Trilobite - Elrathia kingii
Middle Cambrian - 505 mya
Wheeler Formation
Delta, Utah
ITEM # TRILO-Utah-0005
This is a excellent example of the Ptychopariid trilobite Elrathia kingii from the Wheeler Formation near Delta, Utah.
Western Utah is one of the best-known Cambrian fossil localities in the world. The Wheeler Shale and Marjum Formation, strata of Middle Cambrian age, exhibit various exposures throughout the House Range and nearby mountain ranges west of the town of Delta, Utah. The Wheeler Shale is named for a major feature in the House Range, the Wheeler Amphitheater. The Wheeler Shale contains interbeds of shaley limestone, mudstone, and thin platy limestone. Much of the Wheeler Shale is not particularly fossiliferous, but certain layers contain abundant trilobites and other shelly fossils. The Wheeler Shale also is known for a diverse biota of soft-bodied fossils, including many of the same taxa found in the Burgess Shale.
In the Cambrian, the continent of Laurentia (now the majority of North America), was equatorial, and oriented about ninety degrees from its current position. Close to the shorelines of Laurentia, limestone was deposited as shallow-ater reefs. Beyond the limestone belt, fine sediments built in deeper offshore contours, sometimes rapidly via undersea landslides off the reef platform. These offshore deposits along the paleoequator include much of the Wheeler Shale, the Burgess Shale of western Canada, and other sites from California through Utah to the Northwest territories of Canada. All of these sites yield remarkably preserved Cambrian fossils.
The most famous Wheeler Shale fossil is the trilobite Elrathia kingi; so common at some sites that specimens are commercially quarried and are made into novelty accessories, as well as sold to collectors and institutions all over the world. However, Elrathia is just one of about fifteen trilobite genera of the Wheeler Shale. Bathyuriscus fimbriatus is also relatively common at certain sites. Even more abundant are several species of agnostid trilobites, such a Peronopsis interstricta. These are typically less than a centimeter in length.
E. kingii occupied the exaerobic zone, at the boundary of anoxic and dysoxic bottom waters. E. kingii consistently occur in settings below the oxygen levels required by other contemporaneous epifaunal and infaunal benthic biota and may have derived energy from a food web that existed independently of phototrophic primary productivity. Although other fossil organisms are known to have preferred such environments, E. kingii is the earliest-known inhabitant of them, extending the documented range of the exaerobic ecological strategy into the Cambrian Period.
E. kingii is a medium-sized trilobite with a smooth sub-ovate carapace that is tapered towards the rear. The thorax is usually 13 segments, and the pygidium has four axial rings and a long terminal piece. Posterior margin of the pygidium has a long broad medial notch. In contrast, E. marjum usually has 12 segments, 5 axial rings, lacks a notched posterior margin and possess incipient antero-lateral spines.
Ptychopariida is a large, heterogeneous order of trilobite containing some of the most primitive species known. Many date to the Early Cambrian Period, but the order was extant through the Late Ordivician. Many of the offshoot species are difficult to classify in this single order.
The thorax is large and is typically made up of eight or more segments. The thorax is usually much longer than the pygidium, which is usually small. In some species the pygidium is outlined with a flat border.
This large specimen measures approximately 1 3/16-inches long on a matrix measuring 3 3/4 inches by 2 1/4 inches.
Wheeler Formation
Delta, Utah
ITEM # TRILO-Utah-0005
This is a excellent example of the Ptychopariid trilobite Elrathia kingii from the Wheeler Formation near Delta, Utah.
Western Utah is one of the best-known Cambrian fossil localities in the world. The Wheeler Shale and Marjum Formation, strata of Middle Cambrian age, exhibit various exposures throughout the House Range and nearby mountain ranges west of the town of Delta, Utah. The Wheeler Shale is named for a major feature in the House Range, the Wheeler Amphitheater. The Wheeler Shale contains interbeds of shaley limestone, mudstone, and thin platy limestone. Much of the Wheeler Shale is not particularly fossiliferous, but certain layers contain abundant trilobites and other shelly fossils. The Wheeler Shale also is known for a diverse biota of soft-bodied fossils, including many of the same taxa found in the Burgess Shale.
