#fossils

• 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.
• Acanthopore — A microscopic, tubular skeletal structure found in the calcareous colonies of certain fossil or extant bryozoans. This micro-pore houses a spine-like element (acanthostyle) likely serving a defensive, cleaning, or structural support function for adjacent zooecia, making it an essential morphological indicator in taxonomy and evolutionary studies.
• Acanthosphere — A rigid, spherical skeletal shell, either siliceous or calcareous, featuring prominent radiating, spine-like projections (acanthis), characteristic of certain microscopic marine protozoans such as radiolarians or acantharians. It serves a mechanical defense role and aids in buoyancy within the water column, while also being a crucial microfossil for dating geological strata.
• Ammonites — The plural form of amonit; an extensive group of fossil marine cephalopod mollusks characterized by chambered spiraled shells, similar to the modern nautilus. In historical geology, these representatives serve as essential index fossils for delineating and dating sedimentary biozones of past eras, providing clues about prehistoric ocean climate and dynamics.
• Ammonitids — Scientific name or comprehensive taxonomic classification (Ammonitida) that groups together the orders and families of true ammonites, characterized by shells with highly complex and branched suture lines. These fossil marine cephalopod mollusks dominated the seas during the Jurassic and Cretaceous periods, disappearing completely during the mass extinction at the end of the Mesozoic era.
• Ammonoids — Scientific name or higher taxonomic classification (Ammonoidea) that includes all species of fossil marine cephalopod mollusks related to true ammonites, globally distributed from the Devonian to the Cretaceous. These prehistoric organisms are distinguished by the unique structure of their external, spiraled, and chambered shells, serving as essential index fossils in stratigraphy.
• Anisian — A geological stage or substage located at the base of the Middle Triassic epoch, chronologically spanning from approximately 247 to 242 million years ago. As an adjective, the term refers to rocks, sediments, or fossils formed during this time interval, internationally defined by the appearance of specific ammonite and conodont assemblages within reference Alpine geological sections.
• Anisodont — Having teeth that are unequal in size, shape, or structure; the term specifically describes a type of asymmetric dentition found in certain extinct reptiles or mammals, where the elements of the dental arch visibly differ from one another. As a masculine noun, it defines an organism or a fossil specimen characterized by this anatomical conformation adapted for specific feeding or predatory habits.
• Anthracotherium — An extinct genus of hippopotamus-like artiodactyl ungulates within the family Anthracotheriidae, that lived during the Oligocene and Miocene epochs across Eurasia and Africa, adapted to a semi-aquatic lifestyle.
• Australopithecines — A generic term utilized in the plural to designate a broad group of early hominins belonging to the subtribe Australopithecina, including the genera Australopithecus and Paranthropus. As a plural adjective, it describes anatomical traits, cranial structures, or primitive bipedal locomotion specific to these primates.