Publications by authors named "Ryosuke Motani"

32 Publications

Functional morphology of vertebrate claws investigated using functionally based categories and multiple morphological metrics.

J Morphol 2021 Mar 18;282(3):449-471. Epub 2021 Jan 18.

University of California, Davis, Davis, California, USA.

The link between claw morphology and function has been historically difficult to quantify, analyze, and interpret. In this study, the functional morphology of vertebrate claws is analyzed using measurements taken from 80 modern claw specimens spanning birds, mammals, and one reptile. Claw measurements were chosen for their potential biomechanical significance and a revised, expanded categorization of claw function is defined and used. This categorization scheme is the result of an extensive literature review and is based on the observed mechanics of claw function rather than the animal's overall ecology, an important departure from the norm followed in previous studies. A principal component analysis of the claw measurements reveals that some of the morphological disparity is related to functional differences; however, different functional categories are not clearly separated based solely on morphology. A linear discriminant analysis successfully classifies 81.25% of the claw specimens to their documented functional categories. When the posterior probabilities of each classification are examined, and the next highest probabilities are considered, the analysis is able to successfully classify 96.25% of the claw specimens. Expressing angle measurements in terms of lengths prior to analysis and incorporating cross-sectional shape data both serve to reduce the misclassification rate. The use of biomechanically meaningful claw measurements and categories based on function (rather than ecology) improves confidence in the ability to infer claw function based on morphology using discriminant analysis methods. While overall claw morphology is most certainly the result of multiple factors (e.g., growth, size, etc.), this study establishes that it reflects mechanical function more than previously demonstrated.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/jmor.21317DOI Listing
March 2021

Evidence Supporting Predation of 4-m Marine Reptile by Triassic Megapredator.

iScience 2020 Jul 29:101347. Epub 2020 Jul 29.

The Geoscience Museum, Hebei GEO University, No. 136 East Huai'an Road, Shijiazhuang, Hebei 050031, People's Republic of China.

Air-breathing marine predators have been essential components of the marine ecosystem since the Triassic. Many of them are considered the apex predators but without direct evidence-dietary inferences are usually based on circumstantial evidence, such as tooth shape. Here we report a fossil that likely represents the oldest evidence for predation on megafauna, i.e., animals equal to or larger than humans, by marine tetrapods-a thalattosaur (∼4 m in total length) in the stomach of a Middle Triassic ichthyosaur (∼5 m). The predator has grasping teeth yet swallowed the body trunk of the prey in one to several pieces. There were many more Mesozoic marine reptiles with similar grasping teeth, so megafaunal predation was likely more widespread than presently conceived. Megafaunal predation probably started nearly simultaneously in multiple lineages of marine reptiles in the Illyrian (about 242-243 million years ago).
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.isci.2020.101347DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7520894PMC
July 2020

Repeated evolution of durophagy during ichthyosaur radiation after mass extinction indicated by hidden dentition.

Sci Rep 2020 05 8;10(1):7798. Epub 2020 May 8.

Department of Research, Anhui Geological Museum, Jiahe Road 999, Hefei, Anhui, 230031, China.

Marine tetrapods quickly diversified and were established as marine top predators after the end-Permian Mass extinction (EPME). Ichthyosaurs were the forerunner of this rapid radiation but the main drivers of the diversification are poorly understood. Cartorhynchus lenticarpus is a basal ichthyosauriform with the least degree of aquatic adaptation, holding a key to identifying such a driver. The unique specimen appeared edentulous based on what was exposed but a CT scanning revealed that the species indeed had rounded teeth that are nearly perpendicular to the jaw rami, and thus completely concealed in lateral view. There are three dental rows per jaw ramus, and the root lacks infoldings of the dentine typical of ichthyopterygians. The well-developed and worn molariform dentition with three tooth rows supports the previous inference that the specimen is not of a juvenile. The premaxilla and the corresponding part of the dentary are edentulous. Molariform dentition evolved three to five times independently within Ichthyosauriformes in the Early and Middle Triassic. Convergent exploitation of hard-shelled invertebrates by different subclades of ichthyosauriforms likely fueled the rapid taxonomic diversification of the group after EPME.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41598-020-64854-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7210957PMC
May 2020

The new ichthyosauriform (Reptilia, Ichthyosauromorpha) from Majiashan, Chaohu, Anhui Province, China.

PeerJ 2019 9;7:e7561. Epub 2019 Sep 9.

Department of Research, Anhui Geological Museum, Hefei, Anhui, People's Republic of China.

