There was a missing link in the family tree of Tyrannosaurus rex until the fossil of a tyrannosaur was unearthed in the United States. Daspletosaurus wilsoni, a carnivorous dinosaur that existed 76.5 million years ago, may have been the progenitor of the well-known T. rex. The fossil demonstrates that the evolutionary line to Tyrannosaurus evolved more linearly than previously supposed and explains the connections of two additional Daspletosaurus species.
Small hornlets are arranged in a distinctive pattern around the eye, making the new species easy to spot.
The evolution of tyrannosaurs can be further illuminated by the discovery of Daspletosaurus wilsoni. (Credit: The Rudolf Hima and Badlands Dinosaur Museum)
Not only is Tyrannosaurus rex a favorite in popular media, but it is also one of the best-studied predatory dinosaurs from the Cretaceous era. Studies have focused on a variety of aspects, such as population density, eye size, and short limbs. T. rex’s ancestry is still a mystery. For instance, there’s some question as to whether or not three sets of bones that have been attributed to it really belong to entirely distinct species. Not much is known about it, not even about its most likely predecessors, the daspletosaurs.
Meat-Eating “Sisyphus”
A fossil dating back 76.5 million years has been discovered, which may provide light on the T. rex’s prehistoric ancestry. An entirely new tyrannosaurid species has been identified in the Judith River Formation in northwestern Montana. Skull and spinal column fragments, together with a rib and a metatarsal, were discovered, and the dinosaur was named Daspletosaurus wilsoni. The ancient tyrannosaur’s head measured 1.05 meters in length. This means that, relative to Tyrannosaurus rex, this predatory dinosaur was relatively small.
Almost all of the skull’s bones are here. (Credit: Credit: Elías Warshaw & Denver Fowler).
Montana State University paleontologist Elias Warshaw and North Dakota’s Badlands Dinosaur Museum paleontologist Denver Fowler investigated the specimen and came up with the name “Sisyphus.” This is a reference to the “Sisyphus effort” their coworkers put into digging it up. Eight meters of rock had to be excavated before they could even see the bones.
Daspletosaurus’ Missing Link in Its Family Tree
The excavation was fruitful, however, since “Sisyphus” provides significant insight into the evolution of tyrannosaurids. The paleontologists note that the prominent horns surrounding Sisyphus’ eyes are reminiscent of primitive tyrannosaurids seen in earlier strata.
Connecting the dots between Daspletosaurus wilsoni and both D. torosus and D. horneri, which are known as Daspletosaurs. (Credit: Warshaw & Fowler/PeerJ)
However, the predatory dinosaur also shows elements of current species, such as a larger eye socket and increased air pockets in the skull, which are characteristics of T. rex and other dinosaurs. According to Warshaw and Fowler, Daspletosaurus wilsoni represents a “missing link” in the evolution of tyrannosaurids because of its blend of ancient and modern features.
The research suggests that the newly found fossil represents a link between the 77 million year old Daspletosaurus torosus and the younger, 75 million year old Daspletosaurus horneri. Before this discovery, it was unclear whether these two Daspletosaurus species were related or had developed independently. However, the newly revealed connection suggests that they were closely linked, and so formed an evolutionary branch that, presumably, resulted in the creation of Tyrannosaurus rex.
More Evidence for the Linearity of Dinosaur Evolution
Anagenesis, often known as “linear evolution,” is the process by which one species directly gives rise to another. Consequently, the tyrannosaurid family is added to the increasing list of dinosaurs for whom such anagenesis is documented. As a result, linear evolution may have been more common among dinosaurs than previously imagined.
Cooked by fire: As early as 780,000 years ago, early humans cooked their food by fire, as findings from Israel now prove. They are the earliest clear evidence of cooking among our ancestors. These are fossil fish teeth that show changes in their structure typical of controlled heating. This suggests that the early humans living in this area caught and cooked these fish in the nearby lake – presumably in some kind of earth oven, as the archaeologists report.
For the development of our ancestors and their increasingly large brains, nutrition and the use of fire played a crucial role. This is because cooked food is easier to digest, and the body can better tap into the nutrients. Early humans were therefore able to get more energy from cooked or roasted meat, fish, and plant foods. They thus needed less time to obtain food and had free resources for cultural development.
However, it is unclear since when early humans specifically cooked their food. It is true that there are one million-year-old traces of fireplaces of Homo erectus. However, it is disputed whether the bones and plant remains found in them were only burned or cooked in a controlled manner. Clear evidence of cooking was around 170,000 years old at the earliest and comes from Neanderthals and Homo sapiens.
