An official website of the United States government
Two recently discovered vertebrae collections from the Gabbs Formation in New York Canyon, Nevada, USA are among the first Late Triassic pistosauroid fossils reported from North America. Pistosauroidea were a group of long-necked secondarily aquatic reptiles that belong to the clade sauropterygia. Pistosauroids first evolved in the Triassic Period but later became an integral part of the Mesozoic marine ecosystem as the iconic plesiosaurs during the Jurassic and Cretaceous Periods. Our findings include a single small centrum from near the Triassic/Jurassic boundary and a block of similarly sized associated vertebrae from the early Rhaetian. The vertebrae exhibit a uniquely pistosauroid external morphology. The centrum is antero-posteriorly narrow but dorso-ventrally tall with gently amphicoelous faces. The histology revealed through micro-CT scanning, is also diagnostically pistosauroid. In sagittal cross-section, a denser layer of bone is visible along the faces of the centrum, while a unique V-shaped texture extending from the base of the neural canal is visible in transverse cross-section. The New York Canyon locality has long been renowned as a reference section for the Late Triassic and Triassic/Jurassic boundary but has only recently become a focus for vertebrate research. The Gabbs Formation at this locality is a relatively shallow marine environment and ranges from mid ramp to inner ramp. Vertebrate material has been noted throughout New York Canyon, nearly all of which has been identified as ichthyosaur, but these discoveries have shown the potential for the area as an important site for Late Triassic sauropterygians which have a poor record globally and were previously unknown from North America. Despite the limited nature of this new material, it is significant in providing evidence of the presence of pistosauroids in the Late Triassic of Eastern Panthalassa and helps fill in the exceptionally sparse history of sauropterygians in the Triassic of cordilleran North America.
more »
« less
Actinopterygian and chondrichthyan ichthyoliths reveal enhanced cosmopolitanism in Late Triassic marine ecosystems
The Late Triassic was a time of major evolutionary transition for marine vertebrates, with the emergence of important new clades and the expansion of durophagy. The diversity record of shallow marine vertebrates has been limited by poor preservation, and palaeogeographic ranges of common marine vertebrates is poorly constrained. Isolated ichthyoliths are an important resource for documenting taxonomic and ecological diversity in shallow marine environments and have a relatively high preservation potential. Here, we report the first Upper Triassic elasmobranchs, neopterygians and chondrosteans from Nevada, and contribute 14 new generic occurrences. The vertebrates represented in this survey include teeth of specialised durophages and piscivores, and a tentative reconstruction of the shallow marine ecosystem trophic niches based on dietary interpretations and known shelly macrofossils from this locality. The ichthyolith assemblage exhibited greater similarity to low-latitude Europe than high-latitude Canada localities, and the results of this study suggest that several taxa previously considered to be endemic to Europe may be cosmopolitan. The present study highlights the need for additional research in early Mesozoic ichthyoliths in order to establish diversity patterns, paleobiogeographic ranges, and timing of adaptive radiations among key groups of marine vertebrates in the Triassic Period in suboptimal preservation conditions.
more »
« less
- Award ID(s):
- 1654088
- PAR ID:
- 10430647
- Date Published:
- Journal Name:
- Historical Biology
- ISSN:
- 0891-2963
- Page Range / eLocation ID:
- 1 to 14
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Body sizes of marine amniotes span six orders of magnitude, yet the factors that governed the evolution of this diversity are largely unknown. High primary production of modern oceans is considered a prerequisite for the emergence of cetacean giants, but that condition cannot explain gigantism in Triassic ichthyosaurs. We describe the new giant ichthyosaur Cymbospondylus youngorum sp. nov. with a 2-meter-long skull from the Middle Triassic Fossil Hill Fauna of Nevada, USA, underscoring rapid size evolution despite the absence of many modern primary producers. Surprisingly, the Fossil Hill Fauna rivaled the composition of modern marine mammal faunas in terms of size range, and energy-flux models suggest that Middle Triassic marine food webs were able to support several large-bodied ichthyosaurs at high trophic levels, shortly after ichthyosaur origins.more » « less
-
