Getting unhooked: comment on the hypothesis that heteromorph ammonites were attached to kelp branches on the sea floor, as proposed by

Landman, Neil H.; Kruta, Isabelle; Denton, John S. S.; Cochran, J. Kirk

doi:10.1093/mollus/eyv067

Cited by 9 publications

(3 citation statements)

References 12 publications

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“…scaphitids) clung to macroalgae with their umbilical opening [see also Vašíček & Wiedmann (1994) for Leptoceratoidinae such as Karsteniceras ]. However, direct evidence for such associations has not been found yet, rendering this idea speculative (Landman et al ., 2016 a ). The fossil record of non‐calcified macroalgae is sparse; potential biomarkers like sterols may help to identify their presence.…”

Section: Ecological Interactionsmentioning

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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Section: Ecological Interactionsmentioning

confidence: 99%

Recent advances in heteromorph ammonoid palaeobiology

et al. 2021

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“…for breeding. Implying semelparity, these macroconchs would have stayed stationary until the end of their life, thus making their shells the ultimate shelter for the developing eggs (Arkhipkin, 2014(Arkhipkin, , 2016; but also see Landman et al, 2016).…”

Section: Taphonomic Modelmentioning

confidence: 99%

Evidence for semi-sessile early juvenile life history in Cretaceous ammonites

Stinnesbeck

Frey

Zell

2016

Palaeogeography, Palaeoclimatology, Palaeoecology

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“…Okamoto 1993; Kaplan 2002; Arkhipkin 2014; Landman et al . 2016; Peterman et al . 2020a, 2020b; Hoffmann et al .…”

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Evolutionary process of extremely twisted heteromorph ammonites from the Upper Cretaceous of Japan

Misaki,

Okamoto,

Maeda

2023

Papers in Palaeontology

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The heteromorph ammonite Pravitoceras sigmoidale with extremely twisted retroversal hook and its probable ancestors, Didymoceras awajiense and D. morozumii, occur mainly in the Upper Cretaceous Izumi and Sotoizumi groups in southwest Japan. Their morphological characteristics were investigated in this study. Morphotypes I–II were recognized in D. morozumii. Morphotypes III–V were recognized in D. awajiense. Morphotypes VI–VIII were recognized in P. sigmoidale. Moreover, all morphotypes were recognized in both the dextral and sinistral forms of these three species. Based on the morphological and stratigraphic relationships, it is considered that the evolutionary process of these species is divided into three steps: (1) shift from morphotypes I–II to III; (2) increase in variation from morphotypes III to III–V; and (3) shift from morphotypes III–V to VI–VIII. By comparing these morphotypes based on the ‘growing tube model’ belonging to the moving frame analysis, it is seen that there are no significant gaps of coiling patterns in the evolutionary processes of this lineage. Meanwhile, morphotypes III–V of D. awajiense have a larger morphological variation than morphotypes I–II of D. morozumii and morphotypes VI–VIII of P. sigmoidale. These results, and the radiometric ages from previous studies, suggest that D. awajiense, with considerable variation between ancestor and descendant species, existed in a short interval. It seems that P. sigmoidale occurred after the continuous but rapid and drastic morphological evolution from D. morozumii via D. awajiense.

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Getting unhooked: comment on the hypothesis that heteromorph ammonites were attached to kelp branches on the sea floor, as proposed by

Cited by 9 publications

References 12 publications

Recent advances in heteromorph ammonoid palaeobiology

Recent advances in heteromorph ammonoid palaeobiology

Evidence for semi-sessile early juvenile life history in Cretaceous ammonites

Evolutionary process of extremely twisted heteromorph ammonites from the Upper Cretaceous of Japan

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