In the Cambrian, the continent of Laurentia (now the majority of North America), was equatorial, and oriented about ninety degrees from its current position. Close to the shorelines of Laurentia, limestone was deposited as shallow-ater reefs. Beyond the limestone belt, fine sediments built in deeper offshore contours, sometimes rapidly via undersea landslides off the reef platform. These offshore deposits along the paleoequator include much of the Wheeler Shale, the Burgess Shale of western Canada, and other sites from California through Utah to the Northwest territories of Canada. All of these sites yield remarkably preserved Cambrian fossils.
The most famous Wheeler Shale fossil is the trilobite Elrathia kingi; so common at some sites that specimens are commercially quarried and are made into novelty accessories, as well as sold to collectors and institutions all over the world. However, Elrathia is just one of about fifteen trilobite genera of the Wheeler Shale. Bathyuriscus fimbriatus is also relatively common at certain sites. Even more abundant are several species of agnostid trilobites, such a Peronopsis interstricta. These are typically less than a centimeter in length.
E. kingii occupied the exaerobic zone, at the boundary of anoxic and dysoxic bottom waters. E. kingii consistently occur in settings below the oxygen levels required by other contemporaneous epifaunal and infaunal benthic biota and may have derived energy from a food web that existed independently of phototrophic primary productivity. Although other fossil organisms are known to have preferred such environments, E. kingii is the earliest-known inhabitant of them, extending the documented range of the exaerobic ecological strategy into the Cambrian Period.
E. kingii is a medium-sized trilobite with a smooth sub-ovate carapace that is tapered towards the rear. The thorax is usually 13 segments, and the pygidium has four axial rings and a long terminal piece. Posterior margin of the pygidium has a long broad medial notch. In contrast, E. marjum usually has 12 segments, 5 axial rings, lacks a notched posterior margin and possess incipient antero-lateral spines.
Ptychopariida is a large, heterogeneous order of trilobite containing some of the most primitive species known. Many date to the Early Cambrian Period, but the order was extant through the Late Ordivician. Many of the offshoot species are difficult to classify in this single order.
The thorax is large and is typically made up of eight or more segments. The thorax is usually much longer than the pygidium, which is usually small. In some species the pygidium is outlined with a flat border.
This large specimen measures approximately 1 3/16-inches long on a matrix measuring 3 3/4 inches by 2 1/4 inches.
$
40.00
Trilobite - Modocia typicalis
Middle Cambrian
Marjum Formation
Delta, Utah
ITEM # TRILO-Utah-0004
This is an extremely-large and museum-quality example of the Ptychopariid trilobite Modocia typicalis from the Middle Cambrian of Utah. Modocia typicalis is a member of the Order Ptychopariida, Family Marjumiidae.
Western Utah is one of the best-known Cambrian fossil localities in the world. The Wheeler Shale and Marjum Formation, strata of Middle Cambrian age, exhibit various exposures throughout the House Range and nearby mountain ranges west of the town of Delta, Utah. The Wheeler Shale is named for a major feature in the House Range, the Wheeler Amphitheater. The Wheeler Shale contains interbeds of shaley limestone, mudstone, and thin platy limestone. Much of the Wheeler Shale is not particularly fossiliferous, but certain layers contain abundant trilobites and other shelly fossils. The Wheeler Shale also is known for a diverse biota of soft-bodied fossils, including many of the same taxa found in the Burgess Shale.
In the Cambrian, the continent of Laurentia (now the majority of North America), was equatorial, and oriented about ninety degrees from its current position. Close to the shorelines of Laurentia, limestone was deposited as shallow-ater reefs. Beyond the limestone belt, fine sediments built in deeper offshore contours, sometimes rapidly via undersea landslides off the reef platform. These offshore deposits along the paleoequator include much of the Wheeler Shale, the Burgess Shale of western Canada, and other sites from California through Utah to the Northwest territories of Canada. All of these sites yield remarkably preserved Cambrian fossils.
