Friday, November 10, 2017

Ammonoid Family Reunions

Two family reunions occurred in the distant past, the Prionitids and the Cardioceratids, this is a short review of those events.  The thing that draws attention to these two reunions is that members of the two families gathered in abundance and almost to the mutual exclusion of other families.  Both are recorded in rocks representing a relatively short time-span, a single biozone, the smallest standard unit used in biostratigraphy, representing a few hundred thousand years more or less.

PRIONITIDAE Hyatt, 1900:



Prionitids

About 251mya the Family Prionitidae met in what is now the western USA.  This event took place all over the world (? Tethys and northern Panthalassa), but for this report I will stick to the event and those attending in the western US.  This Family started with the Genus Meekoceras in the Early Smithian and culminated with the family reunion in the Late Smithian with at least 6 species in 4 genera with a few in open nomenclature.

·         Anasibirites Mojsisovics, 1896                     2 species
·         Hemiprionites Spath, 1929                            2 species
·         Wasatchites Mathews, 1929                          1 species
·         Arctoprionites Spath, 1930                            1 species

With a few Xenoceltitids and Hedenstroemiids.  (See Brayard et al. 2013, Jattiot et al. 2017, Mathews 1929, Smith 1932, for composition of the fauna and Jattiot et al. 2015 for a revision of Anasibirites) Recorded in the Thaynes Group, UAZ5 of Jattiot et al. 2017
Prionitid localities (from Brayard et al 2013)

CARDIOCERATINAE Siemiradzki, 1891:



Cardioceratids

About 162mya the Subfamily Cardioceratinae gathered in the Sundance Sea that covered much of Montana and Wyoming along with parts of Utah, Colorado, Idaho, and South Dakota.  This reunion started with Quenstedtoceras and Pavloviceras coming in from the north in Montana, and closed with 18 species in 4 genera and 3 subgenera. 

·             Cardioceras Neumayr & Uhlig, 1881         
o   Scarburgiceras Buckman, 1924    6 species
o   Cardioceras Buckman, 1923         1 species
o   Goliathiceras Buckman, 1919       2 species
·             Scoticardioceras Buckman, 1925                     2 species
·            Vertebriceras Buckman, 1920                          4 species
·            Cawtoniceras Buckman, 1923                         3 species

With rare Perisphinctids.  (see Imlay 1982, and Reeside 1919 for composition of the fauna, and Howarth 2017 for a revision of the Stephanoceratoidea)  This reunion is recorded in the cordatum Zone of the Swift Formation of Montana, the Sundance Formation of Wyoming, Montana, and South Dakota, and the Stump Formation of Utah, Idaho, and Colorado. 
Cardioceratid localities (from Imlay 1982)



Localities for the reunions in the western US are shown, but the events were probably global.


References:

Brayard, A., Bylund, K. G., Jenks, J., Stephen, D. A., Olivier, N., Escarguel, G., Fara, E. & Vennin, E., 2013, Smithian ammonoid faunas from Utah: implications for Early Triassic biostratigraphy, correlations and basinal paleogeography. Swiss Journal of Paleontology 132:141-219

Howarth, Michael K., 2017, Part L, Revised, Volume 3B, Chapter 6: Systematic descriptions of the Stephanoceratoidea and Spiroceratoidea. Treatise Online 84:1–101, 66 fig.

Imlay, R. W., 1982, Jurassic (Oxfordian and Late Callovian) Ammonites from the Western Interior Region of the United States, U.S.G.S. Professional Paper 1232, 44 p., 26 pls.

Jattiot, R., Bucher, H., Brayard, A., Monnet, C., Jenks, J. F. & Hautmann, M., 2015, Revision of the genus Anasibirites Mojsisovics (Ammonoidea): an iconic and cosmopolitan taxon of the late Smithian (Early Triassic) extinction. Papers in Palaeontology 2 (1):155 –188.

Jattiot, R., Bucher, H., Brayard, A., Brosse, M., Jenks, J.F., Bylund, K.G., 2017, Smithian ammonoid faunas from northeastern Nevada: implications for Early Triassic biostratigraphy and correlation within the western USA basin. Palaeontographica A (Paleozoology, Stratigraphy), doi: 10.1127/pala/2017/0070.

