An extinct ribbonlike sea creature about the size of a human hand was one of the earliest animals to evolve a precursor of a backbone. Scientists recently identified the animal’s nerve cord by using a topsy-turvy twist. They turned its fossils upside down.
Paleontologist Charles Doolittle Wolcott first encountered fossils of Pikaia in the Burgess Shale deposits of British Columbia, dating to 508 million years ago, and described them in a 1911 treatise. The animal measured roughly 6.3 inches (16 centimeters) long and had a flattened, sinuous body and a tiny head, tipped with two tentacles and fringed with external gills. These were originally thought to be rudimentary legs, so the animal was positioned with these structures facing downward.
In 2012, after decades of studying Pikaia fossils, researchers described its fossilized internal structures in great detail. They identified a long strand near the belly as a blood vessel and named a sausage-shaped 3D structure running below the animal’s back as a dorsal organ, possibly used for internal support, though such an organ was anatomically unlike anything seen in fossils or in living animals.
However, recent analysis of Pikaia fossils by another team of scientists, published June 11 in the journal Current Biology, has upended this view and all other earlier studies about Pikaia.
According to the researchers, earlier anatomical interpretations positioned the animal wrong side up. The so-called dorsal organ was actually located in the belly and was Pikaia’s gut. The presumed blood vessel was a nerve cord, a feature associated with the animal group known as chordates, in the phylum Chordata.
All chordates, such as vertebrates, eel-like lancelets, and tunicates, or sea squirts, at some point in their lives have a flexible, rod-shaped nerve structure called a notochord in their backs.
Pikaia was initially thought to be a worm, then was later upgraded to an early type of chordate, based on features such as shapes of certain muscles and the position of its anus. But experts were uncertain about where exactly Pikaia belonged on the chordate family tree.
With the description of a nerve cord, Pikaia can now be considered part of the foundational lineage of all chordates, even though it has no direct descendants that are alive today, the study authors reported.
Inverting Pikaia “clarifies things a lot,” said evolutionary biologist Dr. Jon Mallatt, a clinical professor at the University of Idaho. Mallatt, who was not involved in the new research, published a paper on Pikaia in 2013, working from the established (and upside-down) body position.
In retrospect, the truth was “hiding in plain sight,” and the reversal in orientation resolves questions about why Pikaia’s purported blood vessel and dorsal structure clashed with established anatomical features in other chordates, Mallatt said.
“Pikaia’s suddenly become a lot less weird,” he said.
New orientation
Reevaluating which way was up for Pikaia originated years ago with a coauthor of the new study, Dr. Jakob Vinther, a lecturer in macroevolution at the University of Bristol in the United Kingdom, said lead study author Giovanni Mussini, a researcher and doctoral candidate in the department of Earth sciences at the University of Cambridge in the UK.
There were a number of reasons for revisiting earlier interpretations of the fossils, Mussini told CNN. For one, there was the enigma of what scientists had believed was the dorsal organ’s position. Its placement — near what was supposedly Pikaia’s back — seemingly ruled out the possibility that the organ could be a gut.
Once Pikaia was flipped upside down, however, the organ’s location and features made more sense anatomically. It broadened and extended into the animal’s pharynx, the throat region where a gut typically connects to a mouth. Its 3D status could be explained by the presence of chemically reactive tissues — hallmarks of a gut. In other Burgess Shale fossils, abundant ions and reactive compounds that are typically found in gut tissue cause digestive structures to mineralize more quickly than the rest of the body, and thereby retain more of their original shapes. Structures inside Pikaia’s organ were possibly remnants of swallowed food, according to the study.
In an inverted Pikaia, the external gills that formerly pointed down were now angled upward, as are external gills in modern mudskippers and axolotls.
Flipping Pikaia also changed the orientation of muscle groups that bunch together in a wave formation. These muscles, called myomeres, are a key feature in vertebrates. In Pikaia’s new position, the strongest flex point of these muscles is along its back, which is also true for the arrangement of myomeres in other animals with backbones.
“It makes Pikaia’s movement consistent with what we see in modern chordates,” Mussini said.
Finding the nerve
Pikaia’s presumed blood vessel was also anatomically puzzling, as it lacked the branches typically found in vertebrate blood vessels.
“It’s a single line going through most of the body up until the head, where it bifurcates into those two strands into the tentacles,” Mussini said.
An important part of recognizing the structure as a nerve cord was fossilized nervous systems in other animals from the Cambrian Period (541 million to 485.4 million years ago) that were discovered over the past decade, Mussini added.
“We have a better understanding of how nerve cords and other tissues fossilize because we’ve been lucky enough to find quite a few Cambrian nervous systems preserved in other deposits,” he said, “mostly from Chinese fossils that came to light in the last few years.”