The most famous Wheeler Shale fossil is the trilobite Elrathia kingi; so common at some sites that specimens are commercially quarried and are made into novelty accessories, as well as sold to collectors and institutions all over the world. However, Elrathia is just one of about fifteen trilobite genera of the Wheeler Shale. Bathyuriscus fimbriatus is also relatively common at certain sites. Even more abundant are several species of agnostid trilobites, such a Peronopsis interstricta. These are typically less than a centimeter in length.
Ptychopariida is a large, heterogeneous order of trilobite containing some of the most primitive species known. Many date to the Early Cambrian Period, but the order was extant through the Late Ordivician. Many of the offshoot species are difficult to classify in this single order.
The thorax is large and is typically made up of eight or more segments. The thorax is usually much longer than the pygidium, which is usually small. In some species the pygidium is outlined with a flat border.
This very large specimen measures approximately 1 5/8-inches long on a matrix measuring 4 inches by 3 1/2 inches.
Marjum Formation
Delta, Utah
ITEM # TRILO-Utah-0004
This is an extremely-large and museum-quality example of the Ptychopariid trilobite Modocia typicalis from the Middle Cambrian of Utah. Modocia typicalis is a member of the Order Ptychopariida, Family Marjumiidae.
Western Utah is one of the best-known Cambrian fossil localities in the world. The Wheeler Shale and Marjum Formation, strata of Middle Cambrian age, exhibit various exposures throughout the House Range and nearby mountain ranges west of the town of Delta, Utah. The Wheeler Shale is named for a major feature in the House Range, the Wheeler Amphitheater. The Wheeler Shale contains interbeds of shaley limestone, mudstone, and thin platy limestone. Much of the Wheeler Shale is not particularly fossiliferous, but certain layers contain abundant trilobites and other shelly fossils. The Wheeler Shale also is known for a diverse biota of soft-bodied fossils, including many of the same taxa found in the Burgess Shale.
In the Cambrian, the continent of Laurentia (now the majority of North America), was equatorial, and oriented about ninety degrees from its current position. Close to the shorelines of Laurentia, limestone was deposited as shallow-ater reefs. Beyond the limestone belt, fine sediments built in deeper offshore contours, sometimes rapidly via undersea landslides off the reef platform. These offshore deposits along the paleoequator include much of the Wheeler Shale, the Burgess Shale of western Canada, and other sites from California through Utah to the Northwest territories of Canada. All of these sites yield remarkably preserved Cambrian fossils.
The most famous Wheeler Shale fossil is the trilobite Elrathia kingi; so common at some sites that specimens are commercially quarried and are made into novelty accessories, as well as sold to collectors and institutions all over the world. However, Elrathia is just one of about fifteen trilobite genera of the Wheeler Shale. Bathyuriscus fimbriatus is also relatively common at certain sites. Even more abundant are several species of agnostid trilobites, such a Peronopsis interstricta. These are typically less than a centimeter in length.
Ptychopariida is a large, heterogeneous order of trilobite containing some of the most primitive species known. Many date to the Early Cambrian Period, but the order was extant through the Late Ordivician. Many of the offshoot species are difficult to classify in this single order.
The thorax is large and is typically made up of eight or more segments. The thorax is usually much longer than the pygidium, which is usually small. In some species the pygidium is outlined with a flat border.
This very large specimen measures approximately 1 5/8-inches long on a matrix measuring 4 inches by 3 1/2 inches.
$
450.00
Trilobite - Modocia typicalis
Middle Cambrian
Marjum Formation
Delta, Utah
ITEM # TRILO-Utah-0003
This is a museum-quality example of the Ptychopariid trilobite Modocia typicalis from the Middle Cambrian of Utah. Modocia typicalis is a member of the Order Ptychopariida, Family Marjumiidae.
