Fossils illuminate dinosaur evolution in eastern North America
Tyrannosaurus rex, the fearsome predator that once roamed what is now western North America, appears to have had an East Coast cousin.
A new study by Yale undergraduate Chase Doran Brownstein describes two dinosaurs that inhabited Appalachia — a once isolated land mass that today composes much of the eastern United States — about 85 million years ago: an herbivorous duck-billed hadrosaur and a carnivorous tyrannosaur. The findings were published Aug. 25 in the journal Royal Society Open Science.
The two dinosaurs, which Brownstein described from specimens housed at Yale’s Peabody Museum of Natural History, help fill a major gap in the North American fossil record from the Late Cretaceous and provide evidence that dinosaurs in the eastern portion of the continent evolved distinctly from their counterparts in western North America and Asia, Brownstein said.
“These specimens illuminate certain mysteries in the fossil record of eastern North America and help us better understand how geographic isolation — large water bodies separated Appalachia from other landmasses — affected the evolution of dinosaurs,” said Brownstein, who is entering his junior year at Yale College. “They’re also a good reminder that while the western United States has long been the source of exciting fossil discoveries, the eastern part of the country contains its share of treasures.”
For most of the second half of the Cretaceous, which ended 66 million years ago, North America was divided into two land masses, Laramidia in the West and Appalachia in the East, with the Western Interior Seaway separating them. While famous dinosaur species like T. rex and Triceratops lived throughout Laramidia, much less is known about the animals that inhabited Appalachia. One reason is that Laramidia’s geographic conditions were more conducive to the formation of sediment-rich fossil beds than Appalachia’s, Brownstein explained.
The specimens described in the new study were discovered largely during the 1970s at the Merchantville Formation in present day New Jersey and Delaware. They constitute one of the only known dinosaur assemblages from the late Santonian to early Campanian stages of the Late Cretaceous in North America. This fossil record period, dating from about 85 to 72 million years ago, is limited, Brownstein noted.
Brownstein examined a partial skeleton of a large predatory therapod, concluding that it is probably a tyrannosaur. He noted that the fossil shares several features in its hind limbs with Dryptosaurus, a tyrannosaur that lived about 67 million years ago in what is now New Jersey. The dinosaur has different hands and feet than T. rex, including massive claws on its forelimbs, suggesting that it represents a distinct family of the predators that evolved solely in Appalachia.
“Many people believe that all tyrannosaurs must have evolved a specific set of features to become apex predators,” Brownstein said. “Our fossil suggests they evolved into giant predators in a variety of ways as it lacks key foot or hand features that one would associate with western North American or Asian tyrannosaurs.”
The partial skeleton of the hadrosaur provided important new information on the evolution of the shoulder girdle in that group of dinosaurs, Brownstein found. The hadrosaur fossils also provide one of the best records of this group from east of the Mississippi and include some of the only infant/perinate (very young) dinosaur fossils found in this region.
Brownstein, who works as a research associate at the Stamford Museum and Nature Center in Stamford, Connecticut, has previously published his paleontological research in several peer-journals, including Scientific Reports, the Journal of Paleontology, and the Zoological Journal of the Linnaean Society. In addition to eastern North American fossils, he currently focuses his research on the evolution of fishes, lizards, and birds. He is particularly interested in how geographic change and other factors contribute to how fast different types of living things evolve.
He currently works in the lab of Thomas J. Near, curator of the Peabody Museum’s ichthyology collections and professor and chair of the Department of Ecology and Evolutionary Biology at Yale. Brownstein also collaborates with Yale paleontologists Jacques Gauthier and Bhart-Anjan Bhullar in the Department of Earth and Planetary Sciences.
While Brownstein is considering pursuing an academic career in evolutionary biology, he says his research is driven by enjoyment.
“Doing research and thinking about these things makes me happy,” he said. “Like biking, it’s something I love to do.”
