Browsing by Author "Clarke, Julia A."
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ItemThe anatomy and taxonomy of the exquisitely preserved Green River Formation (early Eocene) lithornithids (Aves) and the relationships of Lithornithidae. (Bulletin of the American Museum of Natural History, no. 406)(American Museum of Natural History., 2016-06-30) Nesbitt, Sterling J.; Clarke, Julia A.Fossil remains of Paleogene Palaeognathae are poorly documented and are exceedingly rare. One group of palaeognaths, the lithornithids, is well represented in the Paleogene of North America. Nevertheless, few specimens of the same species are known from each of those Paleogene geologic units. Here, we report five new partial skeletons of lithornithids from the Fossil Butte Member of the Green River Formation (early Eocene) of Wyoming. One spectacularly preserved specimen is identified as the holotype of a new species, Calciavis grandei, gen. et sp. nov., and fully described. Preserved soft tissues (e.g., feathers, pes scales) surround the nearly articulated and complete skeleton. A second well-preserved but disarticulated skeleton is referred to this new taxon. We conclude that there are only two lithornithid taxa in the Green River Formation after careful comparisons with the other known taxon from the same geological unit, Pseudocrypturus cercanaxius. Morphological data generated from the new taxon and other Green River Formation lithornithid specimens were integrated into a osteology-only phylogenetic data set containing stem avians as outgroups and extinct and extant members of Palaeognathae (Tinamidae, ratites) and Neognathaes (Anseriformes, Galliformes, Neoaves), unnamed lithornithid specimens, and the following named lithornithid taxa: Lithornis plebius, Lithornis promiscuus, Lithornis celetius, Paracathartes howardae. We find a monophyletic Lithornithidae (containing Calciavis grandei, Pseudocrypturus cercanaxius, Lithornis plebius, Lithornis promiscuus, Lithornis celetius, Paracathartes howardae) as the sister taxon of Tinamidae at the base of Palaeognathae and also recover a monophyletic Ratitae in the morphology-only analysis. A Lithornithidae-Tinamidae relationship, which could imply a broad Northern Hemisphere distribution in the Paleogene for this total group retracted to the present day Neotropical distribution after the Eocene, is weakly supported in our analysis and is also supported by other lines of evidence such as eggshell morphology. Relationships among flightless palaeognaths and assessment of character homology in this group remain problematic. Indeed, when the morphological analyses were constrained to enforce topologies recovered from all recent analyses of molecular sequence data and retroelement insertions, Lithornithidae is no longer recovered with Tinamidae, which is nested within the now paraphyletic ratites, but remains at the base of Palaeognathae. Thus, regardless of the position of Tinamidae, Lithornithidae is recovered at the base of the clade. However, evidence that many, if not all, of these "ratite" lineages independently evolved similar morphologies related to large size and flight loss suggests that the proposed position of the Lithornithidae remains tentative. Significant morphological variation within Lithornithidae should be captured in inclusive future analyses through use of species terminals. ItemThe basal penguin (Aves, Sphenisciformes) Perudyptes devriesi and a phylogenetic evaluation of the penguin fossil record. (Bulletin of the American Museum of Natural History, no. 337)(American Museum of Natural History., 2010) Ksepka, Daniel T.; Clarke, Julia A.We present the first detailed description of Perudyptes devriesi, a basal penguin from the middle Eocene (~42 Ma) Paracas Formation of Peru, and a new analysis of all published extinct penguin species as well as controversial fragmentary specimens. The Perudyptes devriesi holotype includes key regions of the skull and significant postcranial material, thus helping to fill a major phylogenetic and stratigraphic (~20 million year) gap between the earliest fossil penguins (Waimanu manneringi and Waimanu tuatahi, ~58-61.6 Ma) and the next oldest partial skeletons. Perudyptes devriesi is diagnosable by five autapomorphies: (1) an anteroventrally directed postorbital process, (2) marked anterior expansion of the