Asaphida
Encyclopedia
Asaphida is a large, morphologically diverse order
of trilobite
found in strata
dated from the Middle Cambrian
to the Silurian
. The order contains six superfamilies (Anomocaroidea, Asaphoidea, Cyclopygoidea, Dikelocephaloidea, Remopleuridoidea and Trinucleioidea), but no suborders. Asaphids comprise some 20% of described fossil
trilobites.
The Asaphida generally have cephalon (head) and pygidium
(tail) parts similar in size, and most species have a prominent median ventral suture. Heads are often flat, and carapace furrows in the head area are often faint or not visible. Thoracic segments typically number 5 - 12, though some species have as few as two and some as many as 30. They also generally have a wide doublure, or rim, that surrounds the cephalon. This causes some specimens to be described as having a characteristic "snowplow" shaped cephalon. Eyes are typically large.
One Asaphida line, the Superfamily Asaphoidea, shows a continuous evolution
of eyestalks, from ones with mere eye stubs to Asaphus kowalewskii
, a trilobite popular with collectors that sported long, eye-tipped stalks. This line is found in the Middle Ordovician Asery Level deposits of the Volkhov River
region near Saint Petersburg
, Russia
. During the Ordovician, what is now Eastern Europe
was a shallow inland sea. This eye-stalk development is believed to be an adaptation to changes in turbidity during this time, with eye-stalked trilobites like A. kowalewski presumably arising in a time of increased turbidity. One thought is that this trilobite may have lain in wait for prey buried in the bottom sediment
with only its periscope eyestalks protruding.
The major extinction event marking the end of the Ordovician Period reduced the diversity of all trilobite orders with most asaphid families disappearing. The only surviving asaphids were members of superfamily Trinucleioidea, and they too disappeared before the end of the Silurian
Period.
The following families are included:
Anomocaroidea
Asaphoidea
Trinucleioidea
Dikelocephaloidea
Cyclopygoidea
Remopleuridoidea
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
of trilobite
Trilobite
Trilobites are a well-known fossil group of extinct marine arthropods that form the class Trilobita. The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period , and they flourished throughout the lower Paleozoic era before...
found in strata
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
dated from the Middle Cambrian
Cambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
to the Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
. The order contains six superfamilies (Anomocaroidea, Asaphoidea, Cyclopygoidea, Dikelocephaloidea, Remopleuridoidea and Trinucleioidea), but no suborders. Asaphids comprise some 20% of described fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
trilobites.
The Asaphida generally have cephalon (head) and pygidium
Pygidium
The pygidium is the posterior body part or shield of crustaceans and some other arthropods, such as insects and the extinct trilobites. It contains the anus and, in females, the ovipositor...
(tail) parts similar in size, and most species have a prominent median ventral suture. Heads are often flat, and carapace furrows in the head area are often faint or not visible. Thoracic segments typically number 5 - 12, though some species have as few as two and some as many as 30. They also generally have a wide doublure, or rim, that surrounds the cephalon. This causes some specimens to be described as having a characteristic "snowplow" shaped cephalon. Eyes are typically large.
One Asaphida line, the Superfamily Asaphoidea, shows a continuous evolution
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
of eyestalks, from ones with mere eye stubs to Asaphus kowalewskii
Asaphus kowalewskii
Asaphus kowalewskii is one of the 35 species of trilobite of the genus Asaphus...
, a trilobite popular with collectors that sported long, eye-tipped stalks. This line is found in the Middle Ordovician Asery Level deposits of the Volkhov River
Volkhov River
Volkhov is a river in Novgorod Oblast and Leningrad Oblast in northwestern Russia.-Geography:The Volkhov flows out of Lake Ilmen north into Lake Ladoga, the largest lake of Europe. It is the second largest tributary of Lake Ladoga. It is navigable over its whole length. Discharge is highly...
region near Saint Petersburg
Saint Petersburg
Saint Petersburg is a city and a federal subject of Russia located on the Neva River at the head of the Gulf of Finland on the Baltic Sea...
, Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
. During the Ordovician, what is now Eastern Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
was a shallow inland sea. This eye-stalk development is believed to be an adaptation to changes in turbidity during this time, with eye-stalked trilobites like A. kowalewski presumably arising in a time of increased turbidity. One thought is that this trilobite may have lain in wait for prey buried in the bottom sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
with only its periscope eyestalks protruding.
The major extinction event marking the end of the Ordovician Period reduced the diversity of all trilobite orders with most asaphid families disappearing. The only surviving asaphids were members of superfamily Trinucleioidea, and they too disappeared before the end of the Silurian
Silurian
The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443.7 ± 1.5 Mya , to the beginning of the Devonian Period, about 416.0 ± 2.8 Mya . As with other geologic periods, the rock beds that define the period's start and end are well identified, but the...
Period.
The following families are included:
Anomocaroidea
- Andrarinidae
- Anomocarellidae
- AnomocaridaeAnomocaridaeAnomocaridae is a family of trilobites, containing the following genera:*Abharella*Afghanocare*Amginia*Anomocare*Anomocarina*Anomocarioides*Anomocariopsis*Callaspis*Chondranomocare*Dilatalimbus*Elandaspis...
- Aphelaspididae
- Parabolinoididae
- Pterocephalidae
Asaphoidea
- AsaphidaeAsaphidaeAsaphidae is a family of trilobites in the order Asaphida, containing the following genera:*Anataphrus*Araiocaris*Asaphellus*Asaphus*Atopasaphus*Aulacoparia*Aulacoparina*Australopyge*Baltiites*Banqiaoites...
- Ceratopygidae
Trinucleioidea
- Alsataspididae
- Dionididae
- Liostracinidae
- Raphiophoridae
- Trinucleidae
Dikelocephaloidea
- DikelocephalidaeDikelocephalidaeDikelocephalidae is a family of trilobites, containing the following genera:*Berkeia*Blandicephalus*Briscoia*Camaraspoides*Dikelocephalus*Elkia*Goumenzia*Hoytaspis*Iranella*Kasachstanaspis*Monocheilus...
- Eurekiidae
- Loganellidae
- PtychaspididaePtychaspididaePtychaspididae is a family of trilobites, containing the following genera:*Alborsella*Changia*Eoptychaspis*Eowuhuia*Euptychaspis*Idiomesus*Kathleenella*Keithia*Keithiella*Macronoda*Plectrella...
- Saukiidae
Cyclopygoidea
- Cyclopygidae
- Nileidae
- Taishunghaniidae
Remopleuridoidea
- Auritamiidae
- Bohemillidae
- Hungaiidae
- Idahoiidae
- Remopleurididae