Researchers have identified tiny fossils from the Shuijingtuo Formation (Cambrian Stage 3) of South China that could transform our understanding of cephalopod evolution. The newly described species, Eoceras shaanxiense, provides the oldest known evidence of a primordial siphuncle, a crucial anatomical feature that enabled cephalopods to regulate buoyancy and eventually become some of the oceans’ most successful predators.

Measuring only a few millimetres in length, Eoceras shaanxiense possessed a straight (orthoconic) shell divided into a series of chambers. Researchers also identified a segmented tube running through these chambers. This structure is interpreted as an early form of the siphuncle seen in later cephalopods such as nautiloids and ammonites.

Eoceras shaanxiense life reconstruction. The earliest evidence of a siphuncle structure within a cephalopod. The siphuncle enables cephalopods to become active swimmers (nektonic) and helped establish a predatory habit through long-term regulation of the animal’s buoyancy. Picture credit: Dinghua Yang.

Picture credit: Dinghua Yang

The Significance of Eoceras shaanxiense

The siphuncle is one of the defining characteristics of the Cephalopoda. Cephalopods are members of the Mollusca phylum and include extant animals such as squid, octopi, nautiloids and cuttlefish.

CollectA Nautilus pompilius sometimes referred to as the “Emperor nautilus” because of its large size.  This is a model of an extant nautiloid.

The image (above) shows a replica of an extant cephalopod (Nautilus pompilius). This model is part of a series of invertebrate figures created by CollectA.

To view the CollectA model range: CollectA Invertebrate Models.

Extinct cephalopods include the extremely diverse ammonites and the belemnites which play important roles in the relative dating of rocks.  The siphuncle links the shell chambers. It allows gas and fluid to be regulated, enabling the animal to control its buoyancy. Combined with jet propulsion, this remarkable adaptation helped cephalopods leave the sea floor and adopt an active swimming lifestyle (nektonic). Until now, the evolutionary origin of this important feature had remained a mystery because of a substantial gap in the fossil record between molecular evidence and the earliest accepted cephalopod fossils. The discovery of Eoceras shaanxiense helps close that gap.

Magnified images showing Eoceras fossil material used in the study. Note scale bar equals 2 mm. The fossils are approximately 520 million years old. Picture credit: Song Zuchen and Jakob Vinther.

Picture credit: Song Zuchen and Jakob Vinther

Documenting an Early Stage in the Evolution of a Chambered Shell

The research team concluded that the fossil documents an early stage in the evolution of the chambered shell, known as the phragmocone. As the animal grew, it formed new chambers while maintaining a connection with older ones through the segmented tube. This evolutionary innovation laid the foundations for the extraordinary success of cephalopods over the next 500 million years.

Commenting on the discovery, Mike from Everything Dinosaur said:

“Even the smallest fossils can have an enormous scientific impact. Eoceras shaanxiense provides an exciting glimpse into how one of nature’s most sophisticated marine adaptations first evolved.”

This important fossil demonstrates that the evolutionary history of cephalopods began earlier than previously recognised. Furthermore, it provides valuable new evidence explaining how these iconic marine invertebrates developed the buoyancy-control system that helped them dominate ancient seas for hundreds of millions of years.

Everything Dinosaur acknowledges the assistance of one of the study’s authors in the compilation of this article.

The scientific paper: “Earliest siphuncle-bearing cephalopod from the early Cambrian” by Zuchen Song, Bing Pan, Junfeng Guo, Jakob Vinther, Guoxiang Li, Jian Han, Heyo Van Iten, Xiaofang Zhao, Xianzhi Pei, Jiaxin Peng, Yaqin Qiang, Boyao Zhang and Hanjie Wen published in the journal Nature.

A new species of duck-billed dinosaur has been named.  It is a lambeosaurine and it has been named Plesiolophus warnerensis.  The researchers, writing in the “Canadian Journal of Earth Sciences”, conclude that at present it cannot be excluded as a potential ancestor to the iconic Parasaurolophus.