Story Source:
Materials provided by Yale University. Original written by Mike Cummings. Note: Content may be edited for style and length.
Journal Reference:
- Chase Doran Brownstein. Dinosaurs from the Santonian–Campanian Atlantic coastline substantiate phylogenetic signatures of vicariance in Cretaceous North America. Royal Society Open Science, 2021; 8 (8): 210127 DOI: 10.1098/rsos.210127
New fossils show what the ancestral brains of arthropods looked like
Exquisitely preserved fossils left behind by creatures living more than half a billion years ago reveal in great detail identical structures that researchers have long hypothesized must have contributed to the archetypal brain that has been inherited by all arthropods. Arthropods are the most diverse and species-rich taxonomic group of animals and include insects, crustaceans, spiders and scorpions, as well as other, less familiar lineages such as millipedes and centipedes.
The fossils, belonging to an arthropod known as Leanchoilia, confirm the presence — predicted by earlier studies in genetics and developmental biology of insect and spider embryos — of an extreme frontal domain of the brain that is not segmented and is invisible in modern adult arthropods. Despite being invisible, this frontal domain gives rise to several crucial neural centers in the adult arthropod brain, including stem cells that eventually provide centers involved in decision-making and memory. This frontal domain was hypothesized to be distinct from the forebrain, midbrain and hindbrain seen in living arthropods, and it was given the name prosocerebrum, with “proso” meaning “front.”
Described in a paper published today in the journal Current Biology, the fossils provide the first evidence of the existence of this discrete prosocerebral brain region, which has a legacy that shows up during the embryonic development of modern arthropods, according to paper lead author Nicholas Strausfeld, a Regents Professor of Neuroscience at the University of Arizona.
“The extraordinary fossils we describe are unlike anything that has been seen before,” Strausfeld said. “Two nervous systems, already unique because they are identically preserved, show that half a billion years ago this most anterior brain region was present and structurally distinct before the evolutionary appearance of the three segmental ganglia that denote the fore-, mid- and hindbrain.”
The term ganglion refers to a system of networks forming a nerve center that occurs in each segment of the nervous system of an arthropod. In living arthropods, the three ganglia that mark the three-part brain condensed together to form a solid mass, obscuring their evolutionary origin as segmented structures.
Fossils of Brain Tissue are Extremely Rare
Discovered in deposits of the Kaili formation — a geological formation in the Guizhou province of southwest China — the fossilized remains of Leanchoilia date back to the Cambrian period, about 508 million years ago. The Kaili fossils occur in sedimentary rock that has high concentrations of iron, the presence of which probably helped preserve soft tissue, which subsequently was replaced by carbon deposits.
“The Kaili fossils open a window for us to glimpse the body plan evolution of animals that lived more than half a billion years ago,” said the paper’s first author, Tian Lan of the Guizhou Research Center for Palaeobiology at Guizhou University in China. “For the first time, we now know that arthropod fossils of the Kaili formation have the potential to preserve neural tissue that show us the primitive brain of the early stem arthropod existing at the dawn of the animal world.”
“Nervous systems, as other soft tissues, are difficult to fossilize,” added co-author Pedro Martinez of the Universitat de Barcelona and Institut Catalá in Barcelona, Spain. “This makes the study of the early evolution of neural systems a challenging task.”
The fossils also shed new light on the evolutionary origin of two separate visual systems in arthropod evolution: pairs of front-facing eyes or sideward looking eyes, the descendants of which are still present in species living today.
Many arthropods, including insects and crustaceans, have a distinct bilateral pair of faceted compound eyes and another set of less obvious eyes — with more primitive architecture — known as nauplius eyes, or ocelli. These are structurally similar to the principal eyes of spiders and scorpions. These simpler eyes correspond to the prosocerebrum’s forward eyes in Leanchoilia, in line with evidence obtained by previous studies analyzing gene expression patterns during embryonic development of living arthropods.
