George D. Stanley

Evolution of the coral-zooxanthellae symbiosis during the Triassic: a geochemical approach

Scleractinian corals first appeared during Triassic time in tropical shallow water envi- ronments. Controversy surrounds the paleoecology of scleractinian corals of the Late Triassic. Were they like their living counterparts, capable of supporting reefs, or had they not yet coevolved the important association with zooxanthellae that facilitated reef growth and construction? Indirect evidence suggests that some Upper Triassic corals from the Tethys played important constructional roles as reef builders within tropical carbonate complexes of the Tethys. To evaluate this idea, we have employed a geochemical approach based on isotope fractionation to ascertain if Late Triassic corals once possessed zooxanthellae. We have determined evidence for the ancient presence of algal symbiosis in 13 species of Triassic scleratinians from reef complexes in Turkey and northern Italy. In contrast, two higher latitude Jurassic species used as a control group for isotope analysis, lacked isotopic indications of symbiosis. These findings, together with stratigraphic and paleoecologic criteria, support the contention that Late Triassic scleractinian corals inhabiting shallow-water carbonate complexes of the Tethys were predominantly zooxanthellate, like their living counterparts from present day reefs. We view the zooxanthellate condition in calcifying reef organisms as a necessary prerequisite for constructional reef development. Our results emphasize the power of stable isotope studies in helping to answer paleobiological questions.

Early history of scleractinian corals and its geological consequences

Conventional views have implied that scleractinian corals were hermatypic and thus were potentially reef building from the onset of their appearance in early Mesozoic time in shallow-shelf carbonate environments. However, for almost 25 m.y. they held rather subordinate positions and generally did not participate in extensive ecologic reef framework. Evidence from both North America and Europe demonstrates that Triassic corals had ecologic preferences quite different from those in the Cenozoic. A key step in the evolutionary success of these corals may have been the advent of a symbiotic association with algae. This association, believed to have developed at the end of the Triassic, could have been responsible for thrusting scleractinians into prominent positions as reef builders and may account for their dramatic radiation in Mesozoic time.

Giant alatoform bivalves in the Upper Triassic of western North America

ABSTRACT. Large, alatoform bivalves, Wallowaconcha raylenea gen. et sp. nov., from the Upper Triassic of north-eastern Oregon, are described and placed in a new family, Wallowaconchidae, within the Megalodontoidea, which also contains the families Megalodontidae and Dicerocardiidae (herein transferred). Major character innovations of wallowaconchids are the internal partitioning of wings and development of non-articulating thin vanes on the hingeplate. The wallowaconchid hinge, which changed during ontogeny, differs greatly from the hinge of other bivalves. Wallowaconchids probably evolved from a species of the megalodontid Triadomegalodon. Although wallowaconchids are homeomorphs of the alate Permian alatoconchid bivalves, hinge structure shows that these two groups are unrelated. Large wings on wallowaconchids were used for snowshoe support. They may have utilized elaborate vanes and wing chambers to culture microbial symbionts, either microalgae or bacteria. These bivalves are endemic to displaced island arc terranes in western North America, occurring in Yukon, Canada (Stikine terrane), Oregon, USA (Wallowa terrane), and Sonora, Mexico (Antimonio terrane). They occupied environmental niches similar to those of large megalodontid bivalves of Triassic tropical provinces.

Triassic corals and spongiomorphs from Hells Canyon, Wallowa Terrane, Oregon

Twenty-one species of corals and three species of spongiomorphs occur in a series of richly fossiliferous, molluscandominated beds with silicified bioclasts in the Upper Triassic Martin Bridge Limestone of Hells Canyon, Oregon. Two of these, Maeandrostylis grandiseptus and Recticostastraea wallowaensis are new species. Recticostastraea is designated as a new genus. The fauna is early Norian and occurs in the island arc Wallowa terrane, one of many tectonostratigraphic terranes in western North America. Like other examples, it appears to have developed independently of the North American craton and to have links with Wrangellia. The fossil corals and spongiomorphs are para-autochthonous, occurring in a series of tempestite beds. They are interpreted to have inhabited a shallow-water carbonate platform that developed around a tropical island arc following cessation of volcanic activity. The corals and spongiomorphs are associated with abundant gastropods and a diverse epifaunal suspension-feeding bivalve fauna. Relative to the corals, branching spongiomorphs, Spongiomorpha ramosa, are more abundant and occur with relatively common branching, sheet to plate-like, colonial corals. Solitary corals are relatively rare. The associated bedded limestone includes a variety of shallow-water microfacies but throughout the Hells Canyon sequence, reef structure is absent. Together, the 24 coral and spongiomorph taxa show mixed paleogeographic affinities with Upper Triassic faunas known only from alpine regions of the western Tethys (five species), the Pamir Mountains, U.S.S.R. (two species), and the island of Timor (one species). Five additional species are pan-Tethyan and exceptionally cosmopolitan, but 11 species (45.8%) occur only in displaced terranes. Of these, a significant component (six species) is endemic to the Wallowa terrane. At least four Hells Canyon taxa, previously thought endemic to North American terranes, have recently been reported from the high-latitude Koryak terrane of northeastern U.S.S.R., a displaced tropical volcanic terrane of the northwestern Pacific. For Triassic corals, this is the first example of a clear link between western Pacific and eastern Pacific terranes. Less similarity exists with the Wrangell Mountains, Alaska, where identical age lower Norian silicified corals and spongiomorphs are known.