Many of these fossils were arthropods — invertebrates with exoskeletons — with living relatives such as insects, arachnids and crustaceans; comparing the fossils with modern arthropods helped paleontologists to identify preserved internal tissues. One example is a fossil specimen of the Cambrian arthropod Mollisonia, which showed brain organization comparable with that of living spiders, scorpions and horseshoe crabs, Mussini said.
While there are no living analogues for Pikaia, the fossil arthropod data gave the scientists a more detailed frame of reference for Pikaia’s nerve cord. Like other fossilized nervous tissue, the nerve cord in Pikaia was dark, rich in carbon and relatively brittle compared with other fossilized tissues.
This nerve cord solidifies Pikaia’s status as a chordate, placing it “pretty much at the base of what we would consider traditional chordates,” Mallatt said.
Much about Pikaia’s anatomy remains a mystery, but looking at it from a new angle could offer fresh insights into its puzzling array of features, Mussini said.
“A lot of these details have come to light only in the last 10 or 12 years,” Mussini added. “The authors of the 2012 paper can certainly be forgiven for not bringing these details to the conversation, because it’s a work in progress.”
Mindy Weisberger is a science writer and media producer whose work has appeared in Live Science, Scientific American and How It Works magazine.
NAIROBI, Kenya (AP) — The body of Ugandan Olympic athlete Rebecca Cheptegei — who died after being set on fire by her partner in Kenya — was received Friday by family and anti-femicide crusaders, ahead of her burial a day later.
Cheptegei’s family met with dozens of activists Friday who had marched to the Moi Teaching and Referral Hospital’s morgue in the western city of Eldoret while chanting anti-femicide slogans.
She is the fourth female athlete to have been killed by her partner in Kenya in yet another case of gender-based violence in recent years.
Viola Cheptoo, the founder of Tirop Angels – an organization that was formed in honor of athlete Agnes Tirop, who was stabbed to death in 2021, said stakeholders need to ensure this is the last death of an athlete due to gender-based violence.
“We are here to say that enough is enough, we are tired of burying our sisters due to GBV,” she said.
It was a somber mood at the morgue as athletes and family members viewed Cheptegei’s body which sustained 80% of burns after she was doused with gasoline by her partner Dickson Ndiema. Ndiema sustained 30% burns on his body and later succumbed.
Ndiema and Cheptegei were said to have quarreled over a piece of land that the athlete bought in Kenya, according to a report filed by the local chief.
Cheptegei competed in the women’s marathon at the Paris Olympics less than a month before the attack. She finished in 44th place.
Cheptegei’s father, Joseph, said that the body will make a brief stop at their home in the Endebess area before proceeding to Bukwo in eastern Uganda for a night vigil and burial on Saturday.
“We are in the final part of giving my daughter the last respect,” a visibly distraught Joseph said.
He told reporters last week that Ndiema was stalking and threatening Cheptegei and the family had informed police.
Four in 10 women or an estimated 41% of dating or married Kenyan women have experienced physical or sexual violence perpetrated by their current or most recent partner, according to the Kenya Demographic and Health Survey 2022.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
VICTORIA – The British Columbia government is partnering with a bear welfare group to reduce the number of bears being euthanized in the province.
Nicholas Scapillati, executive director of Grizzly Bear Foundation, said Monday that it comes after months-long discussions with the province on how to protect bears, with the goal to give the animals a “better and second chance at life in the wild.”
Scapillati said what’s exciting about the project is that the government is open to working with outside experts and the public.
“So, they’ll be working through Indigenous knowledge and scientific understanding, bringing in the latest techniques and training expertise from leading experts,” he said in an interview.
B.C. government data show conservation officers destroyed 603 black bears and 23 grizzly bears in 2023, while 154 black bears were killed by officers in the first six months of this year.
Scapillati said the group will publish a report with recommendations by next spring, while an independent oversight committee will be set up to review all bear encounters with conservation officers to provide advice to the government.
Environment Minister George Heyman said in a statement that they are looking for new ways to ensure conservation officers “have the trust of the communities they serve,” and the panel will make recommendations to enhance officer training and improve policies.
Lesley Fox, with the wildlife protection group The Fur-Bearers, said they’ve been calling for such a committee for decades.
“This move demonstrates the government is listening,” said Fox. “I suspect, because of the impending election, their listening skills are potentially a little sharper than they normally are.”
Fox said the partnership came from “a place of long frustration” as provincial conservation officers kill more than 500 black bears every year on average, and the public is “no longer tolerating this kind of approach.”
“I think that the conservation officer service and the B.C. government are aware they need to change, and certainly the public has been asking for it,” said Fox.
Fox said there’s a lot of optimism about the new partnership, but, as with any government, there will likely be a lot of red tape to get through.
“I think speed is going to be important, whether or not the committee has the ability to make change and make change relatively quickly without having to study an issue to death, ” said Fox.
This report by The Canadian Press was first published Sept. 9, 2024.
