Some paleontologists have suggested that Apatosaurus, a huge dinosaur, was able to gallop.
Main Conclusion
Apatosaurus was probably not able to gallop.
Intermediate Conclusion
Galloping would probably have broken Apatosaurus’s legs.
Evidence
Experiments with modern bones show how much strain they can withstand before breaking.
By taking into account the diameter and density of Apatosaurus leg bones, it is possible to calculate that those bones could not have withstood the strains of galloping.
Evaluate
Whenever we do Main Conclusion / Role, we remind ourselves that 85% of the time it's an upside down argument (the conclusion appears earlier than the support).
Specifically about 65% of them are pivot/rebuttal conclusions and about 25% are first-sentence conclusions.
Since this paragraph begins with an Attribution (some P's have suggested that), we'd anticipate a pivot-pushback from the author.
We get that at the start of the 2nd sentence with "This however is unlikely". As soon as we can tell the author is supporting that idea, we know that this was our conclusion.
The next clause begins with the Support Indicator "because galloping ...".
Goal
We want the best meaning match for "This is unlikely". Since it is a rebuttal, we need to articulate the rebuttal conclusion.
THIS = Apatosaurus was able to gallop.
So we want, "Apatosaurus was likely not able to gallop".