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Early Mammals Acted More Like Reptiles, Says Study

KEY POINTS

  • Scientists said early mammals led a less active but much longer lives
  • They analyzed teeth fossils of earliest mammals, the Morganucodon and Kuehneotherium
  • The study suggested that mammals developed some characteristics like warm-bloodedness at a later period

The first mammals that roamed the Earth millions of years ago functioned and acted more like reptiles even with their already advanced body structures, a new study showed. 

The research, published in Nature Communications, suggested there might be an overlap between warm-bloodedness and cold-bloodedness as mammals evolved in the past. It may be noted that mammals are considered as warm-blooded animals while reptiles are cold-blooded. 

As part of the study, a team of paleontologists analyzed teeth fossils from two of the earliest mammals, the Morganucodon and Kuehneotherium, which lived alongside early dinosaurs nearly 200 million years ago. This was the first time researchers used powerful X-rays to examine ancient fossils.

The team scanned the fossilized cementum of the teeth fossils. The cementum is what attaches the teeth into the socket in the gum of mammals and it continues to grow throughout life.

The paleontologists studied the tree-like growth rings in the tooth sockets, which helped them understand the lifespan of the ancient mammals and how they evolved during the early Jurassic period. 

They found that although Morganucodon and Kuehneotherium had features similar to their modern counterparts, including bigger brains, they lived more like lizards.  

“They were otherwise quite mammal-like in their skeletons, skulls and teeth. They had specialized chewing teeth, relatively large brains and probably had hair, but their long lifespan shows they were living life at more of a reptilian pace than a mammalian one,” Dr. Elis Newham, lead author of the study and a research associate at the University of Bristol, said in a press release. 

“There is good evidence that the ancestors of mammals began to become increasingly warm-blooded from the Late Permian, more than 270 million years ago, but, even 70 million years later, our ancestors were still functioning more like modern reptiles than mammals,” Newham added. 

The researcher explained that even though the ancient mammals acted more like reptiles, it was found that their bone tissues endured sustained physical activities, suggesting that they were capable of foraging and hunting. They were more active than small reptiles but not as energetic as the mammals, Newham explained.  

Dinosaurs Pictured, an animatronic life-size dinosaur ahead of an interactive exhibition in Jurassic Kingdom, at Osterley Park in west London. Photo: REUTERS/Toby Melville

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Double jeopardy for ecologically rare birds and terrestrial mammals

endangered species
Credit: Pixabay/CC0 Public Domain

Common assumptions notwithstanding, rare species can play unique and essential ecological roles. After studying two databases that together cover all known terrestrial mammals and birds worldwide, scientists from the CNRS, the Foundation for Biodiversity Research (FRB), Université Grenoble Alpes, and the University of Montpellier have demonstrated that, though these species are found on all continents, they are more threatened by human pressures than ecologically common species and will also be more impacted by future climate change. Thus, they are in double jeopardy. The researchers’ findings, published in Nature Communications (October 8, 2020), show that conservation programs must account for the ecological rarity of species.


It has long been thought that rare species contribute little to the functioning of ecosystems. Yet recent studies have discredited that idea: Rarity is a matter not only of the abundance or geographical range of a species, but also of the distinctiveness of its ecological functions. Because these functionally distinct species are irreplaceable, it is essential we understand their ecological characteristics, map their distributions, and evaluate how vulnerable they are to current and future threats.

Using two databases that collect information on the world’s terrestrial mammals (4,654 species) and birds (9,287 species), scientists from the FRB’s Center de Synthèse et d’Analyse de la Biodiversité (CESAB), CNRS research laboratories, Université Grenoble Alpes, the University of Montpellier, and partner institutes divided the earth’s surface into 50 × 50 km squares and determined the number of ecologically rare species within each. They showed that ecological rarity among mammals is concentrated in the tropics and the southern hemisphere, with peaks on Indonesian islands, in Madagascar, and in Costa Rica. Species concerned are mostly nocturnal frugivores, like bats and lemurs, and insectivores, such as small rodents. Ecologically rare bird species are mainly found in tropical and subtropical mountainous regions, especially in New Guinea, Indonesia, the Andes, and Central America. The birds in question are essentially frugivorous or nectarivorous, hummingbirds being an example. For birds and terrestrial mammals alike, islands are hotspots of ecological rarity.

