Article Spotlight: Plectronoceratids (Cephalopoda) from the latest Cambrian at Black Mountain

by | Mar 19, 2024 | Article Spotlight

"Shedding light on the origin and early evolution of the earliest known cephalopod fossils to better understand their evolutionary history"

We describe Sinoeremoceras marywadeae sp. nov. from numerous, well-preserved specimens, allowing investigation of ontogenetic trajectories and intraspecific variability, which in turn enables improved interpretations of the three-dimensional siphuncle morphology. The material was collected by Mary Wade and colleagues during the 1970s and 1980s, from the lower Ninmaroo Formation at Black Mountain (Mount Unbunmaroo), Queensland, Australia. Despite the collecting effort, diverse notes and early incomplete drafts, Mary Wade never published this material before her death in 2005. The specimens provide novel insights into the three-dimensional morphology of the siphuncle based on abundant material, prompting a general revision of the order Plectronoceratida.

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In the Press

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For All Readers - AI Explainer

Unraveling the Mysteries of Ancient Cephalopods

What is the significance of the research on Plectronoceratids from the latest Cambrian?

This research delves into the earliest known cephalopod fossils, shedding light on the origin and early evolution of these mollusks, which is crucial for understanding their evolutionary history.

Where were the new specimens discovered, and why are they important?

Over 200 new specimens were found in the lower Ninmaroo Formation at Black Mountain, Queensland, Australia, collected decades ago by Mary Wade. These specimens are significant because they provide unprecedented insights into the three-dimensional morphology of the Plectronoceratid siphuncle.

What insights did the study reveal about the siphuncle morphology of Plectronoceratids?

The study uncovered complex three-dimensional structures of the siphuncle, including highly oblique segments, an elongated middorsal portion called the septal flap, and laterally expanded segments known as siphuncular bulbs. Previous misinterpretations were due to the reliance on longitudinal sections, which failed to capture the true complexity of the siphuncle.

How did the findings impact the taxonomy of Plectronoceratids?

The research led to a revision of the order Protactinoceratida and the families Protactinoceratidae and Balkoceratidae, which are now considered junior synonyms of Plectronoceratida and Plectronoceratidae, respectively. The number of valid genera was reduced from eighteen to three, clarifying the classification of these ancient cephalopods.

What are the broader implications of this study?

This study highlights the importance of considering three-dimensional morphology in fossil analysis and emphasizes the need for revisiting and revising taxonomy based on new insights. Additionally, it underscores the significance of the Black Mountain specimens in furthering our understanding of cephalopod evolution and the origin of the siphuncle.



Plectronoceratids (Cephalopoda) from the latest Cambrian at Black Mountain, Queensland, reveal complex three-dimensional siphuncle morphology, with major taxonomic implications

The Plectronoceratida includes the earliest known cephalopod fossils and is thus fundamental to a better understanding of the origin and early evolution of this group of molluscs. The bulk of described material comes from the late Cambrian Fengshan Formation in North China with isolated occurrences in South China, Laurentia, Kazakhstan and Siberia. Knowledge of their morphology and taxonomy is limited in that most specimens were only studied as longitudinal sections, which are prone to misinterpretations due to variations in the plane of section. We describe more than 200 new specimens, which exceeds the entire hitherto published record of plectronoceratids. 

Sinoeremoceras marywadeae sp. nov. from the lower Ninmaroo Formation, Unbunmaroo Member (BMT 1), Black Mountain, near Boulia, Queensland, Australia.



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