment of Faxinalipterus minimus after additional mechanical preparation of the holotype. Our interpretations on the identity of several bones differ from those of the original description, and we found no support favoring pterosaur affinities for the taxon. The maxilla previously referred to Faxinalipterus minimus is disassociated from this taxon and referred to a new putative pterosauromorph described here from a partial skull and fragmentary postcranial elements. Maehary bonapartei gen. et sp. nov. comes from the same fossiliferous site that yielded Faxinalipterus minimus, but the lack of overlapping bones hampers comparisons between the two taxa. Our phylogenetic analysis places Faxinalipterus minimus within Lagerpetidae and Maehary bonapartei gen. et sp. nov. as the earliest-diverging member of Pterosauromorpha. Furthermore, the peculiar morphology of the new taxon reveals a new dental morphotype for archosaurs, characterized by conical, unserrated crowns, with a pair of apicobasally oriented grooves. These two enigmatic archosaurs expand our knowledge on the Caturrita Formation fauna and reinforce the importance of its beds on the understanding of Late Triassic ecosystems.
Exquisite discoveries and new interpretations regarding an enigmatic group of cursorial avemetatarsalians led to a new phylogenetic hypothesis regarding pterosaur affinities. Previously thought to be dinosaur precursors, lagerpetids are now considered to be the closest relatives to pterosaurs. This new hypothesis sheds light on a new explorable field, especially regarding the character acquisition and evolution within the pterosaur lineage. In the present study, the morphospace occupation of distinct skeletal regions of lagerpetids withing the morphological spectrum of avemetatarsalians is investigated. This approach indicates which portions of the skeleton are more similar to the anatomy of pterosaurs and which portions present different homoplastic signals. The analyses demonstrates that the craniomandibular traits of lagerpetids are pterosaur‐like, the pectoral girdle and forelimb are dinosauromorph‐like and the axial skeleton and the pelvic girdle and hindlimb are unique and highly specialized among the analysed sample. So, despite the close phylogenetic relationships, the postcranial skeleton of lagerpetids and pterosaurs are very different. The occurrence of two distinct and highly specialized groups of pterosauromorphs coexisting with a wide ecological range of dinosauromorphs during Triassic suggests pressure for new niches occupation.
Anurognathids are an elusive group of diminutive, potentially arboreal pterosaurs. Even though their monophyly has been well-supported, their intrarelationships have been obscure, and their phylogenetic placement even more. In the present work, we present a new genus and species from the Middle-Late Jurassic Tiaojishan Formation, the third nominal anurognathid species from the Jurassic of China. The new species provides new information concerning morphological diversity for the group. Furthermore, we provide a new phylogenetic analysis incorporating into a single data set characters from diverging phylogenetic proposals. Our results place them as the sister-group of Darwinoptera + Pterodactyloidea, as basal members of the Monofenestrata.
Morphology forms the most fundamental level of data in vertebrate palaeontology because it is through interpretations of morphology that taxa are identified, creating the basis for broad evolutionary and palaeobiological hypotheses. Assessing maturity is one of the most basic aspects of morphological interpretation and provides the means to study the evolution of ontogenetic changes, population structure and palaeoecology, life‐history strategies, and heterochrony along evolutionary lineages that would otherwise be lost to time. Saurian reptiles (the least‐inclusive clade containing Lepidosauria and Archosauria) have remained an incredibly diverse, numerous, and disparate clade through their ~260‐million‐year history. Because of the great disparity in this group, assessing maturity of saurian reptiles is difficult, fraught with methodological and terminological ambiguity. We compiled a novel database of literature, assembling >900 individual instances of saurian maturity assessment, to examine critically how saurian maturity has been diagnosed. We review the often inexact and inconsistent terminology used in saurian maturity assessment (e.g. ‘juvenile’, ‘mature’) and provide routes for better clarity and cross‐study coherence. We describe the various methods that have been used to assess maturity in every major saurian group, integrating data from both extant and extinct taxa to give a full account of the current state of the field and providing method‐specific pitfalls, best practices, and fruitful directions for future research. We recommend that a new standard subsection, ‘Ontogenetic Assessment’, be added to the Systematic Palaeontology portions of descriptive studies to provide explicit ontogenetic diagnoses with clear criteria. Because the utility of different ontogenetic criteria is highly subclade dependent among saurians, even for widely used methods (e.g. neurocentral suture fusion), we recommend that phylogenetic context, preferably in the form of a phylogenetic bracket, be used to justify the use of a maturity assessment method. Different methods should be used in conjunction as independent lines of evidence when assessing maturity, instead of an ontogenetic diagnosis resting entirely on a single criterion, which is common in the literature. Critically, there is a need for data from extant taxa with well‐represented growth series to be integrated with the fossil record to ground maturity assessments of extinct taxa in well‐constrained, empirically tested methods.