parasphenoid rostrum, (3) posterior trochlear ridge of the humerus projecting distal to the middle trochlear ridge and conformed as a large, broadly curved surface, (4) convex articular surface for the antitrochanter of the femur, and (5) extremely weak anterior projection of the lateral condyle of the tibiotarsus. The skull of Perudyptes is characterized by deep temporal fossae and an elongate, narrow beak that differs from other reported stem penguins in its short mandibular symphysis. The wing skeleton of Perudyptes preserves a combination of plesiomorphic features also observed in the basal penguin Waimanu and derived features shared with more crownward penguins. Features of the wing optimized as primitive for Sphenisciformes include retention of a discrete dorsal supracondylar tubercle on the humerus and presence of a modestly projected pisiform process on the carpometacarpus. Derived features present in Perudyptes and all more crownward penguins, but absent in Waimanu, include a more flattened humerus, development of a trochlea for the tendon of m. scapulotriceps at the distal end of the humerus, and bowing of the anterior face of the carpometacarpus. A combined molecular and morphological dataset for Spheniciformes was expanded by adding 25 osteological and soft tissue characters as well as 11 taxa. In agreement with previous results, Perudyptes devriesi is identified as one of the most basal members of Sphenisciformes. This analysis also confirms the placement of the middle/late Miocene (~11-13 Ma) fossil Spheniscus muizoni as a member of the Spheniscus clade and places the late Miocene (~10 Ma) Madrynornis mirandus as sister taxon to extant Eudyptes. These two species, known from relatively complete partial skeletons, are the oldest crown clade penguin fossils and represent well-corroborated temporal calibration points for the Spheniscus-Eudyptula divergence and Megadyptes-Eudyptes divergence, respectively. Our results reaffirm that the Miocene penguin taxon Palaeospheniscus, recently proposed to represent a member of the crown radiation, belongs outside of the crown clade Spheniscidae. The phylogenetic positions of small Eocene Antarctic penguin taxa (Delphinornis, Marambiornis, and Mesetaornis) recently proposed as possible direct ancestors to crown Spheniscidae were further evaluated using alternate coding strategies for incorporating scorings from isolated elements that preserve critical morphologies and are thought to represent these taxa, although they cannot yet be reliably assigned to individual species. Under all scoring regimes, Delphinornis, Marambiornis, and Mesetaornis were recovered as distantly related to Spheniscidae. Using synapomorphies identified in the primary analysis, we evaluated the phylogenetic position of fragmentary specimens, including the holotypes of valid but poorly known species, specimens currently unassignable to the species level, and morphologically distinct specimens that have not yet been named. All pre-Miocene specimens can be excluded from Spheniscidae based on presence of plesiomorphies lost in all crown penguins, consistent with a recent radiation for the penguin crown clade. This study provides additional support for a scenario of penguin evolution characterized by an origin of flightlessness near the K-T boundary, dispersal throughout the Southern Hemisphere during the early Paleogene, and a late Cenozoic origin for the crown clade Spheniscidae. Stratigraphic distribution and phylogenetic relationships of fossil penguins are consistent with distinct radiations during the Eocene, Oligocene, and Miocene. While the Eocene and Oligocene penguin faunas are similar in many respects, the Miocene fauna is characterized by smaller average size and novel cranial morphologies, suggesting that an ecological shift in diet occurred close to the origin of crown Spheniscidae. ItemDescription of the earliest fossil penguin from South America and first Paleogene vertebrate locality of Tierra Del Fuego, Argentina. American Museum novitates ; no. 3423(New York, NY : American Museum of Natural History, 2003) Clarke, Julia A.; Olivero, Eduardo B.; Puerta, Pablo.We report the discovery of the first vertebrate from the Paleogene of Tierra del Fuego (Isla Grande), Argentina, in southernmost South America. The specimen consists of parts of an associated pelvic girdle