The Ordovician is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period 485.4 million years ago (Ma) to the start of the Silurian Period 443.8 Mya.
A trace fossil, also known as an ichnofossil, is a fossil record of biological activity by lifeforms but not the preserved remains of the organism itself. Trace fossils contrast with body fossils, which are the fossilized remains of parts of organisms' bodies, usually altered by later chemical activity or mineralization. The study of such trace fossils is ichnology and is the work of ichnologists.
The rugosa, also called the tetracorallia or horn coral, are an extinct order of solitary and colonial corals that were abundant in Middle Ordovician to Late Permian seas.
Bioerosion describes the breakdown of hard ocean substrates – and less often terrestrial substrates – by living organisms. Marine bioerosion can be caused by mollusks, polychaete worms, phoronids, sponges, crustaceans, echinoids, and fish; it can occur on coastlines, on coral reefs, and on ships; its mechanisms include biotic boring, drilling, rasping, and scraping. On dry land, bioerosion is typically performed by pioneer plants or plant-like organisms such as lichen, and mostly chemical or mechanical in nature.
Tabulata, commonly known as tabulate corals, are an order of extinct forms of coral. They are almost always colonial, forming colonies of individual hexagonal cells known as corallites defined by a skeleton of calcite, similar in appearance to a honeycomb. Adjacent cells are joined by small pores. Their distinguishing feature is their well-developed horizontal internal partitions (tabulae) within each cell, but reduced or absent vertical internal partitions. They are usually smaller than rugose corals, but vary considerably in shape, from flat to conical to spherical.
Stromatoporoidea is an extinct clade of sea sponges common in the fossil record from the Middle Ordovician to the Late Devonian. They can be characterized by their densely layered calcite skeletons lacking spicules. Stromatoporoids were among the most abundant and important reef-builders of their time, living close together in flat biostromes or elevated bioherms on soft tropical carbonate platforms.
A calcite sea is a sea in which low-magnesium calcite is the primary inorganic marine calcium carbonate precipitate. An aragonite sea is the alternate seawater chemistry in which aragonite and high-magnesium calcite are the primary inorganic carbonate precipitates. The Early Paleozoic and the Middle to Late Mesozoic oceans were predominantly calcite seas, whereas the Middle Paleozoic through the Early Mesozoic and the Cenozoic are characterized by aragonite seas.
An aragonite sea contains aragonite and high-magnesium calcite as the primary inorganic calcium carbonate precipitates. The chemical conditions of the seawater must be notably high in magnesium content relative to calcium for an aragonite sea to form. This is in contrast to a calcite sea in which seawater low in magnesium content relative to calcium favors the formation of low-magnesium calcite as the primary inorganic marine calcium carbonate precipitate.
Trypanites is a narrow, cylindrical, unbranched boring which is one of the most common trace fossils in hard substrates such as rocks, carbonate hardgrounds and shells. It appears first in the Lower Cambrian, was very prominent in the Ordovician Bioerosion Revolution, and is still commonly formed today. Trypanites is almost always found in calcareous substrates, most likely because the excavating organism used an acid or other chemical agent to dissolve the calcium carbonate. Trypanites is common in the Ordovician and Silurian hardgrounds of Baltica.
Cornulitida is an extinct order of encrusting animals from class Tentaculita, which were common around the globe in the Ordovician to Devonian oceans, and survived until the Carboniferous. Organisms that may be the oldest cornulitids have been found in Cambrian sediments of Jordan.
Gastrochaenolites is a trace fossil formed as a clavate (club-shaped) boring in a hard substrate such as a shell, rock or carbonate hardground. The aperture of the boring is narrower than the main chamber and may be circular, oval, or dumb-bell shaped. Gastrochaenolites is most commonly attributed to bioeroding bivalves such as Lithophaga and Gastrochaena. The fossil ranges from the Ordovician to the Recent. The first Lower Jurassic Gastrochaenolites ichnospecies is Gastrochaenolites messisbugi Bassi, Posenato, Nebelsick, 2017. This is the first record of boreholes and their producers in one of the larger bivalves of the globally occurring Lithiotis fauna which is a unique facies in the Lower Jurassic Tethys and Panthalassa.
