''Bothriolepis'' (from el, βόθρος , 'trench' and el, λεπίς 'scale') was a widespread, abundant and diverse
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
antiarch
Antiarchi ("opposite anus") is an order of heavily armored placoderms. The antiarchs form the second-most successful group of placoderms after the arthrodires in terms of numbers of species and range of environments. The order's name was coi ...
placoderms that lived during the
Middle to
Late Devonian
The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wher ...
period of the
Paleozoic Era
The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon.
The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838
by combining the Greek words ''palaiós'' (, "old") and ' ...
. Historically, ''Bothriolepis'' resided in an array of paleo-environments spread across every paleocontinent, including near shore marine and freshwater settings.
Most species of ''Bothriolepis'' were characterized as relatively small,
benthic
The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...
, freshwater
detritivore
Detritivores (also known as detrivores, detritophages, detritus feeders, or detritus eaters) are heterotrophs that obtain nutrients by consuming detritus (decomposing plant and animal parts as well as feces). There are many kinds of invertebrates, ...
s (organisms that obtain nutrients by consuming decomposing plant/animal material), averaging around in length.
[ However, the largest species, ''B. rex'', had an estimated bodylength of . Although expansive with over 60 species found worldwide,] comparatively ''Bothriolepis'' is not unusually more diverse than most modern bottom dwelling species around today.
Classification
''Bothriolepis'' is a genus placed within the placoderm order Antiarchi. The earliest antiarch placoderms first appeared in the Silurian
The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...
period of the Paleozoic Era and could be found distributed on every paleocontinent
A paleocontinent or palaeocontinent is a distinct area of continental crust that existed as a major landmass in the geological past. There have been many different landmasses throughout Earth's time. They range in sizes, some are just a collection ...
by the Devonian period. The earliest members of ''Bothriolepis'' appear by the Middle Devonian. Antiarchs, as well as other placoderms, are morphologically diverse and are characterized by bony plates that cover their head and the anterior part of the trunk. Early ontogenetic stages of placoderms had thinner bony plates within both the head and trunk-shield, which allowed for easy distinction between early placoderm ontogenetic stages within the fossil record and taxa that possessed fully developed bony plates but were small by characterization. Placoderm bony plates were generally made up of three layers, including a compact basal lamellar bony layer, a middle spongy bony layer and a superficial layer; ''Bothriolepis'' can be classified as a placoderm since it possesses these layers. Placoderms were extinct by the end of the Devonian. Placodermi is a paraphyletic
In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...
group of the clade Gnathostomata
Gnathostomata (; from Greek: (') "jaw" + (') "mouth") are the jawed vertebrates. Gnathostome diversity comprises roughly 60,000 species, which accounts for 99% of all living vertebrates, including humans. In addition to opposing jaws, living ...
, which includes all jawed vertebrates. It is unclear exactly when gnathostomes emerged, but the scant early fossil record indicates that it was sometime in the Early Palaeozoic era. The last species of ''Bothriolepis'' died out, together with the rest of Placodermi, at the end of the Devonian period.
General anatomy
Head
There are two openings through the head of ''Bothriolepis'': a keyhole opening along the midline on the upper side for the eyes and nostrils and an opening for the mouth on the lower side near the anterior end of the head. A discovery regarding preserved structures that appear to be nasal capsules confirms the belief that the external nasal openings lay on the dorsal side of the head near the eyes. Additionally, the position of the mouth on the ventral side of the skull is consistent with the typical horizontal resting orientation of ''Bothriolepis''. It had a special feature on its skull, a separate partition of bone below the opening for the eyes and nostrils enclosing the nasal capsules called a preorbital recess.