Western Utah is one of the best-known Cambrian fossil localities in the world. The Wheeler Shale and Marjum Formation, strata of Middle Cambrian age, exhibit various exposures throughout the House Range and nearby mountain ranges west of the town of Delta, Utah. The Wheeler Shale is named for a major feature in the House Range, the Wheeler Amphitheater. The Wheeler Shale contains interbeds of shaley limestone, mudstone, and thin platy limestone. Much of the Wheeler Shale is not particularly fossiliferous, but certain layers contain abundant trilobites and other shelly fossils. The Wheeler Shale also is known for a diverse biota of soft-bodied fossils, including many of the same taxa found in the Burgess Shale.
In the Cambrian, the continent of Laurentia (now the majority of North America), was equatorial, and oriented about ninety degrees from its current position. Close to the shorelines of Laurentia, limestone was deposited as shallow-ater reefs. Beyond the limestone belt, fine sediments built in deeper offshore contours, sometimes rapidly via undersea landslides off the reef platform. These offshore deposits along the paleoequator include much of the Wheeler Shale, the Burgess Shale of western Canada, and other sites from California through Utah to the Northwest territories of Canada. All of these sites yield remarkably preserved Cambrian fossils.
The most famous Wheeler Shale fossil is the trilobite Elrathia kingi; so common at some sites that specimens are commercially quarried and are made into novelty accessories, as well as sold to collectors and institutions all over the world. However, Elrathia is just one of about fifteen trilobite genera of the Wheeler Shale. Bathyuriscus fimbriatus is also relatively common at certain sites. Even more abundant are several species of agnostid trilobites, such a Peronopsis interstricta. These are typically less than a centimeter in length. Here are eight representative species of the Wheeler Shale:
Ptychopariida is a large, heterogeneous order of trilobite containing some of the most primitive species known. Many date to the Early Cambrian Period, but the order was extant through the Late Ordivician. Many of the offshoot species are difficult to classify in this single order.
The thorax is large and is typically made up of eight or more segments. The thorax is usually much longer than the pygidium, which is usually small. In some species the pygidium is outlined with a flat border.
This specimen measures approximately 5/8-inch long on a matrix measuring 7 inches by 6 inches. There is also a small Peronopsis sp. on this plate.
Marjum Formation
Delta, Utah
ITEM # TRILO-Utah-0003
This is a museum-quality example of the Ptychopariid trilobite Modocia typicalis from the Middle Cambrian of Utah. Modocia typicalis is a member of the Order Ptychopariida, Family Marjumiidae.
Western Utah is one of the best-known Cambrian fossil localities in the world. The Wheeler Shale and Marjum Formation, strata of Middle Cambrian age, exhibit various exposures throughout the House Range and nearby mountain ranges west of the town of Delta, Utah. The Wheeler Shale is named for a major feature in the House Range, the Wheeler Amphitheater. The Wheeler Shale contains interbeds of shaley limestone, mudstone, and thin platy limestone. Much of the Wheeler Shale is not particularly fossiliferous, but certain layers contain abundant trilobites and other shelly fossils. The Wheeler Shale also is known for a diverse biota of soft-bodied fossils, including many of the same taxa found in the Burgess Shale.
In the Cambrian, the continent of Laurentia (now the majority of North America), was equatorial, and oriented about ninety degrees from its current position. Close to the shorelines of Laurentia, limestone was deposited as shallow-ater reefs. Beyond the limestone belt, fine sediments built in deeper offshore contours, sometimes rapidly via undersea landslides off the reef platform. These offshore deposits along the paleoequator include much of the Wheeler Shale, the Burgess Shale of western Canada, and other sites from California through Utah to the Northwest territories of Canada. All of these sites yield remarkably preserved Cambrian fossils.