Relics of thousands of fish
Carp skull similar to those caught by early humans.
But now, for the first time, archaeologists have found clear traces of cooking as early as the time of Homo erectus. The fossil evidence for this was discovered by Irit Zohar of Tel Aviv University and her team at the Gesher Benot Ya’aqov site in northern Israel. Stone tools, traces of fire, and food remains from hunter-gatherers from around 780,000 years ago have been found there. In addition to animal bones, the remains of thousands of fish that were caught in nearby Lake Hula and then consumed are found there.
What is striking is that the more than 40,000 fish remains come primarily from only two fish species – the two large, particularly nutritious barbel species, Luciobarbus longiceps and Carasobarbus canis. Curiously, however, the research team found hardly any bones of these fish species, although they would normally be preserved, but almost exclusively the pharyngeal teeth of these barbels.
Traces of moderate heat
In search of an explanation, Zohar and her team examined the fish teeth more closely using X-ray diffraction analysis. The crystal structure of the enamel thus made visible can reveal, among other things, whether the teeth were once heated and to what extent. In fact, it showed that a large proportion of the fish teeth found near the fireplaces had been exposed to temperatures of 570 to 930 degrees Fahrenheit (300 to 500 degrees Celsius).
“The enlargement of the apatite crystals in the enamel of the fish teeth shows us that the fish were only exposed to moderate heat and were not burned,” explains co-author Jens Najorka of the Natural History Museum in London. This suggests that early humans cooked the lake-caught fish in a controlled way in the fire. “We can refute an alternative explanation that people consumed the fish fresh or dried and then only burned the remains, because then the enamel would have been more altered,” the researchers said.
Cooking the fish could also explain why hardly any fish bones were preserved. Cooking softened the bones, which caused them to disintegrate more quickly over time.
First evidence of controlled cooking
According to the researchers, their findings suggest that early humans on the shores of Lake Hula ate cooked or steamed fish as early as 780,000 years ago. It’s the earliest evidence that our ancestors cooked their food in some way. Fish prepared in this way were not only nutritious and filling, but they were also available year-round, unlike many wild foods.
The hominids of Gesher Benot Ya’aqov thus had an abundant source of food, even in winter. The ability to cook their food, marked an important milestone in evolutionary development, because it enabled the optimal use of available food resources. It’s quite possible that early humans at that time cooked not only fish, but also various animal and plant foods.
Cooked in an earth oven
Because no fossil remains of the early humans of Gesher Benot Ya’aqov have been found so far, it is still unclear whether they were representatives of Homo erectus or another species. Also, still puzzling is the cooking method they used. No traces of cooking utensils have survived, either at this site or elsewhere, from this period. However, archaeologists suspect that the people at that time cooked their fish in a kind of earth oven, as is still common today among some primitive peoples. (Nature Ecology & Evolution, 2022; doi: 10.1038/s41559-022-01910-z)
There is a true treasure mine of the world’s earliest fish fossils in China, uncovered by paleontologists. The fossils, which are as ancient as 439 million years, prove that the first animals with jaws appeared earlier than previously believed. Scientists have published their findings in no less than four separate issues of “Nature,” and among them are the earliest known examples of cartilaginous fish and jawed armored fish fossils. This provides fresh data on the evolution of fish and the first vertebrates with jaws, which includes humans.
Almost all living vertebrates have their ancestry in ancient fish since they were the first vertebrates to develop a jaw. In the end, they gave rise to the Gnathostomata group, which literally means “jawed mouth,” to which we modern humans also now belong. However, the development of the first fishes, and therefore our earliest predecessors, has been the least explored area of evolutionary biology.
Dreadful gap in fossil records
Approximately 439–436 million years ago is when the Chongqing Lagerstätte was formed. Xiushanosteus mirabilis (2a and 2b), an armored-jawed fish, and Shenacanthus vermiformis (1a, 1b), an ancient shark and ray relative, have both been discovered on this slab. (Y.-A. Zhu et al/Nature 2022)
The issue is that, according to DNA analyses, the first gnathostomes likely arose around 450 million years ago. However, fossils that would have been present in the same period are now absent. But fish fossils are so plentiful in the Devonian Period, which began about 419 million years ago, that it is sometimes known as the Age of Fishes. In the previous decade, paleontologists in China made the first discoveries of fish fossils that date back 425 million years.