Jaw
A new sample from the Gogo Formation
The Gogo Formation in the Kimberley region of Western Australia is a Lagerstätte that exhibits exceptional preservation of a Devonian reef community. The formation is named after Gogo Station, a cattle station where outcrops appear and fossils ...
in the Canning Basin of Western Australia has provided evidence regarding the morphological features of the visceral jaw elements of ''Bothriolepis''. Using the sample, it is evident that the mental plate (a dermal bone that forms the upper part of the jaw) of antiarchs is homologous with the suborbital plate found in other placoderms. The lower jawbone consists of a differentiated blade and biting portions. Next to the mandibular joint are the prelateral and infraprelateral plates, which both are canal-bearing bones. The palatoquadrate In some fishes, the palatoquadrate is the dorsal component of the mandibular arch, the ventral one being Meckel's cartilage. The palatoquadrate forms from splanchnocranium in various chordates including placoderms and acanthodians.
See also
* H ...
lacks a high orbital process and was attached only to the ventral part of the mental plate, proving that the ethmoidal region of the braincase (the region of the skull that separates the brain and nasal cavity) was in fact deeper than originally believed. In addition to the above-listed sample from the Gogo Formation, several other specimens have been found with mouthparts held in the natural position by a membrane that covers the oral region and attaches to the lateral and anterior margins of the head. ''Bothriolepis'' has a jaw in which the two halves are separate and in the adult are functionally independent.
Trunk
''Bothriolepis'' had a slender trunk that was likely covered in soft skin with no scales or markings. The orientation that appears to have been mostly stable for resting was the dorsal surface up, evidenced by the flat surface on the ventral side. The trunk's outline suggests that there may have been a notochord
In anatomy, the notochord is a flexible rod which is similar in structure to the stiffer cartilage. If a species has a notochord at any stage of its life cycle (along with 4 other features), it is, by definition, a chordate. The notochord consis ...
present surrounded by a membranous sheath, however, there is no direct evidence of this since the notochord is made up of soft tissue, which is not typically preserved in the fossil record. Similar to other antiarch
Antiarchi ("opposite anus") is an order of heavily armored placoderms. The antiarchs form the second-most successful group of placoderms after the arthrodires in terms of numbers of species and range of environments. The order's name was coi ...
s, the thoracic
The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the crea ...
shield of ''Bothriolepis'' was attached to its heavily armored head. Its box-like body was enclosed in armor plates, providing protection from predators. Attached to the ventral surface of the trunk is a large, thin, circular plate marked by deep-lying lines and superficial ridges. This plate lies just below the opening to the cloaca
In animal anatomy, a cloaca ( ), plural cloacae ( or ), is the posterior orifice that serves as the only opening for the digestive, reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles and birds, a ...
.
Dermal skeleton
The dermal skeleton is organized in three layers: a superficial lamellar layer, a cancellous spongiosa, and a compact basal lamellar layer. Even in early ontogeny, these layers are apparent in specimen of ''Bothriolepis canadensis''. The compact layers develop first.[ The superficial layer is speculated to have denticles that may have been made of cellular bone.]
Fins and tail
''Bothriolepis'' had a long pair of spine-like pectoral fin
Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as ...
s, jointed at the base, and again a little more than halfway along. These spike-like fins were probably used to lift the body clear off the bottom; its heavy armor would have made it sink quickly as soon as it lost forward momentum. It may also have used its pectoral fins to throw sediment (mud, sand or otherwise) over itself. In addition to the pectoral fins, it also had two dorsal fins: a low, elongated anterior dorsal fin and a high rounded posterior dorsal fin —though the hypothesized structure of the dorsal fins varies based on the specific species of ''Bothriolepis'' and has been modified several times in the reconstructions released by researchers as new information has become available. The caudal tail
Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as see ...
was elongated, ending in a narrow band, but is unfortunately rarely preserved in fossils. Although there is no agreed-upon explanation of their function, ''Bothriolepis'' also had two membranous, ventral frills located on the posterior end of the trunk carapace on either side of the tail that each has two distinct regions. There is no evidence that the frills were involved in support of the skeleton but it is possible that they either functioned as fins or were involved in reproduction, and may have even been present in one sex but not the other.