Leanchoilia‘s sideward eyes, on the other hand, relate to the protocerebrum, which is the segmental ganglion defining the arthropod forebrain, lying just behind the prosocerebrum. In living arthropods, the protocerebrum provides the compound eyes of insects and crustaceans, or the lateral single-lens eyes of arachnids, centipedes and millipedes. The visual centers serving those eyes also belong to the brain’s protocerebral region.
Strausfeld explained that in living arthropods, the protocerebrum, or forebrain, has incorporated — in a way, swallowed up — the ancient centers provided by the prosocerebrum, so that it is no longer discernible as a distinct anatomical entity.
The fossils are so well-preserved that they demonstrate that in addition to frontward eyes, the prosocerebrum has also given rise to ganglia associated with the labrum, or “upper lip,” of modern arthropods. The fossils also confirm an earlier hypothesis suggesting that the labrum must have originally evolved from the grasping appendages of Radiodonta, a group of stem-arthropods that were top predators during the Cambrian period.
“When compared with other, similar fossil material belonging to more advanced lineages, the organization of the Leanchoilia brain demonstrates that the ganglionic arrangement of the early brain underwent condensation and fusion of its components, which explains why in living species the prosocerebrum cannot be individually distinguished,” Strausfeld said.
Implications for Brain Evolution in Vertebrates
In addition to closing a century-old gap in the understanding of arthropod brain evolution, the findings have important implications for the early evolution of vertebrate brains, Strausfeld said.
Although simple, fishlike animals existed at the same time as these now-fossilized arthropods, there are no convincing fossils of their brains and, thus, neither fossil evidence nor anatomical evidence for a prosocerebrum in vertebrates. Yet, modern studies show that genes defining the fore- mid- and hindbrains of, for example, mice correspond to genes defining the three ganglionic divisions of the arthropod brain. And in vertebrates, certain crucial centers involved in decision making and in learning and memory have some genetic correspondences with the higher centers in the arthropod brain, which originated in the ancient arthropod prosocerebrum.
Thus, it is plausible that even earlier than the Cambrian period, possibly even before the evolution of segmentally organized body plans, the common ancestor of both vertebrates and invertebrates possessed basic circuits for simple cognition and decision making. And while an ancient prosocerebral-like brain might have been present in the very early ancestors of vertebrates, no such fossil has even suggested evidence for a discrete, nonsegmental domain.
“Nevertheless, one can reasonably speculate that vertebrates have embedded in their ‘modern’ brains parts of an ancient, non-segmented brain that has so far only been demonstrable in an early arthropod, such as Leanchoilia,” Strausfeld said.
Additional co-authors on the study are Yuanlong Zhao of the Guizhou Research Center for Palaeobiology at Guizhou University in Guiyang, China; Fangchen Zhao of the State Key Laboratory of Palaeobiology and Stratigraphy of the Chinese Academy of Sciences in Nanjing, China; and You He of Shanghai Synchrotron Radiation Facility.
Story Source:
Materials provided by University of Arizona. Original written by Daniel Stolte. Note: Content may be edited for style and length.
Journal Reference:
- Tian Lan, Yuanlong Zhao, Fangchen Zhao, You He, Pedro Martinez, Nicholas J. Strausfeld. Leanchoiliidae reveals the ancestral organization of the stem euarthropod brain. Current Biology, 2021; DOI: 10.1016/j.cub.2021.07.048
Study of tyrannosaur braincases shows more variation than previously thought
Among the fierce carnivores that lived during the late Cretaceous was a predator named Daspletosaurus. The massive tyrannosaur, about nine metres long, lived in the coastal forest of what is now Alberta around 75 million years ago — preceding the more famous T. rex by about 10 million years.
For the first time, scientists in Canada and Argentina have used CT scans to digitally reconstruct the brain, inner ear, and surrounding bones (known as the braincase) of two well-preserved Daspletosaurus specimens.
