Love Nest: Sauropod anatomy and nest-excavation behavior

SEBASTIÁN APESTEGUÍA

La Plata

Jornada; XX Jornadas Argentinas de Paleontologia de Vertebrados; 2004

Museo de La Plata

Although as graviportal as most sauropods, titanosaurs developed features that permitted increased motor capabilities. Among their anatomical innovations is the reacquisition of the olecranon (unique within Sauropoda), a character related to an increased mobility of the arm or excavation behavior. Another titanosaur feature, exaggerated in Neuquensaurus, is the trend of enlargement of the sacrum and expansion of the anterolateral wings of the ilia. These combined features are also remarkably found in the extinct therizinosaurid theropods and the extant xenarthrans. In the latter, the sacral region (plus femur) works as attachment for the iliopsoas complex, the shortening of which in humans (due to sleeping in fetal position), affects the thoracolumbar and sacroiliac area. This complex allows edentates to curve the anterior part of the torso thus acquiring a bowed back and an oblique sub-bipedal posture, with the massive synsacrum acting as center of mass and the manus, now devoid of supporting function, slightly touch the ground, and are freed for excavation (Dasypus) or defensive (Myrmecophaga) behavior. In titanosaurs, the curved opisthocoelous back is indeed an evolutionary constraint produced by their evolution from a brachiosaurid-like ancestor and a later reduction of the forelimbs not accompanied by horizontalization of the sacrum, which remained oblique. Additionally, the loss of hyposphene-hypantrum articulations increased their mobility, even considering dorsal scutes. Titanosaurs are the only reported sauropods capable of colony nest excavation. Although they could have excavated with their massive hindfeet, their lighter forelimbs (when compared to basal titanosauriforms), their U-shaped manii, and the other anatomical traits here described prompts the possibility of a manual excavation.