93-647: Chondrichthyes ( / k ɒ n ˈ d r ɪ k θ i iː z / ; from Ancient Greek χόνδρος ( khóndros ) 'cartilage' and ἰχθύς ( ikhthús ) 'fish') is a class of jawed fish that contains the cartilaginous fish or chondrichthyans , which all have skeletons primarily composed of cartilage . They can be contrasted with the Osteichthyes or bony fish , which have skeletons primarily composed of bone tissue . Chondrichthyes are aquatic vertebrates with paired fins , paired nares , placoid scales , conus arteriosus in
186-543: A pitch accent . In Modern Greek, all vowels and consonants are short. Many vowels and diphthongs once pronounced distinctly are pronounced as /i/ ( iotacism ). Some of the stops and glides in diphthongs have become fricatives , and the pitch accent has changed to a stress accent . Many of the changes took place in the Koine Greek period. The writing system of Modern Greek, however, does not reflect all pronunciation changes. The examples below represent Attic Greek in
279-452: A Silurian placoderm, Wangolepis of Silurian China and possibly Vietnam, is known only from a few fragments that currently defy attempts to place them in any of the recognized placoderm orders. So far, only three officially described Silurian placoderms are known from more than scraps: The first officially described Silurian placoderm is an antiarch, Shimenolepis , which is known from distinctively ornamented plates from Hunan , China. It
372-539: A feature shared by birds and some ichthyosaurs . Early arthrodires, such as the genus Arctolepis , were well-armoured fishes with flattened bodies. The largest member of this group, Dunkleosteus , was a true "superpredator" of the latest Devonian period, reaching 3 to as much as 8 metres in length. In contrast, the long-nosed Rolfosteus measured just 15 cm. Fossils of Incisoscutum have been found containing unborn fetuses, indicating that arthrodires gave birth to live young. Antiarchi ("opposite anus") were
465-468: A group of chimaera-like placoderms closely related to the rhenanid placoderms. Superficially, acanthoracids resembled scaly chimaeras or small, scaly arthrodires with blunt rostrums . They were distinguished from chimaeras by a pair of large spines that emanate from their chests, the presence of large scales and plates, tooth-like beak plates, and the typical bone-enhanced placoderm eyeball. They were distinguished from other placoderms due to differences in
558-477: A lack of contemporaneous evidence. Several theories exist about what Hellenic dialect groups may have existed between the divergence of early Greek-like speech from the common Proto-Indo-European language and the Classical period. They have the same general outline but differ in some of the detail. The only attested dialect from this period is Mycenaean Greek , but its relationship to the historical dialects and
651-419: A lesser degree. Pamphylian Greek , spoken in a small area on the southwestern coast of Anatolia and little preserved in inscriptions, may be either a fifth major dialect group, or it is Mycenaean Greek overlaid by Doric, with a non-Greek native influence. Regarding the speech of the ancient Macedonians diverse theories have been put forward, but the epigraphic activity and the archaeological discoveries in
744-442: A long time ago. However, there is currently no evidence of this. All chondrichthyans breathe through five to seven pairs of gills , depending on the species. In general, pelagic species must keep swimming to keep oxygenated water moving through their gills, whilst demersal species can actively pump water in through their spiracles and out through their gills. However, this is only a general rule and many species differ. A spiracle
837-489: A mosaic of chondrichthyan and acanthodian traits. Dating back to the Middle and Late Ordovician Period, many isolated scales, made of dentine and bone, have a structure and growth form that is chondrichthyan-like. They may be the remains of stem -chondrichthyans, but their classification remains uncertain. The earliest unequivocal fossils of acanthodian-grade cartilaginous fishes are Qianodus and Fanjingshania from
930-513: A mosaic of tubercles. Like Stensioella heintzi , the pseudopetalichthids' placement within Placodermi is suspect. The matter is not easy to resolve because there are no complete, undamaged and articulated specimens. The anatomical studies done on the crushed specimens that have been found indicate that if they are placoderms, they may be a group more advanced than the ptyctodonts . As such, placoderm experts consider Pseudopetalichthyida to be
