Triassic fossils found stratigraphically above 'Jurassic' eolianites necessitate the revision of lower Mesozoic stratigraphy in Picket Wire Canyonlands, south-central Colorado

Heckert, Andrew B.; Sload, Eric J.; Lucas, Spencer G.; Schumacher, Bruce A.

doi:10.2113/gsrocky.47.1.37

Cited by 3 publications

(9 citation statements)

References 21 publications

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“…The stratigraphic context of Trullidens purgatorii n. gen. n. sp. is in a poorly known sequence of Upper Triassic red beds originally mentioned by Stanton (1905), and recently re-discovered and re-interpreted (Schumacher, 2002; Heckert et al, 2012). The sequence is poorly known due to limited exposure and difficult accessibility.…”

Section: Introductionmentioning

confidence: 86%

“…1.2). A distinctive bed of vertebrate bone-bearing, lenticular, limestone-pebble conglomerate is present as the basal unit of the Upper Triassic sequence directly overlying the top of the Jelm Formation (Heckert et al, 2012). These rocks are exposed as cliffs and benches along the Purgatoire River and its side canyons.…”

Section: Geological Settingmentioning

confidence: 99%

“…The sequence is poorly known due to limited exposure and difficult accessibility. The strata represent a fluvio-lacustrine depositional setting and preserve a fossil biota typical of the Late Triassic of western North America (Heckert et al, 2012). The geographic isolation of these rocks from other Upper Triassic sequences in western North America renders exact stratigraphic and geochronologic correlation difficult, but limited biochronologic evidence suggests a middle Norian age.…”

Section: Introductionmentioning

confidence: 99%

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New sphenodontian (Reptilia: Lepidosauria) from a novel Late Triassic paleobiota in western North America sheds light on the earliest radiation of herbivorous lepidosaurs

et al. 2021

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Herbivory is a common ecological function among extant lepidosaurs, but little is known about the origin of this feeding strategy within Lepidosauria. Here we describe a sphenodontian (Lepidosauria) from the Late Triassic of western North America, Trullidens purgatorii n. gen. n. sp., that reveals new aspects of the earliest radiation of herbivorous lepidosaurs. This taxon is represented by an isolated lower jaw with robust structure bearing transversely widened dentition and extensive wear facets, suggesting a masticatory apparatus specialized for herbivory. An unusual ‘incisor-like’ tooth is present at the anterior end of the jaw; a unique feature among lepidosaurs, this tooth is convergent with the incisors of extant rodents and lagomorphs. Phylogenetic analyses support the placement of this taxon within opisthodontian sphenodontians, a group sharing derived cranio-dental morphologies specialized for herbivory. The new taxon was recovered in a recently discovered and unnamed series of Upper Triassic strata in southeastern Colorado, USA, exposed in Canyons incised by the Purgatoire River and its tributaries. These strata comprise a dominantly red-bed sequence of conglomerates, sandstones, and siltstones deposited in a fluvio-lacustrine setting, preserving a Late Triassic biota of invertebrate and vertebrate ichnofossils, plant macrofossils, bony fish, temnospondyl amphibians, and reptiles. We use aetosaur osteoderms as biostratigraphic links to the nearby Chinle Formation of Arizona, USA, establishing a middle Norian age for these strata. The presence of an opisthodontian from western equatorial Pangaea in the Norian Stage reveals a near-global radiation of this clade across the Pangaean supercontinent during the Late Triassic. UUID: http://zoobank.org/A737c03f-863a-488e-a860-5cc914548774.

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Section: Introductionmentioning

confidence: 86%

Section: Geological Settingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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New sphenodontian (Reptilia: Lepidosauria) from a novel Late Triassic paleobiota in western North America sheds light on the earliest radiation of herbivorous lepidosaurs

et al. 2021

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“…The base of the unit interfi ngers with the sandy coastal eolianite facies of the Lyons Sandstone (Butters, 1913;Tieje, 1923;Struby, 1957;Willhour, 1958;Pearson, 1972Pearson, , 1976Courtright, 1974;Deacon et al, 2014;Fig. 4), and it is capped by the coastal eolia nite facies of the Jelm Formation (Heaton, 1939;Pipiringos, 1968;Courtright, 1974;Picard, 1978;Heckert et al, 2012). In the upper half of the Lykins Formation, there is a prominent color change in the siliciclastics, where the unit changes from pale at its bottom to dark reddish-brown at its top, and the abundance and thickness of interbedded very fi ne sandstones increases.…”

Section: Sedimentology and Stratigraphymentioning

confidence: 99%

“…Revised age constraints for the Lykins Formation are based on data discussed in the text. The Jelm Formation age is based on Heckert et al (2012) and the mollusks in the upper Forelle Member are from Wiggs (1986).…”

Section: Acknowledgmentsmentioning

confidence: 99%

The Permian-Triassic transition in Colorado

Hagadorn

Whiteley

Lahey

et al. 2016

Unfolding the Geology of the West

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The Lykins Formation and its equivalents in Colorado are a stratigraphically poorly constrained suite of redbeds and intercalated stromatolitic carbonates, which is hypothesized to span the Permian-Triassic boundary. Herein we present a preliminary detrital zircon geochronology, new fossil occurrences, and δ 13 C chemostratigraphy for exposures along the Front Range and in southeastern Colorado, to refi ne understanding of the unit's age and depositional history. Detrital zircons from the uppermost Lykins Formation and an overlying eolianite consist of a complex and highly diverse primary and multi-cycle grain population transported from Laurentian and Gondwanan terranes, potentially both by wind and water. Youngest concordant zircons do not rule out deposition of the uppermost Lykins Formation during a portion of Early Triassic time. Conodonts from the lower Lykins Formation require Middle Permian (Guadalupian) deposition. Conodont alteration indices of 1 indicate the unit has a shallow burial history and is amenable to paleomagnetic inquiry. Conodonts, together with other vertebrate, invertebrate, microfossil, and trace fossils, suggest a very shallow to emergent marine origin for the unit's most substantial carbonates, and hint at a marine origin for the unit's intercalated gypsum-anhydrite members. Chemostratigraphy corroborates fi eld evidence of emergence and karst development capping certain units, like the Forelle Limestone Member of the Lykins Formation, where potential sequence boundaries appear to be punctuated by a short-lived meteoric signature. Results presented here are a progress report of ongoing work in these successions. This fi eld trip consists of a brief tour through exposures of the Lykins Formation, in which we will examine well-known localities as well as view new ones for which we seek insights.

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North America’s largest assemblage of Late Jurassic dinosaur trackways, a new look at the Purgatoire Valley dinosaur tracksite (Dinosaur Lake), Morrison Formation, southeastern Colorado, United States

Schumacher

Lockley

2022

Historical Biology

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Triassic fossils found stratigraphically above 'Jurassic' eolianites necessitate the revision of lower Mesozoic stratigraphy in Picket Wire Canyonlands, south-central Colorado

Cited by 3 publications

References 21 publications

New sphenodontian (Reptilia: Lepidosauria) from a novel Late Triassic paleobiota in western North America sheds light on the earliest radiation of herbivorous lepidosaurs

New sphenodontian (Reptilia: Lepidosauria) from a novel Late Triassic paleobiota in western North America sheds light on the earliest radiation of herbivorous lepidosaurs

The Permian-Triassic transition in Colorado

North America’s largest assemblage of Late Jurassic dinosaur trackways, a new look at the Purgatoire Valley dinosaur tracksite (Dinosaur Lake), Morrison Formation, southeastern Colorado, United States

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