and limb that are identified as belonging to the penguin stem clade (Aves: Pansphenisciformes). The specimen, from an exposure of the Leticia Formation (late middle Eocene), is the earliest known penguin (pansphenisciform) from South America. It is more than 20 million years older than the earliest previously recorded South American penguins (from the late Oligocene-early Miocene) and, thus, almost doubles their known record on the continent. A detailed description of the new specimen and a discussion of its implications for the understanding of penguin morphological evolution are provided. The new specimen and other fossil penguins do not currently point to the origin of extant, or crown clade, penguin lineages (Spheniscidae), by the Eocene, only to the divergence of the penguin stem lineage from its sister taxon by this time. The new fossil has several morphologies that differ from all extant penguins but are shared with other fossil penguin taxa, suggesting they may be outside Spheniscidae. However, in a discussion of the current status of penguin systematics, we suggest the urgent need for comprehensive phylogenetic analysis of fossil and extant penguins to clarify the timing and pattern of penguin diversification. The specimen was recovered from a newly identified fossil vertebrate locality, an exposure of the Eocene Leticia Formation at Punta Torcida on the Atlantic shore of southeastern Tierra del Fuego, Argentina. The new locality is introduced, and a brief geologic description is made, highlighting the potential of the shallow marine sediments of the Leticia Formation for contributing to our knowledge of the Paleogene vertebrate fossil record of Tierra del Fuego, and of southern South America, generally. ItemHigh resolution images for 'The anatomy and taxonomy of the exquisitely preserved Green River Formation (early Eocene) lithornithids (Aves) and the relationships of Lithornithidae. (Bulletin of the American Museum of Natural History, no. 406)'(American Museum of Natural History., 2016-06-30) Nesbitt, Sterling J.; Clarke, Julia A.High resolution images for 'The anatomy and taxonomy of the exquisitely preserved Green River Formation (early Eocene) lithornithids (Aves) and the relationships of Lithornithidae. (Bulletin of the American Museum of Natural History, no. 406)' - http://hdl.handle.net/2246/6664 ItemThe morphology and phylogenetic position of Apsaravis ukhaana from the late Cretaceous of Mongolia. American Museum novitates ; no. 3387(New York, NY : American Museum of Natural History, 2002) Clarke, Julia A.; Norell, Mark.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.The avialan taxon Apsaravis ukhaana from the late Cretaceous of southern Mongolia is completely described and its phylogenetic position is evaluated. Apsaravis ukhaana is from continental sandstones exposed at the locality of Ukhaa Tolgod, Omnogov Aimag, Mongolia. The holotype specimen consists of the nearly complete, articulated skeleton of a small volant avialan. Apsaravis ukhaana is unambiguously differentiated from other avialans based on the presence of several unique morphologies: a strong tubercle on the proximal humerus, a hypertrophied trochanteric crest on the femur, and extremely well-projected posterior wings of a surface of the distal tibiotarsus that in Aves articulates with the tibial cartilage. Ten other homoplastic characters optimize as autapomorphies of Apsaravis ukhaana in the phylogenetic analysis. They are as follows: ossified mandibular symphysis; dentary strongly forked posteriorly; hooked acromion process on scapula; highly angled dorsal condyle of humerus; humeral condyles weakly defined; distal edge of humerus angling strongly ventrally; humerus flared dorsoventrally at its distal terminus; lateral condyle of tibiotarsus wider than medial one; neither condyle of tibiotarsus tapering toward the midline; and metatarsal II trochlea rounded rather than ginglymoid. Phylogenetic placement of Apsaravis ukhaana as the sister taxon of Hesperornithes + Aves resulted from analysis of 202 characters scored for 17 avialan ingroup taxa. The implications of Apsaravis ukhaana, and the results of the phylogenetic analysis, for the evolution of flight after its origin and character support for enantiornithine monophyly are extensively discussed. ItemMorphology, phylogenetic taxonomy, and systematics