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from article Devonian
Devonian, the fourth period of the Paleozoic Era.
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from article Devonian
Biostratigraphic zones based on conodonts (left) plotted to show approximate correspondence to the chronostratigraphic stages and series which compose the Devonian System (right) and relative sea-level changes (center) showing major fluctuations…
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from article Devonian
Reconstruction of Middle Devonian continental positions based on distribution of lithologic climatic indicators. Probable ocean currents derived from this paleogeography explain the biogeographic realms. Kolyma and Tarim are microcontinents of the…
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from article Obolellida
Obolella. (a) Shell exterior (after J. Hall and J. M. Clarke, An introduction to the study of the Brachiopoda intended as a handbook for the use of students, Report of the N.Y. State Geologist for 1891, 1894). (b) Dorsal valve interior, and (c)…
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from article Enantiornithes
Protopteryx, the most primitive known enantiornithine bird, collected from the Early Cretaceous of Hebei Province, northern China.
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from article Paleoecology
Zonation of Silurian (425 million year old) marine communities in the Welsh Basin, United Kingdom. Marine animal communities were typically arranged in belts parallel to the shoreline and related to water depth. A classic study using fossil…
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from article Paleoecology
Classification of shales in terms of percentages of three benthic habitat groups: epifaunal suspension-feeding bivalves (those living at the sediment-water interface and filtering seawater), infaunal (living within and feeding on the sediment), and…
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from article Paleoecology
Comparison of four developmental stages in four ancient reef masses. (After K. R. Walker and L. P. Alberstadt, Ecological succession as an aspect of structure in fossil communities, Paleobiology, 3:238–257, 1975)
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from article Paleoecology
Formation and burial sequence of Bobcaygeon hardground. (a) Soft-bottom community of strophomenid brachiopods and infaunal burrowers inhabiting carbonate mud. (b) Hardground community consisting of boring and encrusting organisms. (c)…
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from article Paleoecology
Tiering or vertical depth stratification in marine communities through time. Note the rapid rise of the highest-tier (level) organisms (crinoids or sea lilies, bryozoans) from a few centimeters to over a meter above the sea floor during the…
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from article Paleoecology
The three great marine evolutionary faunas of the Phanerozoic. The Cambrian fauna, composed of trilobites, primitive groups of brachiopods, and mollusks, arose early during that period to a diversity of about 50 families, and then dwindled during…
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from article Quaternary
Quaternary, the second period of the of the Cenozoic Era.
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from article Placodermi
Two cladograms portraying differing concepts of relationships of orders of placoderms: (a) according to Denison (after R. H. Denison, Placodermi, vol. 2 of O. Kuhn and H. P. Schultz, eds., Handbook of Palaeoichthyology, 1978); and (b) according to…
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from article Placodermi
Stensioella heintzi in dorsal view; length about 10 in. (25 cm).
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from article Placodermi
Pseudopetalichthys problematica, ventral view; length about 6 in. (15 cm).
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from article Placodermi
Gemuendina stuertzi from the Lower Devonian of Germany; restoration in dorsal aspect.
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from article Placodermi
Rhamphodopsis threiplandi from the Middle Devonian of Scotland. Restoration of skeleton with outline of body in lateral aspect.
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from article Placodermi
Romundina stellina, head and shoulder girdle in lateral view; length about 1.2 in. (3 cm).
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from article Placodermi
Lunaspis broilii from the Lower Devonian of Germany; restoration in dorsal aspect.
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from article Placodermi
Phyllolepis orvini from the Upper Devonian of Greenland. The restoration of the dermal armor is shown in dorsal aspect. The outline of the front of the head and the body is hypothetical, but shows how the fish might have appeared in life.
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from article Placodermi
Representative arthrodires. (a) Cranial and thoracic shields of giant Upper Devonian Dunkelosteus (Dinichthys), a brachythoracic arthrodire showing reduction of thoracic shield, large nuchal gap, and elevated cranio-thoracic joint. Length of…
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from article Placodermi
Pterichthyodes (Ptericthys), a Middle Devonian antiarch. (a) Lateral view showing scale-covered tail; about 15 cm (6 in.) in length. (b) Dorsal and (c) ventral views of the armor. (After Traquair)
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from article Phanerozoic
Phanerozoic, the present geologic eon representing the past half-billion years.