Their results, published online today in the Canadian Journal of Earth Sciences, counter a prevailing view that dinosaur brains and the bones enclosing and protecting them varied little within species, or among closely related species, especially when compared with changes observed in other parts of the skeleton. “Our study with the two Daspletosaurus specimens suggests otherwise,” explains Dr. Tetsuto Miyashita, palaeontologist with the Canadian Museum of Nature and senior author of the study.
“We know that tyrannosaurs had relatively good-sized brains for a dinosaur, and this study shows that this pattern holds for Daspletosaurus. Furthermore, based on the shapes of the brain, ear structure, and braincase, we suggest that these two specimens represent distinct species of daspletosaurs.”
Access to a braincase, the internal part of the skull that surrounds and protects the brain, helps unlock one of the most complex parts of dinosaur anatomy. This requires advanced medical technology such as a CT scanner to image the internal spaces hidden underneath thick bones, with the resulting hundreds of hours of work to reconstruct the brain and other fleshy parts slice by slice. Therefore, most studies on dinosaur brains have each focused on one specimen from a representative species of the group. As an exception, Tyrannosaurus rex has several such reconstructions of their brains. Now, this new study investigates two remarkably well-preserved skulls of Daspletosaurus, a much rarer tyrannosaur than T. rex.
One belongs to the original specimen of Daspletosaurus, which is prominently displayed at the Canadian Museum of Nature in Ottawa. Unearthed in 1921 along the banks of Alberta’s Red Deer River, its description in 1970 as Daspletosaurus torosus (“muscular frightful lizard)” by Dr. Dale Russell ushered in the modern era of research on tyrannosaurids. The second specimen, uncovered in 2001, is with the Royal Tyrrell Museum of Palaeontology in Alberta. Miyashita is continuing to study it with Dr. Philip Currie of the University of Alberta, another author of the study.
Study of the braincase structure and its endocranial cavity provides insights on the brain itself, as well as characteristics such as the layout of cranial nerves, and some aspects of the sensory biology such as auditory and visual anatomy that drove the life of the dinosaur.
Dr. Ariana Paulina Carabajal, a dinosaur braincase expert in Argentina and study co-author at the Instituto de Investigaciones en Biodiversidad y Medioambiente (CONICET-Universidad Nacional del Comahue), provided the detailed models of the brain and inner ear anatomy and related structures. Among the findings were the presence of large bony canals that would have transmitted thick nerve bundles that moved the eyeballs. The researchers also describe large air sacs that filled up most of the braincase bones, which is in line with the limited studies known of other tyrannosaurs.
“These cavities within the bones not only make the huge skull lighter, but also are related to the middle region of the ear,” explains Paulina Carabajal. “The cavities probably helped to amplify sound and assist the system that communicates to the left and right ears, allowing the brain to determine where a sound is coming from.”
Yet, even within the two braincases of Daspletosaurus, there were differences. “It was surprising to see so many variations in the braincases even though the skeletons are similar,” says Miyashita, who offers that their study provides a good reason to look at more braincases within similar groups of dinosaurs, or even within species.
“Researchers have looked inside so few braincases in dinosaurs, typically one each for whatever species they studied, that this reinforced the assumption that these structures don’t change much within and among species. We just haven’t looked inside enough skulls to document variation.”
Additional authors of the paper, entitled “Two braincases of Daspletosaurus (Theropoda: Tyrannosauridae): anatomy and comparison,” are Thomas Dudgeon, and Dr. Hans Larsson of McGill University, who contributed the scanning data for the Canadian Museum of Nature specimen. The study authors are grateful to the Montfort Hospital in Ottawa, the University of Alberta Hospital in Edmonton, and the Canada Diagnostic Centre in Calgary for access to their CT scanners.
Story Source:
Materials provided by Canadian Museum of Nature. Note: Content may be edited for style and length.
