Lars Schmitz

Nocturnality in Dinosaurs Inferred from Scleral Ring and Orbit Morphology

Comparison of eye structures between fossils and modern species suggests that Mesozoic archosaurs were active day and night. 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.

Nocturnality constrains morphological and functional diversity in the eyes of reef fishes

BackgroundAmbient light levels are often considered to drive the evolution of eye form and function. Diel activity pattern is the main mechanism controlling the visual environment of teleost reef fish, with day-active (diurnal) fish active in well-illuminated conditions, whereas night-active (nocturnal) fish cope with dim light. Physiological optics predicts several specific evolutionary responses to dim-light vision that should be reflected in visual performance features of the eye.ResultsWe analyzed a large comparative dataset on morphological traits of the eyes in 265 species of teleost reef fish in 43 different families. The eye morphology of nocturnal reef teleosts is characterized by a syndrome that indicates better light sensitivity, including large relative eye size, high optical ratio and large, rounded pupils. Improved dim-light image formation comes at the cost of reduced depth of focus and reduction of potential accommodative lens movement. Diurnal teleost reef fish, released from the stringent functional requirements of dim-light vision have much higher morphological and optical diversity than nocturnal species, with large ranges of optical ratio, depth of focus, and lens accommodation.ConclusionsPhysical characteristics of the environment are an important factor in the evolution and diversification of the vertebrate eye. Both teleost reef fish and terrestrial amniotes meet the functional requirements of dim-light vision with a similar evolutionary response of morphological and optical modifications. The trade-off between improved dim-light vision and reduced optical diversity may be a key factor in explaining the lower trophic diversity of nocturnal reef teleosts.

Nocturnality in synapsids predates the origin of mammals by over 100 million years.

Nocturnality is widespread among extant mammals and often considered the ancestral behavioural pattern for all mammals. However, mammals are nested within a larger clade, Synapsida, and non-mammalian synapsids comprise a rich phylogenetic, morphological and ecological diversity. Even though non-mammalian synapsids potentially could elucidate the early evolution of diel activity patterns and enrich the understanding of synapsid palaeobiology, data on their diel activity are currently unavailable. Using scleral ring and orbit dimensions, we demonstrate that nocturnal activity was not an innovation unique to mammals but a character that appeared much earlier in synapsid history, possibly several times independently. The 24 Carboniferous to Jurassic non-mammalian synapsid species in our sample featured eye morphologies consistent with all major diel activity patterns, with examples of nocturnality as old as the Late Carboniferous (ca 300 Ma). Carnivores such as Sphenacodon ferox and Dimetrodon milleri, but also the herbivorous cynodont Tritylodon longaevus were likely nocturnal, whereas most of the anomodont herbivores are reconstructed as diurnal. Recognizing the complexity of diel activity patterns in non-mammalian synapsids is an important step towards a more nuanced picture of the evolutionary history of behaviour in the synapsid clade.

First record of Placodontoidea (Reptilia, Sauropterygia, Placodontia) from the Eastern Tethys

DA-YONG JIANG, RYOSUKE MOTANI, WEI-CHENG HAO, OLIVIER RIEPPEL, YUAN-LIN SUN, LARS SCHMITZ, and ZUO-YU SUN Department of Geology and Geological Museum, Peking University, Beijing 100871, P. R. China, djiang@pku.edu.cn; Department of Geology, University of California, Davis, California 95616-8605, U.S.A; Department of Geology, The Field Museum, Chicago, Illinois 60605-2496, U.S.A., rieppel@fieldmuseum.org.

PHYLOGENETIC VERSUS FUNCTIONAL SIGNALS IN THE EVOLUTION OF FORM-FUNCTION RELATIONSHIPS IN TERRESTRIAL VISION

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 Pagels 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.

A NEW MIXOSAURID ICHTHYOSAUR FROM THE MIDDLE TRIASSIC OF CHINA

Abstract We describe the new ichthyosaur taxon Mixosaurus panxianensis, sp. nov., from the Middle Triassic of Guizhou Province, China. Diagnostic characters of the new species include a short posteroventral jugal process and the absence of external contact between jugal and quadratojugal. The morphologic description of the type specimens amends the knowledge of the postorbital region and the postcranium of the Mixosauridae. The holotype of Mixosaurus maotaiensis, which is very fragmentary and has no taxonomic value at the species level, is found to be undiagnostic, and hence the lately introduced, monospecific genus name for this species needs to be abandoned. Phylogenetic analysis strongly supports the monophyly of the family Mixosauridae. Furthermore, the analysis shows a bifurcation of the family into two sister groups, suggesting the presence of two genera, Mixosaurus and Phalarodon. Mixosaurus, characterized by a relatively short and wide humerus, includes M. panxianensis sp. nov., M. cornalianus, and M. kuhnschnyderi. Synapomorphies of Phalarodon, which contains P. fraasi, P. callawayi, and P. atavus, are a narial shelf and the absence of a maxillary dental groove.