Tiny Sea Anemone from the Lower Cambrian of China

Background Abundant fossils from the Ediacaran and Cambrian showing cnidarian grade grossly suggest that cnidarian diversification occurred earlier than that of other eumetazoans. However, fossils of possible soft-bodied polyps are scanty and modern corals are dated back only to the Middle Triassic, although molecular phylogenetic results support the idea that anthozoans represent the first major branch of the Cnidaria. Because of difficulties in taxonomic assignments owing to imperfect preservation of fossil cnidarian candidates, little is known about forms ancestral to those of living groups. Methods and Findings We have analyzed the soft-bodied polypoid microfossils Eolympia pediculata gen. et sp. nov. from the lowest Cambrian Kuanchuanpu Formation in southern China by scanning electron microscopy and computer-aided microtomography after isolating fossils from sedimentary rocks by acetic acid maceration. The fossils, about a half mm in body size, are preserved with 18 mesenteries including directives bilaterally arranged, 18 tentacles and a stalk-like pedicle. The pedicle suggests a sexual life cycle, while asexual reproduction by transverse fission also is inferred by circumferential grooves on the body column. Conclusions The features found in the present fossils fall within the morphological spectrum of modern Hexacorallia excluding Ceriantharia, and thus Eolympia pediculata could be a stem member for this group. The fossils also demonstrate that basic features characterizing modern hexacorallians such as bilateral symmetry and the reproductive system have deep roots in the Early Cambrian.

Middle Triassic coral growth bands and their implication for photosymbiosis

Abstract In living zooxanthellate corals, photosymbiosis explains increased metabolism and accelerated skeletal growth, accounting for the success of these corals in shallow-water tropical reefs. Mesozoic corals of the order Scleractinia appeared in the geologic record during the Middle Triassic, but it was not until the Late Triassic that these corals became prominent reef builders—a change hypothesized to coincide with the advent of photosymbiosis. There is considerable discussion, however, concerning algal symbiosis and the timing of their co-evolution with corals. Thus, the beginning of photosymbiosis in the earliest corals of the Middle Triassic has not been established, nor whether their paleoecology was similar to that of modern corals. Many massive colonial reef-building corals lay down thick, discrete bands in their skeletons that record annual growth. We discovered and illustrate here growth bands in Middle Triassic corals from central Nevada, in particular Ceriostella variabilis, whose skeletal structure and bands are well-preserved in Middle Triassic biostromes of central Nevada. To test the photosymbiosis hypothesis we studied colony growth forms in these fossil corals and performed a quantitative analysis of the bands, both in C. variabilis and in a morphologically similar living zooxanthellate reef coral, Montastraea faveolata. Results of these analyses revealed growth bands and colony shapes almost identical in both living and fossil corals. These findings suggest that photosymbiosis was present in Middle Triassic corals at a very early stage in their Mesozoic history. Scleractinians were also likely zooxanthellate from the onset of their Middle Triassic occurrence but for unexplained reasons were not as efficient as modern corals in building reefs.