Journal Reference:
- Ariana Paulina Carabajal, Philip J. Currie, Thomas W. Dudgeon, Hans C.E. Larsson, Tetsuto Miyashita. Two braincases of Daspletosaurus (Theropoda: Tyrannosauridae): anatomy and comparison. Canadian Journal of Earth Sciences, 2021; 1 DOI: 10.1139/cjes-2020-0185
Discovery of prehistoric mammals suggests rapid evolution of mammals after dinosaur extinction
Research published today in the peer-reviewed Journal of Systematic Palaeontology describes the discovery of three new species of ancient creatures from the dawn of modern mammals, and hints at rapid evolution immediately after the mass extinction of the dinosaurs.
These prehistoric mammals roamed North America during the earliest Paleocene Epoch, within just a few hundred thousand years of the Cretaceous-Paleogene boundary that wiped out the dinosaurs. Their discovery suggests mammals diversified more rapidly after the mass extinction than previously thought.
New-to-science, the creatures discovered are Miniconus jeanninae, Conacodon hettingeri, and Beornus honeyi. They differ in size — ranging up to a modern house cat, which is much larger than the mostly mouse to rat-sized mammals that lived before it alongside the dinosaurs in North America.
Each have a suite of unique dental features that differ from each other.
Beornus honeyi, in particular has been named in homage to The Hobbit character Beorn, due to the appearance of the inflated (puffy) molars (cheek teeth).
The new group belong to a diverse collection of placental mammals called archaic ungulates (or condylarths), primitive ancestors of today’s hoofed mammals (eg, horses, elephants, cows, hippos).
Paleontologists from the University of Colorado in Boulder unearthed parts of lower jaw bones and teeth — which provide insights into the animals’ identity, lifestyle and body size.
The three new species belong to the family Periptychidae that are distinguished from other ‘condylarths’ by their teeth, which have swollen premolars and unusual vertical enamel ridges. Researchers believe that they may have been omnivores because they evolved teeth that would have allowed them to grind up plants as well as meat, however this does not rule out them being exclusively herbivores.
The mass extinction that wiped out the non-avian dinosaurs 66 million years ago is generally acknowledged as the start of the ‘Age of Mammals’ because several types of mammal appeared for the first time immediately afterwards.
As lead author Madelaine Atteberry from the University of Colorado Geological Sciences Department in the USA explains, “When the dinosaurs went extinct, access to different foods and environments enabled mammals to flourish and diversify rapidly in their tooth anatomy and evolve larger body size. They clearly took advantage of this opportunity, as we can see from the radiation of new mammal species that took place in a relatively short amount of time following the mass extinction.”
Atteberry and co-author Jaelyn Eberle, a curator in the Museum of Natural History and Professor of Geological Sciences at the University of Colorado, studied the teeth and lower jaw bones of 29 fossil ‘condylarth’ species to determine the anatomical differences between the species, and used phylogenetic techniques to understand how the species are related to each other and to other early Paleocene ‘condylarths’ in the western United States.
The evidence supports the discovery of these three new species to science.
About the size of a marmot or house cat, Beornus honeyi was the largest; Conacodon hettingeri is similar to other species of Conacodon, but differs in the morphology of its last molar, while Miniconus jeanninae is similar in size to other small, earliest Paleocene ‘condylarths’, but is distinguished by a tiny cusp on its molars called a parastylid.
“Previous studies suggest that in the first few hundred thousand years after the dinosaur extinction (what is known in North America as the early Puercan) there was relatively low mammal species diversity across the Western Interior of North America, but the discovery of three new species in the Great Divide Basin suggests rapid diversification following the extinction,” says Atteberry. “These new periptychid ‘condylarths’ make up just a small percentage of the more than 420 mammalian fossils uncovered at this site. We haven’t yet fully captured the extent of mammalian diversity in the earliest Paleocene, and predict that several more new species will be described.”
Story Source:
Materials provided by Taylor & Francis Group. Note: Content may be edited for style and length.