Soft anatomy
Structures composed of soft tissue are typically not preserved in fossils because they break down easily and decompose much faster than hard tissues, meaning that the fossil record often lacks information regarding the internal anatomy of fossil species. Preservation of soft tissue structures can sometimes occur, however, if sediments fill the internal structures of an organism upon or after its death. Robert Denison's paper titled "The Soft Anatomy of ''Bothriolepis''" explores the forms and organs of ''Bothriolepis''. These internal structures were preserved when different types of sediments surrounding the exterior of the animal-filled the internal carapaces (only organs that communicate with the exterior could be preserved in this manner). Three different sediment types were identified within the different sections of ''Bothriolepis'': the first a pale greenish-gray medium-textured sandstone largely consisting of calcite; the second similar but finer sediment which preserves many of the organ forms; and the third distinct, fine-grained siltstone consisting of quartz, mica and other minerals but no calcite. These sediments helped preserve the following internal elements:
Alimentary system
In general, the alimentary system of ''Bothriolepis'' –which includes the organs involved in ingestion, digestion, and removal of waste– can be described as simple and straight, unlike that of humans. It begins at the anterior end of the organism with a small mouth cavity located over the posterior area of the upper jaw plates. Posteriorly from the mouth, the alimentary system extends into a wider and dorso-ventrally flattened region called the pharynx
The pharynx (plural: pharynges) is the part of the throat behind the mouth and nasal cavity, and above the oesophagus and trachea (the tubes going down to the stomach and the lungs). It is found in vertebrates and invertebrates, though its struc ...
, from which both the gills and lungs arise. The esophagus
The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...
, which is also characterized as a dorso-ventrally flattened tube, extends from the mouth into the stomach and leads to a flattened ellipsoidal structure. This structure may be homologous to the anterior end of the intestine found in other fish. The flatness of these structures may have been exaggerated when the fossil specimens experienced tectonic deformation through geologic time. The intestine begins narrowly on the anterior end, expands transversely, and then again narrows posteriorly towards the cylindrical rectum, which terminates just within the posterior end of the trunk carapace. While the alimentary system is primitive in nature and lacks an expanded stomach region, it is specialized by an independently acquired complex spiral valve, comparable to that in elasmobranchs
Elasmobranchii () is a Class (biology), subclass of Chondrichthyes or cartilaginous fish, including sharks (superorder Selachii), Batoidea, rays, skate (fish), skates, and sawfish (superorder Batoidea). Members of this subclass are characteris ...
and many bony fish and similar to that found in some sharks. A single fold of tissue rolled upon its own axis forms this specialized spiral valve.
Gills
It is inferred that the gills of ''Bothriolepis'' are of the primitive type, though their structure is still not well understood. Laterally, they are enclosed by an opercular fold and are found in the space beneath the lateral part of the head shield, extending medially underneath the neurocranium
In human anatomy, the neurocranium, also known as the braincase, brainpan, or brain-pan is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calvaria (skull), ...
. Compared to the gills of normally-shaped fish, the gill region of ''Bothriolepis'' is considered to be placed more dorsally, is anteriorly more crowded, and in general is relatively short and broad.
Paired ventral sacs
Extending posteriorly from the trunk carapace are paired ventral sacs that extend to the anterior end of the spiral intestine. The sacs seem to originate at the pharynx as a single median tube, which then broadens posteriorly and eventually splits into two sacs that may be homologous to the lung
The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of t ...
s of certain dipnoans and tetrapods
Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids (reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct therapsids ...
. It has been hypothesized that these lungs, coupled with the jointed arms and rigid, supportive skeleton, would have allowed ''Bothriolepis'' to travel on land. Additionally, as Robert Denison states because there is no evidence of a connection between the external naris
A nostril (or naris , plural ''nares'' ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbi ...
and mouth, ''Bothriolepis'' likely breathed similarly to present-day lungfish, i.e., by placing the mouth above the water's surface and swallowing air.