Mathews, Asa A. L., 1929, The Lower Triassic Cephalopod Fauna of the Fort Douglas Area, Utah, Walker Museum Memoirs Vol.1 No.1 University of Chicago Press, 46 p., 11 pls.

Reeside, J. B., Jr., 1919, Some American Jurassic Ammonites of the Genera Quenstedticeras, Cardioceras and Amoeboceras, Family Cardioceratidae, U.S.G.S. Professional Paper 118, 64 p., 24 pls.

Smith, J. P., 1932, Lower Triassic Ammonoids of North America, U.S.G.S. Professional Paper 167,199 p., 81 pls. 

Thursday, July 20, 2017

Fish near the Early Triassic Equator!



Romano, C., Jenks, J., Jattiot, R., Scheyer, T., Bylund, K., & Bucher, H. 2017. Marine Early Triassic Actinopterygii from Elko County (Nevada, USA): Implications for the Smithian equatorial vertebrate eclipse. Journal of Paleontology, 1-22. doi:10.1017/jpa.2017.36

Abstract

The Early Triassic vertebrate record from low paleolatitudes is spotty, which led to the notion of an ‘equatorial vertebrate eclipse’ during the Smithian. Here we present articulated ray-finned fishes (Actinopterygii), collected from the marine Lower Triassic Thaynes Group at three new localities in Elko County (Nevada, USA), which were deposited within the equatorial zone. From the Smithian of the Winecup Ranch, we describe two partial skulls of the predatory actinopterygian Birgeria (Birgeriidae), attributed to B. americana new species and Birgeria sp. Birgeria americana n. sp. is distinguished from other species by a less reduced operculogular series. With an estimated total length of 1.72–1.85m, it is among the largest birgeriids. We confirm that Birgeria encompasses species with either two or three rows of teeth on the maxilla and dentary, and suggest that species with three well-developed rows are restricted to the Early Triassic. From the latest Smithian of Palomino Ridge, we present a three-dimensional, partial skull of the longirostrine predator Saurichthys (Saurichthyidae). This and other occurrences indicate that saurichthyids were common in the western USA basin. From the early late Spathian of Crittenden Springs, we describe a posterior body portion (Actinopterygii indet.). This find is important given the paucity of Spathian osteichthyan sites. We provide a summary of Early Triassic vertebrate occurrences in the United States, concluding that vertebrate fossils remain largely unstudied. The presence of predatory vertebrates in subequatorial latitudes during the Smithian confirms that Early Triassic trophic chains were not shortened and contradicts the ‘equatorial vertebrate eclipse’.

Friday, April 28, 2017

An Early Triassic Starfish from Utah

The Starfish shortly after mechanical decomposition of a limestone slab in the field near Torrey, Utah.
Superstesaster promissor gen. et sp. nov., a new starfish (Echinodermata, Asteroidea) from the Early Triassic of Utah, USA, filling a major gap in the phylogeny of asteroids

Friday, February 17, 2017

Unexpected Early Triassic marine ecosystem

Our latest work.

Artistic reconstruction of the Paris Biota. Artistic view of the early Spathian diversified and complex marine ecosystem of southeastern Idaho as revealed by the Paris Biota (with permission of Jorge Gonzalez).


A. Brayard, L. J. Krumenacker, J. P. Botting, J. F. Jenks, K. G. Bylund, E. Fara, E. Vennin,
N. Olivier, N. Goudemand, T. Saucède, S. Charbonnier, C. Romano, L. Doguzhaeva, B. Thuy,
M. Hautmann, D. A. Stephen, C. Thomazo, G. Escarguel, Unexpected Early Triassic marine
ecosystem and the rise of the Modern evolutionary fauna. Sci. Adv. 3, e1602159 (2017).

