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Professor Loren E. Babcock and Dr H. Gregory McDonald discuss the historical significance of palaeontology, focusing on key figures’ contributions to the field and their studies of the ground sloth, Megalonyx

Palaeontology occupies a rather unique place in the public imagination – usually the word conjures up visions of large, scary, extinct monsters. This makes for good entertainment, but the reality is much more nuanced and both technically and historically fascinating. The roots of palaeontology’s common perception were established in the late 1700s, soon after major political and social upheaval in France and North America. Study of ancient life forms shifted from mere cataloguing, similar to today’s biodiversity inventories, to a scientific endeavour with overtones of social messaging paralleling contemporary thinking and events. More than two centuries later, we continue to witness changing perceptions of ancient life paralleling aspects of our social environment and our understanding of long-term climatic and environmental changes.

The emergence of palaeontology and the giant sloth

Historical figures that stand out at the time palaeontology emerged as a scientific discipline include Georges Cuvier (1768–1832), the ‘father of both comparative anatomy and vertebrate palaeontology’ in France, and Thomas Jefferson (1743–1826) in the United States. Both were influenced by the renowned French naturalist Georges- Louis LeClerc, the Comte de Buffon (1707–1788). Cuvier (1796, published 1800) solidified the concept of species’ extinction using the mammoth as an example. Also in 1796, he described the skeleton of a giant ground sloth, Megatherium, from Argentina. These two studies marked a turning point in the study of ancient life.

Within a year of Cuvier’s description of the sloth, in 1797 (published 1799), Jefferson proposed the name Megalonyx (Greek for ‘giant claw’) for the second known fossil sloth based on bones of a claw-bearing animal dug from a saltpeter mine in a West Virginia cavern. Initially, he interpreted the animal as a giant carnivore, comparing measurements of Megalonyx to a large African lion as a refutation of Buffon’s Theory of New World Degeneracy. Jefferson’s science reflected an opposition to some ideas rooted in colonialism. Just days before his lecture to the American Philosophical Society, Jefferson encountered Cuvier’s description of Megatherium, noting the similarity with his Megalonyx. The lecture was hastily and incompletely revised, and Megalonyx was reinterpreted as an ‘animal of the clawed kind,’ a possible herbivore rather than an apex predator. Nevertheless, the image of Megalonyx as a giant monster stuck. The paper was published two years later, accompanied by a more thorough description of the remains by Caspar Wistar. In 1822, Anton-Gaëtan Desmarest gave Megalonyx a species name,
M. jeffersonii, in honour of Thomas Jefferson.

Prior to his description of the ground sloth, Jefferson’s interest in ancient animals, which he did not accept as extinct, included publishing brief notes on the ‘incognitum’ (now known to be the mastodon) remains from Virginia. His interest in Megalonyx and the mastodon, a proboscidean, ultimately would play a key role in the exploration of the North American continent. For much of his life, Jefferson considered neither Megalonyx nor mastodon to be extinct. As the Corps of Discovery Expedition set out to explore the Louisiana Territory in 1804, Meriwether Lewis and William Clark received instructions to bring back evidence that both animals were still living in the American West.

The first Megalonyx mount

Initially known from mostly isolated bones, the first relatively complete skeletal remains of Megalonyx were dug from a farmer’s field in Ohio, US, in 1890. These were used to reconstruct a complete skeleton, with the missing parts filled in from other fossils. The skull was a plaster cast from a much smaller individual, and the hips were reconstructed based on the much larger Megatherium. Additional bones were added to the tail, lengthening it so the mount could stand like a tripod on its hind legs with its tail dragging on the ground. This mash-up, though anatomically incorrect, followed a pattern in use for other skeletons from at least the mid-1800s. Skeletal reconstructions of animals, including dinosaurs, were often mounted this way. The first Megalonyx mount, with its elongated, dragging tail, helped provide a stable engineering solution to mounting fragile ancient skeletons of large bipedal animals in an upright, formidable stance. The skeleton from Ohio was originally supported further at the front by a tree trunk, as if the animal were stripping leafy vegetation for food but still channeling the effect of a fearsome animal rearing on its hind legs.