Petroxestes is a shallow, elongate boring originally found excavated in carbonate skeletons and hardgrounds of the Upper Ordovician of North America. These Ordovician borings were likely made by the mytilacean bivalve Corallidomus as it ground a shallow groove in the substrate to maintain its feeding position. They are thus the earliest known bivalve borings. Petroxestes was later described from the Lower Silurian of Anticosti Island (Canada) by Tapanila and Copper (2002) and the Miocene of the Caribbean by Pickerill et al. (2001).
The order Microconchida is a group of small, spirally-coiled, encrusting fossil "worm" tubes from the class Tentaculita found from the Upper Ordovician to the Middle Jurassic (Bathonian) around the world. They have lamellar calcitic shells, usually with pseudopunctae or punctae and a bulb-like origin. Many were long misidentified as the polychaete annelid Spirorbis until studies of shell microstructure and formation showed significant differences. All pre-Cretaceous "Spirorbis" fossils are now known to be microconchids. Their classification at the phylum level is still debated. Most likely they are some form of lophophorate, a group which includes phoronids, bryozoans and brachiopods. Microconchids may be closely related to the other encrusting tentaculitoid tubeworms, such as Anticalyptraea, trypanoporids and cornulitids.
Sphenothallus is a problematic extinct genus lately attributed to the conulariids. It was widespread in shallow marine environments during the Paleozoic.
Anticalyptraea is a fossil genus of encrusting tentaculitoid tubeworms from the Silurian to Devonian of Europe and North America . Anticalyptraea commonly encrust various invertebrate fossils such as stromatoporoids, rugose corals, bryozoans, brachiopods and crinoids, but they can also be common on the hardgrounds.
Osprioneides is an ichnogenus of unbranched, elongate borings in lithic substrate with oval cross−section, single−entrance and straight, curved or irregular course. Osprioneides kampto Beuck and Wisshak, 2008 is the largest known Palaeozoic boring trace. It occurs in the Ordovician and Silurian (Wenlock) of Baltica. The borings are up to 120 mm long measuring 5–17 mm in diameter. The distribution of Osprioneides is more environmentally limited than that of Trypanites in the Silurian of Saaremaa, Estonia (Baltica). Osprioneides probably occurred only in large hard substrates of relatively deepwater muddy bottom open shelf environments. Osprioneides were relatively rare, as compared to Trypanites-Palaeosabella borings in the Wenlock of Saaremaa.
Cornulites is a genus of cornulitid tubeworms. Their shells have vesicular wall structure, and are both externally and internally annulated. They usually occur as encrusters on various shelly fossils. Their fossils are known from the Middle Ordovician to the Carboniferous.
Conchicolites is a fossil genus of cornulitid tubeworms. Their shells lack vesicular wall structure and have a smooth lumen. They are externally covered with transverse ridges. Some species have spines. They usually occur as encrusters on various shelly fossils. Their fossils are known from the Late Ordovician to the Devonian.
Burrinjuckia is an ichnogenus of bioclaustrations. Burrinjuckia includes outgrowths of the brachiopod's secondary shell with a hollow interior in the mantle cavity of a brachiopod. Burrinjuckia was probably a parasite. They have a stratigraphic range from the Late Ordovician to the Devonian. The earliest Burrinjuckia species B. clitambonitofilia Vinn, Wilson and Toom, 2014 occurs in brachiopod Clitambonites squamatus from the Late Ordovician oilshale of Estonia.
Olev Vinn is Estonian paleobiologist and paleontologist.
Hardground in the Liberty Formation (Upper Ordovician) of southern Ohio.
Cross-section of an Upper Ordovician hardground from Kentucky. The light-colored vertical elements are borings ( Trypanites ) filled with dolomite. The scale bar is 1.0 cm.
A Middle Ordovician hardground from the Kanosh Formation of Utah with echinoderm holdfasts cemented to its upper surface. The scale bar is 1.0 cm.
Petroxestes borings in an Upper Ordovician hardground, southern Ohio.
Trypanites borings in an Upper Ordovician hardground, Indiana.
Carbonate hardground with an encrusting bryozoan; Kanosh Formation (Middle Ordovician) of Utah; scale in mm.
Cross-section of a carbonate hardground encrusted by oysters and bored by bivalves (Gastrochaenolites); Carmel Formation (Middle Jurassic) of southern Utah.
Trypanites borings in an Upper Ordovician hardground from northern Kentucky.
Carbonate hardground; Ora Formation, Upper Cretaceous (Turonian), southern Israel.
