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Results 21 through 40 out of 190

in category paleontology


21: Reptile-like physiology in Early Jurassic stem-mammals

Elis Newham, Pamela G Gill et al.

1,562 downloads (posted 30 Sep 2019)

There is uncertainty regarding the timing and fossil species in which mammalian endothermy arose, with few studies of stem-mammals on key aspects of endothermy such as basal or maximum metabolic rates, or placing them in the context of living vertebrate metabolic ranges. Synchrotron X-ray imaging of incremental tooth cementum shows two Early Jurassic stem-mammals, Morganucodon and Kuehneotherium , had lifespans (a basal metabolic rate proxy) considerably longer than comparably sized living mammals, but similar to reptiles. Morganucodon also had femoral blood flow rates (a maximum metabolic rate proxy) intermediate between living mammals and reptiles. This shows maximum metabolic rates increased evolutionarily before basal rates, and that contrary to previous suggestions of a Triassic origin, Early Jurassic stem-mammals lacked the endothermic metabolism of living mammals. One Sentence Summary Surprisingly long lifespans and low femoral blood flow suggest reptile-like physiology in key Early Jurassic stem-mammals.


22: The locomotor and predatory habits of unenlagiines (Theropoda, Paraves): inferences based on morphometric studies and comparisons with Laurasian dromaeosaurids

Federico A. Gianechini, Marcos D. Ercoli et al.

1,555 downloads (posted 18 Feb 2019)

Unenlagiinae is mostly recognized as a subclade of dromaeosaurids. They have the modified pedal digit II that characterize all dromeosaurids, which is typically related to predation. However, derived Laurasian dromaeosaurids (eudromaeosaurs) differ from unenlagiines in having a shorter metatarsus and pedal phalanx II-1, and more ginglymoid articular surfaces in metatarsals and pedal phalanges. Further, unenlagiines have a subarctometatarsal condition, which could have increased the mechanical efficiency during locomotio...


23: Bayesian Tip-dated Phylogenetics: Topological Effects, Stratigraphic Fit and the Early Evolution of Mammals

Benedict King, Robin Beck

1,545 downloads (posted 29 Jan 2019)

The incorporation of stratigraphic data into phylogenetic analysis has a long history of debate, but is not currently standard practice for palaeontologists. Bayesian tip-dating (or morphological clock) phylogenetic methods have returned these arguments to the spotlight, but how tip-dating affects the recovery of evolutionary relationships has yet to be fully explored. Here we show, through analysis of several datasets with multiple phylogenetic methods, that topologies produced by tip-dating are outliers when compared ...


24: The Long Limb Bones of the StW 573 Australopithecus Skeleton from Sterkfontein Member 2: Descriptions and Proportions

Jason L. Heaton, Travis Rayne Pickering et al.

1,471 downloads (posted 31 Dec 2018)

Due to its completeness, the A.L. 288-1 (Lucy) skeleton has long served as the archetypal bipedal Australopithecus. However, there remains considerable debate about its limb proportions. There are three competing, but not necessarily mutually exclusive, explanations for the high humerofemoral index of A.L. 288-1: (1) a retention of proportions from an Ardipithecus-like most recent common ancestor (MRCA); (2) indication of some degree of climbing ability; (3) allometry. Recent discoveries of other partial skeletons of Au...


25: Powered flight potential approached by wide range of close avian relatives but achieved selectively

R. Pei, Michael Pittman et al.

1,461 downloads (posted 18 Apr 2020)

Evolution of birds from non-flying theropod dinosaurs is a classic evolutionary transition, but a deeper understanding of early flight has been frustrated by disagreement on the relationships between birds (Avialae) and their closest theropod relatives. We address this through a larger, more resolved evolutionary hypothesis produced by a novel automated analysis pipeline tailored for large morphological datasets. We corroborate the grouping of dromaeosaurids + troodontids (Deinonychosauria) as the sister taxon to birds ...


26: Evolution of crab eye structures and the utility of ommatidia morphology in resolving phylogeny

Javier Luque, W. Ted Allison et al.

1,444 downloads (posted 07 Oct 2019)

Image-forming compound eyes are such a valuable adaptation that similar visual systems have evolved independently across crustaceans. But if different compound eye types have evolved independently multiple times, how useful are eye structures and ommatidia morphology for resolving phylogenetic relationships? Crabs are ideal study organisms to explore these questions because they have a good fossil record extending back into the Jurassic, they possess a great variety of optical designs, and details of eye form can be com...