The most famous Wheeler Shale fossil is the trilobite Elrathia kingi; so common at some sites that specimens are commercially quarried and are made into novelty accessories, as well as sold to collectors and institutions all over the world. However, Elrathia is just one of about fifteen trilobite genera of the Wheeler Shale. Bathyuriscus fimbriatus is also relatively common at certain sites. Even more abundant are several species of agnostid trilobites, such a Peronopsis interstricta. These are typically less than a centimeter in length. Here are eight representative species of the Wheeler Shale:
Ptychopariida is a large, heterogeneous order of trilobite containing some of the most primitive species known. Many date to the Early Cambrian Period, but the order was extant through the Late Ordivician. Many of the offshoot species are difficult to classify in this single order.
The thorax is large and is typically made up of eight or more segments. The thorax is usually much longer than the pygidium, which is usually small. In some species the pygidium is outlined with a flat border.
This specimen measures approximately 5/8-inch long on a matrix measuring 7 inches by 6 inches. There is also a small Peronopsis sp. on this plate.
$
150.00
Trilobite - Peronopsis interstricta
Early Cambrian
Weeks Formation
Delta, Utah
ITEM# TRILO-Utah-0001
Very nice example of the trilobite Peronopsis interstricta from the Cambrian of Utah. Peronopsis interstricta is a member of the Order Agnostida, Family Peronopsidae.
Agnostida (the agnostids) is an order of trilobite. These small trilobites first appeared toward the end of the Early Cambrian and thrived in the Middle Cambrian. They are present in the lower Cambrian fossil record along with trilobites from Orders Redlichiida, Corynexochida, and Ptychopariida. The last agnostids went extinct in the Late Ordovician.
The Agnostida are divided into two suborders -- Agnostina and Eodiscina -- that are then divided into a number of families. As a group, agnostids have pygidia (tails) that are so similar in size and shape to their cephalons (heads) that it is difficult to distinguish which end is which. Most agnostid species were eyeless.
The systematic position of Order Agnostida within Class Trilobita remains uncertain, and there has been continuing debate whether they are trilobites or a stem group. The challenge to the status has focused on the Agnostina partly because juveniles of one genus have been found with legs greatly different from those of adult trilobites, suggesting they are separately descended from Crustaceans. Other researchers have suggested, based on cladistic analyses, that Eodiscina and Agnostida are closely united, and that the Eodiscina descended from the trilobite Order Ptychopariida.
Scientists have long debated whether the agnostids lived a pelagic or a benthic lifestyle. Their lack of eyes, a morphology not well-suited for swimming, and their fossils found in association with other benthic trilobites all suggest a benthic (bottom-dwelling) mode of life. They likely lived on areas of the ocean floor that received little or no light and fed on detritus that descended from upper layers of the sea to the bottom. In contrast, their wide geographic dispersion in the fossil record is uncharacteristic of benthic animals, suggesting a pelagic existence. The thoracic segment appears to form a hinge between the head and pygidium allowing for a bivalved ostracodan-type lifestyle. Furthermore, the orientation of the thoracic appendages appears ill suited for benthic living.
Agnostina are generally referred to simply as "agnostids" even though they probably should be called "agnostines".
Western Utah is one of the best-known Cambrian fossil localities in the world. The Wheeler Shale and Marjum Formation, strata of Middle Cambrian age, exhibit various exposures throughout the House Range and nearby mountain ranges west of the town of Delta, Utah. The Wheeler Shale is named for a major feature in the House Range, the Wheeler Amphitheater. The Wheeler Shale contains interbeds of shaley limestone, mudstone, and thin platy limestone. Much of the Wheeler Shale is not particularly fossiliferous, but certain layers contain abundant trilobites and other shelly fossils. The Wheeler Shale also is known for a diverse biota of soft-bodied fossils, including many of the same taxa found in the Burgess Shale.
In the Cambrian, the continent of Laurentia (now the majority of North America), was equatorial, and oriented about ninety degrees from its current position. Close to the shorelines of Laurentia, limestone was deposited as shallow-ater reefs. Beyond the limestone belt, fine sediments built in deeper offshore contours, sometimes rapidly via undersea landslides off the reef platform. These offshore deposits along the paleoequator include much of the Wheeler Shale, the Burgess Shale of western Canada, and other sites from California through Utah to the Northwest territories of Canada. All of these sites yield remarkably preserved Cambrian fossils.
