In scientific writing, proper terminology is everything. I learned early on that many of my favorite turns of phrase were technically incorrect - and I have been working to improve my writing and editing ever since. Below, I've included some of my "favorite" stylistic oddities. . .hopefully this is useful for at least a few readers! This may be old hat for some of you - in that case, please post a comment with your own grammatical grumblings.
"Outcrops" as a verb
Despite rampant misuse, there is no verb form of "outcrop."
Incorrect: "The Barstow Formation outcrops in southern California."
Correct: "The Barstow Formation crops out in southern California."
A clade is, by definition, monophyletic. So, save your space and only use one of the two words!
Incorrect: "Dinosauria is a monophyletic clade."
Correct 1: "Dinosauria is monophyletic."
Correct 2: "Dinosauria is a clade."
"Data is. . ."
The word "data" is plural; "datum" is the singular. You're bucking against popular culture, but think of how delightfully smug you can feel whenever you use the words correctly.
Incorrect: "The data is overwhelming."
Correct 1: "The data are overwhelming."
Correct 2: "The datum is overwhelming, which is odd because it's only a single measurement."
"e.g." and "i.e."
"E.g." is an abbreviation from the Latin "exempli gratia", basically translating as "for example." "I.e." is the abbreviated form of the Latin "id est", translating as "that is." The meaning for the former should be pretty clear; the latter is used when one wishes to provide further clarification of a point.
Incorrect 1: "Many dinosaurs are found in the Hell Creek Formation (i.e., Triceratops and Tyrannosaurus)."
Correct 1: "Many dinosaurs are found in the Hell Creek Formation (e.g., Triceratops and Tyrannosaurus).
Incorrect 2: "Bird skeletons are pneumatized; e.g., they are filled with air sacs."
Correct 2: "Bird skeletons are pneumatized; i.e., they are filled with air sacs."
Lower/Upper vs. Early/Late
Unless you have had a solid introduction to geology (and even then, it's easy to forget), most people probably don't know that there is a major nitpicky difference between Upper Cretaceous and Late Cretaceous. The Upper/Lower designation refers to lithostratigraphic divisions of rocks; they are not the same as the geochronologic ages of the rocks. In other words - Upper Cretaceous refers to a physical lump of sedimentary rocks; Late Cretaceous refers to the age of these rocks. Whenever I try to figure out which word to use, I concentrate on whether I'm talking about time (Early/Late) or position in the rock column (Lower/Upper).
Incorrect 1: These Early Cretaceous rocks are full of fossils.
Correct 1: These Lower Cretaceous rocks are full of fossils.
Incorrect 2: Tyrannosaurus is Upper Cretaceous in age.
Correct 2: Tyrannosaurus is Late Cretaceous in age.
Want some more? The style guide for Journal of Vertebrate Paleontology (available in PDF format) has lots more great hints and tips!