### Fossilized Excrement and Regurgitation Offer Insights Into Dinosaurs’ Ascendancy
Paleontologists have consistently aimed to uncover how dinosaurs, originally small and seemingly trivial within the larger ecosystem, came to rule terrestrial life during the Mesozoic Era. A recent study published in *Nature* provides clarification on this evolutionary enigma, utilizing an unusual yet profoundly insightful resource: fossilized excrement and regurgitated material, collectively known as bromalites. These trace fossils present a distinctive view into ancient ecosystems, offering vital revelations regarding the diets, behaviors, and environmental adjustments of early dinosaurs.
—
### Defining Bromalites
Bromalites encompass trace fossils that consist of coprolites (fossilized excrement), regurgitated substances, and other remnants from an organism’s digestive system. In contrast to paleofeces, which preserve organic elements that can be chemically examined, coprolites are entirely fossilized, with organic substances replaced by minerals like silicates and calcium carbonates. Nonetheless, they continue to be a wealth of information for paleontologists.
For instance, the discovery of bone fragments within a coprolite indicates a carnivorous diet, whereas plant materials imply herbivory. The dimensions, form, and internal makeup of coprolites can also unveil details about the physiology and feeding preferences of the creature that produced them. Spiral-shaped coprolites, for example, are frequently linked to ancient sharks, known for their spiral intestines.
—
### Research: Reconstructing Ancient Food Networks
The research group, spearheaded by evolutionary biologist Martin Qvarnström from Uppsala University in Sweden, examined 532 bromalites gathered from eight locations in the Polish Basin. These samples, originating from the Late Triassic and Early Jurassic epochs (around 237–145 million years ago), were analyzed using various advanced methodologies:
1. **Microscopy**: Thin slices of bromalites were digitally captured under a microscope to scrutinize their internal structure.
2. **Synchrotron Microtomography**: This high-fidelity imaging approach enabled the team to create 3D digital reconstructions of the interiors of the bromalites.
3. **Chromatography and Mass Spectrometry**: These techniques were employed to extract and analyze plant remains, which were further evaluated using scanning electron microscopy.
By juxtaposing their findings with existing data from fossilized skeletons and footprints, the researchers successfully identified the producers of the bromalites, their feeding habits, and their relative sizes. This information facilitated the reconstruction of food webs for specific epochs, providing an in-depth view of how ecosystems transformed during the Late Triassic and Early Jurassic periods.
—
### Competing Theories: Why Did Dinosaurs Ascend to Dominance?
The study sought to investigate two rival theories regarding the ascent of dinosaurs:
1. **Competitive Replacement Model**: This conventional perspective posits that dinosaurs outperformed other species due to superior adaptations, including more efficient physiologies, anatomical advancements, and specialized feeding strategies.
2. **Opportunistic Replacement Model**: This alternative theory argues that dinosaurs seized opportunities presented by environmental upheavals, such as volcanic eruptions and climate shifts, that resulted in the decline of other species. The adaptability of dinosaurs allowed them to flourish in these swiftly changing environments.
—
### Key Results: Support for Opportunistic Replacement
The analysis conducted by the researchers lends credence to the opportunistic replacement model, particularly in the Polish Basin. Their results suggest that the emergence of dinosaurs was not purely due to inherent advantages but significantly shaped by stochastic (random) environmental factors. Notable findings include:
– **Dietary Flexibility**: Early dinosaurs exhibited remarkable adaptability, capable of ingesting a diverse range of food sources. This versatility likely provided them with an advantage in ecosystems experiencing rapid changes.
– **Climatic Changes**: Fluctuations in climate and vegetation during the Late Triassic and Early Jurassic may have prompted shifts in feeding patterns, favoring species that could take advantage of new food opportunities.
– **Gradual Development**: The progression from small omnivorous dinosaur ancestors to larger herbivorous and carnivorous dinosaurs occurred incrementally, indicating that the dominance of dinosaurs resulted from prolonged ecological and evolutionary processes rather than immediate competition.
—
### Broader Ramifications and Future Investigations
The findings of this study underscore the significance of environmental influences in guiding evolutionary paths. However, as Lawrence Tanner of Le Moyne College notes in an accompanying commentary, the research has limitations in scope and context. Expanding this methodology to additional regions and ecosystems could yield a more complete understanding of the global factors fostering the rise of dinosaurs.
“This study enhances our comprehension of dinosaur diversification and dominance by providing empirical evidence for a mechanism driven by random events,” Tanner states. “However, additional research is essential to construct a more nuanced understanding of the relationship between Late Triassic environmental disruptions and the rise of dinosaurs.”
—
### Conclusion
Through the examination of fossilized excrement and regurgitated material
