Synonymy of the ammonite genus Ponteixites Warren with Rhaeboceras Meek

Grier, James W.; Grier, Joyce C.; Larson, Neal L.; Petersen, Jack G.

doi:10.2113/gsrocky.42.2.123

Cited by 5 publications

(6 citation statements)

References 7 publications

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“…This area has been previously described by Bishop (, ), Clement (), Grier et al . (, ), Grier & Grier (), Walaszczyk et al . () and Landman et al .…”

Section: Geological Settingmentioning

confidence: 98%

Nautilid nurseries: hatchlings and juveniles of Eutrephoceras dekayi from the lower Maastrichtian (Upper Cretaceous) Pierre Shale of east‐central Montana

Landman

Grier

Cochran

et al. 2018

LET

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The nautilid Eutrephoceras dekayi (Morton 1834) is relatively abundant in the lower Maastrichtian (Upper Cretaceous) Pierre Shale of east-central Montana. We analysed the morphology, size frequency distribution, and isotope composition of a large collection of 220 well-preserved specimens including hatchlings, juveniles and adults. The newly hatched shell is approximately 14 mm in diameter with a body chamber one-third whorl in angular length terminating in the nepionic constriction. Internally, the embryonic shell contains five septa. Juveniles are abundant and comprise twothirds of the sample whereas sub-adults, defined by the incipient flattening of the venter, are rare. Adults comprise approximately one-third of the sample and average 100 mm in diameter. The co-occurrence of newly hatched shells, small juveniles and adults suggests that the eggs were laid in the same area in which the hatchlings developed. Based on the excellent preservation of the juveniles, we conclude that they did not float into the area after death, but lived in the region, implying that this area served as a nursery for young animals. The calculated temperatures of the embryonic shells are similar to those of the post-embryonic shells and generally range from 16 to 18°C. Upon hatching, the nautilids probably followed a demersal mode of life and lived in well-oxygenated water ≤50 m deep. An examination of lethal injuries (puncture holes) suggests that all ontogenetic stages were equally vulnerable to predation. The proximity of the site to the Sheridan Delta suggests that the specimens were smothered by sudden pulses of sediment transported into the area by major storms.

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“…This area has been previously described by Bishop (, ), Clement (), Grier et al . (, ), Grier & Grier (), Walaszczyk et al . () and Landman et al .…”

Section: Geological Settingmentioning

confidence: 98%

Nautilid nurseries: hatchlings and juveniles of Eutrephoceras dekayi from the lower Maastrichtian (Upper Cretaceous) Pierre Shale of east‐central Montana

Landman

Grier

Cochran

et al. 2018

LET

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“…1a). This area has been described previously by Bishop (1967Bishop ( , 1973, Clement (1986), Grier and Grier (1998), and Grier et al (1992Grier et al ( , 2007. At the time of deposition of the concretion, the shoreline of the Western Interior Seaway was approximately 80 km to the south along the margin of the Sheridan Delta (Reiskind 1975).…”

Section: Geologic Settingmentioning

confidence: 73%

3-D orientation and distribution of ammonites in a concretion from the Upper Cretaceous Pierre Shale of Montana

Landman

Grier²,

Grier

et al. 2015

Swiss J Palaeontol

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One of the most common modes of preservation of ammonites in the Upper Cretaceous US Western Interior is in concretions. We examine an accumulation of ammonites from a single concretion in the lower Maastrichtian Pierre Shale of eastern Montana. The concretion is an oblate spheroid 50 cm in length and 26 cm in diameter, with its long axis parallel to the substrate. It contains approximately 90 ammonite specimens representing three species of Hoploscaphites including adults and juveniles. The concretion also contains other fauna, primarily bivalves and gastropods. A total of 33 ammonites, mostly adults, are concentrated in a cluster that spans 71 % of the length of the concretion (called the ''sculpture''). 3-D measurements of the ammonites in the sculpture reveal that (1) the shells dip at all angles, with a significant trend toward more horizontal from west to east; (2) the shells dip with a highly significant bias toward the east, suggesting a current from that direction; and (3) a highly significant number of the shells that are non-vertical face with their left side up. Most of the shells show lethal damage as indicated by missing pieces of body chamber. After settling to the bottom, the shells may have piled up against each other, creating a sediment trap. Other organisms such as scavenging gastropods may have been attracted to the site to feed on the stranded ammonite carcasses. The chambers of the ammonite phragmocones and even some of the body chambers are empty, suggesting relatively rapid burial. Oxygen and carbon isotopic analyses of the ammonite shells reveal that they preserve their original isotopic signature. The values of d 13 C of the carbonate cement in the concretionary matrix are much lighter than those in the ammonite shells and imply that cementation of the concretion occurred in association with the decomposition of organic matter.