Despite the original interpretation presented by Denison in 1941, not all paleontologists agree that placoderms like ''Bothriolepis'' actually possessed lungs. For example, in his paper ''"Lungs" in Placoderms, a Persistent Palaeobiological Myth Related to Environmental Preconceived Interpretations'', D. Goujet suggests that although traces of some digestive organs may be apparent from the sedimentary structures, there is no evidence supporting the presence of lungs in the samples from the Escuminac formation of Canada upon which the original assertion was based. He notes that the worldwide distribution of ''Bothriolepis'' is restricted to strictly marine environments, and thus believes that the presence of lungs in ''Bothriolepis'' is uncertain. Further investigation of the fossils is likely necessary to reach a conclusion about the presence of lungs in ''Bothriolepis''.
Feeding
''Bothriolepis'', as with all other antiarchs, are thought to have fed by directly swallowing mouthfuls of mud and other soft sediments in order to digest detritus
In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...
, small or microorganisms, algae, and other forms of organic matter in the swallowed sediments. Additionally, the positioning of the mouth on the ventral side of its head further suggests that ''Bothriolepis'' was likely a bottom-feeder. The regular presence of "carbonaceous material in the alimentary tract" is believed to indicate that most of its diet consisted of plant material.
Distribution
''Bothriolepis'' fossils are found in Middle and Late Devonian
The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...
strata (from 387 to 360 million years ago). Because the fossils are found in freshwater sediments, ''Bothriolepis'' is presumed to have spent most of its life in freshwater
Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...
rivers and lakes, but was probably able to enter salt water
Saline water (more commonly known as salt water) is water that contains a high concentration of dissolved salts (mainly sodium chloride). On the United States Geological Survey (USGS) salinity scale, saline water is saltier than brackish water, ...
as well, because its range appeared to have corresponded with the Devonian continental coastlines. Large groupings of ''Bothriolepis'' specimens have been found in Asia, Europe, Australia (Gogo Formation
The Gogo Formation in the Kimberley region of Western Australia is a Lagerstätte that exhibits exceptional preservation of a Devonian reef community. The formation is named after Gogo Station, a cattle station where outcrops appear and fossils ...
), Pennsylvania (Catskill Formation), Quebec ( Escuminac Formation), Virginia (Chemung), Colorado, Cuche Formation
The Cuche Formation ( es, Formación Cuche, Cc) is a geological formation of the Floresta Massif, Altiplano Cundiboyacense in the Eastern Ranges of the Colombian Andes. The sequence of siltstones, shales, and sandstone beds dates to the Late Devo ...
( Boyacá, Colombia), and all around the world.
Catskill Formation site
The Catskill Formation
The Devonian Catskill Formation or the Catskill Clastic wedge is a unit of mostly terrestrial sedimentary rock found in Pennsylvania and New York. Minor marine layers exist in this thick rock unit (up to ). It is equivalent to the Hampshire For ...
(Upper Devonian, Famennian Stage), located in Tioga County, Pennsylvania
Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...
, is the site of a large sample of small individuals of ''Bothriolepis''. The sample was collected from a series of rock slabs that consisted of partial or complete, articulated, external skeletons. More than two hundred individuals were found packed closely together with little to no overlap. From this sample, much information regarding characteristics of juvenile ''Bothriolepis'' can be determined. A morphometric study performed by Jason Downs and co-authors highlights certain characteristics that indicate juvenility in ''Bothriolepis'', including a moderately large head and moderately large orbital fenestra
The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...
—both of which are characteristics also recognized by Erik Stensio in 1948 in the smallest ''B. canadensis'' individuals. Several other features that Stensio marked indicative of young individuals can also be seen exhibited in the Catskill sample. These features include "delicate dermal bones with ornament consisting of continuous anastomosing ridges rather than tubercles, a dorsal trunk shield narrower than long and with a continuous and pronounced dorsal median ridge, and a pre-median plate that is wider than it is long".