The most famous Wheeler Shale fossil is the trilobite Elrathia kingi; so common at some sites that specimens are commercially quarried and are made into novelty accessories, as well as sold to collectors and institutions all over the world. However, Elrathia is just one of about fifteen trilobite genera of the Wheeler Shale. Bathyuriscus fimbriatus is also relatively common at certain sites. Even more abundant are several species of agnostid trilobites, such a Peronopsis interstricta. These are typically less than a centimeter in length.
This specimen is approximately 5/16 inches long on a matrix measuring 1.5 inches by 1.25 inches.
Weeks Formation
Delta, Utah
ITEM# TRILO-Utah-0001
Very nice example of the trilobite Peronopsis interstricta from the Cambrian of Utah. Peronopsis interstricta is a member of the Order Agnostida, Family Peronopsidae.
Agnostida (the agnostids) is an order of trilobite. These small trilobites first appeared toward the end of the Early Cambrian and thrived in the Middle Cambrian. They are present in the lower Cambrian fossil record along with trilobites from Orders Redlichiida, Corynexochida, and Ptychopariida. The last agnostids went extinct in the Late Ordovician.
The Agnostida are divided into two suborders -- Agnostina and Eodiscina -- that are then divided into a number of families. As a group, agnostids have pygidia (tails) that are so similar in size and shape to their cephalons (heads) that it is difficult to distinguish which end is which. Most agnostid species were eyeless.
The systematic position of Order Agnostida within Class Trilobita remains uncertain, and there has been continuing debate whether they are trilobites or a stem group. The challenge to the status has focused on the Agnostina partly because juveniles of one genus have been found with legs greatly different from those of adult trilobites, suggesting they are separately descended from Crustaceans. Other researchers have suggested, based on cladistic analyses, that Eodiscina and Agnostida are closely united, and that the Eodiscina descended from the trilobite Order Ptychopariida.
Scientists have long debated whether the agnostids lived a pelagic or a benthic lifestyle. Their lack of eyes, a morphology not well-suited for swimming, and their fossils found in association with other benthic trilobites all suggest a benthic (bottom-dwelling) mode of life. They likely lived on areas of the ocean floor that received little or no light and fed on detritus that descended from upper layers of the sea to the bottom. In contrast, their wide geographic dispersion in the fossil record is uncharacteristic of benthic animals, suggesting a pelagic existence. The thoracic segment appears to form a hinge between the head and pygidium allowing for a bivalved ostracodan-type lifestyle. Furthermore, the orientation of the thoracic appendages appears ill suited for benthic living.
Agnostina are generally referred to simply as "agnostids" even though they probably should be called "agnostines".
Western Utah is one of the best-known Cambrian fossil localities in the world. The Wheeler Shale and Marjum Formation, strata of Middle Cambrian age, exhibit various exposures throughout the House Range and nearby mountain ranges west of the town of Delta, Utah. The Wheeler Shale is named for a major feature in the House Range, the Wheeler Amphitheater. The Wheeler Shale contains interbeds of shaley limestone, mudstone, and thin platy limestone. Much of the Wheeler Shale is not particularly fossiliferous, but certain layers contain abundant trilobites and other shelly fossils. The Wheeler Shale also is known for a diverse biota of soft-bodied fossils, including many of the same taxa found in the Burgess Shale.
In the Cambrian, the continent of Laurentia (now the majority of North America), was equatorial, and oriented about ninety degrees from its current position. Close to the shorelines of Laurentia, limestone was deposited as shallow-ater reefs. Beyond the limestone belt, fine sediments built in deeper offshore contours, sometimes rapidly via undersea landslides off the reef platform. These offshore deposits along the paleoequator include much of the Wheeler Shale, the Burgess Shale of western Canada, and other sites from California through Utah to the Northwest territories of Canada. All of these sites yield remarkably preserved Cambrian fossils.