The discovery of Plesiolophus warnerensis is helping palaeontologists to better understand the early evolution of some of the most recognisable duck-billed dinosaurs. Researchers have described this newly named hadrosaur from southern Alberta, and it could represent one of the earliest known members of the lineage that eventually gave rise to the famous crested dinosaur Parasaurolophus.

The fossils were excavated from the Oldman Formation (Campanian) of Alberta, Canada. Although lambeosaurine hadrosaurs are abundant in the younger Dinosaur Park Formation, they are much rarer in the underlying Oldman Formation. As a result, Plesiolophus warnerensis provides valuable new information about an important stage in hadrosaur evolution.

The partial skull roof and braincase of the newly described lambeosaurine Plesiolophus warnerensis. This holotype fossil is specimen number TMP 2016.023.0039. Picture credit: McFeeters et al.

Picture credit: McFeeters et al

The partial skull fossil was discovered by renowned fossil hunter Wendy Sloboda. Such is her reputation for finding fossils, Wendy has been invited to join field teams searching for dinosaur remains in Mongolia, Greenland, France and Argentina. She was honoured in 2015 with the naming of the centrosaurine Wendiceratops.

To read about the discovery and naming of Wendiceratops: Wendiceratops from Southern Alberta.

Part of the Skull Roof and Braincase

The fossil material consists of part of the skull roof and braincase from an adult animal. Despite being incomplete, the specimen preserves several distinctive anatomical features. These characteristics enabled the research team to identify it as a new genus and species. Furthermore, the skull exhibits features that firmly place Plesiolophus within the Parasaurolophini, the group that includes Parasaurolophus.

Interestingly, the skull also retains several ancestral features that had disappeared in later relatives. This unique combination of primitive and more advanced characteristics makes Plesiolophus warnerensis particularly significant. It provides a rare glimpse into an evolutionary transition that eventually led to the spectacular cranial crests seen in later lambeosaurine dinosaurs.

PNSO Wyatt the Parasaurolophus dinosaur model in lateral view, a stunning replica of a Late Cretaceous duck-billed dinosaur. Picture credit: Everything Dinosaur.

Picture credit: Everything Dinosaur

The image (above) shows a model of the iconic crested dinosaur Parasaurolophus. This Late Cretaceous, herbivorous dinosaur with its long head crest is one of the most recognisable of all the Dinosauria.  The Parasaurolophus model comes from the popular PNSO model range.

To view the extensive range of PNSO models and figures: PNSO Age of Dinosaurs Models.

Plesiolophus warnerensis

To investigate its evolutionary relationships, the scientists compared Plesiolophus warnerensis with eighty-seven other dinosaur species. Their phylogenetic analysis consistently recovered the new taxon as one of the earliest members of the North American Parasaurolophini lineage.

The researchers noted that this newly described hadrosaur does not possess many unique features found only in this species. Consequently, they cannot rule out the possibility that it was close to the ancestry of Parasaurolophus, fossils of which occur in the younger Dinosaur Park Formation. While the available evidence does not allow the researchers to identify it as a direct ancestor, the discovery highlights an important chapter in the evolution of these remarkable duck-billed dinosaurs.

Commenting on the research, Mike from Everything Dinosaur explained:

“Discoveries such as Plesiolophus warnerensis help fill important gaps in the fossil record. Every new fossil provides another piece of the evolutionary puzzle, allowing scientists to build a clearer picture of how iconic dinosaurs such as Parasaurolophus evolved over millions of years.”

The discovery of Plesiolophus warnerensis also provides new insights into dinosaur communities that lived in Laramidia around 77 million years ago. As additional fossils are found, palaeontologists will continue to refine their understanding of how lambeosaurine dinosaurs diversified and evolved during the Late Cretaceous.

Everything Dinosaur acknowledges the assistance of Dr Bradley McFeeters who supplied the image of the dinosaur braincase included in this article.

The scientific paper: “A new parasaurolophin dinosaur (Hadrosauridae: Lambeosaurinae) from the Oldman Formation of southern Alberta” by Bradley D. McFeeters, David C. Evans, Michael J. Ryan, and Hillary C. Maddin published in the Canadian Journal of Earth Sciences.

The multi-award-winning Everything Dinosaur website: Dinosaur and Prehistoric Animal Figures.