Eosacantha
Encyclopedia
Eosacantha is an extinct genus
of tortoise beetle
in the family Chrysomelidae and containing a single
species Eosacantha delocranioides. The species is known only from the Middle Eocene Parachute Member, part of the Green River Formation
, in the Piceance Creek Basin, Garfield County
, northwestern Colorado
, USA.
, specimen number "USNM 79136". The specimen is complete but of unidentified sex, preserved as a compression fossil
in sedimentary rock. It was recovered from outcrops of the Green River Formation
's Parachute Member, locality 41140, exposed in the Anvil Points area of Garfield County, Colorado
, USA. The type specimen is currently preserved in the Department of Paleobiology collections housed in the National Museum of Natural History
, located in Washington, D.C.
, USA. Eosacantha was first studied by Caroline S. Chaboo and Michael S. Engel
of the University of Kansas
, Lawrence, Kansas
, USA. Their 2009 type description of the genus and species was published online and in print in the journal Systematic Entomology
. The generic
name was coined by Chaboo and Engel from a combination of the Greek
() meaning "dawn" and the Greek word () meaning "thorny". The etymology
of the specific epithet is in reference to the general resemblance to some modern species in the genus Delocrania.
When described, Eosacantha delocranioides along with Denaeaspis chelonopsis were among the oldest derived tortoise beetles in the fossil record. The nearest modern relatives to Eosacantha in the tribe Notosacanthini are restricted to African, tropical Asian, and Australian regions. The loss of the tribe from North America may be related to specialization of the beetles to specific plant hosts that were lost due to the extensive climatic shifts during the Late Eocene – Early Oligocene transition.
are preserved with a clear yellowish coloration
with a darkening of the elytra towards the marginal disk. The type specimen is small: 3.12 millimetre (0.122834645669291 in) wide by 3.2 mm (0.125984251968504 in) long. The antennae, composed of 11 segments, are notably short in length and have an overall clavate morphology. Antennomeres seven through eleven form a weak club at the tip of the antenna.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of tortoise beetle
Tortoise beetle
The tortoise beetles are an artificial grouping of tribes within the leaf beetle subfamily Hispinae. In past classifications, they have been variously placed as a family or a subfamily ; when it was recognized that this group was not monophyletic, it was split and the resulting tribes were...
in the family Chrysomelidae and containing a single
Monotypic
In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...
species Eosacantha delocranioides. The species is known only from the Middle Eocene Parachute Member, part of the Green River Formation
Green River Formation
The Green River Formation is an Eocene geologic formation that records the sedimentation in a group of intermountain lakes. The sediments are deposited in very fine layers, a dark layer during the growing season and a light-hue inorganic layer in winter. Each pair of layers is called a varve and...
, in the Piceance Creek Basin, Garfield County
Garfield County, Colorado
Garfield County is the eighth most extensive and the twelfth most populous of the 64 counties of the State of Colorado of the United States. The county population was 43,791 at U.S. Census 2000. The county is named in honor of United States President James A. Garfield...
, northwestern Colorado
Colorado
Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...
, USA.
History and classification
Eosacantha delocranioides is known only from one fossil, the holotypeHolotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
, specimen number "USNM 79136". The specimen is complete but of unidentified sex, preserved as a compression fossil
Compression fossil
A compression fossil is a fossil preserved in sedimentary rock that has undergone physical compression. While it is uncommon to find animals preserved as good compression fossils, it is very common to find plants preserved this way...
in sedimentary rock. It was recovered from outcrops of the Green River Formation
Green River Formation
The Green River Formation is an Eocene geologic formation that records the sedimentation in a group of intermountain lakes. The sediments are deposited in very fine layers, a dark layer during the growing season and a light-hue inorganic layer in winter. Each pair of layers is called a varve and...