27: Crustaceans as hosts of parasites throughout the Phanerozoic

Adiёl A. Klompmaker, Cristina M. Robins et al.

1,435 downloads (posted 31 Dec 2018)

The fossil record of crustaceans as hosts of parasites has yielded three confirmed associations: epicaridean isopod-induced swellings on Jurassic-Recent decapod crustaceans, feminization of Cretaceous and Miocene male crabs possibly caused by rhizocephalan barnacles, and presumed pentastomids on/in Silurian ostracods. Cestode platyhelminth hooks and swellings by entoniscid isopods may be recognized in the future. Relative to 2014, we report an increase of 41% to 124 fossil decapod species with epicaridean-induced swelli...


28: Endochondral bone in an Early Devonian ‘placoderm’ from Mongolia

Martin D. Brazeau, Sam Giles et al.

1,433 downloads (posted 10 Jun 2020)

Endochondral bone is the main internal skeletal tissue of nearly all osteichthyans—the group comprising more than 60,000 living species of bony fishes and tetrapods. Chondrichthyans (sharks and their kin) are the living sister group of osteichthyans and have cartilaginous endoskeletons, long considered the ancestral condition for all jawed vertebrates (gnathostomes). The absence of bone in modern jawless fishes and the absence of endochondral ossification in early fossil gnathostomes appears to lend support to this conc...


29: New opabiniid diversifies the weirdest wonders of the euarthropod lower stem group

Stephen Pates, Joanna M Wolfe et al.

1,423 downloads (posted 11 Mar 2021)

Once considered "weird wonders" of the Cambrian, the emblematic Burgess Shale animals Anomalocaris and Opabinia are now recognized as lower stem-group euarthropods. Anomalocaris and its relatives (radiodonts) had a worldwide distribution and survived until at least the Devonian, whereas - despite intense study - Opabinia remains the only formally described opabiniid to date. Here we reinterpret a fossil from the Wheeler Formation of Utah as a new opabiniid, KUMIP 314087. By visualizing the sample of phylogenetic topolog...



Arturo Tozzi

1,408 downloads (posted 01 Sep 2016)

We display a detailed description of mimetic muscles in extinct human species, framed in comparative and phylogenetic contexts. Using known facial landmarks, we assessed the arrangement of muscles of facial expression in Homo sapiens, neanderthalensis, erectus, heidelbergensis and ergaster. In modern humans, several perioral muscles are proportionally smaller in size (levator labii superioris, zygomaticus minor, zygomaticus major and triangularis) and/or located more medially (levator labii superioris, zygomaticus minor...


31: A new genus of horse from Pleistocene North America

Peter D. Heintzman, Grant D Zazula et al.

1,372 downloads (posted 24 Jun 2017)

The extinct New World stilt-legged, or NWSL, equids constitute a perplexing group of Pleistocene horses endemic to North America. Their slender distal limb bones resemble those of Asiatic asses, such as the Persian onager. Previous palaeogenetic studies, however, have suggested a closer relationship to caballine horses than to Asiatic asses. Here, we report complete mitochondrial and partial nuclear genomes from NWSL equids from across their geographic range. Although multiple NWSL equid species have been named, our pal...


32: The tapejarid pterosaur Tupandactylus imperator from Crato Formation and the preservation of cranial integuments

Hebert Bruno Nascimento Campos, Edio-Ernst Kischlat

1,357 downloads (posted 06 Feb 2020)

The group Tapejaridae forms a clade of toothless pterosaurs easily recognized by their premaxillary sagittal crests and particularly large nasoantorbital fenestrae. The tapejarids represent the most representative group of pterosaurs from the Lower Cretaceous Crato Formation of the Araripe Basin (Northeastern Brazil). The holotype of the large tapejarid Tupandactylus imperator Campos and Kellner, 1997 is known by two main slabs from the New Olinda Member of the Crato Formation, however, only one of the slabs containing ...


33: Transitional evolutionary forms and stratigraphic trends in chasmosaurine ceratopsid dinosaurs : evidence from the Campanian of New Mexico

Denver Warwick Fowler, Elizabeth Anne Freedman Fowler

1,353 downloads (posted 25 Nov 2019)

Three new chasmosaurines from the Kirtland Formation (~75.0 - 73.4 Ma), New Mexico, form morphological and stratigraphic intermediates between Pentaceratops (~74.7 - 75Ma, Fruitland Formation, New Mexico) and Anchiceratops (~72 - 71Ma, Horseshoe Canyon Formation, Alberta). The new specimens exhibit gradual enclosure of the parietal embayment that characterizes Pentaceratops, providing support for the phylogenetic hypothesis that Pentaceratops and Anchiceratops are closely related. This stepwise change of morphologic cha...


