The purpose of this segment is to demonstrate how Kubrick seems to be alluding to the evidence that sites like Stonehenge were in fact "ancient eclipse computers", meaning that ape/early man were not in fact as dumb as "modern man" thinks they were [conceding that modern man CAN still think], and reflecting Zarathustra's message that "once you were apes, and even now, too, man is more ape than any ape"
In ancient folklore there WAS a character called Moon-Watcher and he had a very complex job year round because he had to observe and plot [using Aubry Holes in case of Stonehenge] the path of the moon to determine the all important NODES that are vital for an eclipse. This theory is neither proven or disproven SO is the IDEAL vehicle for Kubrick to weave his magic.
Then starting at 1:11 we see [especially from the leopard's eyes] that it is getting darker, but NO sunset. The leopard has just killed a zebra but is very nervous and rather than eating his kill, he just looks around and growls. The same for the apes who instinctively go back to their cave as if it is night time but they just sit there wondering who "pulled the curtain".
One ape tries to tell the leopard to shut up and the others tell HIM to not upset the leopard, who is still growling. Then as they sit in silence we see Moon-Watcher "doing his thing" in watching [and remembering?] what is going on in the sky.
The leopard is used by Kubrick to "time stamp" the leopard and apes as happening at same time in the above 2 minutes of darkness, but in general Kubrick does not time stamp scenes, meaning for example that it may not be the next morning after the eclipse that the apes awake to find Santa has been and has dug a hole and planted a monolith without waking a single ape.
By that bit of frivolity I am saying that IMHO Kubrick intends that the monolith [in all scenes] is to be taken to be "symbolic" only - a McGuffin if you will [Kubrick describes it as a "Jungian archetype"]. I think he confirms that in the "Last Supper" scene where the large pod [as well as a monolith] somehow fits through a normal door and then disappears, meaning that similarly with the ape monolith we are not meant to see it as an actual block of rock but merely symbolic of an "inspirational happening" [in this case the recent eclipse].
So we then go through the "glory be to God" worshiping of the monolith, but IMHO it is the next scene that matters more, although without time stamping we don't know how soon after the symbolic monolith this happens.
We see that Moon-Watcher has a sort of "Observatory" and as he goes into it the other apes obediently get lost. Note how the first thing he does is clears the ground to make a "drawing board", after which he keeps looking up to make sightings of his markers and then looking back down to plot them on his drawing board [from 4:40 to 5:10].
So this is his version of the ancient eclipse computer and he kinda smiles [apes have thin smiles] and thinks back to the previous vision of an eclipse about to happen [or just happened] with the sun and moon lining up over the symbolic monolith, and most IMPORTANTLY The Sunrise fanfare plays for a second time to tell us that THIS is an INSPIRATIONAL moment in the movie, and IMHO Kubrick is showing the ape version of Archimedes formulating his famous solution by sitting, thinking in his bathtub, per:.
"Archimedes then took to the streets naked, so excited by his discovery that he had forgotten to dress, crying "Eureka!", (Greek: meaning "I have found it!")."
And it seems very clear that Kubrick is using the fact that "inspiration breeds more inspiration" where in solving his "science problem" [and being able to PREDICT the next eclipse, thus becoming a true leader] he casually bashes a bone in celebration and [ho hum] spawns another "solution to an unstructured problem" as the MBAs say, ie using bone to kill animals.
He then throws the bone into the air as his Eureka, but much more because of his science vision than his killing vision, and this bone falls to the ground, NOT taken up by man.
Finally we see apes go to next step of using a bone to "wage war" over another ape tribe, and in victory an ape throws this bone also high into the air.
However this time there is no Zarathustra fanfare, so while it may have also been "inspirational" to the apes, the movie says it was not a "GOOD" inspiration, AND this time it IS "taken up" by man as we see the ultimate "weapon of mass destruction" with an atomic warhead in space.