Handbook of Avian Anatomy: Nomina Anatomica Avium

The total-evidence approach to divergence time dating uses molecular and morphological data from extant and fossil species to infer phylogenetic relationships, species divergence times, and macroevolutionary parameters in a single coherent framework. Current model-based implementations of this approach lack an appropriate model for the tree describing the diversification and fossilization process and can produce estimates that lead to erroneous conclusions. We address this shortcoming by providing a total-evidence method implemented in a Bayesian framework. This approach uses a mechanistic tree prior to describe the underlying diversification process that generated the tree of extant and fossil taxa. Previous attempts to apply the total-evidence approach have used tree priors that do not account for the possibility that fossil samples may be direct ancestors of other samples, that is, ancestors of fossil or extant species or of clades. The fossilized birth–death (FBD) process explicitly models the diversification, fossilization, and sampling processes and naturally allows for sampled ancestors. This model was recently applied to estimate divergence times based on molecular data and fossil occurrence dates. We incorporate the FBD model and a model of morphological trait evolution into a Bayesian total-evidence approach to dating species phylogenies. We apply this method to extant and fossil penguins and show that the modern penguins radiated much more recently than has been previously estimated, with the basal divergence in the crown clade occurring at ∼12.7 ∼12.7 Ma and most splits leading to extant species occurring in the last 2 myr. Our results demonstrate that including stem-fossil diversity can greatly improve the estimates of the divergence times of crown taxa. The method is available in BEAST2 (version 2.4) software www.beast2.org with packages SA (version at least 1.1.4) and morph-models (version at least 1.0.4) installed.

Bayesian Total-Evidence Dating Reveals the Recent Crown Radiation of Penguins

Testing models of macroevolution, and especially the sufficiency of microevolutionary processes, requires good collaboration between molecular biologists and paleontologists. We report such a test for events around the Late Cretaceous by describing the earliest penguin fossils, analyzing complete mitochondrial genomes from an albatross, a petrel, and a loon, and describe the gradual decline of pterosaurs at the same time modern birds radiate. The penguin fossils comprise four naturally associated skeletons from the New Zealand Waipara Greensand, a Paleocene (early Tertiary) formation just above a well-known Cretaceous/Tertiary boundary site. The fossils, in a new genus (Waimanu), provide a lower estimate of 61-62 Ma for the divergence between penguins and other birds and thus establish a reliable calibration point for avian evolution. Combining fossil calibration points, DNA sequences, maximum likelihood, and Bayesian analysis, the penguin calibrations imply a radiation of modern (crown group) birds in the Late Cretaceous. This includes a conservative estimate that modern sea and shorebird lineages diverged at least by the Late Cretaceous about 74 +/- 3 Ma (Campanian). It is clear that modern birds from at least the latest Cretaceous lived at the same time as archaic birds including Hesperornis, Ichthyornis, and the diverse Enantiornithiformes. Pterosaurs, which also coexisted with early crown birds, show notable changes through the Late Cretaceous. There was a decrease in taxonomic diversity, and small- to medium-sized species disappeared well before the end of the Cretaceous. A simple reading of the fossil record might suggest competitive interactions with birds, but much more needs to be understood about pterosaur life histories. Additional fossils and molecular data are still required to help understand the role of biotic interactions in the evolution of Late Cretaceous birds and thus to test that the mechanisms of microevolution are sufficient to explain macroevolution.