of Ichthyornis and Apatornis (Avialae, Ornithurae). Bulletin of the AMNH ; no. 286(New York, NY : American Museum of Natural History, 2004) Clarke, Julia A.; Peabody Museum of Natural History.Charles Darwin commented that Ichthyornis, as one of the "toothed birds" from the late Cretaceous of Kansas, offered some of "the best support to the theory of evolution" (in litt., C. Darwin to O.C. Marsh, August 31, 1880). Ichthyornis figures no less prominently today. It is one of the closest outgroups to crown clade Aves, and remains one of the only Mesozoic avialans known from more than a handful of specimens. As such, Ichthyornis is an essential taxon for analyses of deep divergences within Aves because of its influence in determining the morphologies ancestral to the crown clade. Ichthyornis, however, has languished in need of new anatomical description and taxonomic revision. Many of the best Ichthyornis specimens were largely inaccessible, plastered into Yale Peabody Museum (YPM) exhibit mounts for nearly a century. The focus of this study was the entire YPM Ichthyornis collection, the largest at any institution. The elements removed from the mounts were identified to the specimens with which they were originally associated. Detailed morphological study of the 81 YPM specimens yielded the following results: (1) there is evidence for only one species of Ichthyornis, rather than the eight previously proposed; (2) 78 specimens are part of this species, Ichthyornis dispar; (3) two previously identified species are not part of Ichthyornis; and (4) one new species is identified. This analysis also provided a case study in the application of phylogenetic nomenclature at the species level. The morphology of Ichthyornis dispar is described in detail from the holotype and referred specimens. Phylogenetic analyses of 202 morphological characters, scored for 24 terminal taxa, evaluated the relationships among Mesozoic ornithurines including Ichthyornis dispar and the newly identified taxa. Analysis of 23 core taxa produced two most parsimonious trees (L: 384, CI: 0.66). Marsh's "Ichthyornithiformes" is not monophyletic: Two previously named species of Ichthyornis as well as Apatornis celer are placed as more closely related to or as part of Aves. The results of the phylogenetic analyses have implications for previous hypotheses of the timing and pattern of the origin of Aves. ItemNew avialan remains and a review of the known avifauna from the late Cretaceous Nemegt Formation of Mongolia. American Museum novitates ; no. 3447(New York, NY : American Museum of Natural History, 2004) Clarke, Julia A.; Norell, Mark.; Mongolian-American Museum Paleontological Project.; Mongolyn Shinzhlėkh Ukhaany Akademi.Small vertebrates have remained relatively poorly known from the Nemegt Formation, although it has produced abundant and well-preserved large dinosaur remains. Here we report three new avialan specimens from the late Cretaceous (Maastrichtian) of Omnogov Aimag, Mongolia. These fossils were collected from the Nemegt Formation exposed at the locality of Tsaagan Khushu in the southern Gobi Desert. All of the new finds are partial isolated bones with a limited number of preserved morphologies; however, they further understanding of dinosaur diversity in the late Cretaceous of Mongolia and, specifically, from the Nemegt Formation. The new specimens are described and evaluated in phylogenetic analyses. These analyses indicate that all three fossils are placed as part of the clade Ornithurae. Avialan diversity of the Nemegt Formation is reviewed and briefly compared with that of the underlying Djadokhta and Barun Goyot Formations. These formations have been considered to represent at least two distinct late Cretaceous environments, with the Nemegt typically interpreted as representing more humid conditions. Ornithurine and enantiornithine birds are known from the Nemegt as well as the Djadokhta and Barun Goyot Formations, although ornithurine remains are more common in the Nemegt. No avialan species known from the Djadokhta, or Barun Goyot, are also known from the Nemegt Formation and, overall, the avialan taxa from these formations do not appear more closely related to each other than to other avialans. Whether these faunal differences are best interpreted as environmental, temporal, or sampling/preservational should