The pterosaurs first appear in the fossil record in the middle of the Late Triassic. Their earliest representatives are known from Northern Hemisphere localities but, by the end of the Jurassic Period, this clade of flying reptiles achieved a global distribution, as well as high levels of diversity and disparity. Our understanding of early pterosaur evolution and the fundamental interrelationships within Pterosauria has improved dramatically in recent decades. However, there is still debate about how the various pterosaur subgroups relate to one another and about which taxa comprise these. Many recent phylogenetic analyses, while sampling well from among the known Triassic and Early Jurassic pterosaurs, have not included many non-pterosaurian ornithodirans or other avemetatarsalians. Given the close relationship between these groups of archosaurs, the omission of other ornithodirans and avemetatarsalians has the potential to adversely affect the results of phylogenetic analyses, in terms of character optimisation and ingroup relationships recovered. This study has addressed this issue and tests the relationships between the early diverging pterosaur taxa following the addition of avemetatarsalian taxa and anatomical characters to an existing early pterosaur dataset. This study has, for the first time, included taxa that represent the aphanosaurs, lagerpetids, silesaurids and dinosaurs, in addition to early pterosaurs. Anatomical characters used in other recent studies of archosaurs and early dinosaurs have also been incorporated. By expanding the outgroup taxa and anatomical character coverage in this pterosaur dataset, better resolution between the taxa within certain early pterosaur subclades has been achieved and stronger support for some existing clades has been found; other purported clades of early pterosaurs have not been found in this analysis—for example there is no support for a monophyletic Eopterosauria or Eudimorphodontidae. Further support has been found for a sister-taxon relationship between Peteinosaurus zambelli and Macronychoptera, a clade here named Zambellisauria (clade nov.), as well as for a monophyletic and early diverging Preondactylia. Some analyses also support the existence of a clade that falls as sister-taxon to the zambellisaurs, here named Caviramidae (clade nov.). Furthermore, some support has been found for a monophyletic Austriadraconidae at the base of Pterosauria. Somewhat surprisingly, Lagerpetidae is recovered outside of Ornithodira sensu stricto , meaning that, based upon current definitions at least, pterosaurs fall within Dinosauromorpha in this analysis. However, fundamental ornithodiran interrelationships were not the focus of this study and this particular result should be treated with caution for now. However, these results do further highlight the need for broader taxon and character sampling in phylogenetic analyses, and the effects of outgroup choice on determining ingroup relationships.
Significance
Reptiles of the Mesozoic Era are known for their remarkable size: dinosaurs include the largest known land animals, and their relatives, the pterosaurs, include the largest creatures to ever fly. The origins of these groups are poorly understood, however. Here, we present a species ( Kongonaphon kely ) from the Triassic of Madagascar close to the ancestry of dinosaurs and pterosaurs, providing insight into the early evolution of those groups. Kongonaphon is a surprisingly small animal (estimated height, ∼10 cm). Analysis of ancestral body size indicates that there was a pronounced miniaturization event near the common ancestor of dinosaurs and pterosaurs. Tiny ancestral body size may help explain the origins of flight in pterosaurs and fuzzy integument in both groups.
Two tooth morphotypes corresponding to one or two tetrapod species from the Late Jurassic or Earliest Cretaceous locality of Ksar Metlili (KM), Anoual Syncline (eastern Morocco), are reported and described. These teeth cannot be related to any of the identified vertebrate major groups of this site. They are tricusped and uniradiculate, with a high and large main central cusp mesio-distally surrounded by two smaller accessory cusps. Their morphology is reminiscent of several taxa such as pterosaurs, notosuchians and mammals, with which they are compared here. These morphotypes are tentatively referred to cf. Cynodontia indet. They would be the most recent non-mammaliaform cynodonts reported in Africa and among the latest described. The KM specimens display remarkable plesiomorphic dental features with respect to known contemporaneous non-mammaliaform cynodonts. They might indicate the survival of a relict lineage in a North African refugium.