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from article Phanerozoic
Geologic time scale showing the eons, eras, and periods of the Phanerozoic; epochs of the Cenozoic Era; and major events in the history of life. Geologic ages are given in millions of years ago (Ma). The beginning of the Archean Eon is undefined at…
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from article Reptilia
Desert tortoise (Gopherus agassizii). (Photo courtesy of Joshua Tree National Park, California; National Park Service)
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from article Reptilia
Western ground snake (Sonora semiannulata). (Photo courtesy of Tonto National Monument, Arizona; National Park Service)
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from article Reptilia
Greater short-horned lizard (Phrynosoma hernandesi). (Photo courtesy of Lake Mead National Recreation Area, Arizona/Nevada; National Park Service)
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from article Archaeopteryx
Cast of the Archaeopteryx fossil specimen located at the Berlin Natural History Museum. In particular, it shows clearly the spread-out wings and long clawed fingers of this fossil bird. (Photo copyright © Natural History Museum, London)
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from article Calcarea
A calcareous sponge belonging to the family Leucettidae (order Clathrinida). (Credit: Bernard Dupont)
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from article Calcarea
Grades of construction of the water-current system in Calcarea: (a) asconoid type; (b) syconoid type without cortex; (c) syconoid type with cortex; (d) intermediate or transitional stage between syconoid and leuconoid types; (e) leuconoid type.…
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from article Calcarea
Spicule formation in the calcareous sponges: (a, b, c) early stages in secretion of the triactine spicule; (d) late stage of spicule formation. (Copyright © McGraw-Hill Education)
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from article Halimeda
Halimeda kanaloana found in the waters off Hawaii. (Photo courtesy of the Deep Water Macroalgal Meadows 2004 Exploration, Office of Ocean Exploration, National Oceanic and Atmospheric Administration)
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from article Sphaeractinoidea
Sphaeractinoid Actinostromaria rhodaclada, Cretaceous, Jura Mountains: (a) tangential and (b) longitudinal section, ×6. (From A. Steiner, 1932)
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from article Arthropoda
The insects are the largest group within the phylum Arthropoda. Some of the most visually appealing insects are the butterflies (order Lepidoptera). (Credit: Shutterstock)
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from article Arthropoda
Crustaceans constitute some of the most notable arthropods. The Chesapeake blue crab (Callinectes sapidus) is native to the western Atlantic Ocean and Gulf of Mexico. (Credit: Sandy Franz/Getty Images)
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from article Arthropoda
Body segmentation is a fundamental characteristic of the arthropods. The Madagascan fire millipede (Aphistogoniulus corallipes) has numerous leg-bearing segments. (Copyright © McGraw-Hill Education)
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from article Arthropoda
Diagram of the position of principal internal organs in a typical arthropod. (Copyright © McGraw-Hill Education)
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from article Arthropoda
Fossil of a trilobite, showing its distinctive flattened oval shape and crosswise division of the body (into a head, a thorax, and a pygidium). (Credit: Shutterstock)
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from article Lissamphibia
Pedicellate teeth in Lissamphibia: (a) salamander; (b) apodan; (c) frog. Teeth are from the lower jaw (a, b) or upper jaw inverted (c) and are viewed from inside the mouth. (After T. Parsons and E. E. Williams, The teeth of Amphibia and their…
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from article Lissamphibia
Operculum-stapes complex of a primitive salamander (skin removed to show internal structures).
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from article Crustacea
Some crustaceans in their respective habitats, mostly reduced but not to same scale. Orders are in parentheses. (a) Marine forms and common names: Pollicipes, goose barnacle; Balanus, acorn barnacle; Mysis, opossum shrimp; Orchestia, sand hopper;…
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from article Crustacea
Diagram of the fifth pleonal somite of the crayfish, with its paired fifth pleopods.
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from article Crustacea
External morphology of a shrimp. (After P. A. McLaughlin, Comparative Morphology of Recent Crustacea, W. H. Freeman, 1980)
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from article Crustacea
Cephalic and thoracic appendages of representative crustaceans: (a–d) antennules; (e–h) mandibles; (i–l ) thoracopods. (a) Brachypoda; (b) Leptostraca; (c, d) Decapoda; (e) Brachypoda; (f) Stomatopoda; (g) Mysida; (h) Decapoda; (i) Anostraca; (j)…
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from article Crustacea
Nauplii of (a) Triops cancriformis (Notostraca); (b) Branchinecta occidentalis (Anostraca); (c) Lernaeocera branchialis (Siphonostomatoida); (d) Haemocera danae (Monstrilloida); (e) Meganyctiphanes norvegica (Euphausiacea); (f) Sacculina carcini…
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from article Crustacea
Larval stages of representative crustaceans: (a) cyprid larva of Sessilia; (b) pseudolarva of Stomatopoda; (c) phyllosoma larva of Decapoda; (d) zoeal larva of Decapoda; (e) megalopa of Decapoda. (After P. A. McLaughlin, Comparative Morphology of…
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from article Crustacea
Chart of the classification of Crustacea; no indication of phylogenetic relationships is implied. (Modified from D. E. Bliss, ed., The Biology of Crustacea, vols. 1–10, Academic Press, 1982–1985)
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from article Crustacea
Late Devonian malacostracan Palaeopalaemon newberryi Whitfield, considered to be the earliest decapod crustacean. (After F. R. Schram, R. M. Feldmann, and M. J. Copeland, J. Paleontol., 52:1381, 1978)
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from article Glyptodont
A glyptodont skeleton belonging to the type genus, Glyptodon. (Credit: Gyik Toma)
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from article Glyptodont
Reconstruction of Glyptotherium texanum from Arizona. (Credit: David D. Gillette; illustration by Bonnie Dalzell)