Morphological differences between the eyeballs of nocturnal and diurnal amniotes revisited from optical perspectives of visual environments

Eyes are expected to be adapted to the physical characteristics of the visual environment, yet previous analyses failed to corroborate this observation. We demonstrate that nocturnal, crepuscular/cathemeral, and diurnal activity patterns occupy distinct areas in morphospace and are identified with high accuracies based on a discriminant analysis of visual performance features. Not only nocturnal and diurnal diel activity patterns are reflected in macroscopic morphology of the eyeball, but also the crepuscular/cathemeral patterns. The eyeball morphology of the latter was believed to be undistinguishable between diurnal and nocturnal types. We show that all three categories can be delineated with high accuracies.

Macropredatory ichthyosaur from the Middle Triassic and the origin of modern trophic networks

The biotic recovery from Earth’s most severe extinction event at the Permian-Triassic boundary largely reestablished the preextinction structure of marine trophic networks, with marine reptiles assuming the predator roles. However, the highest trophic level of todays marine ecosystems, i.e., macropredatory tetrapods that forage on prey of similar size to their own, was thus far lacking in the Paleozoic and early Mesozoic. Here we report a top-tier tetrapod predator, a very large (>8.6 m) ichthyosaur from the early Middle Triassic (244 Ma), of Nevada. This ichthyosaur had a massive skull and large labiolingually flattened teeth with two cutting edges indicative of a macropredatory feeding style. Its presence documents the rapid evolution of modern marine ecosystems in the Triassic where the same level of complexity as observed in today’s marine ecosystems is reached within 8 My after the Permian-Triassic mass extinction and within 4 My of the time reptiles first invaded the sea. This find also indicates that the biotic recovery in the marine realm may have occurred faster compared with terrestrial ecosystems, where the first apex predators may not have evolved before the Carnian.

Quantitative estimates of visual performance features in fossil birds

Eyeball structures such as the lens diameter (LD) and axial length are generally assumed to be highly correlated with optically meaningful parameters. However, these optical constraints on eyeball macroanatomy have never been tested explicitly. Tradeoffs between benefits of improved visual performance and cost of adaptation from an increase of tissue production predict that when eyeball size increases, optical parameters such as posterior nodal distance and maximum entrance pupil diameter should increase isometrically with eyeball axial length and LD, respectively. Here I show quantitatively that the interspecific allometry of the avian eye largely follows this predicted isometry. Additionally, I elaborate a method to estimate optically significant eyeball soft‐tissue dimensions from scleral ring and orbit morphology based on analyses of interspecific allometry in Aves. The stringent correlations between avian eyeball morphology and optical function render this system ideal for the analysis of form–function relationships and allow for an accurate estimate of optically significant eyeball soft‐tissue dimensions such as diameter, axial length, and LD in fossil species. J. Morphol. 2009.

A New Middle Triassic Eosauropterygian (Reptilia, Sauropterygia) from Southwestern China

Abstract A new eosauropterygian genus and species is described from the middle Anisian (Middle Triassic) of Panxian (Guizhou Province, southwestern China). The new taxon is characterized by an unique specialization of the jaws that form an elongate pointed rostrum furnished with numerous small, monocuspid and vertically oriented teeth with a basally expanded crown and pointed tip, which is quite unlike any other sauropterygian known. Other diagnostic characters include: frontals paired; parietal unpaired; pineal foramen located centrally in broad parietal skull table; two carpal ossification; ilium with distinct preacetabular process at the base of the dorsally extending iliac blade; pubis plate-like and of rounded contours; two tarsal ossifications. The curved and distally expanded humerus, the reversed topological relationship of the clavicle and scapula, and the presence of three sacral ribs indicate sauropterygian affinities of the new taxon, whereas the ‘butterfly-shaped’ or ‘cruciform’ facet for the neural arch on the dorsal centrum surface indicate its eosauropterygian status.