Archosaurs is the clade composed by birds (Aves) and crocodiles, alligators, and the gharial (Crocodylia). This relatedness is not obvious and for a long time was not taken into account, as birds were seen as a group separate even from the rest of reptiles. Both avians and crocodylians are morphologically very distinct and in many aspects different from each other and from the ancestral forms within Archosauria. The skulls of birds are composed of thin and light bones, many fused to each other, and others articulating in mobile joints allowing the beak to move and bend with respect to the rest of the skull. In crocodylians the skulls are massive and heavy, a solid akinetic structure built to crush prey. The accompanying muscle system, attaching onto and responsible for the movement of the head, jaws, eyes, or tongue, is equally distinct. As a result of the striking differences and the relatively recent realization of crocodylians and avians being closely related, the comparison of their anatomy has never been very straightforward. This chapter’s goal is to provide a review of archosaur anatomy and to give at least some sense of the similarities and differences between archosaur musculature.
Pterosaurs were the first vertebrates to evolve powered flight and the largest animals to ever take wing. The pterosaurs persisted for over 150 million years before disappearing at the end of the Cretaceous, but the patterns of and processes driving their extinction remain unclear. Only a single family, Azhdarchidae, is definitively known from the late Maastrichtian, suggesting a gradual decline in diversity in the Late Cretaceous, with the Cretaceous–Paleogene (K-Pg) extinction eliminating a few late-surviving species. However, this apparent pattern may simply reflect poor sampling of fossils. Here, we describe a diverse pterosaur assemblage from the late Maastrichtian of Morocco that includes not only Azhdarchidae but the youngest known Pteranodontidae and Nyctosauridae. With 3 families and at least 7 species present, the assemblage represents the most diverse known Late Cretaceous pterosaur assemblage and dramatically increases the diversity of Maastrichtian pterosaurs. At least 3 families—Pteranodontidae, Nyctosauridae, and Azhdarchidae—persisted into the late Maastrichtian. Late Maastrichtian pterosaurs show increased niche occupation relative to earlier, Santonian-Campanian faunas and successfully outcompeted birds at large sizes. These patterns suggest an abrupt mass extinction of pterosaurs at the K-Pg boundary.
The Triassic Period saw the first appearance of numerous amniote lineages (e.g. Lepidosauria, Archosauria, Mammalia) that defined Mesozoic ecosystems following the end Permian Mass Extinction, as well as the first major morphological diversification of crown-group reptiles. Unfortunately, much of our understanding of this event comes from the record of large-bodied reptiles (total body length>1 m). Here we present a new species of drepanosaurid (small-bodied, chameleon-like diapsids) from the Upper Triassic Chinle Formation of New Mexico. Using reconstructions of micro-computed tomography data, we reveal the three-dimensional skull osteology of this clade for the first time. The skull presents many archaic anatomical traits unknown in Triassic crown-group reptiles (e.g. absence of bony support for the external ear), whereas other traits (e.g. toothless rostrum, anteriorly directed orbits, inflated endocranium) resemble derived avian theropods. A phylogenetic analysis of Permo-Triassic diapsids supports the hypothesis that drepanosaurs are an archaic lineage that originated in the Permian, far removed from crowngroup Reptilia. The phylogenetic position of drepanosaurids indicates the presence of archaic Permian clades among Triassic small reptile assemblages and that morphological convergence produced a remarkably bird-like skull nearly 100 Myr before one is known to have emerged in Theropoda.
While pterosaurs occur in the Lower Jurassic strata of Britain and Germany, only the family Rhamphorhynchidae is currently known found in both. A newly discovered humerus from the Whitby Mudstone Formation of Lincolnshire challenges this and is distinguished from all other Lower Jurassic British pterosaurs by its possession of a quadrangular deltopectoral crest. This is a rare morphotype which only occurs in Eudimorphodon, Austriadraco, Raeticodactylus, Carniadactylus and Campylognathoides. The Lincolnshire humerus compares well with these taxa but is identified as a cf. Campylognathoides sp. based on its age and palaeobiogeography. The genus Campylognathoides is a common pterosaur in the Toarcian Posidonia Shale of Germany and the new humerus supports continuity of pterosaur populations across central Laurasia.
