bicephaly, is a rare developmental disorder that's typically caused by the incomplete splitting of a single embryo during the formation of identical twins. It results in conjoined twins that share one body but have two fully formed, independent heads.

Zak Mertz, CEO of New England Wildlife Centers, which includes the Cape Wildlife Center, said the recently discovered diamondback terrapin (Malaclemys terrapin) is an uncommon example of bicephaly in turtles. Both genetics and epigenetics ‪—‬ the study of how genes and environment can interact ‪—‬ are thought to play a role in the condition's development.

"Our understanding based on the available research is that bicephaly is caused by both genetic and epigenetic factors," Mertz told Live Science in an email.

"It may have to do with the relatively long lifespan of the turtles, their preference for returning to the same nesting sites, and a limited gene pool due to their conservation status," he said."It may also be influenced by environmental factors, such as the temperature, humidity during incubation, physical characteristics of the nesting sites, or potentially even things the parents are exposed to in the environment."

Having two heads is rare but not unprecedented. According to the center, this is the third bicephalic terrapin found in the area in the past five years, providing another opportunity to learn more about the animals. Other wild animals with bicephaly have been found in recent years, including a two-headed porpoise found off the coast of the Netherlands and a two-headed dolphin that was found on a Turkish beach.

A 2021 study found that rare two-headed and partially duplicated sea turtle embryos and hatchlings showed significant craniofacial and spinal abnormalities and were generally smaller than typical hatchlings. The research found bicephalic turtles faced survival challenges because their abnormal anatomy could impair coordinated movement, feeding, and other functions essential for survival, highlighting the importance of monitoring such deformities as potential indicators of population and environmental health.

Diamondback terrapins are found in brackish marshlands along the Atlantic and Gulf coasts of the United States. Brackish waters have more salt than fresh water but less salt than seawater, and often occur where the freshwater of a lake or river meets the salty sea. These terrapins are classified as threatened by the Massachusetts Endangered Species Act, and their broader conservation status at the federal level is currently under review.

Veterinarians are monitoring the rare terrapin's health closely. "It is fascinating and an area that certainly merits more study," Mertz said. "We are excited to care for these two and learn as much as we can to inform future study in the process."

'> Rare two-headed turtle hatchling discovered on Cape Cod strong El Niño has brought a rare gift to Chile's Atacama Desert: rain. In one of the driest places on Earth, that rare moisture has awakened millions of seeds and bulbs that can remain dormant underground for years, transforming the landscape into a spectacular carpet of color.

Known locally as "desierto florido," or "flowering desert," the phenomenon is one of nature's most remarkable transformations. Patches of purple, pink, white, red and yellow now spread across hillsides and plains that for much of the year appear almost completely lifeless.

"It is a unique phenomenon; there are more than 200 plant species," Jorge Carabantes, head of the Protected Areas Department at the National Forest Corp. (CONAF) in Chile, told The Associated Press. "This is a flowering event that is obviously extraordinary and unusual, very different from other blooms that occur elsewhere on the globe."

Typically, the Atacama gets just 0.6 inches (15 mm) of rain a year. But thanks to the super El Niño, record levels of rain fell between July and August in several Chilean regions, including levels not seen since the 1950s, with some areas receiving more than 7 inches (190 millimeters), Carabantes told the AP.

While this unprecedented precipitation has caused flooding in some areas of Chile, it's created a 6,560-square-mile (17,000 square kilometers) swath of flowering blooms across the Atacama Desert. This is the most extensive desert bloom since 1997, CONAF representatives told the AP.

For photographers and tourists, the landscape is breathtaking, with bright colors contrasted against the dark Atacama mountains and Chile's cloudless skies. But the bloom is fleeting; by the end of the Southern Hemisphere's spring, many of the flowers will disappear, leaving behind seeds and bulbs waiting for the next extraordinary rains.

Here are five photos from Getty Images photographer Javier Torres that showcase the beauty of this rare event.

'> Colorful wildflowers bloom across Chile's Atacama Desert in wake of 'super' El Niño

In the study, published Friday (Oct. 2) in the journal Science Advances, the researchers argue that the absence of animal fossils in some exceptionally well-preserved ancient rocks doesn't mean the animals were absent from history. Instead, they suggest that the fossil record may be missing a key chapter of animal evolution, potentially pushing the origins of animals back to between 800 million and 700 million years ago.

This would place the emergence of animals deep within the Neoproterozoic era (1 billion to 539 million years ago), possibly before or during some of Earth's most extreme ice ages.