Late Triassic marine macrofaunal assemblages of Aotearoa (New Zealand) exhibit remarkably low diversity, high endemism, and synchronous faunal turnover, and present a complicated array of bottom-water oxygenation indicators. Here we present the results of three bulk sampling campaigns representing marine communities across both the North and South Islands. Four biofacies are present, beginning with Halobia biofacies in the Oretian (lower Norian). The Otamitan (middle Norian) deposits are characterized by two successive biofacies, the Manticula/Hokonuia biofacies and the high diversity brachiopod biofacies of the upper Otamitan. The Warepan (upper Norian) deposits are recognized by the Monotis biofacies. The four biofacies persist across different regions, displaying nearly identical turnover events despite sedimentological variations. However, the bivalve and brachiopod genera exhibit differential shell bed-forming capabilities in different regions. Only the bivalve Monotis was observed in dense shell beds in all three regions sampled. In the northernmost region sampled (including Kiritehere Beach), shell beds are the primary presentation for fossils irrespective of the taxa. We present a comparison of the sedimentological characteristics between shell bed and non-shell bed deposits. Large and/or inflated bivalves are not uncommon, but essentially no burrowing organisms are present. These findings provide crucial insights into the dynamic nature of Triassic marine ecosystems, shedding light on the paleontological diversity patterns and ecological structure of high-latitude systems during hot-house intervals. The persistence of the same biofacies over a broad spatial extent emphasizes the strong influence of regional environmental conditions on the establishment and maintenance of marine communities.more » « less
-
The Junggar and Turpan basins of Xinjiang, northwest China, host a well-preserved terrestrial Permo-Triassic boundary sequence exposed on the flanks of the Bogda Mountains. During the Permo-Triassic, this region was located in mid-latitude northeast Pangaea (~45°N), making it an important comparison to the higher latitude record preserved in the South African Karoo Basin (~60°S). Broad similarities exist between the tetrapod records of both areas, such as the reported co-occurrence of Dicynodon-grade dicynodontoids and Lystrosaurus in the upper Permian and the high abundance of Lystrosaurus in the Lower Triassic. In the Bogda sections, the Permo-Triassic boundary falls within the upper Guodikeng Formation (= upper Wutonggou low order cycle), but several horizons have been proposed based on biostratigraphy, chemostratigraphy, and paleomagnetic data. A new Bayesian age model calibrated by multiple radiometric dates and tied to detailed litho- and cyclostratigraphic data offers new insight into the location of the Permo-Triassic boundary in Xinjiang and the opportunity to reconsider tetrapod occurrences in a highly resolved chronostratigraphic framework. We investigated the positions of new and historic tetrapod specimens relative to the revised Permo-Triassic boundary, including uncertainties about the locations of key historic specimens. The stratigraphic range of Dicynodon-grade dicynodontoids in Xinjiang is poorly constrained: most specimens, including the holotype of Jimusaria sinkianensis, cannot be precisely placed relative to the Permo-Triassic boundary. A new specimen of Turfanodon sp. for which we have reliable data occurs in the upper Permian. Despite their previous treatment as Permian in age, most Bogda chroniosuchians were collected in strata above the Permo- Triassic boundary and the therocephalian Dalongkoua fuae also may be Triassic. Some prior placements of the Permo- Triassic boundary in Xinjiang imply an upper Permian lowestoccurrence for Lystrosaurus, but all Lystrosaurus specimens that we can precisely locate fall above the Permo-Triassic boundary. The high abundance of Lystrosaurus in the Early Triassic of Xinjiang likely parallels an Early Triassic age for the interval of greatest Lystrosaurus abundance in the Karoo Basin, but additional research is needed to determine whether there was a single, globally synchronous time of highest Lystrosaurus abundance.more » « less
-
The fossil record of temnospondyl amphibians in the immediate wake of the Permo-Triassic mass extinction captures extensive taxic and ecological diversity, with most records known from high paleolatitudinal settings. In southern Pangea, the most substantial records come from South Africa and Australia, with a total of over 20 taxa presently recognized. Temnospondyls have also been known from correlated horizons in the lower Fremouw Formation of Antarctica since the late 1960s, but these records are mostly fragmentary, thereby limiting taxonomic resolution to the family level and subsequent biostratigraphic correlations and comparisons between high-latitude basins. Here we report substantial new material of the amphibamiform Micropholis stowi, a relic dissorophoid previously known only from the Katberg Formation (Lystrosaurus declivis Assemblage Zone) of South Africa, from the lower Fremouw Formation. The exceptional preservation of the recently recovered material permits not only confident taxonomic referral but also tentative association of several individuals to the broad-headed morph of the taxon. The recognition of M. stowi in Antarctica represents only the fourth geographic occurrence of a dissorophoid from southern Pangea and supports the hypothesis that high-latitude environments served as refugia for temnospondyls during the mass extinction. In the case of M. stowi, such refugia permitted the persistence of a predominantly Permo-Carboniferous clade, and the Antarctic records discussed here further hint at a poorly sampled cryptic distribution, both of amphibamiforms in southern Pangea and of small-bodied temnospondyls in early Mesozoic deposits.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1080/08912963.2022.2131405