Early Penguin Fossils, Plus Mitochondrial Genomes, Calibrate Avian Evolution

The Miocene epoch (23.03–5.33 Ma) was a time interval of global warmth, relative to today. Continental configurations and mountain topography transitioned towards modern conditions, and many flora and fauna evolved into the same taxa that exist today. Miocene climate was dynamic: long periods of early and late glaciation bracketed a ∼2 Myr greenhouse interval – the Miocene Climatic Optimum (MCO). Floras, faunas, ice sheets, precipitation, pCO2, and ocean and atmospheric circulation mostly (but not ubiquitously) covaried with these large changes in climate. With higher temperatures and moderately higher pCO2 (∼400–600 ppm), the MCO has been suggested as a particularly appropriate analogue for future climate scenarios, and for assessing the predictive accuracy of numerical climate models – the same models that are used to simulate future climate. Yet, Miocene conditions have proved difficult to reconcile with models. This implies either missing positive feedbacks in the models, a lack of knowledge of past climate forcings, or the need for re‐interpretation of proxies, which might mitigate the model‐data discrepancy. Our understanding of Miocene climatic, biogeochemical, and oceanic changes on broad spatial and temporal scales is still developing. New records documenting the physical, chemical, and biotic aspects of the Earth system are emerging, and together provide a more comprehensive understanding of this important time interval. Here we review the state‐of‐the‐art in Miocene climate, ocean circulation, biogeochemical cycling, ice sheet dynamics, and biotic adaptation research as inferred through proxy observations and modelling studies.

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The Miocene: The Future of the Past

Higher-order phylogeny of modern birds (Theropoda, Aves: Neornithes) based on comparative anatomy: I. – Methods and characters [X1228] (matrix)

Avian feathers have many different functions. They provide insulation and capacity for flight among others. The remiges are flight feathers connected to the rear portion of the wing. Those attached to the ulna are termed the secondary remiges. In many birds the attachment points are traceable as more or less marked tuberosities and/or pits organized in linear series (Edgington &Miller 1942). Such tuberosities are called ‘ulnar quill knobs’ or ‘remigial papillae’, and their morphology appears to be unrelated to flight performance in extant birds (Hieronymus 2015). Ulnar quill pits have been found in some non-volant seabirds, such as modern penguins (Sphenisciformes: Spheniscidae) and Cenozoic plotopterids (Pelecaniformes: Plotopteridae) (e.g. Mayr 2004). Procellariiformes, the closest living relatives to penguins, possess papillae not pits (Hieronymus 2015, table 1). In the case of Sphenisciformes, birds with a fossil record extending to the Palaeocene (66.0–56.0Ma) and already very diverse in the Eocene (56.0–33.9Ma) (Jadwiszczak 2009), the term remex is rather confusing though. Since at least the latter epoch, penguins have been apparently characterized by the lack of differentiation between greater coverts and remiges (Clarke et al. 2010). Reported here is a penguin ulna from the Late Eocene of Seymour Island (Antarctic Peninsula) showing the only known quill pits of early Sphenisciformes and, hence, indirectly extending our knowledge on the feathering of these birds. It comes from the same time period as the unique fossilized feathers of a giant penguin from Peru described by Clarke et al. (2010). The fossil bone discussed here is an almost complete ulna, partially covered by matrix together with a fragmentary cervical vertebra (Fig. 1c), probably belonging to the same individual, from the Eocene La Meseta Formation (Seymour Island). It was collected in 2012 by TM, in the upper part of the unit Telm7 (or Submeseta Allomember; Late Eocene), within the Swedish locality NRM2, south-east of the Argentine Marambio Base (64°14.778'S, 56°37.169'W). The specimen is permanently deposited in the palaeozoological collections of the Naturhistoriska riksmuseet, Stockholm, Sweden (NRM-PZ). The comparative material comprises ulnae of modern penguins (Fig. 1a & b) housed at the Natural History Museum at Tring, UK (NHMUK).

First report on quill pits in early penguins

Here, we report on two tarsometatarsi assignable to relatively small-sized Eocene Antarctic penguins, housed in the palaeozoological collections of Naturhistoriska riksmuseet, Stockholm. The Priabo...

A new small-sized penguin from the late Eocene of Seymour Island with additional material of Mesetaornis polaris

Traces of skeletal response to trauma are poorly documented for early (i.e. Paleogene, 66–23 Ma) penguins (Sphenisciformes) and infectious diseases that afflicted these seabirds have not been previously put on record. We report osteomyelitis (OM), typically a bacterial infection of bone, in a proximal pedal phalanx of a ‘giant’ penguin from the Eocene (56–34 Ma) of West Antarctica. Osteomyelitis had apparently complicated healing of a fracture. The injury left an oblique scar within the proximal aspect of the plantar surface, resulting in deformation of the articular surface. The recognised evidence of OM includes characteristic periosteal reaction as well as focal bone-loss and necrosis.

