The ESCONI January 2021 Paleontology Meeting will be held on January 16th, 2021 at 7:30 PM via Zoom. The topic is "Giant Heteromorph Ammonites" by Professor Linda Ivany of Syracuse University. Professor Ivany wrote a paper called "Growth Rate and Ecology of the Giant Heteromorph Ammonite Diplomoceras maximum Using Stable Isotopes of Accretionary Shell Carbonate". It was presented at the 51st Annual Meeting (2016) of the Geological Society of America.
Abstract
Diplomoceras maximum is a large, hamitocone heteromorph ammonite with a shell that resembles a giant paperclip. A 1.5 meter long specimen representing more than 3 meters of linear shell growth from the late Cretaceous Lopez de Bertodano Formation of Seymour Island, Antarctica , now resides at the Paleontological Research Institution (PRI) in Ithaca, NY. Its growth rate and ecology have been the subject of much discussion but are completely unknown. Stable carbon and oxygen isotope analysis of serially sampled shell material can provide insight into the growth and habitat of these peculiar cephalopods. A roughly half-meter section of shell containing a hook and both adjoining portions of shafts, with aperture diameter ~15 cm, was sampled at a resolution of 5 samples per sculptural rib on the shell (total of 145 analyses). 5180 values vary between +1.9 to -1 .7%0, roughly the same range expressed by co-occurring benthic mollusks. A 15-point moving average defines a broad sinusoid that likely reflects ~1 .5 years of shell growth. If so, and if accretion were constant, the PRI animal would have been about 9 years old at death. Superimposed on this sinusoid is regular variation of up to 2%o that corresponds to sculptural ribs and covaries with o13C, suggesting the potential for disequilibrium effects during precipitation of ribs or, potentially, repeated vertical migrations through the water column. Carbon isotope values overlap those of typical benthic mollusks and other ammonites, but also include extremely negative values (+1.7 to -30%0). Values are low between ribs and higher on them; regular swings to low values become significantly more extreme in the hook than they are in the shafts. If related to disequilibrium and/or incorporation of metabolic CO2, this suggests more rapid growth in the hook section. Exceedingly negative i5 13C values may also reflect precipitation in the presence of methane, as suggested in the literature by unusual carbonate precipitates, chemosymbiotic cold-seep bivalve taxa , and very low o13C values of cemented burrow fills. Taken together, our data suggest a pelagic habit near the bottom, with a vertically oriented shell, closely associated with cold methane seeps. Shell growth is fast, consistent with living coleoids, and large individuals are likely less than 10 years old at death.
Recommended Citation
Artruc, Emily G., "Growth Rate and Ecology of the Giant Heteromorph Ammonite Diplomoceras maximum Using Stable Isotopes of Accretionary Shell Carbonate" (2016). Honors Theses. 112. https://digitalcommons.esf.edu/honors/112
That study was the subject of an IFLScience post back in November 2020, where they described it as a paperclip shaped animal.
Diplomoceras maximum from the Cretaceous of Seymour Island, Antarctica. Image by Jonathan R. Hendricks for the Digital Atlas of Ancient Life and the Paleontological Research Institution.
Marine species include some of the most hydrodynamically shaped creatures on Earth, which figures when you consider Darwin’s theory of natural selection likely favored animals that were good at chasing after or escaping prey/predators in the water. It’s perhaps then difficult to imagine how an animal shaped like a giant paperclip came to be but that’s exactly what was swimming around in the ocean in the late Cretaceous.
Diplomoceras maximum, a squid-like creature with a spiral calcified shell à la Microsoft's Clippy, lived around 68 million years ago. It was about 1.5-meters (5 feet) in length and was a member of a class of tentacled cephalopods commonly known as ammonites. While much remains a mystery about these strangely shaped sea creatures, new research announced at an online meeting of the Geological Society of America has uncovered new evidence that they had a very long life expectancy.
Linda Ivany at Syracuse University, New York, and colleague Emily Artruc were investigating chemical signatures in specimens of D. maximum when they made the discovery. Testing samples of a fossil, they focused on the carbon and oxygen isotopes along a 50-centimeter (almost 20-inch) section of shell, which revealed a repeating pattern in its isotopic signatures. The researchers interpret this as a translation of the annual release of methane from the seafloor, which is expelled by microbes that break down organic matter.
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