Paleontology, also spelled palaeontology or palæontology (/ˌpeɪliɒnˈtɒlədʒi,ˌpæli-,-ən-/), is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene Epoch (roughly 11,700 years before present). It includes the study of fossils to classify organisms and study interactions with each other and their environments (their paleoecology). Paleontological observations have been documented as far back as the 5th century BCE. The science became established in the 18th century as a result of Georges Cuvier's work on comparative anatomy, and developed rapidly in the 19th century. The term itself originates from Greek παλα'palaios, "old, ancient", ὄν, on (gen.ontos), "being, creature", and λόγος, logos, "speech, thought, study".
Body fossils and trace fossils are the principal types of evidence about ancient life, and geochemical evidence has helped to decipher the evolution of life before there were organisms large enough to leave body fossils. Estimating the dates of these remains is essential but difficult: sometimes adjacent rock layers allow radiometric dating, which provides absolute dates that are accurate to within 0.5%, but more often paleontologists have to rely on relative dating by solving the "jigsaw puzzles" of biostratigraphy (arrangement of rock layers from youngest to oldest). Classifying ancient organisms is also difficult, as many do not fit well into the Linnaean taxonomy classifying living organisms, and paleontologists more often use cladistics to draw up evolutionary "family trees". The final quarter of the 20th century saw the development of molecular phylogenetics, which investigates how closely organisms are related by measuring the similarity of the DNA in their genomes. Molecular phylogenetics has also been used to estimate the dates when species diverged, but there is controversy about the reliability of the molecular clock on which such estimates depend. (Full article...)
Like other abelisaurids, Majungasaurus was a bipedalpredator with a short snout. Although the forelimbs are not completely known, they were very short, while the hindlimbs were longer and very stocky. It can be distinguished from other abelisaurids by its wider skull, the very rough texture and thickened bone on the top of its snout, and the single rounded horn on the roof of its skull, which was originally mistaken for the dome of a pachycephalosaur. It also had more teeth in both upper and lower jaws than most abelisaurids.
The top image is a nodule containing a calymenid trilobite fossil. The bottom images show the extracted fossil (right) and the natural mold it left behind in the counterpart section of the nodule (left).
Photo credit: Thomas Bresson