Even though scientists haven't found undisputed animal fossils from the Neoproterozoic, that doesn't mean animals didn't live at that time. Fossils can be absent from rocks for several reasons, including because scientists are looking in the wrong places or the conditions were unsuitable for creating fossils, making it difficult to determine the earliest evolved animals.

"Until that evidence becomes available, the precise birth date of the animal kingdom remains uncertain," study co-author Ross Anderson, an associate professor of natural history at the University of Oxford, said in a statement.

Where are the animals?

Until now, most researchers relied on the well-preserved rocks from the Ediacaran period, including the roughly 590 million-year-old Weng'an Biota in China, to investigate the timing of animal evolution. Because rock deposits there contain uniquely preserved microscopic organisms but no definitive animal fossils, experts have sometimes treated them as a kind of upper limit for when animals could have evolved.

"So the game is basically how much does it predate our first fossil discovery by and what happened in that evolutionary black box between when they actually originated versus when we get our first fossil window," Karma Nanglu, an assistant professor of evolutionary paleobiology at the University of California, Riverside who wasn't involved with the study, told Live Science.

But the researchers wondered whether other fossil sites from known animal periods actually had evidence of animal fossils.

To find out, Anderson and his colleagues studied more than 140 samples from the Kheseen Biota in Mongolia, which is more than 40 million years younger than the 590 million-year-old Weng'an Biota deposit. Given that it's a younger deposit, the researchers hypothesized that there should be evidence of animal life left in the rock. Using electron scanning microscopy, the researchers saw microscopic fossils preserved in extraordinary detail, including tiny, spherical organisms and embryo-like structures containing internal cells.

Yet, despite the quality of preservation, the researchers couldn't identify any of the microfossils as animals. That's important, because by the time the Kheseen Biota was deposited, animals were present elsewhere on Earth.

"The Kheseen Biota breaks the argument that the exceptional microfossils of Weng'an mean we would have seen animal fossils in the assemblage had they existed at the time," Anderson said. "The Kheseen microfossils are just as well-preserved, yet animals continue to be absent — despite the fact we know at that point they existed."

Using molecular clocks

Given the absence of fossil evidence, Anderson and his collaborators turned to another common method used to date ancient life: molecular clocks. Molecular clocks estimate when evolutionary lineages diverged by comparing genetic differences among living organisms and combining those differences with rates of genetic change. For example, if two bird species have five DNA changes and one DNA change takes about 1 million years to accumulate, scientists could estimate that the two species diverged around 5 million years ago.

"Molecular clocks are useful when we don't have a particularly good fossil record for a group of interest or a time period of interest," Nanglu said.

When the analysis was constrained by the younger Weng'an deposit, the estimated origin of animals was comparatively recent. When they used older geological constraints — specifically rock formations in Norway, Australia and Arizona deposited between around 850 million and 730 million years ago that have been used in the past for trying to find animals' early ancestors, the timeline changed. By comparing modern animal DNA to reference dates from the fossil record along with evolutionary rates of change — their estimate shifted back by roughly 200 million years, to between about 800 million and 700 million years ago.

"Pre-Ediacaran animal body fossils still elude us, and this analysis does not prove that animals existed 800 million years ago," study first author Orin Lole Durbin, a doctoral student of paleobiology at Virginia Tech who was a University of Oxford undergraduate at the time of the study, said in the statement. "Meanwhile, our molecular-clock analyses show how much further back their evolutionary history could extend."

Could animals have lived before "Snowball Earth"?

There are other clues that animals may have a longer history.

Chemical fossils, or biomarkers, have been interpreted as evidence consistent with sponges living at least 650 million years ago, tens of millions of years prior to the oldest known animal fossils.

If animals did originate 800 million years ago, their emergence would also intersect with the Cryogenian period, which began around 720 million years ago as part of the Neoproterozoic era. During this interval, Earth experienced enormous glaciations often referred to as "Snowball Earth."

Although there is no definitive answer to whether animals survived this uncertain time, the researchers plan to search additional Neoproterozoic rocks with different environments and preservation conditions to find more evidence for their analysis.

"Fossils themselves are by definition kind of hidden from general sight," Nanglu said."Beyond that there's an even more hidden world, and that has a lot of potential to tell us about animal origins."

Think you know about natural selection? Try your hand at our evolution quiz!

'> Animals may have evolved 200 million years earlier than previously thought, new study suggests "super" El Nino means the U.S. will likely face a higher risk of stormy weather and flooding, so experts are recommending Americans stock up on food.

And flooding is just one of the natural disasters people will face — many people are at risk of wildfires, power outages or earthquakes. While some disasters are unexpected, preparation can make a significant difference in how much they impact peoples' daily lives.

