Dinosaurs so thoroughly dominated the ancient world that they suppressed the evolutionary possibilities open for mammals. This notion has been around for decades now, and it seems to be backed up by the fact that no known mammal became larger than badger-sized during the time dinosaurs were the most prominent animals on land. But, thanks to decades of new fossil discoveries, paleontologists have realized an important twist in the story—it wasn’t dinosaurs that suppressed the evolution of our ancient mammalian ancestors, but other forms of ancient mammal.
Paleontologists who study fossil mammals have suspected the story of “dinosaur dominance” was too simple, but, until now, the critical evidence was missing. Clues that the picture was more complicated now come from a new Current Biology paper by University of Oxford paleontologist Elsa Panciroli and colleagues that followed the evolutionary spread of various mammals during the Age of Dinosaurs—from more ancient types called mammaliaforms to the group of mammals found all around us today, the therians. Because the ancient mammaliaforms diversified and spread into so many forms first, the researchers found, our own mammalian ancestors and relatives didn’t have a chance to truly dig their claws into the world’s ecosystems until after the asteroid strike that sparked a mass extinction 66 million years ago.
The image of what a Mesozoic mammal is—that is, mammals that lived during the Triassic, Jurassic and Cretaceous Periods—has often been stereotyped as a small, snuffling insectivore that foraged at night. And such shrew-like beasts really did exist during the dinosaurian heyday. Yet they weren’t the only form of mammal around.
Just as dinosaurs thrived, paleontologists have learned, so did mammals—albeit at a smaller scale. The Jurassic Castorocauda had a tail like a beaver’s and ate fish like an otter. The 150-million-year-old Fruitafossor, on the other hand, made a living digging termites and other social insects out of the ground like an aardvark, while the Jurassic Vilevolodon was the mammaliaform equivalent of a sugar glider. In fact, some of these mammals even ate dinosaurs. A fossil of the badger-sized, 125-million-year-old Repenomamus was found with baby dinosaurs in its gut contents.
A little bit of evolutionary orientation helps make sense of the picture, especially because Mesozoic mammals were not a monolith. Around 220 million years ago, a group of weasel-like protomammals called cynodonts spun off a new evolutionary branch. These new creatures were small, covered in fuzz, had good hearing, carried their legs beneath their bodies instead of sprawled out like lizards and had mouths full of different types of teeth that could be used for piercing, nipping and grinding. These new creatures were the mammaliaformes, a broad group that eventually included the ancient equivalents of aardvarks, sugar gliders, squirrels, otters and more.
“I think we overlook the diversity of mammal in the time of dinosaurs in much the same way we overlook their diversity on Earth today,” Panciroli says. The fact that prehistoric mammals don’t have dramatic or common names like some dinosaurs do, Panciroli notes, covers over just how varied and strange they were. “Mesozoic mammals had a large diversity of locomotor modes and dietary preferences,” adds University of Bristol paleontologist Melisa Morales Garcia, who was not involved with the new study.
During the Cretaceous one lineage of mammaliaform spun off the therians. Therian mammals are the most numerous and diverse on Earth today, but their ancestors didn’t just evolve in the Cretaceous and wait for the dinosaurs to go away. The mass extinction that ended the Cretaceous took out numerous mammaliaform species as well as the non-bird dinosaurs, and that shift, paleontologists have found, is what allowed therian mammals to thrive.
In their study, Panciroli and colleagues developed a technique to estimate the capacity for different mammaliaform groups to evolve into new forms. Looking at many of the mammaliaforms from the Age of Dinosaurs, for example, paleontologists have found various species that swam, burrowed, climbed and filled other niches in the ancient habitats. Therian mammals do all these things and more today—but, during the Age of Dinosaurs, they didn’t evolve into the broad diversity of shapes and niches as the mammaliaforms. It was only after the mass extinction of 66 million years ago that therians were able to match what the mammaliaforms had done for millions of years.
It wasn’t the dinosaurs that held the therians back. While the presence of dinosaurs of so many shapes and sizes might have prevented mammaliaforms from attaining large body sizes, Morales Garcia notes, other mammaliaforms had a greater amount of evolutionary influence on therians than dinosaurs.
The rise of rodents is one example. The most successful mammaliaform group of all time was the multituberculates—squirrel-like beasts with chisel-like teeth at the front of their mouths and cheek teeth brimming with cusps. They filled the same niche in the Age of Dinosaurs as many mice and squirrels today. But while some multituberculates survived the end-Cretaceous extinction without missing a beat, the species in Asia virtually disappeared. This left an ecological gap that the earliest rodents started to fill, eventually supplanting the multituberculates. Without the extinction to shake things up, rodents probably wouldn’t have been able to get a toehold in Asia and eventually replace the multituberculates.
Even though dinosaurs had a role to play in keeping prehistoric beasts on the small side, the supposed dominance of the dinosaurs isn’t the whole story. It was other mammals, Panciroli and colleagues suggest, that were more influential in the therian backstory. “Now we have a more complex, but clearer, picture of the diversification of mammals,” Morales Garcia adds.