Tracing the Megalonyx’s lineage

Dinosaurs continued to be mounted and reconstructed as tail draggers well into the 20th century, and even today, bipedal ‘tripod’ dinosaur (and giant ground sloth) toys are ubiquitous. Jefferson’s original interpretation of Megalonyx seems to have left an indelible impression on our view of large ancient animals, despite more recent research showing it to have been a rather gentle creature that normally walked on four legs instead of two.

Our current understanding of Megalonyx indicates that it is part of a lineage of ground sloths that originated in South America during the Oligocene Epoch, more than 33 million years ago. Its ancestors made their way to North America about nine million years ago. Megalonyx jeffersonii, which appeared in the Pleistocene Epoch and expanded across the North American continent, was the largest, most widespread, and last species in the genus. Why this highly successful large mammal became extinct 10,000 to 12,000 years ago is still uncertain. Environmental changes, associated with the retreat of glacial ice from the Northern Hemisphere and the arrival of humans and their dogs in the New World, may have contributed to their demise. Megalonyx remains, including those described by Jefferson, are sometimes found in caves, which were used as dens. Slice marks on the bones of some fossils suggest hunting and butchering by Palaeo-Indians. Disease and other factors that are difficult to test from fossil remains may also have taken a toll on Megalonyx populations.

• Comet 3I/ATLAS is the 3rd-known interstellar visitor to our solar system. It came from another star system.
• Researchers found some earlier images of the comet from before its official discovery in July.
• The newly found images provide important clues about 3I/ATLAS, including insights into its origin and composition.

Comet 3I/ATLAS, our 3rd interstellar visitor

A team of researchers, led by Michigan State University, has just completed a new study about the world’s 3rd-known interstellar object, labeled 3I/ATLAS. The scientists said on September 11, 2025, that they found earlier images of 3I/ATLAS from before it was officially discovered last July. The comet was in images that NASA’s TESS space telescope took last May. The images and other data provide important clues about comets originating in other planetary systems and how they compare to comets in our own solar system.

3I/ATLAS is only the 3rd-known interstellar object that astronomers have identified so far (hence the “3I” moniker). First, we spied the now-well-known ‘Oumuamua in 2017. Then, we saw 2I/Borisov in 2019. And now we have 3I/ATLAS, which is still fairly far from the sun. It will cross the orbit of Mars, sweeping near the planet, on October 3.

The researchers published their peer-reviewed findings in The Astrophysical Journal Letters on September 11, 2025.

Early images of comet 3I/ATLAS

Astronomers first found our interstellar visitor on July 1, 2025. The ATLAS survey telescope in Chile first spotted the object.

But researchers at Michigan State University later found earlier images of the comet. Those were from about two months before the official detection, from NASA’s Transiting Exoplanet Survey Satellite (TESS). Astronomers hadn’t identified the object at the time, as it just looked like a faint dot among thousands of background stars. But the images helped show that 3I/ATLAS really was interstellar and didn’t originate in our own solar system.

In addition, the images also show how the comet has evolved over time. In fact, they suggest it had been active for longer than first thought.

Lead author Adina Feinstein at Michigan State University said:

There are so few interstellar objects that we’ve detected in our solar system, and they each seem to be unique. 3I/ATLAS gives us an opportunity to study other solar systems up close and personal, without actually needing to visit them.

As soon as I realized 3I/ATLAS should be in these TESS images, I downloaded them as quickly as I could.

aww yeah ?? ? ??arxiv.org/abs/2507.21967

— ?Adina Feinstein PhD ? (@afeinstein20.bsky.social) 2025-07-30T01:37:23.999Z

Comet 3I/ATLAS starts to reveal its secrets

The images and other data gathered so far show comet 3I/ATLAS is rather unlike comets in our own solar system. Comets typically start to release water vapor and other gases as they get closer to the sun. But with 3I/ATLAS, the images revealed signs of activity much farther from the sun than usual.