Background:
Archosauromorpha originated in the middle-late Permian, radiated during the Triassic, and gave rise to the crown group Archosauria, a highly successful clade of reptiles in terrestrial ecosystems over the last 250 million years. However, scientific attention has mainly focused on the diversification of archosaurs, while their stem lineage (i.e. non-archosaurian archosauromorphs) has often been overlooked in discussions of the evolutionary success of Archosauria. Here, we analyse the cranial disparity of late Permian to Early Jurassic archosauromorphs and make comparisons between non-archosaurian archosauromorphs and archosaurs (including Pseudosuchia and Ornithodira) on the basis of two-dimensional geometric morphometrics.
Results:
Our analysis recovers previously unappreciated high morphological disparity for non-archosaurian archosauromorphs, especially during the Middle Triassic, which abruptly declined during the early Late Triassic (Carnian). By contrast, cranial disparity of archosaurs increased from the Middle Triassic into the Late Triassic, declined during the end-Triassic extinction, but re-expanded towards the end of the Early Jurassic.
Conclusions:
Our study indicates that non-archosaurian archosauromorphs were highly diverse components of terrestrial ecosystems prior to the major radiation of archosaurs, including dinosaurs, while disparity patterns of the Ladinian and Carnian indicate a gradual faunal replacement of stem archosaurs by the crown group, including a short interval of partial overlap in morphospace during the Ladinian.
The Quebrada del Barro Formation (QBF) is part of the continental Marayes-El Carrizal Basin, in NW Argentina. Here we report a diverse faunal assemblage recently discovered in the Quebrada del Barro Formation, along with a preliminary discussion of the taxonomic status and affinities of numerous vertebrate specimens found at two localities where this unit is exposed. The new vertebrate association includes remains of at least 12 different new species related to six major vertebrate groups: Cynodontia, Testudinata, Sphenodontia, Pseudosuchia, Pterosauria, and Dinosauromorpha. The most abundant specimens in this faunal assemblage are opisthodontian sphenodonts, tritheledontid cynodonts and basal sauropodomorph dinosaurs, but the assemblage also includes diagnostic remains of lagerpetid dinosauromorphs, theropods, pterosaurs, basal crocodylomorphs, and stem testudinatans. Several of these groups have also been reported for the Los Colorados Formation (LCF), although the two units differ in their taxonomic content at the species level and in the relative abundance of different taxonomic groups. A comparison of these two faunal assemblage suggest the fauna of QBF is younger than that of LCF and we tentatively assess a late Norian-Rhaetian age for the QBF. Some of the specimens reported here are known from well-preserved specimens and yield important new information for understanding the evolution of these groups, which underscores the relevance of the QBF fauna for assessing the dynamics of the major groups of vertebrates that dominated the terrestrial ecosystems during the early Mesozoic in Pangea.
The biogeographical history of pterosaurs has received very little treatment. Here, we present the first quantitative analysis of pterosaurian biogeography based on an event-based parsimony method (Treefitter). This approach was applied to a phylogenetic tree comprising the relationships of 108 in-group pterosaurian taxa, spanning the full range of this clade's stratigraphical and geographical extent. The results indicate that there is no support for the impact of vicariance or coherent dispersal on pterosaurian distributions. However, this group does display greatly elevated levels of sympatry. Although sampling biases and taxonomic problems might have artificially elevated the occurrence of sympatry, we argue that our results probably reflect a genuine biogeographical signal. We propose a novel model to explain pterosaurian distributions: pterosaurs underwent a series of ‘sweep-stakes’ dispersal events (across oceanic barriers in most cases), resulting in the founding of sympatric clusters of taxa. Examination of the spatiotemporal distributions of pterosaurian occurrences indicates that their fossil record is extremely patchy. Thus, while there is likely to be genuine information on pterosaurian diversity and biogeographical patterns in the current data-set, caution is required in its interpretation.
Two small bones from the Upper Triassic of Cromhall Quarry (Gloucestershire, England), which are referred in the literature to pterosaurian wing metacarpals, are compared with wing metacarpals of unequivocal pterosaur specimens from the Upper Triassic of Italy and Greenland as well as those of the Liassic Dimorphodon macronyx from England. The two are
morphologically distinct from the unequivocal wing metacarpals. Comparison with the phalanges of drepanosauromorphs suggests that they are probably penultimate phalanges of those bizarre diapsids. Drepanosauromorphs are now known from Cromhall Quarry, but they were not in 1990 when the two presumed wing metacarpals were described. There is no definitive evidence of the presence of pterosaurs in the Triassic of the UK.