34: Computed tomography reveals hip dysplasiain the extinct Pleistocene saber-tooth cat Smilodon

Mairin A Balisi, Abhinav K Sharma et al.

1,346 downloads (posted 07 Jan 2020)

Reconstructing the behavior of extinct species is challenging, particularly for those with no living analogues. However, damage preserved as paleopathologies on bone can record how an animal moved in life, potentially reflecting behavioral patterns. Here, we assess hypothesized etiologies of pathology in a pelvis and associated right femur of a Smilodon fatalis saber-toothed cat, one of the best-studied species from the Pleistocene-age Rancho La Brea asphalt seeps, California, USA, using visualization by computed tomogr...


35: Modeling Dragons: Using linked mechanistic physiological and microclimate models to explore environmental, physiological, and morphological constraints on the early evolution of dinosaurs

David Michael Lovelace, Scott A. Hartman et al.

1,318 downloads (posted 02 Oct 2019)

We employed the widely-tested biophysiological modeling software, Niche Mapper™ to investigate the metabolic function of Late Triassic dinosaurs Plateosaurus and Coelophysis during global greenhouse conditions. We tested them under a variety of assumptions about resting metabolic rate, evaluated within six microclimate models that bound paleoenvironmental conditions at 12° N paleolatitude, as determined by sedimentological and isotopic proxies for climate within the Chinle Formation of the southwestern United States. Se...


36: Coral reefs in crisis: The reliability of deep-time food web reconstructions as analogs for the present

Peter D Roopnarine, Ashley A. Dineen

1,297 downloads (posted 04 Mar 2017)

Ongoing anthropogenic alterations of the biosphere have shifted emphasis in conservation biology from individual species to entire ecosystems. Modern measures of ecosystem change, however, lack the extended temporal scales necessary to forecast future change under increasingly stressful environmental conditions. Accordingly, the assessment and reconstruction of ecosystem dynamics during previous intervals of environmental stress and climate change in deep time has garnered increasing attention. The nature of the fossil ...


37: The fast and the frugal: Divergent locomotory strategies drive limb lengthening in theropod dinosaurs

T. Alexander Dececchi, Aleksandra M. Mloszewska et al.

1,296 downloads (posted 27 Sep 2019)

Limb length, cursoriality and speed have long been areas of significant interest in theropod paleobiology as locomotory capacity, especially running ability, is critical in not just in prey pursuit but also to avoid become prey oneself. One aspect that is traditionally overlooked is the impact of allometry on running ability and the limiting effect of large body size. Since several different non-avian theropod lineages have each independently evolved body sizes greater than any known terrestrial carnivorous mammal, ~100...


38: The multi-peak adaptive landscape of crocodylomorph body size evolution

Pedro L. Godoy, Roger B. J. Benson et al.

1,267 downloads (posted 31 Aug 2018)

Background: Little is known about the long-term patterns of body size evolution in Crocodylomorpha, the > 200-million-year-old group that includes living crocodylians and their extinct relatives. Extant crocodylians are mostly large-bodied (3-7 m) predators. However, extinct crocodylomorphs exhibit a wider range of phenotypes, and many of the earliest taxa were much smaller (< 1.2 m). This suggests a pattern of size increase through time that could be caused by multi-lineage evolutionary trends of size increase or by se...


39: The case for species selection

Carl Simpson

1,215 downloads (posted 28 Oct 2016)

The mere existence of speciation and extinction make macroevolutionary processes possible. Speciation and extinction introduce discontinuities in the microevolutionary change within lineages by initiating, disrupting, and terminating the continuity of species lineages. Within a clade, speciation and extinction become potent means of macroevolution in and of themselves. This process, termed species selection, is a macroevolutionary analogue of natural selection, with species playing an analogous part akin to that played ...


40: History is written by the victors: the effect of the push of the past on the fossil record

Graham E Budd, Richard P. Mann

1,208 downloads (posted 27 Sep 2017)

Phylogenies may be modelled using 'birth-death' models for speciation and extinction, but even when a homogeneous rate of diversification is used, survivorship biases can generate remarkable rate heterogeneities through time. One such bias has been termed the 'push of the past', by which the length of time a clade has survived is conditioned on the rate of diversification that happened to pertain at its origin. This creates the illusion of a secular rate slow-down through time that is, rather, a reversion to the mean. H...