's Parachute Member, locality 41140, exposed in the Anvil Points area of Garfield County, Colorado
Garfield County, Colorado
Garfield County is the eighth most extensive and the twelfth most populous of the 64 counties of the State of Colorado of the United States. The county population was 43,791 at U.S. Census 2000. The county is named in honor of United States President James A. Garfield...
, USA. The type specimen is currently preserved in the Department of Paleobiology collections housed in the National Museum of Natural History
National Museum of Natural History
The National Museum of Natural History is a natural history museum administered by the Smithsonian Institution, located on the National Mall in Washington, D.C., United States. Admission is free and the museum is open 364 days a year....
, located in Washington, D.C.
Washington, D.C.
Washington, D.C., formally the District of Columbia and commonly referred to as Washington, "the District", or simply D.C., is the capital of the United States. On July 16, 1790, the United States Congress approved the creation of a permanent national capital as permitted by the U.S. Constitution....
, USA. Eosacantha was first studied by Caroline S. Chaboo and Michael S. Engel
Michael S. Engel
Michael S. Engel is an American paleontologist and entomologist. He has undertaken field work in Central Asia, Asia Minor, and the Western Hemisphere, and published more than 300 papers in scientific journals. He was trained at the University of Kansas where in 1993 he received a B.S. in Cellular...
of the University of Kansas
University of Kansas
The University of Kansas is a public research university and the largest university in the state of Kansas. KU campuses are located in Lawrence, Wichita, Overland Park, and Kansas City, Kansas with the main campus being located in Lawrence on Mount Oread, the highest point in Lawrence. The...
, Lawrence, Kansas
Lawrence, Kansas
Lawrence is the sixth largest city in the U.S. State of Kansas and the county seat of Douglas County. Located in northeastern Kansas, Lawrence is the anchor city of the Lawrence, Kansas, Metropolitan Statistical Area, which encompasses all of Douglas County...
, USA. Their 2009 type description of the genus and species was published online and in print in the journal Systematic Entomology
Systematic Entomology
Systematic Entomology is a scientific journal covering the field of systematic entomology, published by the Royal Entomological Society of London. Having begun in 1932 as Proceedings of the Royal Entomological Society of London, Series B: Taxonomy, the title was changed to ournal of Entomology,...
. The generic
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
name was coined by Chaboo and Engel from a combination of the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
() meaning "dawn" and the Greek word () meaning "thorny". The etymology
Etymology
Etymology is the study of the history of words, their origins, and how their form and meaning have changed over time.For languages with a long written history, etymologists make use of texts in these languages and texts about the languages to gather knowledge about how words were used during...
of the specific epithet is in reference to the general resemblance to some modern species in the genus Delocrania.
When described, Eosacantha delocranioides along with Denaeaspis chelonopsis were among the oldest derived tortoise beetles in the fossil record. The nearest modern relatives to Eosacantha in the tribe Notosacanthini are restricted to African, tropical Asian, and Australian regions. The loss of the tribe from North America may be related to specialization of the beetles to specific plant hosts that were lost due to the extensive climatic shifts during the Late Eocene – Early Oligocene transition.
Description
The E. delocranioides type specimen is a well-preserved complete adult preserved with in a dorsal view showing the antennae and head in full view. The front edge of the pronotum is deeply indented with the head and antennae visible. The elytraElytron
An elytron is a modified, hardened forewing of certain insect orders, notably beetles and a few of the true bugs ; in most true bugs, the forewings are instead called hemelytra, as only the basal half is thickened while the apex is membranous...
are preserved with a clear yellowish coloration
Animal colouration
Animal coloration is the general appearance of an animal resulting from the reflection or emission of light from its surfaces. The mechanisms for colour production in animals include pigments, chromatophores, structural coloration, and bioluminescence....
with a darkening of the elytra towards the marginal disk. The type specimen is small: 3.12 millimetre (0.122834645669291 in) wide by 3.2 mm (0.125984251968504 in) long. The antennae, composed of 11 segments, are notably short in length and have an overall clavate morphology. Antennomeres seven through eleven form a weak club at the tip of the antenna.