A new genus and species of theropod dinosaur from the Cretaceous period has been identified from bones found on the Isle of Wight, the United Kingdom.
The newly-discovered dinosaur roamed the Earth approximately 115 million years ago (Cretaceous period).
It belongs to Tetanurae, a group that includes most theropod dinosaurs, including megalosauroids, allosauroids, tyrannosauroids, ornithomimosaurs, maniraptorans, and birds.
Named Vectaerovenator inopinatus, the ancient creature is estimated to have been up to 4 m (13.1 feet) long.
The fossilized bones from the neck, back and tail of the new dinosaur were found over a period of weeks in 2019 in three separate discoveries, two by individuals and one by a family group, on the foreshore near Knock Cliff on the Isle of Wight.
“The joy of finding the bones we discovered was absolutely fantastic. I thought they were special and so took them along when we visited Dinosaur Isle Museum,” said Robin Ward, a fossil hunter who was with his family visiting the Isle of Wight when they made their discovery.
“They immediately knew these were something rare and asked if we could donate them to the museum to be fully researched.”
“It looked different from marine reptile vertebrae I have come across in the past,” said regular fossil hunter James Lockyer.
“I was walking along the beach, kicking stones and came across what looked like a bone from a dinosaur,” added regular fossil hunter Paul Farrell.
“I was really shocked to find out it could be a new species.”
Vectaerovenator inopinatus had large air spaces in some of the bones, one of the traits that helped the paleontologists identify its theropod origins.
These air sacs, also seen in modern birds, were extensions of the lung, and it is likely they helped fuel an efficient breathing system while also making the skeleton lighter.
“We were struck by just how hollow this animal was — it’s riddled with air spaces. Parts of its skeleton must have been rather delicate,” said lead author Chris Barker, a Ph.D. student at the University of Southampton.
“The record of theropod dinosaurs from the mid Cretaceous period in Europe isn’t that great, so it’s been really exciting to be able to increase our understanding of the diversity of dinosaur species from this time.”
“It is likely that Vectaerovenator inopinatus lived in an area just north of where its remains were found, with the carcass having washed out into the shallow sea nearby.”
The team’s paper will be published in the journal Papers in Palaeontology.
The lumbering crocodylomorph lived during the early Cretaceous period, about 106 million years ago.
A prehistoric ancestor of the crocodile may have walked on two legs, according to a paper published on June 11 in Scientific Reports.
The new research focuses on large footprints in the Jinju rock formation in South Korea. A 2012 investigation of large, poorly defined footprints suggested that they might have come from a flying reptile called a pterosaur, but clearer footprints discovered recently changed the story. The new footprints capture the shape of the ancient creature’s toes and the texture of its skin, both of which are classically crocodilian. But the footprints had another curious feature: there were only prints from back feet.
To paleontologist Martin Lockley, who specializes in trace fossils at the University of Colorado Denver, the lack of front footprints probably means that the ancient crocodile walked only on its back legs. “We have dozens of these things, and not one sign of a front footprint, so we’re pretty convinced,” Lockley tells Science News.
The tracks are between seven and ten inches long and the animal that left them was probably similar in size to modern crocodiles. It lived during the early Cretaceous period, about 106-million years ago. (The late Cretaceous saw the lifetimes of several dinosaur celebrities like Tyrannosaurus rex, Triceratops and Iguanadon.) The muddy, lake-covered coastal area where the ancient crocodylomorphs lived was a prime location to preserve footprints, Tim Vernimmen writes for National Geographic, and thousands of tracks can be found there today.
“When Martin Lockley visited the site in November 2019, I asked him what he thought of these tracks,” Kyung Soo Kim of Chinju National University of Education in Jinju tells National Geographic. “He immediately suggested that they were of the type known as Batrachopus, a crocodylian. I didn't believe it at that time, because I couldn't imagine a bipedal crocodile. But later, I was convinced by the blunt toes, the toe pads, and the details of the skin.”
The find came as a surprise. Paleontologists have found evidence of bipedal crocodiles before in North Carolina, but that animal lived about 231 million years ago, per Science News. That places it during the Triassic period, or at least 70 million years before the Cretaceous.
“No one knew that large bipedal crocs existed in the early Cretaceous,” Lockley tells New Scientist’s Layal Liverpool.
The new footprints suggest that the previously discovered tracks belong to an ancient crocodile, too. But based on the tracks it left behind, the creature was unlike modern crocodiles in more ways than one. For one thing, the tracks it left behind show that the animal put its feet one in front of the other as it walked, instead of keeping each foot in its own lane like modern crocs, National Geographic reports. And the fossilized footprints show no sign of webbing between the toes, which modern crocs have, per New Scientist.
Stony Brook University paleontologist Pedro Godoy tells New Scientist that while he agrees that the tracks don’t belong to a pterosaur, the unusually large size of the tracks makes him think that more evidence is necessary to link them to an ancient crocodile. But to Emory University paleontologist Anthony Martin, the evidence is convincing.