A new species of ichthyosauriform is recognized based on 20 specimens, including nearly complete skeletons, and named . A part of the specimens was previously identified as and is herein reassigned to the new species. The new species differs from existing species of in a suite of features, such as the bifurcation of the caudal peak neural spine and a short femur relative to trunk length. The specimens include both complete and partially disarticulated skulls, allowing rigorous scrutiny of cranial sutures. For example, the squamosal does not participate in the margin of the upper temporal fenestra despite previous interpretations. Also, the frontal unequivocally forms a part of the anterior margin of the upper temporal fenestra, forming the most medial part of the anterior terrace. The skull of the holotype largely retains three-dimensionality with the scleral rings approximately in situ, revealing that the eyeball was uncovered in two different directions, that is, laterally and slightly dorsally through the main part of the orbit, and dorsally through the medial extension of the orbit into the skull roof. This skull construction is likely a basal feature of Ichthyosauromorpha. Phylogenetic analyses place the new species as a sister taxon of .
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.7717/peerj.7561DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6741286PMC
September 2019

Flipper bone distribution reveals flexible trailing edge in underwater flying marine tetrapods.

J Morphol 2019 06 22;280(6):908-924. Epub 2019 Apr 22.

Department of Earth and Planetary Sciences, University of California, Davis, California.

Hydrofoil-shaped limbs (flipper-hydrofoils) have evolved independently several times in secondarily marine tetrapods and generally fall into two functional categories: (1) those that produce the majority of thrust during locomotion (propulsive flipper-hydrofoils); (2) those used primarily to steer and resist destabilizing movements such as yaw, pitch, and roll (controller flipper-hydrofoils). The morphological differences between these two types have been poorly understood. Theoretical and experimental studies on engineered hydrofoils suggest that flapping hydrofoils with a flexible trailing edge are more efficient at producing thrust whereas hydrofoils used in steering and stabilization benefit from a more rigid one. To investigate whether the trailing edge is generally more flexible in propulsive flipper-hydrofoils, we compared the bone distribution along the chord in both flipper types. The propulsive flipper-hydrofoil group consists of the forelimbs of Chelonioidea, Spheniscidae, and Otariidae. The controller flipper-hydrofoil group consists of the forelimbs of Cetacea. We quantified bone distribution from radiographs of species representing more than 50% of all extant genera for each clade. Our results show that the proportion of bone in both groups is similar along the leading edge (0-40% of the chord) but is significantly less along the trailing edge for propulsive flipper-hydrofoils (40-80% of the chord). Both flipper-hydrofoil types have little to no bony tissue along the very edge of the trailing edge (80-100% of the chord). This suggests a relatively flexible trailing edge for propulsive flipper-hydrofoils compared to controller flipper-hydrofoils in line with findings from prior studies. This study presents a morphological correlate for inferring flipper-hydrofoil function in extinct taxa and highlights the importance of a flexible trailing edge in the evolution of propulsive flipper-hydrofoils in marine tetrapods.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/jmor.20992DOI Listing
June 2019

Early Triassic marine reptile representing the oldest record of unusually small eyes in reptiles indicating non-visual prey detection.

Sci Rep 2019 01 24;9(1):152. Epub 2019 Jan 24.

Center of Integrative Research, The Field Museum, Chicago, IL, 60605-2496, USA.

The end-Permian mass extinction (EPME) led to reorganization of marine predatory communities, through introduction of air-breathing top predators, such as marine reptiles. We report two new specimens of one such marine reptile, Eretmorhipis carrolldongi, from the Lower Triassic of Hubei, China, revealing superficial convergence with the modern duckbilled platypus (Ornithorhynchus anatinus), a monotreme mammal. Apparent similarities include exceptionally small eyes relative to the body, snout ending with crura with a large internasal space, housing a bone reminiscent of os paradoxum, a mysterious bone of platypus, and external grooves along the crura. The specimens also have a rigid body with triangular bony blades protruding from the back. The small eyes likely played reduced roles during foraging in this animal, as with extant amniotes (group containing mammals and reptiles) with similarly small eyes. Mechanoreceptors on the bill of the animal were probably used for prey detection instead. The specimens represent the oldest record of amniotes with extremely reduced visual capacity, utilizing non-visual cues for prey detection. The discovery reveals that the ecological diversity of marine predators was already high in the late Early Triassic, and challenges the traditional view that the ecological diversification of marine reptiles was delayed following the EPME.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41598-018-37754-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6345829PMC
January 2019

Separating sexual dimorphism from other morphological variation in a specimen complex of fossil marine reptiles (Reptilia, Ichthyosauriformes, Chaohusaurus).

Sci Rep 2018 10 8;8(1):14978. Epub 2018 Oct 8.

Department of Research, Anhui Geological Museum, Jiahe Road 999, Hefei, Anhui, 230031, People's Republic of China.