Species
Vertebrate paleontology is heavily dependent on the ability to differentiate between different species in a way that is consistent both within a particular genus and across all organisms. The genus ''Bothriolepis'' is no exception to this principle. Listed below are a few of the notable species within ''Bothriolepis''; more than sixty species have been named in total, and it is likely that a sizeable proportion of them are valid due to the cosmopolitan nature of ''Bothriolepis''.
''Bothriolepis canadensis''
''Bothriolepis canadensis'' is a taxon that often serves as a model organism for the order Antiarchi because of its enormous sample of complete, intact specimens found at the Escuminac Formation in Quebec
Quebec ( ; )According to the Canadian government, ''Québec'' (with the acute accent) is the official name in Canadian French and ''Quebec'' (without the accent) is the province's official name in Canadian English is one of the thirtee ...
, Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
. Because of the vast sample size, this species is often used to compare growth data of newly acquired specimens of ''Bothriolepis'', including those found in the Catskill Formation mentioned above. This comparison allows researchers to determine if newly found samples represent juvenile individuals or new "Bothriolepis" species.
''B. canadensis'' was first described in 1880 by J.F. Whiteaves, using a limited number of disfigured samples. The next to propose a reconstruction of the species was W. Patten, who published his findings in 1904 after a discovery of several specimens that were well preserved in 3-D. In 1948, E. Stensio released a detailed depiction of ''B. canadensis'' anatomy using an abundance of material, which eventually became the most widely accepted description of this species. Since Stensio's publication, many others have provided reconstructed models of ''B. canadensis'' with modified aspects of the anatomy, including Vezina's modified single dorsal fin and more recently, reconstructions by Arsenault ''et al'' from specimens with little taphonomic distortion. Presently, the model of Arsenault ''et al''. is regarded to be the most accurate, while there is still much debate about various aspects of this species' external anatomy. Despite the uncertainty, ''B. canadensis'' is still classically considered one of the most well-known species.
The external skeleton
A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...
of ''Bothriolepis canadensis'' is made of cellular dermal bone tissue and is characterized by distinct horizontal zonation or stratification. The model fish has an average total length of and an average dermal armor length of , which accounts for 35.6% of the estimated total length. Like many antiarchs, ''B. canadensis'' also had narrow pectoral fins, a heterocercal
Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...
caudal fin (meaning the notochord extends into the upper lobe of the caudal tail) and a large dorsal fin which likely didn't play an important role in propulsion but instead acted more as a stabilizer.
''Bothriolepis rex''
Originally described by Downs et al. (2016), ''Bothriolepis rex'' is from the Nordstrand Point Formation of Ellesmere Island, Canada. B. rex's body length is estimated at 1.7 meters and is, therefore, the largest known species of ''Bothriolepis''. Its armor is especially thick and dense even when taking its size into account. Downs et al. (2016) suggest that this may have both protected the animal from large predators and served as ballast to prevent this large bottom-dweller from floating to the surface.
''Bothriolepis virginiensis''
Originally described by Weems et al. in 1981, this species, ''Bothriolepis virginiensis'', is from the "Chemung", near Winchester, Virginia
Winchester is the most north western independent city in the Commonwealth of Virginia. It is the county seat of Frederick County, although the two are separate jurisdictions. The Bureau of Economic Analysis combines the city of Winchester wit ...
. Several traits found in ''B. virginiensis'' can also be found in other species of ''Bothriolepis'', (especially ''B. nitida''), including posterior oblique cephalic sensory line grooves that meet relatively far anteriorly on the nuchal plate, relatively elongated orbital fenestra and a low anterior-median-dorsal crest. Characteristics that distinguish ''B. virginiensis'' from other species include but are not limited to fused head sutures, fused elements in adult distal pectoral fin segments and long premedian plate relative to headshield length.
Currently, there is much debate regarding whether the species ''B. virginiensis'' and ''B. nitida'' can actually be distinguished from one another. Thomson and Thomas state that five species of ''Bothriolepis'' from the United States (''B. nitida, B. minor, B. virginiensis, B. darbiensis and B. coloradensis'') are unable to be consistently distinguished from one another. Conversely, Weems asserts that there are several traits that distinguish the species from one another, including several listed above.
