The megaherbivore gap after the non-avian dinosaur extinctions modified trait evolution and diversification of tropical palms

Renske E. Onstein, W. Daniel Kissling, and H. Peter Linder

Summarized by Makayla Palm

What data were used? Qualitative data from modern palm tree fruit, phylogenetic data, and palm tree fossils are used in order to observe changes over time in the taxon Arecaceae, or the palm tree, from the Paleogene Period. After the end-Cretaceous extinction that wiped out the non-avian dinosaurs, mega-herbivores, or any herbivore larger than 1,000 kg ( ~2200 lbs), were nowhere to be found. For the most part, small mammals were left foraging for food, and angiosperms (flower-bearing plants) were able to catch a break. The combination of mammalian seed-spreaders and lack of large herbivores preying on angiosperms (palms in this case) meant that the plants were able to increase in numbers without worrying about defenses. These furry seed-spreaders (small animals that pooped out their seeds) were still spreading, allowing plants to grow and didn’t evolve many defense mechanisms like rough leaves or spines. The researchers hypothesized that they would observe three things about palm diversity in the fossil material from this time: the origin of plant armature (or defense structures like spikes) in the Cretaceous Period because of many large herbivores, the decrease in armature during the Post-Cretaceous Paleogene Megaherbivore Gap (PMHG), and the change in fruit size over time as the plants were able to diversify. 

Methods: Measurements of the palm tree fruit fossil material were taken in order to compare how fruit size changed over time within the megaherbivore gap and observations were made on when these changes in size happened, which supplemented the phylogenetic analysis. Living palms were observed in modern habitats, as were  their interactions with larger herbivores of modern times to better understand how the fossil palms may have interacted with herbivores from the Paleogene.

Results: The hypothesis that the first armature appeared in the Cretaceous was confirmed by fossil material, which indicates an increase in defense likely due to megaherbivores. The armature of plants with larger fruit decreased over time, which also supports the hypothesis of losing these defense structures over time with less predation. Despite the disappearance of megaherbivores in the end-Cretaceous, fruit size stayed relatively large (above 4cm). Plants with larger fruit diversified on a constant scale over time, whereas plants with smaller fruit decreased in diversity, counter to the second hypothesis. Overall, some hypotheses were supported, and some were not. 

 Why is this study important? A lot of end-Cretaceous Period studies focus on the end of the dinosaurs, what caused the mass extinction, and how the age of mammals began. This study shows a different perspective on a well-studied time period by using a combination of paleobotany and vertebrate paleontology, and observing how the absence of large herbivores affected how ancient palm trees changed ecologically. This documented diversity opened new doors for angiosperm evolution and led to an increase in forests, setting the stage for the next era of geologic time in North America, the Cenozoic. 

The big picture: The Paleogene megaherbivore gap is a time in geologic history where the absence of large herbivores after the non-avian dinosaur extinction greatly affected ecosystems and the change in the landscape to more dense forests. The lack of large herbivores to eat plants allowed plants to evolve fewer defensive structures and larger fruit, which allowed them to spread farther distances and in greater numbers, because of the increase in seeds. 

Article Citation: Onstein, R. E., Kissling, W. D., & Linder, H. P. (2022). The megaherbivore gap after the non-avian dinosaur extinctions modified trait evolution and diversification of tropical palms. Proceedings of the Royal Society B, 289(1972), 20212633.

A European Giant: a large spinosaurid (Dinosauria, Theropoda) from the Vectis Formation, (Wealden Group, Early Cretaceous) UK. 

Chris T. Barker​,  Jeremy A.F. Lockwood, Darren Naish, Sophie Brown, Amy Hart, Ethan Tulloch, and Neil J. Gostling

Summarized by Makayla Palm

What data were used? Fossil remains of a new theropod dinosaur from Southern England were discovered and excavated over several months’ time. These bones consisted of post-cranial fragments, or the parts of the skeleton below the skull. Most of the vertebrae, parts of the pelvis, and some ribs were identified from this specimen, also known as the White Rock spinosaurid. Measurements were taken of the fragments, and an evolutionary (phylogenetic) analysis was inferred to see where this theropod may fit on an evolutionary tree. 

Methods: Scientists measured these new bone fragments, and over 1,000 characteristics of the fragments were cataloged in a computer and compared to other theropods in a character database. This database categorizes dinosaurs by the features found within their bones, and accounts for the smallest of variations to be as specific as possible. These features also help place the theropod on a family tree by using computer programs that arrange all of the characters to identify which dinosaurs are closely related to one another.  

Results: This theropod’s size and other morphological features indicate that it is likely closely related to Spinosaurus, but may or may not be in the genus Spinosaurus. There is a lot of weathering of the fossil remains, which makes more specific categorization not possible at this time. The presence of canals within the bones suggests that post-death, something began to eat away at the theropod’s bones. Scientists have seen very similar features before in other Cretaceous theropods, and the canals are likely due to beetle pupae that dug their way through these bones after the dinosaur had died. The phylogenetic tree did not provide enough resolution to confirm a more specific group that this specimen belongs to, but the likelihood that it represents a new type of spinosaurid is high. This specimen is not only the first of its kind found in this geological location, but its size rivals all of the known specimens in Europe. 