The most famous Wheeler Shale fossil is the trilobite Elrathia kingi; so common at some sites that specimens are commercially quarried and are made into novelty accessories, as well as sold to collectors and institutions all over the world. However, Elrathia is just one of about fifteen trilobite genera of the Wheeler Shale. Bathyuriscus fimbriatus is also relatively common at certain sites. Even more abundant are several species of agnostid trilobites, such a Peronopsis interstricta. These are typically less than a centimeter in length.
This specimen is approximately 5/16 inches long on a matrix measuring 1.5 inches by 1.25 inches.
$
100.00
Trilbite - Pseudocybele lemurei
Ordovician - 425 mya
Fillmore Formation
Millard County, Utah
ITEM# TRILO-Utah-0002
This rarely offered trilobite is the phacop trilobite Pseudocybele lemurei, from the Ordovician of Utah. Pseudocybele lemurei is a member of the Order Phacopida, Family Pliomeridae.
Phacopida ("Lens-face") is an order of trilobite that lived from the Ordovician to the Devonian. It is made up of a morphologically diverse group of related suborders.
The origin of the Phacopida order is uncertain. It comprises three suborders (Phacopina, Calymenina, and Cheirurina) which share a distinctive protaspis (developmental stage lacking segments) type. The Cheirurina and Calymenina retain a rostral plate (an apomorphy) but in virtually all Phacopina the free cheeks are yoked as a single piece. This sort of similarity in development suggests phylogenetic unity. The suborder Calymenina is the most primitive of the Phacopida order and shares some characteristics with the order Ptychopariida, though it is not included in the subclass Libristoma.
Phacopida had 8 to 19 thoracic segments and are distinguishable by the expanded glabella, short or absent preglabellar area, and schizochroal (Phacopina) or holochroal (Cheirurina and Calymenina) eyes. Schizochroal eyes are compound eyes with up to around 700 separate lenses. Each lens has an individual cornea which extended into a rather large sclera. The development of schizochroal eyes in phacopid trilobites is an example of post-displacement paedomorphosis. The eyes of immature holochroal Cambrian trilobites were basically miniature schizochroal eyes. In Phacopida, these were retained, via delayed growth of these immature structures (post-displacement), into the adult form.
This specimen measures approximately 1/2 inch long on a matrix measuring 2 inches by 1 1/2 inches.
Fillmore Formation
Millard County, Utah
ITEM# TRILO-Utah-0002
This rarely offered trilobite is the phacop trilobite Pseudocybele lemurei, from the Ordovician of Utah. Pseudocybele lemurei is a member of the Order Phacopida, Family Pliomeridae.
Phacopida ("Lens-face") is an order of trilobite that lived from the Ordovician to the Devonian. It is made up of a morphologically diverse group of related suborders.
The origin of the Phacopida order is uncertain. It comprises three suborders (Phacopina, Calymenina, and Cheirurina) which share a distinctive protaspis (developmental stage lacking segments) type. The Cheirurina and Calymenina retain a rostral plate (an apomorphy) but in virtually all Phacopina the free cheeks are yoked as a single piece. This sort of similarity in development suggests phylogenetic unity. The suborder Calymenina is the most primitive of the Phacopida order and shares some characteristics with the order Ptychopariida, though it is not included in the subclass Libristoma.
Phacopida had 8 to 19 thoracic segments and are distinguishable by the expanded glabella, short or absent preglabellar area, and schizochroal (Phacopina) or holochroal (Cheirurina and Calymenina) eyes. Schizochroal eyes are compound eyes with up to around 700 separate lenses. Each lens has an individual cornea which extended into a rather large sclera. The development of schizochroal eyes in phacopid trilobites is an example of post-displacement paedomorphosis. The eyes of immature holochroal Cambrian trilobites were basically miniature schizochroal eyes. In Phacopida, these were retained, via delayed growth of these immature structures (post-displacement), into the adult form.
This specimen measures approximately 1/2 inch long on a matrix measuring 2 inches by 1 1/2 inches.
$
300.00