The researchers also ranked these species according to their IUCN Red List status and found they made up the bulk of the threatened species categories. That is, ecologically rare mammals account for 71% of Red List threatened species (versus 2% for ecologically common mammals); and ecologically rare birds, 44.2% (versus 0.5% for ecologically common birds). For each species, they determined (i) anthropogenic pressure exerted; (ii) human development indexes (HDIs) of host countries; and (iii) exposure to armed conflicts. The last two of these elements shape conservation policies. The scientists observed that human activity had a greater impact on ecologically rare mammals and birds than on more common species, and that these rare species were found in countries of every kind of profile, irrespective of HDI or the prevalence of warfare. They used models to demonstrate that ecologically rare species will be the greatest victims of climate change, many of them facing extinction within 40 years.

This profiling of ecologically rare species makes it

New species of aquatic mice discovered, cousins of one of the world’s rarest mammals

New species of aquatic mice discovered, cousins of one of the world's rarest mammals
An illustration of one of the newly-described species of stilt mouse, Colomys lumumbai, wading in a stream to hunt. Credit: Velizar Simeonovski, Field Museum

Ninety-three years ago, a scientist trapped a mouse in a stream in Ethiopia. Of all the mice, rats, and gerbils in Africa, it stood out as the one most adapted for living in water, with water-resistant fur and long, broad feet. That specimen, housed at Chicago’s Field Museum, is the only one of its genus ever collected, and scientists think it may now be extinct. But in a new study in the Zoological Journal of the Linnean Society, researchers have verified this semi-aquatic mouse’s closest cousins, including two species new to science.


“These two groups of mice have been confused with one another for a century,” says Julian Kerbis Peterhans, one of the paper’s authors and a researcher at the Field Museum who’s studied these rodents for over 30 years. “They’ve been so elusive for so long, they’re some of the rarest animals in the world, so it’s exciting to finally figure out their family tree.”

“It’s underappreciated how little is known about the biodiversity of small mammals, especially in tropical parts of the world. We’re not discovering a whole lot of new lions, tigers, and bears, but there’s an incredible potential for discovery of new species of small mammals because they’re tough to find,” says Tom Giarla, the paper’s lead author and an assistant professor of biology at Siena College in New York. “And they’re sort of underappreciated animals—they’re really cool when you start to learn about their ecology. These are semi-aquatic mice, so they’re not just your average, everyday rodents.”

There are two main kinds of mice that the researchers focused on: Nilopegamys and Colomys. Nilopegamys (meaning “mouse from the source of the Nile”) is the genus that’s only known from one specimen collected in 1927; the genus Colomys is a little easier to come by, but still difficult to find. While Nilopegamys has only been found in Ethiopia, Colomys have been found throughout the Congo Basin and into the western part of the African continent.

New species of aquatic mice discovered, cousins of one of the world's rarest mammals
Specimens of the stilt mice studied in this paper– the already-known species C. goslingi on the left, and the new species C. lumumbai on the right. Credit: Giarla et al

Colomys‘s name roughly translates to “stilt mouse” for its elongated feet that let it wade in shallow streams to hunt for water-dwelling insects like caddisfly larvae. “These mice are long-footed, kind of like a kangaroo. They sit up on their haunches, and they wade through shallow streams with their whiskers on the water’s surface detecting movements, like sonar,” says Kerbis Peterhans. They have unusually large brains in order to process this sensory information from their whiskers when they hunt. They’re cute, too, he says: “When I caught my first one some 30 years ago, it was the most beautiful African mouse I’d ever seen, it had water repellent fur that’s very thick and lush and