''Bothriolepis nitida''
This species, found in present-day Pennsylvania
Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...
, was originally described by J. Leidy in 1856. As mentioned above, there is much debate regarding the distinguishability between ''B. nitida'' and ''B. virginiensis'', however based on evidence presented by Weems (2004), there are several distinguishable traits specific to each species. ''B. nitida'' has a maximum headshield length of , a narrow and shallow trifid preorbital recess, has an anterior-median-dorsal (AMD) plate that is wider than it is long and a ventral thoracic shield that has convex lateral borders.
''Bothriolepis coloradensis''
First described by Eastman in 1904, this species was found localized in present-day Colorado
Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of t ...
. There is a possibility that this species is similar, if not identical, to ''B. nitida'', however because the material available regarding ''B. coloradensis'' is fragmented, it is impossible to compare the two species with any degree of certainty.
''Bothriolepis africana''
''Bothriolepis africana'' is the ''Bothriolepis'' species known from the highest paleolatitude
Paleomagnetism (or palaeomagnetismsee ), is the study of magnetic fields recorded in rocks, sediment, or archeological materials. Geophysicists who specialize in paleomagnetism are called ''paleomagnetists.''
Certain magnetic minerals in rock ...
, being described from deposits originally laid down within the Late Devonian
The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wher ...
Antarctic circle. Remains have exclusively been recovered from a single carbonaceous shale near the top of the Late Devonian, Famennian
The Famennian is the latter of two faunal stages in the Late Devonian Epoch. The most recent estimate for its duration estimates that it lasted from around 371.1 million years ago to 359.3 million years ago. An earlier 2012 estimate, still used b ...
, Witpoort Formation (Witteberg Group) exposed in a road cutting south of Makhanda/Grahamstown
Makhanda, also known as Grahamstown, is a town of about 140,000 people in the Eastern Cape province of South Africa. It is situated about northeast of Port Elizabeth and southwest of East London, Eastern Cape, East London. Makhanda is the lar ...
in South Africa. This site, the Waterloo Farm lagerstätte
The Waterloo Farm lagerstätte is a Famennian lagerstätte in South Africa that constitutes the only known record of a near-polar Devonian coastal ecosystem.
History and discovery
The Waterloo Farm Lagerstätte is an approximately 360 millio ...
is interpreted as representing a back barrier coastal lagoonal setting with both marine and fluvial influences. Gess observed that ''Bothriolepis'' was less abundant at the Waterloo Farm site than at most ''Bothriolepis''-bearing localities, though a full ontogenetic series is represented. The head and trunk armour lengths ranged between 20 and 300 mm which translates, based on the proportions of two of the smallest individuals (in which tail impressions are preserved) into full body lengths varying between 52 and 780 mm.
According to ''Bothriolepis africana'' was considered to be most closely similar to ''Bothriolepis barretti'' from the late Givetian
The Givetian is one of two faunal stages in the Middle Devonian Period. It lasted from million years ago to million years ago. It was preceded by the Eifelian Stage and followed by the Frasnian Stage. It is named after the town of Givet in Fra ...
of Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...
. The similarities between the two have been used to suggest derivation of ''Bothriolepis africana'' from an East Gondwanan
Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...
environment. [LONG, J. A., ANDERSON, M. E., GESS, R. W.& HILLER, N.(1997).New placoderm fishes from the Late Devonian of South Africa. Journal of Vertebrate Palaeontology 17,253–268.
]
References
External links
{{Taxonbar, from=Q2264010
Antiarchi
Placoderm genera
Placoderms of Africa
Placoderms of Asia
Placoderms of Australia
Placoderms of Antarctica
Placoderms of Europe
Placoderms of North America
Fossils of Canada
Placoderms of South America
Devonian Colombia
Fossils of Colombia
Late Devonian animals
Fossil taxa described in 1840