“[The imprints] really do look like they were made by big crocodilians,” Martin, who was not involved in the new study, tells National Geographic. “Indeed, by ones that were walking on their rear feet and on land. That’s pretty weird. But then again, the Cretaceous was a weird and wondrous time.”
UCMP Berkely- Crocodylomorpha Taxa
The Aldabra white-throated rail bird was declared extinct, a victim of rising sea levels almost 100,000 years ago.
However, the flightless brown bird has recently been spotted – leaving scientists scratching their heads as to how – and why – the species has come back to life.
According to research in the Zoological Journal of Linnean Society, the re-incarnated Aldabra bird is a product of ‘iterative evolution’. That’s when old genes thought to have died out re-emerge at a different point in time.
That means that while a bird’s ancestors might have disappeared, that DNA still remains – and provided the environment is right, there’s nothing to stop those ancient genes from replicating in modern times.
So identical species can indeed produce multiple, slightly evolved offshoots, throughout the course of their species' history.
But don’t get your hopes up that this means dinosaurs and wooly mammoths will be popping up next. This scientific phenomenon only occurs within species that are nearly identical to their ancestors.
While iterative evolution has previously occurred in species such as turtles, it has never been seen in the realm of birds.
“We know of no other example in the rails, or of birds in general, that demonstrates this phenomenon so evidently,” said paleobiologist David Martill, in a statement.
“Only on the Aldabra, which has the oldest palaentological record of any oceanic island within the Indian Ocean region, is fossil evidence available that demonstrates the effects of changing sea levels on extinction and recolonization events.”
2020 was already an interesting and confusing year. Looks like now we have to contend with re-materializing birds, as well.
To better predict the ecological and evolutionary effects of the emerging biodiversity crisis in the modern oceans, we compared the association between extinction threat and ecological traits in modern marine animals to associations observed during past extinction events using a database of 2497 marine vertebrate and mollusc genera. We find that extinction threat in the modern oceans is strongly associated with large body size, whereas past extinction events were either nonselective or preferentially removed smaller-bodied taxa. Pelagic (coastal and middle dwelling ocenic fish) animals were victimized more than benthic (bottom dwelling) animals during previous mass extinctions but are not preferentially threatened in the modern ocean. The differential importance of large-bodied animals to ecosystem function portends greater future ecological disruption than that caused by similar levels of taxonomic loss in past mass extinction events.
Trophy Hunting Sustains, Prospers, and Preserves Wildlife Habitats and Residents- The Story Revealed
To the untrained eye, most fossils don’t appear to be bursting with color. The first scientific analysis of fossil color was published only a decade ago, and until recently, determining the color palette of the prehistoric world seemed an insurmountable task.
Maria McNamara, a paleontologist at University College Cork in Ireland, is trying to piece together the fossil evidence to paint a colorful picture of the past. When people think of paleontology, they often think of hard teeth and bone, but the softer parts of animals, like skin, muscle tissue and internal organs, can be preserved in the fossil record, too. It's much rarer, of course, because the squishy stuff usually rots away, but soft tissues are exactly the kind of specimens McNamara is looking for. She studies tissues from insects and vertebrates in order to envision what these critters looked like and how they interacted with their environments—what their predators were, where they lived, what their mating habits may have been and more.
McNamara will be discussing her work to find the color remnants in fossils at the Smithsonian's National Museum of Natural History’s "Life’s Greatest Hits: Key Events in Evolution" symposium on Friday, March 29, in Washington DC. Ahead of her talk, Smithsonian.com spoke to McNamara to learn more about the colors of the ancient world.
Read more: SMITHSONIAN.COM
Paleontologists have just uncovered the remarkably pristine cranium of an ancient bird along with three partial skulls. These remains combine modern and primitive features in surprising ways to capture a fascinating moment in avian evolution.
The Ichthyornis fossils starkly contrast the skeletons of current birds. Modern birds have less musculature in their jaw and larger braincases than their predecessors. Whereas today’s birds have lightweight, toothless snouts, the fossils have large, toothed upper jaws—more comparable to those of dinosaurs. The Ichthyornis specimens even have openings in the top of their skulls, just like in T. rex fossils, to allow for large muscles.
Beelzebufo ampinga, so named for the ancient deity often called the "Lord of the Flies," was a devilish frog indeed. The species, which lived on the island of Madagascar around 70 million years ago, was likely the biggest frog that ever hopped about the Earth (National Geographic describes it, delightfully, as "beach-ball-size"). And according to new research on its modern cousins published in Scientific Reports, Beelzebufo ampinga may have had jaws powerful enough to obliterate small dinosaurs.
Paleontologists in Argentina have uncovered a dinosaur unlike anything ever seen before. Alive some 140 million years ago, these majestic herbivores featured long, forward-pointing spikes running along their necks and backs. These spikes may have served a defensive role, but their exact purpose now presents a fascinating new mystery.
NATURE.COM Bajadasaurus pronuspinax