The Early Triassic Chaohu Fauna from Anhui Province, China, contains the oldest record of Mesozoic marine reptiles, such as Cartorhynchus and Sclerocormus. Most specimens from the fauna belong to the ichthyosauriform Chaohusaurus, more specifically resembling C. chaoxianensis. However, a wide range of morphological variation exists within about 40 skeletons that have been prepared, likely reflecting mixed signals from both sexual and taxonomic differences. We test whether the sexual and taxonomic signals are separable based on quantification, aided by the knowledge of sexual dimorphism in extant marine tetrapods. There are two different suites of dimorphism that divide the specimens differently from each other yet consistently within each suite, resulting in four morphotypes in combination, likely representing two sexes of two taxa. Presumed males have larger 'organ of prehension' sensu Darwin, specifically limbs in the present case, for a given body length. This sexing criterion is supported by the only specimen of a gravid female, which belongs to the morphotype with short limbs. Males also have larger skulls for the trunk length compared to females. This study demonstrates that sexual and taxonomic signals are separable in fossil reptiles, with a sufficient sample size and careful analyses.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41598-018-33302-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6175944PMC
October 2018

The sea as deathtrap: comment on a paper by miller and wiens.

Ecol Lett 2018 06 2;21(6):938-939. Epub 2018 Apr 2.

Department of Earth and Planetary Sciences, University of California, Davis, Davis, CA, 95616, USA.

Miller & Wiens (2017) claim that low marine as compared with terrestrial diversity results from more frequent extinctions and insufficient time for diversification in marine clades. Their data on marine amniotes are unrepresentative of marine diversity, their analysis of clade dynamics is flawed, and they ignore previously proposed explanations for the diversity difference.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/ele.12886DOI Listing
June 2018

Pre- versus post-mass extinction divergence of Mesozoic marine reptiles dictated by time-scale dependence of evolutionary rates.

Proc Biol Sci 2017 May;284(1854)

Department of Research, Anhui Geological Museum, Jiahe Road 999, Hefei, Anhui 230031, People's Republic of China.

The fossil record of a major clade often starts after a mass extinction even though evolutionary rates, molecular or morphological, suggest its pre-extinction emergence (e.g. squamates, placentals and teleosts). The discrepancy is larger for older clades, and the presence of a time-scale-dependent methodological bias has been suggested, yet it has been difficult to avoid the bias using Bayesian phylogenetic methods. This paradox raises the question of whether ecological vacancies, such as those after mass extinctions, prompt the radiations. We addressed this problem by using a unique temporal characteristic of the morphological data and a high-resolution stratigraphic record, for the oldest clade of Mesozoic marine reptiles, Ichthyosauromorpha. The evolutionary rate was fastest during the first few million years of ichthyosauromorph evolution and became progressively slower over time, eventually becoming six times slower. Using the later slower rates, estimates of divergence time become excessively older. The fast, initial rate suggests the emergence of ichthyosauromorphs after the end-Permian mass extinction, matching an independent result from high-resolution stratigraphic confidence intervals. These reptiles probably invaded the sea as a new ecosystem was formed after the end-Permian mass extinction. Lack of information on early evolution biased Bayesian clock rates.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1098/rspb.2017.0241DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5443947PMC
May 2017

Eccentricity and obliquity paced carbon cycling in the Early Triassic and implications for post-extinction ecosystem recovery.

Sci Rep 2016 06 13;6:27793. Epub 2016 Jun 13.

Dipartimento di Scienze della Terra, Università degli Studi di Milano, Via Mangiagalli 34-20133 Milano, Italy.

The timing of marine ecosystem recovery following the End Permian Mass Extinction (EPME) remains poorly constrained given the lack of radiometric ages. Here we develop a high-resolution carbonate carbon isotope (δ(13)Ccarb) record for 3.20 million years of the Olenekian in South China that defines the astronomical time-scale for the critical interval of major evolutionary and oceanic events in the Spathian. δ(13)Ccarb documents eccentricity modulation of carbon cycling through the period and a strong obliquity signal. A shift in phasing between short and long eccentricity modulation, and amplification of obliquity, is nearly coincident with a 2% decrease in seawater δ(13)CDIC, the last of a longer-term stepped decrease through the Spathian. The mid-Spathian shift in seawater δ(13)CDIC to typical thermocline values is interpreted to record a major oceanic reorganization with global climate amelioration. Coincidence of the phasing shift with the first occurrence of marine reptiles (248.81 Ma), suggests that their invasion into the sea and the onset of a complex ecosystem were facilitated by restoration of deep ocean ventilation linked mechanistically to a change in the response of the oceanic carbon reservoir to astronomical forcing. Together these records place the first constraints on the duration of the post-extinction recovery to 3.35 myr.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/srep27793DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4904238PMC
June 2016

Palaeobiology: Born and Gone in Global Warming.

Authors:
Ryosuke Motani

Curr Biol 2016 06;26(11):R466-8

Department of Earth and Planetary Sciences, University of California, Davis, California 95616, USA. Electronic address:

Why ichthyosaurs - marine Mesozoic reptiles - disappeared before the dinosaur extinction has remained a mystery. New research suggests they may have gone extinct stepwise, during one of the most extreme greenhouse periods in the history of complex life-forms.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.cub.2016.04.014DOI Listing
June 2016

A large aberrant stem ichthyosauriform indicating early rise and demise of ichthyosauromorphs in the wake of the end-Permian extinction.

