Read the passage below. Then, arrange the descriptions of the author's argumentative moves in the chronological order in which they appear in the passage.
For decades, paleontologists assumed that the distinctive dorsal plates of the Stegosaurus functioned primarily as biological armor. This traditional hypothesis, rooted in early twentieth-century paradigms of dinosaur morphology, posited that the plates evolved to defend against apex predators of the Late Jurassic period. However, closer anatomical analyses conducted in the 1980s severely undermined this defensive hypothesis. Fossil records demonstrated that the plates were relatively thin, fragile, and not directly attached to the skeletal spine, rendering them virtually useless for repelling a high-impact predatory attack. Furthermore, the discovery of extensive vascular channels within the plates suggested they were covered in skin and rich in blood vessels—traits counterproductive for armor but highly suggestive of a different evolutionary purpose.
In light of these findings, researchers proposed a thermoregulatory hypothesis, arguing that the highly vascularized plates functioned analogously to the ears of modern elephants. According to this model, the Stegosaurus could dissipate excess body heat by pumping blood into the plates, which would then be cooled by ambient air currents. While elegantly aligning with the anatomical data regarding vascularity, the thermoregulatory hypothesis struggled to explain the staggered, asymmetrical arrangement of the plates along the animal's back, a configuration that offers no distinct aerodynamic advantage for heat exchange.
More recently, paleobiologists have advanced a "display" hypothesis, shifting the focus from physiological utility to intraspecific communication. Proponents of this view argue that the sheer size, unique arrangement, and extensive vascularization of the plates—which could have allowed for rapid, flush-induced color changes—make them ideal structures for species recognition, intimidating rivals, or attracting mates. By recontextualizing the anatomical peculiarities that confounded earlier models, the display hypothesis provides the most comprehensive account to date of this enigmatic morphological feature.
- 1Outlining a historically dominant hypothesis regarding the function of a specific anatomical feature.
- 2Detailing morphological evidence that significantly weakens the plausibility of the initial hypothesis.
- 3Advancing a physiological explanation that accounts for the newly identified structural characteristics.
- 4Endorsing a behavioral theory that resolves anatomical anomalies left unexplained by a prior model.