1023-407: A movable joint between armour surrounding the head and body. As the lower jaw moved down, the head shield moved, allowing for a larger opening. All arthrodires, save for Compagopiscis , lacked teeth, and used instead the sharpened edges of a bony plate, termed a "tooth plate," as a biting surface ( Compagopiscis had true teeth in addition to tooth plates). The eye sockets are protected by a bony ring,
SECTION 10
#17327717648521116-407: A paraphyletic assemblage leading to Chondrichthyes. Some characteristics previously thought to be exclusive to acanthodians are also present in basal cartilaginous fish. In particular, new phylogenetic studies find cartilaginous fish to be well nested among acanthodians, with Doliodus and Tamiobatis being the closest relatives to Chondrichthyes. Recent studies vindicate this, as Doliodus had
1209-550: A prefix /e-/, called the augment . This was probably originally a separate word, meaning something like "then", added because tenses in PIE had primarily aspectual meaning. The augment is added to the indicative of the aorist, imperfect, and pluperfect, but not to any of the other forms of the aorist (no other forms of the imperfect and pluperfect exist). The two kinds of augment in Greek are syllabic and quantitative. The syllabic augment
1302-504: A primitive placoderm, though some paleontologists believe the rationale for the placement is inadequate. The paleontologist Philippe Janvier , as well as other paleontologists, has suggested that Stensioella is not a placoderm, but instead is a holocephalian . If this is true, then the holocephalians diverged from sharks before the Chondrichthyan Devonian radiation. Critics of Janvier's position say that aside from
1395-608: A separate historical stage, though its earliest form closely resembles Attic Greek , and its latest form approaches Medieval Greek . There were several regional dialects of Ancient Greek; Attic Greek developed into Koine. Ancient Greek was a pluricentric language , divided into many dialects. The main dialect groups are Attic and Ionic , Aeolic , Arcadocypriot , and Doric , many of them with several subdivisions. Some dialects are found in standardized literary forms in literature , while others are attested only in inscriptions. There are also several historical forms. Homeric Greek
1488-484: A skinny Gemuendina with thin, strap-like pectoral fins. Similar to those of the Rhenanida, its armour was a complex mosaic of small, scale-like tubercles. The shoulder joints of its armour are similar to other placoderms, and there are superficial similarities in skull plates, and even more superficial similarities between its tubercles and the tubercles of the rhenanids . It is tentatively placed within Placodermi as
1581-439: A spinal cord with spinal nerves. They have several sensory organs which provide information to be processed. Ampullae of Lorenzini are a network of small jelly filled pores called electroreceptors which help the fish sense electric fields in water. This aids in finding prey, navigation, and sensing temperature. The Lateral line system has modified epithelial cells located externally which sense motion, vibration, and pressure in
1674-630: A standard subject of study in educational institutions of the Western world since the Renaissance . This article primarily contains information about the Epic and Classical periods of the language, which are the best-attested periods and considered most typical of Ancient Greek. From the Hellenistic period ( c. 300 BC ), Ancient Greek was followed by Koine Greek , which is regarded as
1767-510: A vowel or /n s r/ ; final stops were lost, as in γάλα "milk", compared with γάλακτος "of milk" (genitive). Ancient Greek of the classical period also differed in both the inventory and distribution of original PIE phonemes due to numerous sound changes, notably the following: The pronunciation of Ancient Greek was very different from that of Modern Greek . Ancient Greek had long and short vowels ; many diphthongs ; double and single consonants; voiced, voiceless, and aspirated stops ; and
1860-570: Is a literary form of Archaic Greek (derived primarily from Ionic and Aeolic) used in the epic poems , the Iliad and the Odyssey , and in later poems by other authors. Homeric Greek had significant differences in grammar and pronunciation from Classical Attic and other Classical-era dialects. The origins, early form and development of the Hellenic language family are not well understood because of