be further investigated. ItemNew avian remains from the Eocene of Mongolia and the phylogenetic position of the Eogruidae (Aves, Gruoidea). American Museum novitates ; no. 3494(New York, NY : American Museum of Natural History, 2005) Clarke, Julia A.; Norell, Mark.; Dashzėvėg, Dėmbėrėliĭn.; Mongolyn Shinzhlekh Ukhaany Akademi.A well-preserved nearly complete avian tarsometatarsus was collected by the 2002 expedition of the Mongolian Academy of Sciences from Upper Eocene deposits exposed at the locality of Alag Tsav in the eastern Gobi Desert (Dornogov Aimag) of Mongolia. The new specimen is identified as part of a proposed Eogruidae clade, although it is unclear whether it is appropriately the holotype of a new species within this clade or referable to a previously named species. The clade Eogruidae has, as its current contents, species named as part of the traditional families Eogruidae + Ergilornithidae, which include several taxa of completely didactylous and apparently flightless birds. Referral of the new fossil to the clade Eogruidae is on the basis of derived reduction/loss of the metatarsal II trochlea. A series of phylogenetic analyses was used to investigate the systematic position of Eogruidae (including the new fossil, IGM 100/1447), which have been proposed to be a dominant part of Eocene to Miocene Asian faunas. First, the Mayr and Clarke (2003) dataset for crown clade Aves was used to investigate placement of Eogruidae within Aves, using a more completely known eogruid, Eogrus aeola, as an exemplar taxon. Eogrus aeola was identical to the new tarsometatarsus for all scored characters. A strict consensus cladogram of three most parsimonious trees from 1000 replicate heuristic searches placed Eogrus aeola in an unresolved polytomy with Psophiidae and Gruidae (trumpeters and cranes). Given the results of this analysis, Eogruidae (including IGM 100/1447) was analyzed in the suborder Grues dataset of Livezey (1998). Eogruidae was placed as the sister taxon to an Aramidae + Gruidae clade in the strict consensus cladogram of the eight most parsimonious trees resulting from a branch and bound search. Because monophyly of the traditional order Gruiformes has been repeatedly questioned, and the outgroups used in the original Grues dataset were identified through analyses assuming monophyly, the impact of removing these assumptions was investigated. Placement was robust to both changing outgroup assumptions and to swapping in the more incompletely known IGM 100/1447 as an exemplar for Eogruidae. ItemA new carinate bird from the late Cretaceous of Patagonia (Argentina). American Museum novitates ; no. 3323(New York, NY : American Museum of Natural History, 2001) Clarke, Julia A.; Chiappe, Luis M.A new bird from the late Cretaceous of Patagonia (Argentina), known from associated wing elements, is described and its phylogenetic position evaluated. Fossil taxa as well as representatives of species of extant birds sampled from lineages considered to be basal within the crown clade were included in a cladistic analysis of 72 characters primarily from the thoracic limb. Based on the results of the phylogenetic analysis and identification of autapomorphies in the specimen, we name a new taxon Limenavis patagonica. Limenavis patagonica is identified as closer to the crown clade than Enantiornithes by the presence of three unambiguous synapomorphies: a fossa (sometimes with two distinguishable subparts) on the dorsal, distalmost extremity of the humerus; distal fusion of metacarpals II and III; and an extensor process on metacarpal I. It is placed closer to the crown clade than Ichthyornis, and, thus, unambiguously as a carinate (see Methods for terminology), by two further synapomorphies: the abruptly truncate contact of the dorsal trochlear surface of the ulna with the ulnar shaft and the loss of a tubercle adjacent to the tendinal groove on the distal ulna. Finally, Limenavis patagonica is diagnosed by three autapomorphies: the attachment of the pars ulnaris of the trochlea humeroulnaris on the proximal ulna developed as a pit-shaped fossa; the location of the pisiform process with its proximal surface at approximately the same level as the proximal surface of metacarpal I; and a scar of the ligamentum collaterale ventrale of the ulna proximodistally elongate and extending down the caudal margin