Recently, paleontologists have begun using Internet databases and Google Earth® as new tools to share data with the scientific community. The newly developed web application PteroTerra (http://pteroterra.herokuapp.com), implemented using the Ruby on Rails® web framework, is a specimen-based pterosaur database that interfaces with Google Earth®. This database currently catalogues over 1300 pterosaur specimens from all over the world and includes information about each specimen such as taxon name, classification, geologic age, geographic location of discovery, geologic formation, rock type, paleoenvironment, articulation, wingspan, proposed diet and housing institution. The application allows users to search for specimens based on keywords and to create groups of pterosaurs based on shared characteristics. Groups can then be downloaded as a.kml file, which can be automatically uploaded into Google Earth® in order to study geographic patterns of pterosaur specimens based on any criteria of interest. The use and continuous updating of PteroTerra will provide pterosaurologists and other paleontologists with a central location for storing and obtaining information about particular pterosaur specimens, as well as a way for researchers to observe pterosaur patterns on a worldwide scale. The principles behind this program can easily be expanded to other fields of study.
This monograph is a detailed analysis of thousands of microvertebrate fossils from seven localities of Otischalkian (early late Carnian) to Adamanian (latest Carnian) age in the Upper Tri- assic Chinle Group across Texas, New Mexico, and Arizona in the southwestern U.S.A.
The localities are Trilophosaurus quarry 1 and two sites near Kalgary in West Texas, Ojo Huelos and Sixmile Spring in New Mexico, and the Krzyzanowski bonebed and Dying Grounds in Arizona. The stratigraphically lowest locality studied was Trilophosaurus quarry 1 in the Colorado City Formation near Otis Chalk. Next lowest was the lower Kalgary locality, a previously- studied site low in the Tecovas Formation of Crosby County. This study is the first to detail the microvertebrate fauna of the nearby upper Kalgary locality, slightly higher in the Tecovas Formation and the type locality of the oldest mammal, Adelobasileus cromptoni Lucas and Hunt. Both New Mexican localities were relatively low, probably about the same stratigraphic level as the upper Kalgary locality, and include the type Ojo Huelos Member (San Pedro Arroyo Formation) deposits in central New Mexico and the Sixmile Spring locality in the Bluewater Creek Formation of west- central New Mexico. The Krzyzanowski bonebed and the Dying Grounds faunas were both derived from the Blue Mesa Member of the Petrified Forest Formation in Arizona. All but the Trilophosaurus quarry and, possibly, the lower Kalgary locality are Adamanian in age. The Trilophosaurus quarry is Otischalkian in age, and its fauna is part of the type assemblage of the Otischalkian land-vertebrate faunachron (lvf). The Dying Grounds fauna is part of the type assemblage of the Adamanian lvf.
Sampled depositional environments include channels, floodplains (including paleosols) and ponds or lakes. The com- position of microvertebrate assemblages generally agrees with facies interpretations of depositional environments. Sharks and osteichthyans are abundant in pond and channel deposits and uncommon to absent in floodplains and paleosols. Amphibians are generally uncommon, although this may be in part becasue few microfossils of amphibians are identifiable as such. Flood- plains and paleosols yield fossils of amniotes (>80%) almost to the exclusion of other taxa.
The actual fossils include teeth, bones, scales, and ossicles of chondrichthyans, osteichthyans, amphibians, and amniote tet- rapods, and include five new species in four new genera and 38 new records of family- or lower-level taxa. Because of the highly variable and fragmentary nature of microvertebrate fossils, many elements are only identifiable to relatively high taxonomic levels (e.g., family). Still, some fossils are identifiable to the genus and even species level, and many of these records have taxonomic, systematic, distributional, and/or biostratigraphic significance. The new records include selachians (5), osteichthyans (9), amphib- ians (2), and 22 new records of amniotes, including procolophonids, Colognathus obscurus (Case), cynodonts, sphenodontians, Trilophosaurus buettneri Case, T. jacobsi Murry, diverse archosauriform reptiles, and dinosaurs, and several re- sults are presented here in systematic order.
Traditionally, pterosaurs have been included within the Archosauriformes and many contemporary workers consider the Pterosauria the sister group to Lagosuchus, Scleromochlus and the Dinosauria. New analyses cast doubts on those relationships because nearly all presumed archosauriform or ornithodire "synapomorphies" are either not present within the Pterosauria or are also present within certain prolacertiform taxa. Recent examinations of the holotypes of Cosesaurus aviceps, Longisquama insignis and Sharovipteryx mirabilis suggest that many characters may be interpreted differently than previously reported. Results of several subsequent cladistic analyses suggest that these three "enigmatic" prolacertiforms, along with the newly described Langobardisaurus, are sister taxa to the Pterosauria based on a suite of newly identified synapomorphies.
