#cretaceous

• Acanthoceras — A genus of extinct fossil cephalopod mollusks (ammonites) within the Acanthoceratidae family, characteristic of the Late Cretaceous epoch. These marine organisms were distinguished by their massive, planospiral coiled shells heavily ornamented with prominent ribs and rows of sharp tubercles or spine-like outgrowths along the outer whorls, serving as critical index fossils for dating geological strata of that period.
• Acteonella — Romanian term (derived from the fossil genus Acteonella) for a type of prehistoric marine gastropod snails, characteristic of the Cretaceous period. Its structural shell is thick, oval or fusiform in shape, smooth, and provided with distinct columellar plications. Acteonella fossils are frequently used in geology as index fossils for dating sedimentary strata and reconstructing ancient equatorial marine environments.
• Albian — The final stratigraphic stage or age of the Early (Lower) Cretaceous epoch, situated in geological chronology after the Aptian and before the Cenomanian, dated approximately between 113 and 100.5 million years ago. As an adjective, it applies to rocks, sediments, limestone deposits, or fossils characteristic of this geological period, extensively studied in Carpathian paleontology.
• Ancyloceras — A genus of fossil ammonites from the Early Cretaceous period, characterized by a partially uncoiled or unusually bent shell, often with an initial spiraled portion followed by a straight shaft and a final hook-like bend. It represents a reference organism in biostratigraphy for the precise dating of marine geological strata.
• Aptian — An upper geological stage of the Lower Cretaceous, chronologically situated between the Barremian and the Albian, structurally characterized by massive sedimentary deposits rich in ammonites and the expansion of specific marine faunas; as an adjective, it describes the rocks, formations, or fossils that formed during this period of Earth's history.
• Baculite — A member of the extinct genus Baculites, representing an Upper Cretaceous ammonite characterized by an almost completely straight, elongated, rod-shaped calcareous shell, unlike classic spiraled ammonites. Geologically, baculite fossils are utilized as highly important index fossils for dating marine sedimentary layers and reconstructing prehistoric ecosystems.