In the wake of the end-Permian mass extinction, the Early Triassic (~251.9 to 247 million years ago) is portrayed as an environmentally unstable interval characterized by several biotic crises and heavily depauperate marine benthic ecosystems. We describe a new fossil assemblage—the Paris Biota—from the earliest Spathian (middle Olenekian, ~250.6 million years ago) of the Bear Lake area, southeastern Idaho, USA. This highly diversified assemblage documents a remarkably complex marine ecosystem including at least seven phyla and 20 distinct metazoan orders, alongwith algae.Most unexpectedly, it combines early Paleozoic and middle Mesozoic taxa previously unknown from the Triassic strata, among which are primitive Cambrian-Ordovician leptomitid sponges (a 200–million year Lazarus taxon) and    gladius-bearing coleoid cephalopods, a poorly documented group before the Jurassic (~50 million years after the Early Triassic). Additionally, the crinoid and ophiuroid specimens show derived anatomical characters that were thought to have evolved much later. Unlike previous works that suggested a sluggish postcrisis recovery and a low diversity for the Early Triassic benthic organisms, the unexpected composition of this exceptional assemblage points toward an early and rapid post-Permian diversification for these clades. Overall, it illustrates a phylogenetically diverse, functionally complex, and trophically multileveled marine ecosystem, from primary producers up to top predators and potential scavengers. Hence, the Paris Biota highlights the key evolutionary position of Early Triassic fossil ecosystems in the transition from the Paleozoic to the Modern marine evolutionary fauna at the dawn of the Mesozoic era.

Saturday, December 31, 2016

Early Triassic Red Beds

Red beds between the lowest ammonoid bearing limestones and the basal conglomerates.  Commonly referred to the Black Dragon Formation (previously a member of the Moenkopi Fm.) or the Woodside Shale.  Exposed all over Utah, SE Idaho and SW Wyoming.

In the San Rafael Swell the lowest (and only) Triassic Limestone contains the Anasibirites Fauna, so the red beds below are older than Late Smithian age.

Lone Rock (right) above ridge of Sinbad Limestone with yellow and red Black Dragon Fm. below.  Foreground is Permian Black Box Dolomite.  On the road to the Black Box, northern San Rafael Swell.
In Weber Canyon the red beds overlie the Dinwoody Fm. and are below beds containing Meekoceras so these beds are either Dienerian or Early Smithian,

Woodside Shale with "Meekoceras Limestone" to the right.  In the canyon of the Weber River, just east of Morgan.

In the Confusion Range of western Utah.  A bed of limestone with large chert nodules and a chert pebble conglomerate separate the two sets of red beds shown (see this old post).  Kashmirites is found just above the calcarenites here and the brachiopod Xestotrema is found in limestones below the Permian red beds so these are probably Dienerian, or earliest Smithian.
Gerster Fm. redbeds (right), Thaynes red beds (center) and calcarenite (left).  Just north of Cowboy Pass in the northern Confusion Range.

Down south near Minersville the red beds are below limestones that contain the Early Smithian ammonoid Vercherites, so the beds here are probably Dienerian.

Moenkopi red beds below microbial limestones near Minersville.
  Farther south, around St. George, the limestones rest directly on the Permian and redbeds of this age are missing.



Monday, February 22, 2016

Early Triassic Thaynes Group Isotopes

C. Thomazo, E. Vennin, A. Brayard, I. Bour, O. Mathieu, S. Elmeknassi, N. Olivier, G. Escarguel, K. G. Bylund, J. Jenks, D. A. Stephen, E. Fara
In the aftermath of the end-Permian mass extinction, Early Triassic sediments record some of the largest Phanerozoic carbon isotopic excursions. Among them, a global Smithian-negative carbonate carbon isotope excursion has been identified, followed by an abrupt increase across the Smithian–Spathian boundary (SSB; ~250.8 Myr ago). This chemostratigraphic evolution is associated with palaeontological evidence that indicate a major collapse of terrestrial and marine ecosystems during the Late Smithian. It is commonly assumed that Smithian and Spathian isotopic variations are intimately linked to major perturbations in the exogenic carbon reservoir. We present paired carbon isotopes measurements from the Thaynes Group (Utah, USA) to evaluate the extent to which the Early Triassic isotopic perturbations reflect changes in the exogenic carbon cycle. The δ13Ccarb variations obtained here reproduce the known Smithian δ13Ccarb-negative excursion. However, the δ13C signal of the bulk organic matter is invariant across the SSB and variations in the δ34S signal of sedimentary sulphides are interpreted here to reflect the intensity of sediment remobilization. We argue that Middle to Late Smithian δ13Ccarb signal in the shallow marine environments of the Thaynes Group does not reflect secular evolution of the exogenic carbon cycle but rather physicochemical conditions at the sediment–water interface leading to authigenic carbonate formation during early diagenetic processes.