Sci Rep 2016 05 23;6:26232. Epub 2016 May 23.

Department of Research, Anhui Geological Museum, Jiahe Road 999, Hefei, Anhui 230031, People's Republic of China.

Contrary to the fast radiation of most metazoans after the end-Permian mass extinction, it is believed that early marine reptiles evolved slowly during the same time interval. However, emerging discoveries of Early Triassic marine reptiles are questioning this traditional view. Here we present an aberrant basal ichthyosauriform with a hitherto unknown body design that suggests a fast radiation of early marine reptiles. The new species is larger than coeval marine reptiles and has an extremely small head and a long tail without a fluke. Its heavily-built body bears flattened and overlapping gastral elements reminiscent of hupehsuchians. A phylogenetic analysis places the new species at the base of ichthyosauriforms, as the sister taxon of Cartorhynchus with which it shares a short snout with rostrally extended nasals. It now appears that ichthyosauriforms evolved rapidly within the first one million years of their evolution, in the Spathian (Early Triassic), and their true diversity has yet to be fully uncovered. Early ichthyosauromorphs quickly became extinct near the Early-Middle Triassic boundary, during the last large environmental perturbation after the end-Permian extinction involving redox fluctuations, sea level changes and volcanism. Marine reptile faunas shifted from ichthyosauromorph-dominated to sauropterygian-dominated composition after the perturbation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/srep26232DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4876504PMC
May 2016

A new Lower Triassic ichthyopterygian assemblage from Fossil Hill, Nevada.

PeerJ 2016 26;4:e1626. Epub 2016 Jan 26.

Natural Resources Canada-Geological Survey of Canada , Vancouver, British Columbia , Canada.

We report a new ichthyopterygian assemblage from Lower Triassic horizons of the Prida Formation at Fossil Hill in central Nevada. Although fragmentary, the specimens collected so far document a diverse fauna. One partial jaw exhibits isodont dentition with blunt tipped, mesiodistally compressed crowns and striated enamel. These features are shared with the Early Triassic genus Utatsusaurus known from coeval deposits in Japan and British Columbia. An additional specimen exhibits a different dentition characterized by relatively small, rounded posterior teeth resembling other Early Triassic ichthyopterygians, particularly Grippia. This Nevada assemblage marks a southward latitudinal extension for Early Triassic ichthyopterygians along the eastern margin of Panthalassa and indicates repeated trans-hemispheric dispersal events in Early Triassic ichthyopterygians.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.7717/peerj.1626DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4741062PMC
February 2016

Adult sex ratio, sexual dimorphism and sexual selection in a Mesozoic reptile.

Proc Biol Sci 2015 Sep;282(1815)

Dipartimento di Scienze della Terra, Università degli Studi di Milano, Via Mangiagalli, Milan 34-20133, Italy.

The evolutionary history of sexual selection in the geologic past is poorly documented based on quantification, largely because of difficulty in sexing fossil specimens. Even such essential ecological parameters as adult sex ratio (ASR) and sexual size dimorphism (SSD) are rarely quantified, despite their implications for sexual selection. To enable their estimation, we propose a method for unbiased sex identification based on sexual shape dimorphism, using size-independent principal components of phenotypic data. We applied the method to test sexual selection in Keichousaurus hui, a Middle Triassic (about 237 Ma) sauropterygian with an unusually large sample size for a fossil reptile. Keichousaurus hui exhibited SSD biased towards males, as in the majority of extant reptiles, to a minor degree (sexual dimorphism index -0.087). The ASR is about 60% females, suggesting higher mortality of males over females. Both values support sexual selection of males in this species. The method may be applied to other fossil species. We also used the Gompertz allometric equation to study the sexual shape dimorphism of K. hui and found that two sexes had largely homogeneous phenotypes at birth except in the humeral width, contrary to previous suggestions derived from the standard allometric equation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1098/rspb.2015.1658DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4614760PMC
September 2015

How warm is too warm for the life cycle of actinopterygian fishes?

Sci Rep 2015 Jul 13;5:11597. Epub 2015 Jul 13.

Department of Evolution and Ecology, University of California, One Shields Avenue, Davis, California 95616.

We investigated the highest constant temperature at which actinopterygian fishes can complete their lifecycles, based on an oxygen supply model for cleavage-stage eggs. This stage is one of the most heat-sensitive periods during the lifecycle, likely reflecting the exhaustion of maternally supplied heat shock proteins without new production. The model suggests that average eggs would not develop normally under a constant temperature of about 36 °C or higher. This estimate matches published empirical values derived from laboratory and field observations. Spermatogenesis is more heat sensitive than embryogenesis in fishes, so the threshold may indeed be lower, at about 35 °C, unless actinopterygian fishes evolve heat tolerance during spermatogenesis as in birds. Our model also predicts an inverse relationship between egg size and temperature, and empirical data support this prediction. Therefore, the average egg size, and hence hatching size, is expected to shrink in a greenhouse world but a feeding function prohibits the survival of very small hatchlings, posing a limit to the shrinkage. It was once suggested that a marine animal community may be sustained under temperatures up to about 38 °C, and this value is being used, for example, in paleotemperature reconstruction. A revision of the value is overdue. (199/200).
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/srep11597DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4648408PMC
July 2015

A New Specimen of Carroll's Mystery Hupehsuchian from the Lower Triassic of China.