But is anyone actually prepared for the worst?

Levels of preparedness vary widely. Some may keep an emergency kit stocked with food, water and first-aid supplies, while others may have an evacuation plan, emergency contacts or designated meeting place for their household. And others do nothing at all. Although a recent study revealed there's no single place on Earth that's best prepared for global disaster, there are steps people can take to feel well equipped.

Experts recommend stocking up on food supplies and other essentials, especially in areas that might be more disaster prone. But how prepared are you? Answer our poll below, and share how you've prepared for emergencies or what you have in your disaster kit in the comments.

'> How prepared are you for a disaster?

"The evidence points to the arrival of humans ancestral to contemporary Indigenous peoples likely near the end of the Last Glacial Maximum, but earlier migrations may also have occurred," study co-authors Bethany Potter, an archaeologist at the Kansas Geological Survey, and Savannah Hay, a biological anthropologist at the University of Kansas, told Live Science in an email.

In a study published online Sept. 23 in the journal Current Opinion in Genetics & Development, the researchers used genetic evidence to investigate the three main archaeological models for Native American origins: an entry into the Americas before the LGM more than 25,000 years ago, entry during the LGM some time between 25,000 and 14,000 years ago, and entry after the LGM more recently than 14,000 years ago, sometimes called the Clovis First theory.

"The reason this topic is so contentious among anthropologists is because not all archaeologists agree about which of the earliest sites are legitimate, and that influences which model they think is most accurate," Potter and Hay said. "We know that humans were definitely in the Americas by about 13,500 years ago. We still don't know if they arrived earlier than that and, if so, how much earlier."

Genetic evidence of the first people in the Americas is scarce. The first whole genome from an ancient Indigenous person, who lived around 4,000 years ago in Greenland, was sequenced in 2010. Since then, the researchers wrote in the study, scientists have published around 250 whole genomes, along with genome-wide data from around 1,200 ancient Indigenous people.

These DNA studies have revealed key information about the first people in the Americas. During the LGM, around 25,000 years ago, a group of people living somewhere near Siberia or Beringia, which included the land bridge connecting Asia to Alaska, split into different groups ‪—‬ ancient Native Americans, ancient Beringians and one or more "ghost" lineages ‪—‬ and moved quickly along the Pacific coast, possibly splitting again around 16,000 years ago into Northern Native Americans and Southern Native Americans.

"Huge gaps in our genetic dataset"

Although the current genetic data lines up with archaeological evidence of people entering the American continents at least 14,000 years ago and perhaps as far back as 21,000 years ago, more DNA evidence is needed to fully understand how and when the first Indigenous people arrived from Siberia.

"There are huge gaps in our genetic dataset," Potter and Hay said. "For example, there are still no published ancient genomes from the Great Plains, despite that being where our lab group is situated." And these gaps could be hiding evidence of earlier migrations.

Human footprints found at White Sands, an archaeological site in New Mexico, have been dated to 23,000 years ago. If this date is correct, it implies that people were living there prior to the LGM. The Acoma Pueblo people living in the region of White Sands today recognize these footprints as traces of their ancestors, Potter and Hay said.

But genetic data from contemporary and ancient Indigenous peoples in the Americas currently shows that the White Sands population did not make a significant genetic contribution to the ancestors of today's Indigenous people, the researchers said. "However, it is possible we have not sampled their descendants' lineage, or that they contributed a low proportion of genetic ancestry to ancient North American populations," they said. "Perhaps we've just not found DNA from the White Sands population yet."

There are several scenarios compatible with a pre-LGM entry of people into the Americas, the researchers wrote, but assessing those models also requires more genetic data. To date, the earliest sampled genome is from a 12,800-year-old individual known as the Anzick-1 child, whose bones were found in Montana. Extrapolation from the DNA of the Anzick child and other early ancestors points to an initial migration that occurred no earlier than 21,000 years ago, Potter and Hay said.

"Expanding geographic coverage in general would be hugely beneficial, but many of us are intentionally slow with our ancient DNA approaches to ensure research relevant to descendant communities is ethical and collaborative," Potter and Hay said.

It is unclear when or if the longstanding question of when people first entered the Americas will be resolved, as current archaeological and genetic evidence do not unequivocally point to a single answer, Potter and Hay said, but "the publication of new ancient genomic data from the Americas is powerful, as it has the potential to fill in these gaps and reframe how we see these early peopling events."

How much do you know about the first people to reach the Americas? Find out with our First Americans quiz!

'> The ancestors of today's Indigenous people arrived in the Americas during the coldest part of the last ice age, study suggests