N. Adam Smith

Endocranial Anatomy of the Charadriiformes: Sensory System Variation and the Evolution of Wing-Propelled Diving

Just as skeletal characteristics provide clues regarding behavior of extinct vertebrates, phylogenetically-informed evaluation of endocranial morphology facilitates comparisons among extinct taxa and extant taxa with known behavioral characteristics. Previous research has established that endocranial morphology varies across Aves; however, variation of those systems among closely related species remains largely unexplored. The Charadriiformes (shorebirds and allies) are an ecologically diverse clade with a comparatively rich fossil record, and therefore, are well suited for investigating interspecies variation, and potential links between endocranial morphology, phylogeny, ecology and other life history attributes. Endocranial endocasts were rendered from high resolution X-ray computed tomography data for 17 charadriiforms (15 extant and two flightless extinct species). Evaluation of endocranial character state changes on a phylogeny for Charadriiformes resulted in identification of characters that vary in taxa with distinct feeding and locomotor ecologies. In comparison with all other charadriiforms, stem and crown clade wing-propelled diving Pan-Alcidae displayed compressed semicircular canals, and indistinct occipital sinuses and cerebellar fissures. Flightless wing-propelled divers have relatively smaller brains for their body mass and smaller optic lobes than volant pan-alcids. Observed differences between volant and flightless wing-propelled sister taxa are striking given that flightless pan-alcids continue to rely on the flight stroke for underwater propulsion. Additionally, the brain of the Black Skimmer Rynchops niger, a taxon with a unique feeding ecology that involves continuous forward aerial motion and touch-based prey detection used both at day and night, is discovered to be unlike that of any other sampled charadriiform in having an extremely large wulst as well as a small optic lobe and distinct occipital sinus. Notably, the differences between the Black Skimmer and other charadriiforms are more pronounced than between wing-propelled divers and other charadriiforms. Finally, aspects of endosseous labyrinth morphology are remarkably similar between divers and non-divers, and may deserve further evaluation.

The Fossil Calibration Database-A New Resource for Divergence Dating

Fossils provide the principal basis for temporal calibrations, which are critical to the accuracy of divergence dating analyses. Translating fossil data into minimum and maximum bounds for calibrations is the most important-often least appreciated-step of divergence dating. Properly justified calibrations require the synthesis of phylogenetic, paleontological, and geological evidence and can be difficult for nonspecialists to formulate. The dynamic nature of the fossil record (e.g., new discoveries, taxonomic revisions, updates of global or local stratigraphy) requires that calibration data be updated continually lest they become obsolete. Here, we announce the Fossil Calibration Database (http://fossilcalibrations.org), a new open-access resource providing vetted fossil calibrations to the scientific community. Calibrations accessioned into this database are based on individual fossil specimens and follow best practices for phylogenetic justification and geochronological constraint. The associated Fossil Calibration Series, a calibration-themed publication series at Palaeontologia Electronica, will serve as a key pipeline for peer-reviewed calibrations to enter the database.

Osteological Histology of the Pan‐Alcidae (Aves, Charadriiformes): Correlates of Wing‐Propelled Diving and Flightlessness

Although studies of osteological morphology, gross myology, myological histology, neuroanatomy, and wing‐scaling have all documented anatomical modifications associated with wing‐propelled diving, the osteohistological study of this highly derived method of locomotion has been limited to penguins. Herein we present the first osteohistological study of the derived forelimbs and hind limbs of wing‐propelled diving Pan‐Alcidae (Aves, Charadriiformes). In addition to detailing differences between wing‐propelled diving charadriiforms and nondiving charadriiforms, microstructural modifications to the humeri, ulnae and femora of extinct flightless pan‐alcids are contrasted with those of volant alcids. Histological thin‐sections of four species of pan‐alcids (Alca torda, †Alca grandis, †Pinguinus impennis, †Mancalla cedrosensis) and one outgroup charadriiform (Stercorarius longicaudus) were compared. The forelimb bones of wing‐propelled diving charadriiforms were found to have significantly thicker (∼22%) cortical bone walls. Additionally, as in penguins, the forelimbs of flightless pan‐alcids are found to be osteosclerotic. However, unlike the pattern documented in penguins that display thickened cortices in both forelimbs and hind limbs, the forelimb and hind limb elements of pan‐alcids display contrasting microstructural morphologies with thickened forelimb cortices and relatively thinner femoral cortices. Additionally, the identification of medullary bone in the sampled †Pinguinus impennis specimen suggests that further osteohistological investigation could provide an answer to longstanding questions regarding sexual dimorphism of Great Auks. Finally, these results suggest that it is possible to discern volant from flightless wing‐propelled divers from fragmentary fossil remains. Anat Rec, 297:188–199, 2014.