PLoS One 2015 27;10(5):e0126024. Epub 2015 May 27.

Center of Integrative Research, The Field Museum, Chicago, Illinois, United States of America.

A new specimen of an enigmatic hupehsuchian genus is reported. The genus was first recognized by Robert L. Carroll and Zhi-ming Dong in 1991, who refrained from naming it because of the poor quality of the only specimen known at the time. After more than two decades, we finally report a second specimen of this genus, which remained unprepared until recently. The new specimen preserves most of the skeleton except the skull, allowing us to erect a new genus and species, Eretmorhipis carrolldongi. The new species shares many characters with Parahupehsuchus longus, including the strange axial skeleton that forms a bony body tube. However, the body tube is short in the new species, being limited to the pectoral region. The vertebral count and limb morphology considerably differ between the new species and P. longus. The forelimb of E. carrolldongi is markedly larger than its hind limb as in Hupehsuchus nanchangensis but unlike in P. longus. The new species is unique among hupehsuchians in a list of features. It has manual and pedal digits that spread radially, forming manus and pes that are almost as wide as long. The third-layer elements of the dermal armor are unusually large, spanning four vertebral segments, yet there are substantial gaps among them. With the addition of the unique paddle, it is now clear that Hupehsuchia had diverse forelimb morphologies spanning from paddles to flippers, unlike ichthyopterygians that were taxonomically more diverse yet only had flippers.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0126024PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4446317PMC
May 2016

Lunge feeding in early marine reptiles and fast evolution of marine tetrapod feeding guilds.

Sci Rep 2015 Mar 10;5:8900. Epub 2015 Mar 10.

Center of Integrative Research, The Field Museum, Chicago. IL 60605-2496, U.S.A.

Traditional wisdom holds that biotic recovery from the end-Permian extinction was slow and gradual, and was not complete until the Middle Triassic. Here, we report that the evolution of marine predator feeding guilds, and their trophic structure, proceeded faster. Marine reptile lineages with unique feeding adaptations emerged during the Early Triassic (about 248 million years ago), including the enigmatic Hupehsuchus that possessed an unusually slender mandible. A new specimen of this genus reveals a well-preserved palate and mandible, which suggest that it was a rare lunge feeder as also occurs in rorqual whales and pelicans. The diversity of feeding strategies among Triassic marine tetrapods reached their peak in the Early Triassic, soon after their first appearance in the fossil record. The diet of these early marine tetrapods most likely included soft-bodied animals that are not preserved as fossils. Early marine tetrapods most likely introduced a new trophic mechanism to redistribute nutrients to the top 10 m of the sea, where the primary productivity is highest. Therefore, a simple recovery to a Permian-like trophic structure does not explain the biotic changes seen after the Early Triassic.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/srep08900DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4354009PMC
March 2015

Trophic convergence drives morphological convergence in marine tetrapods.

Biol Lett 2015 Jan;11(1):20140709

Department of Earth and Planetary Sciences, University of California, Davis, 1 Shields Avenue, Davis, CA 95616, USA.

Marine tetrapod clades (e.g. seals, whales) independently adapted to marine life through the Mesozoic and Caenozoic, and provide iconic examples of convergent evolution. Apparent morphological convergence is often explained as the result of adaptation to similar ecological niches. However, quantitative tests of this hypothesis are uncommon. We use dietary data to classify the feeding ecology of extant marine tetrapods and identify patterns in skull and tooth morphology that discriminate trophic groups across clades. Mapping these patterns onto phylogeny reveals coordinated evolutionary shifts in diet and morphology in different marine tetrapod lineages. Similarities in morphology between species with similar diets-even across large phylogenetic distances-are consistent with previous hypotheses that shared functional constraints drive convergent evolution in marine tetrapods.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1098/rsbl.2014.0709DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4321144PMC
January 2015

A small short-necked hupehsuchian from the lower Triassic of Hubei Province, China.

PLoS One 2014 17;9(12):e115244. Epub 2014 Dec 17.

Center of Integrative Research, The Field Museum, Chicago, Illinois 60605-2496, United States of America.