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“…(2010 b ), Ponteixites following Grier et al . (2007), and the subgenus Tovebirkelundites following Kennedy & Jagt (1998). In the absence of a fully integrated stratigraphic scheme for the subdivision and correlation of all basins, the division of the Maastrichtian into the five bins (early early, late early, early late, late late, and last 0.5 million years) is arbitrary.…”

Section: Heteromorphs Through Timementioning

confidence: 99%

“…Goolaerts (2010) concluded that the cause of the extinction of ammonoids must have been a catastrophic event affecting both heteromorph and monomorph diversity on a global scale, in colder and warmer waters, in shallow and deeper settings, and for a wide variety of taxa exhibiting different food and life strategies. The Chicxulub impact at the Cretaceous/Paleogene (K/Pg) boundary (66 Ma; Schulte et al, 2010) is currently regarded as the most probable trigger for Grier et al (2007), and the subgenus Tovebirkelundites following Kennedy & Jagt (1998). In the absence of a fully integrated stratigraphic scheme for the subdivision and correlation of all basins, the division of the Maastrichtian into the five bins (early early, late early, early late, late late, and last 0.5 million years) is arbitrary.…”

Section: Heteromorphs Through Timementioning

confidence: 99%

Recent advances in heteromorph ammonoid palaeobiology

et al. 2021

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Heteromorphs are ammonoids forming a conch with detached whorls (open coiling) or non‐planispiral coiling. Such aberrant forms appeared convergently four times within this extinct group of cephalopods. Since Wiedmann's seminal paper in this journal, the palaeobiology of heteromorphs has advanced substantially. Combining direct evidence from their fossil record, indirect insights from phylogenetic bracketing, and physical as well as virtual models, we reach an improved understanding of heteromorph ammonoid palaeobiology. Their anatomy, buoyancy, locomotion, predators, diet, palaeoecology, and extinction are discussed. Based on phylogenetic bracketing with nautiloids and coleoids, heteromorphs like other ammonoids had 10 arms, a well‐developed brain, lens eyes, a buccal mass with a radula and a smaller upper as well as a larger lower jaw, and ammonia in their soft tissue. Heteromorphs likely lacked arm suckers, hooks, tentacles, a hood, and an ink sac. All Cretaceous heteromorphs share an aptychus‐type lower jaw with a lamellar calcitic covering. Differences in radular tooth morphology and size in heteromorphs suggest a microphagous diet. Stomach contents of heteromorphs comprise planktic crustaceans, gastropods, and crinoids, suggesting a zooplanktic diet. Forms with a U‐shaped body chamber (ancylocone) are regarded as suspension feeders, whereas orthoconic forms additionally might have consumed benthic prey. Heteromorphs could achieve near‐neutral buoyancy regardless of conch shape or ontogeny. Orthoconic heteromorphs likely had a vertical orientation, whereas ancylocone heteromorphs had a near‐horizontal aperture pointing upwards. Heteromorphs with a U‐shaped body chamber are more stable hydrodynamically than modern Nautilus and were unable substantially to modify their orientation by active locomotion, i.e. they had no or limited access to benthic prey at adulthood. Pathologies reported for heteromorphs were likely inflicted by crustaceans, fish, marine reptiles, and other cephalopods. Pathologies on Ptychoceras corroborates an external shell and rejects the endocochleate hypothesis. Devonian, Triassic, and Jurassic heteromorphs had a preference for deep‐subtidal to offshore facies but are rare in shallow‐subtidal, slope, and bathyal facies. Early Cretaceous heteromorphs preferred deep‐subtidal to bathyal facies. Late Cretaceous heteromorphs are common in shallow‐subtidal to offshore facies. Oxygen isotope data suggest rapid growth and a demersal habitat for adult Discoscaphites and Baculites. A benthic embryonic stage, planktic hatchlings, and a habitat change after one whorl is proposed for Hoploscaphites. Carbon isotope data indicate that some Baculites lived throughout their lives at cold seeps. Adaptation to a planktic life habit potentially drove selection towards smaller hatchlings, implying high fecundity and an ecological role of the hatchlings as micro‐ and mesoplankton. The Chicxulub impact at the Cretaceous/Paleogene (K/Pg) boundary 66 million years ago is the likely trigger for the extinct...

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Synonymy of the ammonite genus Ponteixites Warren with Rhaeboceras Meek

Cited by 5 publications

References 7 publications

Nautilid nurseries: hatchlings and juveniles of Eutrephoceras dekayi from the lower Maastrichtian (Upper Cretaceous) Pierre Shale of east‐central Montana

Nautilid nurseries: hatchlings and juveniles of Eutrephoceras dekayi from the lower Maastrichtian (Upper Cretaceous) Pierre Shale of east‐central Montana

3-D orientation and distribution of ammonites in a concretion from the Upper Cretaceous Pierre Shale of Montana

Recent advances in heteromorph ammonoid palaeobiology

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