A three-dimensional, iron-cemented structure found in the anterior thoracic cavity of articulated Thescelosaurus skeletal remains was hypothesized to be the fossilized remains of the animal’s four-chambered heart. This was important because the finding could be interpreted to support a hypothesis that non-avian dinosaurs were endothermic. Mammals and birds, the only extant organisms with four-chambered hearts and single aortae, are endotherms. The hypothesis that this Thescelosaurus has a preserved heart was controversial, and therefore, we reexamined it using higher-resolution computed tomography, paleohistological examination, X-ray diffraction analysis, X-ray photoelectron spectroscopy, and scanning electron microscopy. This suite of analyses allows for detailed morphological and chemical examination beyond what was provided in the original work. Neither the more detailed examination of the gross morphology and orientation of the thoracic “heart” nor the microstructural studies supported the hypothesis that the structure was a heart. The more advanced computed tomography showed the same three areas of low density as the earlier studies with no evidence of additional low-density areas as might be expected from examinations of an ex situ ostrich heart. Microstructural examination of a fragment taken from the “heart” was consistent with cemented sand grains, and no chemical signal consistent with a biological origin was detected. However, small patches of cell-like microstructures were preserved in the sandstone matrix of the thoracic structure. A possible biological origin for these microstructures is the focus of ongoing investigation.
Fig. S1Elemental profiles of isolated regions within the petrographic section of the fragment from NCSM 15728 shown in Fig. 4. a Elemental profile of nuclei-like structures labeled in Fig. 4b showing abundant iron and oxygen. b EDX spectrum for the cytoplasm-like area in Fig. 4b showing iron, sulfur, and oxygen. Sodium is also detected in lower abundance. c EDX spectrum for membrane-like area is in Fig. 4b showing abundant iron and sulfur. Carbon and oxygen are detected in lesser quantities. (DOC 213 kb)
Fig. S2a X-ray diffraction (XRD) analysis of the embedded block of presumed “heart” material from NCSM 15728 showing broad peaks corresponding to all present minerals. Vertical lines represent the theoretical peak distribution for goethite. b X-ray photoelectron spectroscopy (XPS) analyses for three representative powdered samples of the fragment indicating the presence of iron, oxygen, and silicon. No nitrogen or appreciable carbon is present. (DOC 443 kb)