Why is this study important? This study provides insight into the geologic history of Southern England with the presence of the first known large theropod. First, the Lower Cretaceous geological formations of western Europe have been defined as the origin of the spinosaurids. Secondly, the White Rock spinosaurid appears in the fossil record later than any known spinosaurid on the Island, indicating the presence of spinosaurids to last longer than before. The size of this spinosaurid may have warded off other predators, which might explain why fossils of other theropods have been found this late in other known Spinosaurus– bearing locations. This specimen is classified as a spinosaurid and not a Spinosaurus, because its bones were not preserved well enough to confirm a new taxon of Spinosaurus. More phylogenetic analysis, and the discovery of new material, will provide future insight into its taxonomic placement. 

The big picture: A new theropod has been discovered in Southern England, and its large size and location implies it is not only a new spinosaurid, but also one of the largest theropod dinosaurs in Europe to date. Its presence improves the known range of spinosaurids and may provide new insight into taxonomic variation within the spinosaurids. 

Citation: Barker, Chris T.,  Lockwood, Jeremy A.F., Naish, Darren, Brown, Sophie, Hart, Amy, Tulloch, Ethan, Gostling, Neil J.   “A European Giant: A Large Spinosaurid (Dinosauria: Theropoda) from the Vectis Formation (Wealden Group, Early Cretaceous), UK.” PeerJ, vol. 10, 2022, https://doi.org/10.7717/peerj.13543.

Silurian-Devonian Granites and Associated Intermediate-Mafic Rocks along the Eastern Kunlun Orogen, Western China: Evidence for a Prolonged Post-Collisional Lithospheric Extension

Jinyang Zhang Huanling Lei Changqian Ma Jianwei Li Yuanming Pan 

Summarized by Makayla Palm 

What data were used? The goal of this study was to gain insight into how the Kunlun mountain formation and surrounding area were initially formed. The Kunlun Mountain range primarily has an intermediate and mafic composition, with felsic granite intrusions, or dikes. Dikes are intrusions of magma that cut across previously formed layers and are an indicator of a secondary formation process. Depending on the mineral composition, or silica content, of these dikes (or intrusions) they will be either felsic, intermediate, or mafic, with felsic rocks containing the most silica. There are several kinds of secondary igneous rock formations found in the Kunlun called dikes. If the composition of the dike is different from the surrounding rock, this will provide insight into how the dikes formed in the Kunlun and how it can be explained using plate tectonic theory. 

Granite is a commonly found felsic rock in the Kunlun and is formed intrusively (or underground). The mineral contents of the granite can tell the researchers how fast or slow the magma cooled, which will ultimately help answer the question of how the dikes formed. Within the granite, there were zircon crystals present with radioactive uranium decaying into lead. These ratios were recorded in order to estimate ages within the mountain range to determine when the different magma-cooling events took place. To summarize, this paper uses physical samples of the igneous rocks in the area to study mineral composition and isotope data from these rocks, too. 

Methods: The samples that were collected from different rock types in this area were studied under a microscope in order to observe the composition and individual mineral grains. In plate tectonics, there are two kinds of plates: continental plates and oceanic plates. Granite (felsic) comprises less dense continental plates, while basalt (mafic) comprises a denser oceanic plate. In the Kunlun, the researchers observed several granite inclusions surrounded by mafic rock. The isotope ratios of uranium to lead were recorded and radiometrically dated. These data determine if the different intrusions formed at the same time, or if they formed during several events. This would help support or reject the hypothesis they posed that when the continental and oceanic plates collided, creating the Kunlun Mountains, the edge of the oceanic plate broke while bending under the continental plate (the oceanic plate always goes underneath a continental plate, due to higher density).

Results: The radiometric dating of the granite inside the intrusions (the magma formations added after the formation of the surrounding rock) indicated four different formation events, with the earliest taking place 427-414 million years ago (mya) and the latest from 373-357mya. (For more about how radiometric dating works visit Geologic Time.) The variation in the composition of the rocks (felsic, mafic, etc) indicates a complicated tectonic history; along with the multiple events of granitic intrusions, scientists also found ophiolites (oceanic crust that was pushed onto land during an oceanic- continental plate collision), which indicates that a piece of the oceanic plate was pushed up and broken off during the collision. 

Why is this study important? This study looked to test the hypothesis of a broken oceanic plate’s impact on the formation of the Kunlun mountain range and gain more specific knowledge of its origin. By taking inventory of its intrusive rock formations, getting radiometric dating for these intrusions, and noting the differences in mineral compositions, they were able to confirm their hypothesized four magma events. These events represent different periods of magma formation, which confirms the researcher’s hypothesis about oceanic plate breakage during a collision. 

The big picture: Clues from igneous geology, such as large crystal size, rock type, and mineral composition can give researchers details on how large formation events took place. Isotopes within radiometric dating were used to separate events from one another and place them in chronological order. This particular study answered questions about the origin of the Kunlun Orogen, or mountainous landscapes.

Citation: Zhang, Jinyang, Huanling Lei, Changqian Ma,  Jianwei Li,  Yuanming Pan. “Silurian-Devonian Granites and Associated Intermediate-Mafic Rocks along the Eastern Kunlun Orogen, Western China: Evidence for a Prolonged Post-Collisional Lithospheric Extension.” Gondwana Research, vol. 89, Oct. 2021, pp. 131–146., https://doi.org/10.1016/j.gr.2020.08.019.