The palynological analysis of a new Triassic locality at Syren (Luxembourg) reveals the presence of all typical species of the Rhaetipollis germanicus Assemblage, ascribing a Rhaetian age to the level. The vertebrate fauna is dominated by a marine component with a typical Rhaetian facies association. The enameloid ultrastrucutre shows that "Hybodus" minor is a neoselachian and that teeth previously referred to this species may be attributed to Nemacanthus monilifer. The terrestrial component is very diversified, including Phytosauria, Pterosauria, ?Ornithischia, Cynodontia and Mammalia (Haramiyidae, Morganucodontidae and Kuehneotheriidae). In opposition to the marine component, the terrestrial fauna shows little variation throughout the Rhaetian transgression.
Dinosaurs belong within Archosauria, a wide group of extinct and extant reptiles that also includes modern crocodilians as well as pterosaurs and various basal groups of Triassic age. This chapter considers the origin of the dinosaurs in terms of phylogeny and the timing of events. It discusses the cladistic analysis of Archosauria, followed by an account of the evolutionary events that led to the radiation of the dinosaurs.
Boreopricea funerea from the Lower Triassic of northern Russia is a prolacertiform diapsid, superficially similar to Prolacerta from the Lower Triassic of South Africa. The skull is damaged, but relatively complete. The lower temporal bar is absent. Some parts of the skeleton of Boreopricea, in particular some of the vertebrae and the foot, are well preserved, and offer clear evidence of prolacertiform affinities. Nineteen species of prolacertiform have been described. Their affinities are difficult to resolve because available specimens for many of the taxa are incomplete. A series of cladistic analyses shows the existence of a tanystropheid clade (Tanystropheus, Tanvtrachelos), to which are allied Cosesaurus, Malerisaurus, Boreopricea, and Macrocnemus as successive outgroups. A new synapomorphy of prolacertiforms may be the tight association of astragalus, calcaneum, centrale, and distal tarsal 4 in the ankle, with the centrale in contact with the tibia.
The extremely well-preserved tarsus of the tapejarid Tapejara sp. and the anhanguerid Anhanguera piscator (Pterosauria, Pterodactyloidea) are described and regarded as representative of the ankle structure of Pterosauria. The pterosaur ankle joint (PAJ) shows the following features: astragalus mediolaterally elongated forming a hemicylinder; proximal part of the astragalocalcaneal contact characterized by a ridge bordered on each side by a depression on the astragalus that has a perfect counterpart in the calcaneum, and distal part that is concavoconvex, with the concavity present in the astragalus; calcaneum extremely reduced not reaching the posterior portion of the tarsus; absence of an astragalar posterior groove, perforating foramen, calcaneal tuber, and astragalar ascending process; proximal tarsals fusing very early in ontogeny, forming a tibiotarsus. The main movement between the crus and foot in the PAJ occurs between the proximal and distal tarsals as in the advanced mesotarsal-reversed joint (AM-R). The main differences from the latter are the lack of an ascending process and the extreme reduction of the calcaneum that make the PAJ unique. The absence of an astragalar groove and the reduction of the calcaneum reinforce the hypothesis that pterosaurs are basal ornithodirans and closely related to the Dinosauromorpha. As has been demonstrated by this and other studies, the ankle structure (a complex of characters) is phylogenetically informative and, in the light of characters from other parts of the animal's body, can contribute to a better understanding of archosaur relationships.
The diverse depositional environments and rich fossil assemblages of the early Mesozoic Newark Supergroup of eastern North America can be subdivided into six broad environmental categories ranging from fault-scarp breccias in synsedimentary grabens developed directly along master boundary fault zones to deep-water zones of lakes. Each environmental category is characterized by its own range of taxa and modes of preservation. Environmental zones, except those directly caused by faulting, shifted laterally as lake levels rose and fell. Overt analogy between the lower trophic levels of aquatic ecosystems of modern lakes and those of the early Mesozoic is not appropriate. Diatoms were absent from the phytoplankton and large (0.3–1.0 cm) clam-shrimp comprised most of the zooplankton in Newark lakes, despite the abundant planktivorous fish.