Hupehsuchia is a group of enigmatic Triassic marine reptiles that is known exclusively from two counties in Hubei Province, China. One of the common features of the group was a modestly long neck with nine to ten cervical vertebrae. We report a new species of Hupehsuchia, Eohupehsuchus brevicollis gen. et sp. nov., which for the first time shows a short neck in this group, with six cervicals. The configuration of the skull roof in Eohupehsuchus is also unique among Hupehsuchia, with narrow frontals and posteriorly shifted parietals, warranting recognition of a new species. The taxon superficially resembles Nanchangosaurus in retaining hupehsuchian plesiomorphies, such as low neural spines and small body size. However, its limbs are well-developed, unlike in Nanchangosaurus, although the latter genus is marginally larger in body length. Thus, the individual is unlikely to be immature. Also, Eohupehsuchus shares a suite of synapomorphies with Hupehsuchus, including the second and third layers of dermal ossicles above the dorsal neural spines. A phylogenetic analysis suggests that the new species is not the most basal hupehsuchian despite its short neck, and instead forms the sister taxon of Hupehsuchidae. Until recently, Hupehsuchia contained only two monotypic genera. Now there are at least four genera among Hupehsuchia, and the undescribed diversity is even higher. The left forelimb of the only specimen is incomplete, ending with broken phalanges distally. The breakage could only have occurred pre-burial. The individual may have been attacked by a predator and escaped, given that scavenging is unlikely.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0115244PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4269458PMC
January 2016

A basal ichthyosauriform with a short snout from the Lower Triassic of China.

Nature 2015 Jan 5;517(7535):485-8. Epub 2014 Nov 5.

Department of Research, Anhui Geological Museum, Jiahe Road 999, Hefei, Anhui 230031, China.

The incompleteness of the fossil record obscures the origin of many of the more derived clades of vertebrates. One such group is the Ichthyopterygia, a clade of obligatory marine reptiles that appeared in the Early Triassic epoch, without any known intermediates. Here we describe a basal ichthyosauriform from the upper Lower Triassic (about 248 million years ago) of China, whose primitive skeleton indicates possible amphibious habits. It is smaller than ichthyopterygians and had unusually large flippers that probably allowed limited terrestrial locomotion. It also retained characteristics of terrestrial diapsid reptiles, including a short snout and body trunk. Unlike more-derived ichthyosauriforms, it was probably a suction feeder. The new species supports the sister-group relationships between ichthyosauriforms and Hupehsuchia, the two forming the Ichthyosauromorpha. Basal ichthyosauromorphs are known exclusively from south China, suggesting that the clade originated in the region, which formed a warm and humid tropical archipelago in the Early Triassic. The oldest unequivocal record of a sauropterygian is also from the same stratigraphic unit of the region.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/nature13866DOI Listing
January 2015

The enigmatic marine reptile nanchangosaurus from the lower triassic of Hubei, China and the phylogenetic affinities of Hupehsuchia.

PLoS One 2014 11;9(7):e102361. Epub 2014 Jul 11.

Center of Integrative Research, The Field Museum, Chicago, Illinois, United States of America.

The study of the holotype and of a new specimen of Nanchangosaurus suni (Reptilia; Diapsida; Hupehsuchia) revealed a suite of hitherto unrecognized characters. For example, Nanchangosaurus has bipartite neural spines and its vertebral count is nearly identical to that of Hupehsuchus. It differs from the latter in having poorly developed forelimbs despite the advanced ossification in the rest of the skeleton. Other differences all pertain to hupehsuchian plesiomorphies retained in Nanchangosaurus, such as low neural spines. The relationship of Hupehsuchia within Diapsida was analyzed based on a data matrix containing 41 taxa coded for 213 characters, of which 18 were identified as aquatic adaptations from functional inferences. These aquatic adaptations may be vulnerable to the argumentation of character homology because expectation for homoplasy is high. There is an apparent incongruence between phylogenetic signals from aquatic adaptations and the rest of the data, with aquatic adaptations favoring all marine reptiles but Helveticosaurus to form a super-clade. However, this super-clade does not obtain when aquatic adaptations were deleted, whereas individual marine reptile clades are all derived without them. We examined all possible combinations of the 18 aquatic adaptations (n = 262143) and found that four lineages of marine reptiles are recognized almost regardless of which of these features were included in the analysis: Hupehsuchia-Ichthyopterygia clade, Sauropterygia-Saurosphargidae clade, Thalattosauria, and Helveticosaurus. The interrelationships among these four depended on the combination of aquatic adaptations to be included, i.e., assumed to be homologous a priori by bypassing character argumentation. Hupehsuchia always appeared as the sister taxon of Ichthyopterygia.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0102361PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4094528PMC
March 2015

A carapace-like bony 'body tube' in an early triassic marine reptile and the onset of marine tetrapod predation.

PLoS One 2014 9;9(4):e94396. Epub 2014 Apr 9.

Center of Integrative Research, The Field Museum, Chicago, Illinois, United States of America.