of the brachial impression. Limenavis patagonica is placed just outside the avian crown clade. The shortest tree with the new taxon as part of the crown clade is five steps longer than the most parsimonious topology. ItemNew fossil birds from the earliest Eocene of Mongolia. (American Museum novitates, no. 3934)(American Museum of Natural History., 2019-08-09) Hood, Sarah C.; Torres, Chris R.; Norell, Mark.; Clarke, Julia A.; Mongolian-American Museum Paleontological Project.Understanding of the Asian early Paleogene avifauna is limited relative to that of North American and European avifauna of the same period. While major patterns of mammalian faunal exchange among these three regions across the Paleocene/Eocene boundary have been described, much less is known about the dynamics of bird diversity over the same time interval. Here, we report bird fossils from the earliest Eocene Bumban Member of the Naranbulag Formation in central Mongolia that add to the known record from Asia from just after this boundary. Most of this material, collected by the joint American Museum of Natural History/Mongolia Academy of Sciences expeditions, is referable to a previously described taxon in Presbyornithidae (Anseriformes). However, five isolated elements are identified as comprising at least four species from at least three other major avian clades. While further inclusive phylogenetic analyses of each of these clades are necessary, the new remains represent possible earliest occurrences in Asia of these clades. The material includes a humerus and a furcula from shorebirds (Pan-Charadriiformes), a quadrate from a stem member of the flamingo-grebe lineage (Pan-Mirandornithes), and a coracoid from a stem galliform (Pangalliformes). We also report a humerus with uncertain phylogenetic affinities but with similarities to core Gruiformes. These new fossils expand our knowledge of the Asian avifauna during this time and have the potential to further inform our understanding of the early biogeography of these clades. The shorebird and flamingo-grebe material indicate that both these lineages were present in Asia by the earliest Eocene. The pan-mirandornithine quadrate provides insight into the early feeding ecology of the flamingo-grebe clade. ItemStratigraphy and magnetostratigraphic/faunal constraints for the age of sauropod embryo-bearing rocks in the Neuquén Group (Late Cretaceous, Neuquén Province, Argentina). American Museum novitates ; no. 3290(New York, NY : American Museum of Natural History, 2000) Dingus, Lowell.; Clarke, Julia A.; Scott, Gary Robert, 1946-; Swisher, Carl Celso.; Chiappe, Luis M.; Coria, Rodolfo A.The stratigraphy and age of a sauropod nesting ground containing the first definitive embryonic remains of sauropods preserved inside their eggs is analyzed. The fossil locality, called Auca Mahuevo, occurs in the Anacleto Member of the Río Colorado Formation in Neuquén Province, Argentina. The 5 m thick interval of overbank mudstones containing the fossilized eggs and embryos occurs near the middle of a 35 m sequence of thin, fluvial, concretionary sandstones and thicker units of silty sandstone. Flooding of shallow stream channels deposited overbank silt and mud on the eggs, killing the embryos and initiating the process of fossilization. Egg fragments containing patches of fossilized integument were found as float weathering out of the mudstone on local flats. Complete eggs containing embryonic bones and teeth were quarried from a steep ridge where the mudstone was exposed. Twelve paleomagnetic samples collected throughout the lower 30 m of the section establish the presence of a Reverse geomagnetic polarity interval. This constitutes the first magnetostratigraphic characterization for this part of the Río Colorado Formation and for the late Cretaceous sequence of formations that comprise the Neuquén Group. Biochronologic age estimates for the Río Colorado fauna combined with the Reverse polarity determinations for the fossiliferous sediments in the Anacleto Member argue for an age younger than the long Cretaceous C34 Normal, which ends at the upper boundary of the Sartonian and older than the late Campanian. The Reverse interval containing the fossils at Auca Mahuevo is therefore considered to be early or middle Campanian in age, most likely correlative with C33R between 83.5 and 79.5 Ma.