A few weeks ago, I worshipped in the Manti Utah Temple for the first time. My parents were endowed, married, and sealed there, so it is a special place to me. Amidst my devotions and pondering, I was somewhat taken aback to find paintings of Mesozoic reptiles on the wall of the Creation Room. 
In 1886-87, Carl Christian Anton Christensen (usually CCA Christensen, 1831-1912) painted a 4.9-meter-high mural stretching completely around the Creation Room of the Manti Temple. The mural shows elements of creation up to, but not including, humans. The sequence is clouds and a sphere; volcanoes and storms; sunrise, mountains, and rivers; plants; earliest animals; fowls; non-domestic animals; domestic animals; and water creatures.  The “Earliest Animals,” centered on the back wall, are what caught my attention (see image below). 
The animals in this image seem to be, respectively, (starting at top, moving clockwise) two pterosaurs, a plesiosaur, a
mosasaur [ichthyosaur; see end of post], and a crocodylomorph. Note that these groups are only “dinosaurs” in the popular sense of “extinct reptiles,” so my post title is imprecise. 
I don’t have much to say about the mural itself beyond: “My religion is (was) so cool that we paint(ed) dinosaurs on the walls of one of our most holy buildings!”
I’d like to make a few other points, though. First, Christensen was painting the mural right in the thick of the “Bone Wars,” 1877-1892, a personal conflict between two paleontologists that led to intense exploration for Mesozoic reptile fossils in the American West, with attendant publicity. One of the two scientists even searched for fossils in Utah in 1870.
Second, I don’t know anything about the mural other than its existence. That is, I don’t know about Christensen’s intentions, doctrinal interpretations, sources, consultations with church leaders, etc, nor about any reactions to the mural then or any time since. I am happy, however, to see the Mesozoic represented in the Creation Room and not in the Garden Room, and to have reptiles preceding birds. 
Third, Christensen wasn’t the only one. John Hanson Beadle’s anti-Mormon Polygamy: Or, The Mysteries and Crimes of Mormonism (1882) includes the image below. 
The caption says: “The Salt Lake Basin, as Geologists Represent It Thousands of Years Ago.” Present-day geologists would agree that much of present-day Utah was, in fact, at one point (actually, more than once) part of an inland sea though they would amend the “thousands” to “hundreds of millions.” Beadle’s comment was:
“in the geologic age, an inland sea, in aboriginal times, the retreat of the most abject savages—long a region of misconception and fable—then the chosen home of a strange religion, and but yesterday found to be of use and interest to the civilized world.” 
Some images of other Manti rooms are found here; a BYU Studies article, “Minerva Teichert’s Manti Temple Murals” (Doris R Dant, 38.3 (1999): 6-44) has complete photos of the World Room and a discussion of its painting.
—— Edit, 2013 Aug 05 Mon 0030 CDT ——
 The endowment includes representations of the Creation, the Garden of Eden, and the Fall. In most present-day temples, the settings and events are portrayed by a combination of video and murals in different rooms or exclusively by video. The Manti Temple has no video. Initiates start in the “Creation Room” and move, respectively, to “Garden,” “World” (or “Telestial”), “Terrestrial,” and “Celestial” rooms.
 The sphere/clouds are at front house-left and then proceeds house-right. The sequence is not rigid; there are some domestic and non-domestic animals mixed together. The sequence generally follows Genesis. I got a bit spatially disoriented by time I reached the Creation Room, but I think the congregation / company faces South, which puts the Mesozoic reptiles on the North wall. I am following Richard L Jensen and Richard G Oman’s naming of the “Creation of the Plants,” “Earliest Animals,” “Creation of the Fowls,” “Creation of the Non-domestic Animals,” “Creation of the Domestic Animals,” and “Creation of Water Creatures.” Richard L Jensen and Richard G Oman, C. C. A. Christensen, 1831-1912: Mormon Immigrant Artist, an exhibition at the Museum of Church History and Art (Salt Lake City: The Church of Jesus Christ of Latter-day Saints, 1984), 58-62.
 Jensen and Oman, Christensen, 60.
 The word “dinosaur” dates to 1841 and was invented specifically to distinguish “dinosaurs” from the animals represented here, which were among the earliest Mesozoic fossils recognized by modern science. “Mesozoic Reptiles in Manti” just doesn’t roll of the tongue the way I’d like.
 Jensen and Oman also point out the preponderance of fern-like plants in the Mesozoic part of the mural.
 Bureau of Illustration Buffalo, “The Salt Lake Basin, As Geologists Represent it Thousands of Years Ago,” illustration in Polygamy: Or, The Mysteries and Crimes of Mormonism by John Hanson Beadle and Ovando James Hollister (Philadelphia: National Publishing Co, 1882), 359. I haven’t done a careful comparison, but Polygamy seems to be an updated and expanded version of Beadle’s Life in Utah: The Mysteries and Crimes of Mormonism (Philadelphia: National Publishing Co, 1870). Life in Utah does not have the discussion of geology / paleontology.
 Beadle, Polygamy, 360.