In Omni 1:20-22, we find the following:
And it came to pass in the days of Mosiah, there was a large stone brought unto him with engravings on it; and he did interpret the engravings by the gift and power of God. And they gave an account of one Coriantumr, and the slain of his people. And Coriantumr was discovered by the people of Zarahemla; and he dwelt with them for the space of nine moons. It also spake a few words concerning his fathers. And his first parents came out from the tower, at the time the Lord confounded the language of the people; and the severity of the Lord fell upon them according to his judgments, which are just; and their bones lay scattered in the land northward. (Omni 1:20-22)
As far as these verses are concerned, rather than focus on a "royal descent," I would tend to focus on the idea that a Nephite king and man of God was able to give an interpretation "by the gift and power of God" to a Jaredite monument, and that this sculpted monument was presumably not understood by the people of Zarahemla, who, as we have just established, were Mulekites heavily influenced by Jaredite language and culture. Why weren't the people of Zarahemla able to understand the Jaredite monument themselves? A possible answer is alluded to in some comments by Garth Norman:
In its strictest sense Izapa sculpture is not art but language, because it was created to be read. We tend to think that to really understand an ancient language we have to have a phonetic script to translate so we can get the actual words of texts, then we can really know what they were saying and understand it. That is not the case with Izapa.
Thus Coriantumr's stone might have been one of symbols, not words. Moreover, the true message of these symbols could have been a "mystery" understood only "by the gift and power of God." Of what did the monument testify? It testified that "the severity of the Lord fell upon them according to his judgments, which are just; and their bones lay scattered in the land northward." This is covenant language and implies that the Jaredites (and more especially Coriantumr and all his household) had rejected Jesus Christ and his plan of salvation (read Ether 12:1---13:22; 15:1-4). Now I ask the reader, Could the Izapan monuments, especially Stela 5, be looked at in a similar way? In other words, does Stela 5 contain a "hidden" symbolic message of Jesus Christ and the plan of salvation? Although the full answer to that question is not to be found within the scope of this paper, I can say here that such a concept would not be without support in the text of the Book of Mormon. [Alan C. Miner, "Izapa: A Response to the Question of Geography," Unpublished]