Journal Reference:
- Madelaine R. Atteberry, Jaelyn J. Eberle. New earliest Paleocene (Puercan) periptychid ‘condylarths’ from the Great Divide Basin, Wyoming, USA. Journal of Systematic Palaeontology, 2021; 1 DOI: 10.1080/14772019.2021.1924301
Researchers find a ‘fearsome dragon’ that soared over outback Queensland
Australia’s largest flying reptile has been uncovered, a pterosaur with an estimated seven-metre wingspan that soared like a dragon above the ancient, vast inland sea once covering much of outback Queensland.
University of Queensland PhD candidate Tim Richards, from the Dinosaur Lab in UQ’s School of Biological Sciences, led a research team that analysed a fossil of the creature’s jaw, discovered on Wanamara Country, near Richmond in North West Queensland.
“It’s the closest thing we have to a real life dragon,” Mr Richards said.
“The new pterosaur, which we named Thapunngaka shawi, would have been a fearsome beast, with a spear-like mouth and a wingspan around seven metres.
“It was essentially just a skull with a long neck, bolted on a pair of long wings.
“This thing would have been quite savage.
“It would have cast a great shadow over some quivering little dinosaur that wouldn’t have heard it until it was too late.”
Mr Richards said the skull alone would have been just over one metre long, containing around 40 teeth, perfectly suited to grasping the many fishes known to inhabit Queensland’s no-longer-existent Eromanga Sea.
“It’s tempting to think it may have swooped like a magpie during mating season, making your local magpie swoop look pretty trivial — no amount of zip ties would have saved you.
“Though, to be clear, it was nothing like a bird, or even a bat — Pterosaurs were a successful and diverse group of reptiles — the very first back-boned animals to take a stab at powered flight.”
The new species belonged to a group of pterosaurs known as anhanguerians, which inhabited every continent during the latter part of the Age of Dinosaurs.
Being perfectly adapted to powered flight, pterosaurs had thin-walled and relatively hollow bones.
Given these adaptations their fossilised remains are rare and often poorly preserved.
“It’s quite amazing fossils of these animals exist at all,” Mr Richards said.
“By world standards, the Australian pterosaur record is poor, but the discovery of Thapunngaka contributes greatly to our understanding of Australian pterosaur diversity.”
It is only the third species of anhanguerian pterosaur known from Australia, with all three species hailing from western Queensland.
Dr Steve Salisbury, co-author on the paper and Mr Richard’s PhD supervisor, said what was particularly striking about this new species of anhanguerian was the massive size of the bony crest on its lower jaw, which it presumably had on the upper jaw as well.
“These crests probably played a role in the flight dynamics of these creatures, and hopefully future research will deliver more definitive answers,” Dr Salisbury said.
The fossil was found in a quarry just northwest of Richmond in June 2011 by Len Shaw, a local fossicker who has been ‘scratching around’ in the area for decades.
The name of the new species honours the First Nations peoples of the Richmond area where the fossil was found, incorporating words from the now-extinct language of the Wanamara Nation.
“The genus name, Thapunngaka, incorporates thapun [ta-boon] and ngaka [nga-ga], the Wanamara words for ‘spear’ and ‘mouth’, respectively,” Dr Salisbury said.
“The species name, shawi, honours the fossil’s discoverer Len Shaw, so the name means ‘Shaw’s spear mouth’.”
The fossil of Thapunngaka shawi is on display at Kronosaurus Korner in Richmond.
Story Source:
Materials provided by University of Queensland. Note: Content may be edited for style and length.
Journal Reference:
- Timothy M. Richards, Paul E. Stumkat, Steven W. Salisbury. A new species of crested pterosaur (Pterodactyloidea, Anhangueridae) from the Lower Cretaceous (upper Albian) of Richmond, North West Queensland, Australia. Journal of Vertebrate Paleontology, 2021; e1946068 DOI: 10.1080/02724634.2021.1946068