Cambrian anemones with preserved soft tissue from the Chengjiang biota, China

Hou, X.-G., Stanley Jr, G.D., Zhao, J. & Ma, X.-Y. 2005 09 12: Cambrian anemones withpreserved soft tissue from the Chengjiang biota, China. Lethaia, Vol. 38, pp. 193–203.Oslo. ISSN 0024-1164.The group Cnidaria includes ‘jellyfish’, soft-bodied anemone and anemone-like formsand calcified corals. These diploblastic organisms have a fossil record extending back tothe earliest metazoans of the Neoproterozoic; however certain cnidarians of the subclassZoantharia, characterized by soft-bodied anemone-like forms, are absent or poorlyrepresented in the fossil record. Despite the paucity of fossils, it is thought that calcifi-cation by soft anemone-like animals was responsible for producing the skeleton thatallowed the preservation of the first corals. We report discovery of an abundant assem-blage of in situ soft-bodied polyps with tissues. They are preserved in exquisite detail andcome from the well-known Lower Cambrian Chengjiang biota of Yunnan, China. Thesoft-bodied polyps display a simple anatomy that is comparable to some extant anemonesof the order Actinaria. The new fossils are assigned to Archisaccophyllia kunmingensis n.gen. et n. sp. Their simple and conservative form suggests that these fossils may representsome kind of ancestral rootstock. The preserved life assemblage provides a uniquesnapshot of Lower Cambrian anemone life and provides clues for relationships withextant actiniarians as well as calcified corals. & Actiniaria, anemone, Chengjiang biota,China, Lower Cambrian, soft-bodied fossils.Xian-guang Hou (corresponding author) [xghou@ynu.edu.cn], Jie Zhao [biofeature@hotmail.com] and Xiao-ya Ma [littleya@vip.sina.com], Yunnan Key Laboratory forPalaeobiology, Yunnan University, Kunming 650091, China; George D. Stanley, Jr.[george.stanley@umontana.edu], Department of Geology, The University of Montana,Missoula, MT 59812, USA; 19th August 2004, revised 11th April 2005.

Middle Triassic cnidarians from the New Pass Range, central Nevada

We describe three scleractinian corals and one species of hydrozoan from the New Pass Range, central Nevada, which together constitute the oldest Triassic cnidarian assemblage from North America. They occur in carbonate rocks tentatively correlated with the Augusta Mountain Formation, Star Peak Group. At generic and higher levels, these cnidarians seem representative of early Mesozoic Tethyan faunas and carbonate lithofacies, but they indicate some endemism. Although the original aragonitic skeletons and microstructure are destroyed by recrystallization, the corals still yield important details allowing their correct taxonomic assignment. They contain the minitrabecular cerioid coral, Ceriostella variabilis new genus and species, the thick-trabecular, thamnasteroid coral Mesomorpha newpassensis new species, and an undeterminable cuifastreid coral tentatively assigned to Cuifastraea. The discovery of Mesomorpha marks the first occurrence of this genus outside the Jurassic and Cretaceous seas. Also discovered is a remarkably corallike hydrozoan, Cassianastraea reussi (Laube), already known from the Carnian stage of the western Tethys. This is the first occurrence of this species outside the western Tethys.

The Evolution of the Coral–Algal Symbiosis

The fossil record chronicles the rise, fall, and recovery of reefs. It is a sobering record because of the longevity of post-extinction global reef gaps and the length of time before reef recovery. Intervals when reefs are either entirely absent or greatly reduced range from 1×106 years to as much as 10×106 years in duration. The length of time for recovery has implications for the current environmental crisis. Put into the perspective of the current biotic marine crisis, the implications are bleak for the future evolution of reefs. Although evolution is not predictable, the derivation of meaningful estimates on diversity trends and rates of recovery following mass extinctions, are emerging from the fossil record. A study of the role of zooxanthellate photosymbiosis in the geologic past may provide new insights into both successes and failures on living coral reefs. The integration of biology and the fossil record offers potentials to better understand the current coral reef problems, including the bleaching phenomenon.

Middle Jurassic strata link Wallowa, Olds Ferry, and Izee terranes in the accreted Blue Mountains island arc, northeastern Oregon

Middle Jurassic strata atop the Wallowa terrane in northeastern Oregon link the Wallowa, Izee, and Olds Ferry terranes as related elements of a single long-lived and complex oceanic feature, the Blue Mountains island arc. Middle Jurassic strata in the Wallowa terrane include a dacitic ash-flow deposit and contain fossil corals and bivalves of North American affinity. Plant fossils in fluvial sandstones support a Jurassic age and indicate a seasonal temperate climate. Corals in a transgressive sequence traditionally overlying the fluvial units are of Bajocian age and are closely related to endemic varieties of the Western Interior embayment. They are unlike Middle Jurassic corals in other Cordilleran terranes; their presence suggests that the Blue Mountains island arc first approached the North American craton at high paleolatitudes in Middle Jurassic time. The authors consider the Bajocian marine strata and underlying fluvial volcaniclastic units to be a basin-margin equivalent of the Izee terrane, a largely Middle Jurassic (Bajocian) succession of basinal volcaniclastic and volcanic rocks known to overlie the Olds Ferry and Baker terranes.