Parahupehsuchus longus is a new species of marine reptile from the Lower Triassic of Yuan'an County, Hubei Province, China. It is unique among vertebrates for having a body wall that is completely surrounded by a bony tube, about 50 cm long and 6.5 cm deep, comprising overlapping ribs and gastralia. This tube and bony ossicles on the back are best interpreted as anti-predatory features, suggesting that there was predation pressure upon marine tetrapods in the Early Triassic. There is at least one sauropterygian that is sufficiently large to feed on Parahupehsuchus in the Nanzhang-Yuan'an fauna, together with six more species of potential prey marine reptiles with various degrees of body protection. Modern predators of marine tetrapods belong to the highest trophic levels in the marine ecosystem but such predators did not always exist through geologic time. The indication of marine-tetrapod feeding in the Nanzhang-Yuan'an fauna suggests that such a trophic level emerged for the first time in the Early Triassic. The recovery from the end-Permian extinction probably proceeded faster than traditionally thought for marine predators. Parahupehsuchus has superficially turtle-like features, namely expanded ribs without intercostal space, very short transverse processes, and a dorsal outgrowth from the neural spine. However, these features are structurally different from their turtle counterparts. Phylogeny suggests that they are convergent with the condition in turtles, which has a fundamentally different body plan that involves the folding of the body wall. Expanded ribs without intercostal space evolved at least twice and probably even more among reptiles.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0094396PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3981804PMC
June 2015

Terrestrial origin of viviparity in mesozoic marine reptiles indicated by early triassic embryonic fossils.

PLoS One 2014 12;9(2):e88640. Epub 2014 Feb 12.

Department of Research, Anhui Geological Museum, Hefei, Anhui Province, People's Republic of China.

Viviparity in Mesozoic marine reptiles has traditionally been considered an aquatic adaptation. We report a new fossil specimen that strongly contradicts this traditional interpretation. The new specimen contains the oldest fossil embryos of Mesozoic marine reptile that are about 10 million years older than previous such records. The fossil belongs to Chaohusaurus (Reptilia, Ichthyopterygia), which is the oldest of Mesozoic marine reptiles (ca. 248 million years ago, Early Triassic). This exceptional specimen captures an articulated embryo in birth position, with its skull just emerged from the maternal pelvis. Its headfirst birth posture, which is unlikely to be a breech condition, strongly indicates a terrestrial origin of viviparity, in contrast to the traditional view. The tail-first birth posture in derived ichthyopterygians, convergent with the conditions in whales and sea cows, therefore is a secondary feature. The unequivocally marine origin of viviparity is so far not known among amniotes, a subset of vertebrate animals comprising mammals and reptiles, including birds. Therefore, obligate marine amniotes appear to have evolved almost exclusively from viviparous land ancestors. Viviparous land reptiles most likely appeared much earlier than currently thought, at least as early as the recovery phase from the end-Permian mass extinction.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0088640PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3922983PMC
January 2015

Absence of suction feeding ichthyosaurs and its implications for triassic mesopelagic paleoecology.

PLoS One 2013 11;8(12):e66075. Epub 2013 Dec 11.

Steinmann Institute, Division of Palaeontology, University of Bonn, Bonn, Germany.

Mesozoic marine reptiles and modern marine mammals are often considered ecological analogs, but the extent of their similarity is largely unknown. Particularly important is the presence/absence of deep-diving suction feeders among Mesozoic marine reptiles because this would indicate the establishment of mesopelagic cephalopod and fish communities in the Mesozoic. A recent study suggested that diverse suction feeders, resembling the extant beaked whales, evolved among ichthyosaurs in the Triassic. However, this hypothesis has not been tested quantitatively. We examined four osteological features of jawed vertebrates that are closely linked to the mechanism of suction feeding, namely hyoid corpus ossification/calcification, hyobranchial apparatus robustness, mandibular bluntness, and mandibular pressure concentration index. Measurements were taken from 18 species of Triassic and Early Jurassic ichthyosaurs, including the presumed suction feeders. Statistical comparisons with extant sharks and marine mammals of known diets suggest that ichthyosaurian hyobranchial bones are significantly more slender than in suction-feeding sharks or cetaceans but similar to those of ram-feeding sharks. Most importantly, an ossified hyoid corpus to which hyoid retractor muscles attach is unknown in all but one ichthyosaur, whereas a strong integration of the ossified corpus and cornua of the hyobranchial apparatus has been identified in the literature as an important feature of suction feeders. Also, ichthyosaurian mandibles do not narrow rapidly to allow high suction pressure concentration within the oral cavity, unlike in beaked whales or sperm whales. In conclusion, it is most likely that Triassic and Early Jurassic ichthyosaurs were 'ram-feeders', without any beaked-whale-like suction feeder among them. When combined with the inferred inability for dim-light vision in relevant Triassic ichthyosaurs, the fossil record of ichthyosaurs does not suggest the establishment of modern-style mesopelagic animal communities in the Triassic. This new interpretation matches the fossil record of coleoids, which indicates the absence of soft-bodied deepwater species in the Triassic.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0066075PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3859474PMC
September 2014

Potential enhanced ability of giant squid to detect sperm whales is an exaptation tied to their large body size.

