Bactroceras
Encyclopedia
Bactroceras is a genus
of the family Baltoceratidae
, orthoceroid
cephalapods that lived during the early Middle Ordovician
, from about 472—464 mya, existing for approximately 8 million years.
by Furnish and Glenister(1964) and retained there by Evans (2005).
Some paleontologists have regarded Bactroceras as an early bactritid because of its spherical apex
and ventral siphuncle
.
However, a more recent study has argued that the shell of Bactroceras has important differences from those of true bactritids.
For instance, the first shell chamber of Bactroceras resembles that of other Ordovician
orthocerids, such as Archigeisonoceras and Hedstroemoceras: it is about 10 mm in diameter and is short, forming a spherical cap. True bactritids more strongly resemble late Silurian and Devonian orthocerids, whose first chamber is only about 5 mm across. Moreover, there is a large stratigraphic gap of nearly 50 million years between Bactroceras and the next orthocone
s with a spherical apex and ventral siphuncle.
, the tube connecting its chambers to the animal's body, was ventral, which means that it ran next to the shell wall on the underside of the shell. The first chamber of the shell was spherical. The soft anatomy of the animal was not known, but it lacked mineral deposits in its shell, it may have floated with the point of its shell upward, but somewhat inclined. Bactroceras differs from the later cephalopod Bactrites in being more circular in cross section and having deeper V-shaped ventral lobes.
to Antelope Valley
, Nevada
.
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 the family Baltoceratidae
Baltoceratidae
Baltoceratidae is an extinct family of orthoconic cephalopods belonging to the subclass Nautiloidea endemic to what would be Asia, Australia, Europe, North America, and South America during the Ordovician living from about 480–460 mya, existing for approximately .-Taxonomy:Baltoceratidae was...
, orthoceroid
Orthocerida
Orthocerida is an order of extinct nautiloid cephalopods also known as the Michelinocerda that lived from the Early Ordovician possibly to the Late Triassic . A fossil found in the Caucasus suggests they may even have survived until the Early Cretaceous...
cephalapods that lived during the early Middle Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
, from about 472—464 mya, existing for approximately 8 million years.
Taxonomy
Bactroceras was named by Holm (1898). Its type is Bactroceras avus. It was assigned to the BaltoceratidaeBaltoceratidae
Baltoceratidae is an extinct family of orthoconic cephalopods belonging to the subclass Nautiloidea endemic to what would be Asia, Australia, Europe, North America, and South America during the Ordovician living from about 480–460 mya, existing for approximately .-Taxonomy:Baltoceratidae was...
by Furnish and Glenister(1964) and retained there by Evans (2005).
Some paleontologists have regarded Bactroceras as an early bactritid because of its spherical apex
Apex (mollusc)
Apex is an anatomical term for the tip of the mollusc shell of a gastropod, scaphopod, or cephalopod mollusc.-Gastropods:The word "apex" is most often used to mean the tip of the spire of the shell of a gastropod...
and ventral siphuncle
Siphuncle
The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and Spirula...
.
However, a more recent study has argued that the shell of Bactroceras has important differences from those of true bactritids.
For instance, the first shell chamber of Bactroceras resembles that of other Ordovician
Ordovician
The Ordovician is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago . It follows the Cambrian Period and is followed by the Silurian Period...
orthocerids, such as Archigeisonoceras and Hedstroemoceras: it is about 10 mm in diameter and is short, forming a spherical cap. True bactritids more strongly resemble late Silurian and Devonian orthocerids, whose first chamber is only about 5 mm across. Moreover, there is a large stratigraphic gap of nearly 50 million years between Bactroceras and the next orthocone
Orthocone
An orthocone is a usually long straight shell of a nautiloid cephalopod. During the 18th and 19th centuries, all shells of this type were named Orthoceras, but it is now known that many groups of nautiloids developed or retained this type of shell....
s with a spherical apex and ventral siphuncle.
Morphology
Bactroceras had a thin, cone shaped shell. Its siphuncleSiphuncle
The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and Spirula...
, the tube connecting its chambers to the animal's body, was ventral, which means that it ran next to the shell wall on the underside of the shell. The first chamber of the shell was spherical. The soft anatomy of the animal was not known, but it lacked mineral deposits in its shell, it may have floated with the point of its shell upward, but somewhat inclined. Bactroceras differs from the later cephalopod Bactrites in being more circular in cross section and having deeper V-shaped ventral lobes.
Fossil distribution
Fossils were found in Middle Ordovician strata dating from the Whiterockian/Llanvirnian age. Locations were varied and stretched from New South Wales, Australia to El Puente, BoliviaBolivia
Bolivia officially known as Plurinational State of Bolivia , is a landlocked country in central South America. It is the poorest country in South America...
to Antelope Valley
Antelope Valley (Eureka County)
The Antelope Valley of southern Eureka County is a small 35 mi long valley, surrounded by four mountain ranges. Antelope Wash flows north, to endorheic flatlands at the valley's north end. Eureka, Nevada lies 20 mi east nestled among mountain ranges. From Eureka U.S...
, Nevada
Nevada
Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...
.
Sources
- Fossils (Smithsonian Handbooks) by David Ward
- PaleoBiology Database: Bactroceras, basic info