Best practices for digitally constructing endocranial casts: examples from birds and their dinosaurian relatives

The rapidly expanding interest in, and availability of, digital tomography data to visualize casts of the vertebrate endocranial cavity housing the brain (endocasts) presents new opportunities and challenges to the field of comparative neuroanatomy. The opportunities are many, ranging from the relatively rapid acquisition of data to the unprecedented ability to integrate critically important fossil taxa. The challenges consist of navigating the logistical barriers that often separate a researcher from high‐quality data and minimizing the amount of non‐biological variation expressed in endocasts – variation that may confound meaningful and synthetic results. Our purpose here is to outline preferred approaches for acquiring digital tomographic data, converting those data to an endocast, and making those endocasts as meaningful as possible when considered in a comparative context. This review is intended to benefit those just getting started in the field but also serves to initiate further discussion between active endocast researchers regarding the best practices for advancing the discipline. Congruent with the theme of this volume, we draw our examples from birds and the highly encephalized non‐avian dinosaurs that comprise closely related outgroups along their phylogenetic stem lineage.

Latest Pacific Basin record of a bony-toothed bird (aves, Pelagornithidae) from the Pliocene Purisima Formation of California, U.S.A.

ABSTRACT Fossils of pelagornithids (bony-toothed birds) have been reported from strata of Paleocene to Pliocene age, and from every continent. The extreme fragility of pelagornithid bones has no doubt contributed to their geographically and temporally sporadic record, and thus it has been difficult to appreciate any long-term phylogenetic trends through geologic time for this group. We report a well-preserved partial humerus of the gigantic bird Pelagornis from the late Neogene Purisima Formation of central California. Due to its incompleteness, we refrain from naming a new species. This fossil is fortuitously bracketed by two ash beds, which have been correlated with volcanic rocks at 3.35 ± 0.05 Ma and 2.5 ± 0.2 Ma, indicating a middle to late Pliocene age for this fossil. This fossil extends the record of the pelagornithids in the Northeast Pacific, previously only known up until the early late Miocene (10–12 Ma). This fossil is the latest record of a pelagornithid for the Pacific Basin, and additionally represents the latest reliably dated pelagornithid record worldwide. This record suggests that the pelagornithids survived until the end of the Pliocene, and became extinct during the ocean restructuring and climatic upheavals that caused the demise of many other groups of marine vertebrates at that time.

Rhetoric vs. reality: A commentary on ''Bird Origins Anew'' by A. Feduccia

ABSTRACT Birds are maniraptoran theropod dinosaurs. The evidence supporting the systematic position of Avialae as a derived clade within Dinosauria is voluminous and derived from multiple independent lines of evidence. In contrast, a paucity of selectively chosen data weakly support, at best, alternative proposals regarding the origin of birds and feathers. Opponents of the theory that birds are dinosaurs have frequently based their criticisms on unorthodox interpretations of paleontological data and misrepresentation of phylogenetic systematic methods. Moreover, arguments against the nested position of Avialae in Dinosauria have often conflated the logically distinct questions of avian origins, the evolution of flight, and the phylogenetic distribution of feathers. Motivated by a Perspectives article with numerous factual inaccuracies that recently appeared in The Auk, we provide a review of the full complement of facts pertaining to the avian origins debate and address the misplaced criticisms raised in that opinion paper.