Basically, that means it likely started to release other molecules, such as carbon monoxide and carbon dioxide.

Feinstein said:

That gives us an idea of what comets and asteroids could be made of in systems beyond our own sun. It’s always been assumed that other systems are different from ours, but now we have evidence of how different they might be.

Interstellar visitor comes into focus

After finding that the comet was in the TESS images, the researchers worked on making the images as clear as possible. First, they filtered out the light from nearby stars in the images. Then, they combined multiple images taken across the orbit of 3I/ATLAS.

This helped to bring out additional details of the faint object.

James Webb Space Telescope

Comet 3I/ATLAS will only be visible for another few months before it gets too far away again to observe with telescopes. But in the meantime, astronomers are conducting further observations, including with the James Webb Space Telescope. Indeed, those observations will be invaluable for learning as much about our visitor as we can before it slips back into interstellar space. As co-author John Noonan at Auburn University noted:

Capturing as many observations from this prediscovery period, where 3I/ATLAS may be in telescope images but wasn’t previously identified, is essential to our understanding of how these objects ‘turn on’ as they approach our sun. These interstellar objects have likely not been warmed significantly in millions, if not billions, of years, and any opportunity to see how they responded to that early heating is of interest.

Feinstein added:

Learning about other solar systems places humanity into context. One of life’s greatest questions is ‘are we alone in the universe?’ Each NASA mission gets us a little bit closer to answering this big, overarching question.

Recent observations have also shown that 3I/ATLAS is brightening more quickly than expected. Will it continue to brighten, or is this a temporary outburst? Only time will tell!

Bottom line: Researchers at Michigan State University have found earlier images of comet 3I/ATLAS not seen before. They provide new clues about this interstellar visitor.

Source: Precovery Observations of 3I/ATLAS from TESS Suggest Possible Distant Activity

Via Michigan State University/ EurekAlert!

Read more: Interstellar object 3I/ATLAS brightening quickly

Read more: Interstellar comet 3I/ATLAS shows comet tail in new image

Welcome to Edition 8.11 of the Rocket Report! We have reached the time of year when it is possible the US government will shut down its operations at the end of this month, depending on congressional action. A shutdown would have significant implications for many NASA missions, but most notably a couple of dozen in the science directorate that the White House would like to shut down. At Ars, we will be watching this issue closely in the coming days. As for Artemis II, it seems to be far enough along that a launch next February seems possible as long as any government closure does not drag on for weeks and weeks.

As always, we welcome reader submissions, and if you don’t want to miss an issue, please subscribe using the box below (the form will not appear on AMP-enabled versions of the site). Each report will include information on small-, medium-, and heavy-lift rockets as well as a quick look ahead at the next three launches on the calendar.

Rocket Lab to sell common shares. The space company said Tuesday that it intends to raise up to $750 million by selling common shares, MSN reports. This new at-the-market program replaces a prior agreement that allowed Rocket Lab to sell up to $500 million of stock. Under that earlier arrangement, the company had sold roughly $396.6 million in shares before ending the program.

Seeking to scale up … The program’s structure enables Rocket Lab to sell shares periodically through the appointed agents, who may act as either principals or intermediaries. The larger offering indicates that Rocket Lab is aiming to bolster its cash reserves to support ongoing development of its launch services, including the medium-lift Neutron rocket and spacecraft manufacturing operations. The company’s stock dropped by about 10 percent after the announcement.

Astra targets mid-2026 for Rocket 4 debut. Astra is targeting next summer for the first flight of its Rocket 4 vehicle as the company prepares to reenter the launch market, Space News reports. At the World Space Business Week conference in Paris, Chris Kemp, chief executive of Astra, said the company was on track for a first launch of Rocket 4 in summer 2026 from Cape Canaveral, Florida. He highlighted progress Astra is making, such as tests of a new engine the company developed for the vehicle’s first stage that produces 42,000 pounds of thrust. Two of those engines will power the first stage, while the upper stage will use a single Hadley engine produced by Ursa Major.