The first evidence of an infectious disease in early penguins

Penguins (Aves: Sphenisciformes), wing-propelled diving seabirds, use their hind limbs mainly for steering underwater and walking on land. They are digitigrade animals, although can be plantigrade in slow motion or when at rest (Simpson 1946). Their metatarsal I and two phalanges forming the hallux or hind-toe are vestigial (Fig. 1a & b). Sphenisciformes may have existed in the Cretaceous, but the oldest known fossils are from the Palaeocene. Penguins became diversified and widely distributed by the Late Eocene (Jadwiszczak 2009). Thousands of Eocene penguin bones, assignable to at least ten species, come from Seymour (Marambio) Island, Antarctic Peninsula. Other fossils from this epoch are from South America, New Zealand and Australia (Jadwiszczak 2009). The single most important bone in fossil penguin taxonomy is undoubtedly the tarsometatarsus (Myrcha et al. 2002, Jadwiszczak 2008). This characteristic and morphologically complex skeletal element is the most common choice as a type specimen, especially when the fossil record consists of isolated bones (e.g. Myrcha et al. 2002). Despite the volume of papers on the penguin tarsometatarsus (Myrcha et al. 2002, Jadwiszczak 2008, 2009), there are still many interesting challenges to be explored. One of the most neglected, though greatly important, issues is the existence of the metatarsal I and its continuation, the hallux, in early Sphenisciformes. Presented here are tarsometatarsi of penguins from the Late Eocene of Antarctica that allow the recognition of previously unknown details of their plantar morphology and shed new light on foot evolution in these highly specialized birds. The material discussed here comes from the unit Telm7 or Submeseta Allomember (?Late Middle to Late Eocene) of the Eocene La Meseta Formation on Seymour Island (Antarctic Peninsula; 64817'S, 56845'W; Myrcha et al. 2002). The specimens presented below are housed at the Institute of Biology, University of Bialystok, Poland (IB/P/B).

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0954102013000631

First report on hind-toe development in Eocene Antarctic penguins

The lumbosacral-canal system in birds most likely operates as a sense organ involved in the control of balanced walking and perching, but our knowledge of it is superficial. Penguins constitute interesting objects for the study of this system due to their upright walking, but only the Humboldt penguin, Spheniscus humboldti Meyen, 1834, and some incomplete fossil penguin synsacra have been studied in this respect. Here we give an integrative comparative insight into the synsacral canal of extant Emperor penguin, Aptenodytes forsteri G.R. Gray, 1844, Adelie penguin, Pygoscelis adeliae, (Hombron et Jacquinot, 1841), and Eocene giant Anthropornis Wiman, 1905 and/or Palaeeudyptes Huxley, 1859 Antarctic penguins, using computed tomography imaging and associated data-extraction methodologies, complemented by analytical approaches ranging from geometric morphometrics to modularity, curvature and wavelet analyses. We document that the variability in the number of synsacro-lumbar vertebrae is evolutionarily conserved, and all studied synsacra possess osteological correlates of the lumbosacral-canal system. We also found that Eocene and extant Antarctic penguins were separable on the basis of the main direction of the shape-related (size-independent) variability within said system, and A. forsteri was unique in the entire studied set in terms of the relative cranial shift of this compound structure. Moreover, we suggest that the evolutionary processes, shaping both the terrestrial posture and gait, were responsible for the increased, in extant penguins, simplicity and stability of the synsacral canal cross-sectional periodic patterns as well as pave the way for the lumbosacral-canal system modularity characterized by reduced atomization/complexity. This article is protected by copyright. All rights reserved.

Piotr Jadwiszczak

Papers

First report on quill pits in early penguins

A new small-sized penguin from the late Eocene of Seymour Island with additional material of Mesetaornis polaris

The first evidence of an infectious disease in early penguins

First report on hind-toe development in Eocene Antarctic penguins

An integrative insight into the synsacral canal of fossil and extant Antarctic penguins.