The fossil record and phylogeny of the auklets (Pan-Alcidae, Aethiini)

The auklets Aethia and Ptychoramphus comprise the smallest known Alcidae (Aves, Charadriiformes) and have a fossil record that extends into the Miocene. The evolution of auklets is poorly understood because systematic hypotheses of relationships among extant auklets are largely incongruent, the morphology of auklet fossils has not been evaluated in detail, and extinct species of auklets have not been previously included in a phylogenetic analysis. Previously described auklet fossil remains are reviewed and two new species of auklet, Aethia barnesi sp. nov. and Aethia storeri sp. nov., are described from the Miocene and Pliocene of southern California, USA. Previously described auklet fossil remains, the two newly described extinct species of auklet, and extant species of auklets and other alcids are included in combined phylogenetic analyses of morphological and molecular sequence data. Based on the results of the phylogenetic analyses, the taxonomy of fossils referred to Aethiini is revised and the evolution of the clade is evaluated in a phylogenetic context. The osteological morphology of extinct auklets appears to be little changed from their extant relatives, suggesting that the ecological attributes of these small wing-propelled divers may also be relatively unchanged since the Miocene. http://zoobank.org/urn:lsid:zoobank.org:pub:357ECC1A-DFE5-4C72-9BF2-260A547574C4

A New Species of Auk (Charadriiformes, Pan-Alcidae) from the Miocene of Mexico

A fossil from the Middle Miocene Rosarito Beach Formation of Baja California represents a previously undescribed, auklet-sized species of wing-propelled diving Pan-Alcidae (Aves, Charadriiformes). This new taxon, Divisulcus demerei, is recognized from the presence of a bifurcated scapulotricipital sulcus of the distal end of the humerus, a potentially neomorphic character within Aves. Additionally, the degree of compression of the humeral shaft of this new species is less than that of other pan-alcids. These characters may represent retention of ancestral character states that are associated with the transition to wing-propelled diving from nondiving Charadriiformes. This discovery provides further information regarding paleodiversity in this clade, extends the geographic range of Miocene pan-alcids, and may represent the oldest record of the clade from the Pacific Ocean basin, as previously reported unambiguous records are from Late Miocene or younger deposits (~10–1.6 Ma). Moreover, the age of this new pan-alcid (14–16 Ma) corresponds with the timing of the Middle Miocene climatic optimum, a time for which previous records of Pacific Ocean basin pan-alcids were lacking. Because of the relative incompleteness of the specimen, the systematic position of this new taxon within the Pan-Alcidae from a phylogenetic analysis is not strongly supported. Until additional remains of D. demerei are recovered that can provide additional character data, the affinities of this new taxon within the Pan-Alcidae are uncertain.

Sixteen vetted fossil calibrations for divergence dating of Charadriiformes (Aves, Neognathae)

The Charadriiformes (shorebirds and allies) are an ecologically and morphologically diverse clade with a global geographic distribution. The perceived antiquity of this lineage and the cryptic plumage and morphology of some charadriiforms have made them a frequent focus of study by ornithologists. Likewise, with the relatively recent advent of molecular sequence based divergence estimation methods, no less than seven studies have estimated the timing of cladogenetic events in Charadriiformes. Unfortunately, all of those studies have suffered from poor choice and characterization (i.e., age and taxonomic assignment) of fossil calibrations used for divergence time analysis. Given that studies of both real and simulated data have demonstrated the potential for calibration choice to bias node age estimates, the results of previously published analyses of divergence times for Charadriiformes must, accordingly, be viewed with caution. To alleviate introduction of fossil calibration bias with respect to future analyses of divergence times including Charadriiformes, 16 rigorously evaluated charadriiform fossil calibrations are reported herein. N. Adam Smith. The National Evolutionary Synthesis Center, 2024 W. Main St., Suite A200, Durham, NC, 27705, U.S.A., adam_smith@utexas.edu

Removing the entropy from the definition of entropy: clarifying the relationship between evolution, entropy, and the second law of thermodynamics

Misinterpretations of entropy and conflation with additional misunderstandings of the second law of thermodynamics are ubiquitous among scientists and non-scientists alike and have been used by creationists as the basis of unfounded arguments against evolutionary theory. Entropy is not disorder or chaos or complexity or progress towards those states. Entropy is a metric, a measure of the number of different ways that a set of objects can be arranged. Herein, we review the history of the concept of entropy from its conception by Clausius in 1867 to its more recent application to macroevolutionary theory. We provide teachable examples of (correctly defined) entropy that are appropriate for high school or introductory college level courses in biology and evolution. Finally, we discuss the association of these traditionally physics-related concepts to evolution. Clarification of the interactions between entropy, the second law of thermodynamics, and evolution has the potential for immediate benefit to both students and teachers.