"A giant with prognathism has excess growth hormone until proved otherwise "
If I quote Dr. Don Dragoo, from "Mounds for the dead an analysis of the adena culture" 1958- Page 72, giving the cranial features of the Adena people:
"The face was large both in length and breadth and there was moderate alveolar prognathism. The chin was prominent and broad with bilateral eminences usually present. The cheek bones were large with pronounced lateral projections. The stature was medium to tall and the bones were heavy with prominent areas for muscle attachment. The large male found in subfloor tomb F .28 was exceptional in height. Measurements taken of the skeleton while still in the grave indicated an individual approximately 7.2 feet tall. He would have been a splendid figure in any society and the darling of a primitive basketball team. In all respects the Cresap Mound skeletal material conforms to the physical type of the Kentucky and Ohio Adena mounds as previously described by Snow (1957, p. 47-60). Of the 54 burials, grave objects were found in association with 34 of them. Red ocher was present with 31 burials."
The alveolar prognathism appears to have been a genetic trait, as does the tall to very tall stature.
"It is no little surprise perhaps to conclude that the Adena people stand alone and have few counterparts in the usual skeletal series of archeological origin. One of the outstanding and un-Indian like traits present among the Adena people is their prominent and often bilateral chins. This characteristic structure has been noted before (Webb and Snow 1945, p. 254, 255, and illustrations), and it may be observed in the illustrations of most Adena skulls. One of the skulls from the Dover Mound, Burial 25 (that of a very large, robust, middle-aged man), represents a bilateral chin with a width of 52 mm. (2.05 inches)..." The Dover Mound - Page 38, William S. Webb, Charles E. Snow
From reading Jason Jarrell and Sarah Farmer's book, and articles on-line, I get the impression these physical features were not so much pathological, as they were a racial or genetic variant of existing Native American peoples of the time, these tall honored burials of powerful or important peoples of the Adena culture, I think show us something more akin to the modern Dinka, or Watusi of Africa, (very tall tribal stature, cranial deformation etc.) rather than a few select burials of acromegalics or the very rare individual with gigantism. There are just too many of these skeletons in the literature, from Smithsonian field reports onwards, to statistically account for incidence of gigantism. Perhaps the most glaring reality, is also the fact no evidence of pathology such as acromegaly or gigantism was ever detected (evidence of pituitary tumors in the skulls etc) in these skeletons recovered in the 1950's, whereas occasional skeletons of persons only 3-1/2 feet tall, who had achondroplasia have been recorded in 1950's digs in Georgia. Clinical features that could readily be detected I think, would have been spotted on these very tall mound skeletons, but the general descriptions of these robust, large chinned, tall stature people seems to have been more of a genetic trait than a one off sort of thing. It seems more likely that these were very large, healthy robust people living a more primitive, foraging and hunting lifestyle.