According to the theory, the first jaw could be developed by the now-extinct armored fishes (Placodermi), which had a thick carapace of bone plates on the head and trunk but a still-undeveloped skullcap. This makes them, in theory, the ancestors of modern-day sharks andrays, which are cartilaginous fishes. But how about the bony fish that evolved into the terrestrial vertebrates that also eventually became our ancestors? The answers to these theories are now up for debate once again because of a scarcity of new fossil discoveries.
A prehistoric aquarium
The jawless fish Tujiaaspis vividus demonstrates how the specimen’s remarkable preservation is shedding light on the development of fins in later jawed relatives. (Heming Zhang)
A jawless species, the oldest armored fish to date, and three different early cartilaginous fish, making them the oldest known shark ancestors, were discovered in China’s Chongqing province by paleontologists led by You-an Zhu and Qiang Li of the Chinese Academy of Sciences.
During the first discovery, scientists found the first Silurian fish fossil wholly intact. Over the last two years, researchers have been able to uncover hundreds more fossils with their ongoing digs. This location has the earliest known fossils of jawed vertebrates and fish from 436 million years ago, many of which are very well preserved and complete.
The primary characteristics of the Tujiaaspis fossil and its depiction. (Zhikun Gai et al.)
A fresh perspective on the evolution of vertebrates
Scientists can now test the long-debated theories regarding the evolutionary ancestry of humans. Important as they are for their age alone, the newly found fossils are much more so since they reveal for the first time the whole anatomy of the earliest fishes, from head to tail.
The first thing we can learn from the new discoveries is when vertebrates with jaws first appeared in the timeline. The fossils show that by the early Silurian Period (from 444 Mya to 420 Mya), there was already a great deal of morphological variation among mammals with jaws and wide distribution of the major phylogenetic groupings. This shows that these fishes’ ancestry goes back far further in time than was previously believed, according to researchers.
The first jaws were little and flimsy
The tiny size of the fishes is one of the two most striking traits of this fossil collection, along with its tremendous variety. Since most species are just a few millimeters in length. This may be the reason why so few fossils of ancient fish have been found so far.
Vertebrates with jaws from Chongqing are tiny and fragile, indicating that they were likely poorly preserved outside of certain deposit types. On the other hand, it’s possible that fishes were only regionally spread at the time and the evolution of fishes with jaws was slower than that of their jawless forebears.
Fish with jaws but no frills
An artist’s conception of the complete preservation of Xiushanosteus mirabilis fossils from head to tail. (Heming Zhang)
Yet another finding regarding the early fishes’ appearance is also revealed by the fossils. More than 20 individuals of the armored fish Xiushanosteus mirabilis have been found in Chongqing. These ancient fossils are mostly intact. The tiny Xiushanosteus combines the characteristics of many different types of armored fish.
Exciting, however, is the structure of the armored plates above its skull. The plates include a unique set of sutures that set them apart from the surrounding head plates. Researchers speculate that the change to the bony fishes’ skull plates could make its first appearance here.
Ancestor fishes with shoulder pads
This reconstruction depicts Shenacanthus vermiformis, a small, armored cartilaginous fish that lived in the same ecosystem as its bony counterparts. (Heming Zhang)
Another unique trait may be seen in the remains of two primitive cartilaginous fish, the forerunners of modern sharks and rays. Shenacanthus vermiformis, a species discovered in Chongqing that is around 436 million years old, has many of the normal shark characteristics, but its shoulder region is covered by huge, hard armor plates, like those of an armored fish. Such armored fish and jawless have a full ring of thickened skin parts all the way around their bodies.
The Fanjingshania renovata, a shark fish that lived 439 million years ago and has a striking resemblance to the armored fish due to its armored shoulder region, is a pleasing example of a cartilaginous fish with a comparable structure. On the other hand, the fish has teeth and scales that are similar to those of bony fish. According to the research group led by Qujing Normal University’s first author Plamen Andreev, this combination distinguishes this ancient fish from all other known vertebrates.
New and exciting times
Together, these new fossils provide fascinating light on the timeframe during which the first animals with jaws initially appeared. There will undoubtedly be heated discussions on the unique properties of these new fossils and the complexities of their classification. After all, much remains unknown about the variety of the recently found fishes.
More jawed fishes from the Early Silurian have been found at these locations, although these have not yet been characterized. As a result, the study of primitive jawed fishes has entered a new and interesting epoch. (Nature, 2022; doi: 10.1038/s41586-022-05136-8; doi: 10.1038/s41586-022-05233-8)
