Early trilobites had stomachs, new fossil study finds Remarkable Chinese specimens contradict previous assumptions about trilobite digestive systems and evolution

his photo is of a specimen of the trilobite Palaeolenus lantenoisi from the Guanshan Biota in southern Yunnan Province, China. Rarely are internal organs preserved in fossils, but this specimen shows the digestive system preserved as reddish iron oxides. The digestive system is comprised of a crop (inflated region at top of specimen), lateral glands, and a central canal that runs along the length of the body; the iron oxides that extend beyond the fossil are the remains of gut contents that were extruded during preservation.

Credit: © F. Chen

Exceptionally preserved trilobite fossils from China, dating back to more than 500 million years ago, have revealed new insights into the extinct marine animal's digestive system. Published today in the journal PLOS ONE, the new study shows that at least two trilobite species evolved a stomach structure 20 million years earlier than previously thought.Trilobites are one of the first types of animals to show up in large numbers in the fossil record," said lead author Melanie Hopkins, an assistant curator in the Division of Paleontology at the American Museum of Natural History. "Their exoskeletons were heavy in minerals, and so they preserved really well. But like all fossils, it's very rare to see the preservation of soft tissues like organs or appendages in trilobites, and because of this, our knowledge of the trilobite digestive system comes from a small number of specimens. The new material in this study really expands our understanding."

Trilobites are a group of extinct marine arthropods -- distantly related to the horseshoe crab -- that lived for almost 300 million years. They were extremely diverse, with about 20,000 species, and their fossil exoskeletons can be found all around the world. Most of the 270 specimens analyzed in the new study were collected from a quarry in southern Kunming, China, during an excavation led by Hopkins' co-author, Zhifei Zhang, from Northwest University in Xi'an.

Previous research suggests that two body plans existed for trilobite digestive systems: a tube that runs down the length of the trilobite's body with lateral digestive glands that would have helped process the food; or an expanded stomach, called a "crop," leading into a simple tube with no lateral glands. Until now, only the first type had been reported from the oldest trilobites. Based on this, researchers had proposed that the evolution of the crop came later in trilobite evolutionary history and represented a distinct type of digestive system.

The Chinese trilobite fossils, about 20 percent of which have soft tissue preservation, are dated to the early Cambrian, about 514 million years ago. Contradictory to the previously proposed body plans, the researchers identified crops in two different species within this material. In addition, they found a single specimen that has both a crop and digestive glands -- suggesting that the evolution of trilobite digestive systems is more complex than originally proposed.

The study backs up an earlier announcement made by a separate research team, which found evidence for the unusual crop and gland pairing in a single juvenile trilobite specimen from Sweden from the late Cambrian. But the Chinese material presents the oldest example of this complex digestive system in a mature trilobite, wiping away doubts that the dual structures might just be part of the animal's early development.

"This is a very rigorous study based on multiple specimens, and it shows that we should start thinking about this aspect of trilobite biology and evolution in a different way," Hopkins said.

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Story Source:

Materials provided by American Museum of Natural History.Note: Content may be edited for style and length.

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Journal Reference:

1. Melanie J. Hopkins, Feiyang Chen, Shixue Hu, Zhifei Zhang.The oldest known digestive system consisting of both paired digestive glands and a crop from exceptionally preserved trilobites of the Guanshan Biota (Early Cambrian, China). PLOS ONE, 2017; 12 (9): e0184982 DOI:10.1371/journal.pone.0184982
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Did rapid sea-level rise drown fossil coral reefs around Hawaii?

This is a map showing the location of sample collection off of Kawaihae, Hawaii (blue sphere), and a slope profile (below) showing the backstepping younger and shallower terraces overlaying the targeted reef terrace 150m below sea level.

Credit: Bathymetry data from Monterey Bay Aquarium Research Institute, and figure by Kelsey Sanborn, University of Sydney

Scientists globally are investigating just how quickly sea-level rise can occur as a result of global warming and ice sheets melting.

Recent findings suggest that episodes of very rapid sea-level rise of about 20m in less than 500 years occurred in the last deglaciation, caused by periods of catastrophic ice-sheet collapse as Earth warmed after the last ice age about 20,000 years ago.

Lead author, PhD candidate at the University of Sydney, Kelsey Sanborn, has shown this sea-level rise event was associated with "drowning" or death of coral reefs in Hawaii.

The results are published in leading geosciences journalQuaternary Science Reviews.

The paper provides new evidence of a meltwater pulse (referred to as meltwater pulse 1-A), based on analysis of fossil coral reef samples from off the coast of Kawaihae, on the northwest of the Big Island of Hawaii.

Co-author Associate Professor Jody Webster, from the Geocoastal Research Group at the University of Sydney's School of Geosciences, said although this pulse was greater than current modelling predictions of sea-level rise over the next few hundred years, it provides an example of the risks rapid environmental change poses to our marine ecosystems.

"If we saw a sea-level rise in the future of a similar rate as this past event, it would likely devastate coral reefs and coastal systems," Associate Professor Webster said.

The fossil corals used in this study were collected by a team of technical rebreather scuba divers who dove down to 150 m below present sea level to access the fossil reef. At this depth, more than 130m deeper than where you could dive along their living shallow counterparts today, the divers recovered targeted shallow reef species that were alive over 14,700 years ago.

Lead author Ms Sanborn said this coral reef had been growing for thousands of years, during the initially gradual sea-level rise as the ice sheets of the last ice age began to melt.

"During the meltwater pulse, sea level rose more rapidly than the reef could grow, preventing the photosynthetic algae living within the corals from receiving enough sunlight. This caused the previously thriving fringing reef system to drown, and left it to be overgrown by deep-water algae and other marine life," she said.

Although uncertainty remains regarding how quickly coastal areas could be inundated around the world, understanding how these events occurred in the past are key to understanding the risks we face in the future.

"The fact that this meltwater pulse was large enough to drown a large, active Hawaiian reef system implies that extreme climate change and associated sea-level rise occurred quite rapidly," Ms Sanborn said.

This event is believed to have been brought about by catastrophic melting of the Greenland, and potentially also Antarctic, ice sheets.

"This may help us better predict the extent of future sea-level rise based on how vulnerable the Antarctic ice sheet is to collapse and melting," Ms Sanborn said.

The research was a collaborative effort between the University of Sydney, the University of Tokyo, the University of Florida, the University of Granada, the Monterey Bay Aquarium Research Institute, the University of Hawaii, and the Association for Marine Exploration.

Research Details

As part of the research, Ms Sanborn examined the evidence for reef drowning by identifying the coral reef species which grow within a specific depth range, and dating them using radiocarbon dating.

Taking into account the sinking of the island due to its volcanism, the relative-sea level history of Kawaihae was reconstructed.

The findings suggest that this reef was rapidly drowned by the combined effects of sinking of the island and global sea-level rise.

This is supported by other studies from around the world showing a rapid sea-level rise around 14,700 years ago.

tory Source:

Materials provided by University of Sydney. Note: Content may be edited for style and length.

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Journal Reference:

1. Kelsey L. Sanborn, Jody M. Webster, Yusuke Yokoyama, Andrea Dutton, Juan C. Braga, David A. Clague, Jennifer B. Paduan, Daniel Wagner, John J. Rooney, John R. Hansen.New evidence of Hawaiian coral reef drowning in response to meltwater pulse-1A. Quaternary Science Reviews, 2017; 175: 60 DOI:10.1016/j.quascirev.2017.08.022
2. https://www.sciencedaily.com/releases/2017/09/170928094213.htm