BMC Evol Biol 2013 Oct 15;13:226. Epub 2013 Oct 15.

W,M, Keck Science Department, Claremont McKenna College, Pitzer College, and Scripps College, Claremont, CA 91711, USA.

It has been hypothesized that sperm whale predation is the driver of eye size evolution in giant squid. Given that the eyes of giant squid have the size expected for a squid this big, it is likely that any enhanced ability of giant squid to detect whales is an exaptation tied to their body size. Future studies should target the mechanism behind the evolution of large body size, not eye size. Reconstructions of the evolutionary history of selective regime, eye size, optical performance, and body size will improve the understanding of the evolution of large eyes in large ocean animals.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1186/1471-2148-13-226DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3852725PMC
October 2013

Allometry indicates giant eyes of giant squid are not exceptional.

BMC Evol Biol 2013 Feb 18;13:45. Epub 2013 Feb 18.

Department of Evolution and Ecology, University of California, Davis, CA 95616, USA.

Background: The eyes of giant and colossal squid are among the largest eyes in the history of life. It was recently proposed that sperm whale predation is the main driver of eye size evolution in giant squid, on the basis of an optical model that suggested optimal performance in detecting large luminous visual targets such as whales in the deep sea. However, it is poorly understood how the eye size of giant and colossal squid compares to that of other aquatic organisms when scaling effects are considered.

Results: We performed a large-scale comparative study that included 87 squid species and 237 species of acanthomorph fish. While squid have larger eyes than most acanthomorphs, a comparison of relative eye size among squid suggests that giant and colossal squid do not have unusually large eyes. After revising constants used in a previous model we found that large eyes perform equally well in detecting point targets and large luminous targets in the deep sea.

Conclusions: The eyes of giant and colossal squid do not appear exceptionally large when allometric effects are considered. It is probable that the giant eyes of giant squid result from a phylogenetically conserved developmental pattern manifested in very large animals. Whatever the cause of large eyes, they appear to have several advantages for vision in the reduced light of the deep mesopelagic zone.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1186/1471-2148-13-45DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3661360PMC
February 2013

Phylogenetic versus functional signals in the evolution of form-function relationships in terrestrial vision.

Evolution 2011 Aug 14;65(8):2245-57. Epub 2011 Apr 14.

Department of Geology, University of California, Davis, California 95616, USA.

Phylogeny is deeply pertinent to evolutionary studies. Traits that perform a body function are expected to be strongly influenced by physical "requirements" of the function. We investigated if such traits exhibit phylogenetic signals, and, if so, how phylogenetic noises bias quantification of form-function relationships. A form-function system that is strongly influenced by physics, namely the relationship between eye morphology and visual optics in amniotes, was used. We quantified the correlation between form (i.e., eye morphology) and function (i.e., ocular optics) while varying the level of phylogenetic bias removal through adjusting Pagel's λ. Ocular soft-tissue dimensions exhibited the highest correlation with ocular optics when 1% of phylogenetic bias expected from Brownian motion was removed (i.e., λ= 0.01); the value for hard-tissue data were 8%. A small degree of phylogenetic bias therefore exists in morphology despite of the stringent functional constraints. We also devised a phylogenetically informed discriminant analysis and recorded the effects of phylogenetic bias on this method using the same data. Use of proper λ values during phylogenetic bias removal improved misidentification rates in resulting classifications when prior probabilities were assumed to be equal. Even a small degree of phylogenetic bias affected the classification resulting from phylogenetically informed discriminant analysis.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/j.1558-5646.2011.01271.xDOI Listing
August 2011

Nocturnality in dinosaurs inferred from scleral ring and orbit morphology.

Science 2011 May 14;332(6030):705-8. Epub 2011 Apr 14.

Department of Evolution and Ecology, University of California, Davis, CA 95616, USA.

Variation in daily activity patterns facilitates temporal partitioning of habitat and resources among species. Knowledge of temporal niche partitioning in paleobiological systems has been limited by the difficulty of obtaining reliable information about activity patterns from fossils. On the basis of an analysis of scleral ring and orbit morphology in 33 archosaurs, including dinosaurs and pterosaurs, we show that the eyes of Mesozoic archosaurs were adapted to all major types of diel activity (that is, nocturnal, diurnal, and cathemeral) and provide concrete evidence of temporal niche partitioning in the Mesozoic. Similar to extant amniotes, flyers were predominantly diurnal; terrestrial predators, at least partially, nocturnal; and large herbivores, cathemeral. These similarities suggest that ecology drives the evolution of diel activity patterns.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1126/science.1200043DOI Listing
May 2011

Paleontology. Warm-blooded "sea dragons"?

Authors:
Ryosuke Motani

Science 2010 Jun;328(5984):1361-2

Department of Geology, University of California, Davis, CA 95616, USA.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1126/science.1191409DOI Listing
June 2010