Dicraeosaurid spines. reservoir humps, thermoregulatory sails, excessive displays or multiple defensive horn-spines?,

APESTEGUÍA, SEBASTIÁN; GALLINA, PABLO A.; RIGUETTI, FACUNDO

corrientes

Jornada; XXVIII Jornadas Argentinas de Paleontología de Vertebrados; 2018

universidad del litoral

Since its finding in 1983, Amargasaurus cazaui Sal gad o and Bonaparte, 1991 was an interpretative headache. Although the long and acute neural spines were mainly considered as defensive, the preparation of the specimen revealed the easy breakage of these structures, despite the compositional change implied by fossilization. A recent publication correlated the 2/3 of the distal spine with striated surface as keratinized sheath-covered structures. Though bone is stronger and stiffer in passive situations depending of strain and load, horns and other keratin-based materials are tougher and highly resistant to impact-caused fractures in dry to mesic conditions. Thus the cover sheath may transfer the load to the bony core along a radial direction. Additionally, is improved in slightly bent horns, and in sheaths much longer (double, as in sorne artiodactyls) than neural spines, thus reducing impulsive loads more than other geometries. In extant sauropsids, sheaths exceed less than 100% bony core length. However, keratinous sheath in other dinosaurs (i.e., in ankylosaurs) exceed up to 25% the bony core length. Under a defensive approach, the vast group of acute spines would represent a disturbing fence for a loitering carnivore, but under moderate charge, the breakage would affect only spine tips, not reaching the bone core of them. The acquiring of a defensive or display strategy based only in neural spine resistance is incompatible with their 1O My persistence, unless the lineage had an unknown spine resistance or a superb immunological system. A keratinous sheath is the more compatible of analyzed strategies.