1953-442: Is a small hole found behind each eye. These can be tiny and circular, such as found on the nurse shark ( Ginglymostoma cirratum ), to extended and slit-like, such as found on the wobbegongs (Orectolobidae). Many larger, pelagic species, such as the mackerel sharks (Lamnidae) and the thresher sharks (Alopiidae), no longer possess them. In chondrichthyans, the nervous system is composed of a small brain, 8–10 pairs of cranial nerves, and
SECTION 20
#17327717648522046-418: Is added to stems beginning with consonants, and simply prefixes e (stems beginning with r , however, add er ). The quantitative augment is added to stems beginning with vowels, and involves lengthening the vowel: Some verbs augment irregularly; the most common variation is e → ei . The irregularity can be explained diachronically by the loss of s between vowels, or that of the letter w , which affected
2139-553: Is an exception, as the teeth are lost in adults, only kept on the clasping organ seen on the caudal ventral surface of the male), also called placoid scales (or dermal denticles ), making it feel like sandpaper. In most species, all dermal denticles are oriented in one direction, making the skin feel very smooth if rubbed in one direction and very rough if rubbed in the other. Originally, the pectoral and pelvic girdles, which do not contain any dermal elements, did not connect. In later forms, each pair of fins became ventrally connected in
2232-402: Is assumed that their oral teeth evolved from dermal denticles that migrated into the mouth, but it could be the other way around, as the teleost bony fish Denticeps clupeoides has most of its head covered by dermal teeth (as does, probably, Atherion elymus , another bony fish). This is most likely a secondary evolved characteristic, which means there is not necessarily a connection between
2325-666: Is called 'East Greek'. Arcadocypriot apparently descended more closely from the Mycenaean Greek of the Bronze Age. Boeotian Greek had come under a strong Northwest Greek influence, and can in some respects be considered a transitional dialect, as exemplified in the poems of the Boeotian poet Pindar who wrote in Doric with a small Aeolic admixture. Thessalian likewise had come under Northwest Greek influence, though to
2418-448: Is considered by some linguists to have been closely related to Greek . Among Indo-European branches with living descendants, Greek is often argued to have the closest genetic ties with Armenian (see also Graeco-Armenian ) and Indo-Iranian languages (see Graeco-Aryan ). Ancient Greek differs from Proto-Indo-European (PIE) and other Indo-European languages in certain ways. In phonotactics , ancient Greek words could end only in
2511-408: Is internal. Development is usually live birth ( ovoviviparous species) but can be through eggs ( oviparous ). Some rare species are viviparous . There is no parental care after birth; however, some chondrichthyans do guard their eggs. Capture-induced premature birth and abortion (collectively called capture-induced parturition) occurs frequently in sharks/rays when fished. Capture-induced parturition
2604-415: Is likely monophyletic . The first identifiable placoderms appear in the fossil record during the late Llandovery epoch of the early Silurian. They eventually outcompeted the previously dominant marine arthropods (e.g. eurypterids ) and cephalopod molluscs (e.g. orthocones ), producing some of the first and most infamous vertebrate apex predators such as Eastmanosteus , Dinichthys and
2697-598: Is not clear, as none of the fossil specimens found have preserved mouth parts. Pseudopetalichthyida ("false petalichthyids") is a group of elongated, possibly flattened fishes comprising three, poorly preserved and poorly studied genera. It is known only from rare fossils in Lower Devonian strata in Hunsrück , Germany. Like Stensioella heintzi , and the Rhenanida , the pseudopetalichthids had armour made up of
2790-406: Is often mistaken for natural birth by recreational fishers and is rarely considered in commercial fisheries management despite being shown to occur in at least 12% of live bearing sharks and rays (88 species to date). The class Chondrichthyes has two subclasses: the subclass Elasmobranchii ( sharks , rays, skates, and sawfish ) and the subclass Holocephali ( chimaeras ). To see the full list of
2883-468: The Gogo Formation of Western Australia, had streamlined, bullet-shaped head armor, and Amazichthys , with morphology like that of other fast-swimming pelagic organisms , strongly supporting the idea that many, if not most, arthrodires were active swimmers, rather than passive ambush-hunters whose armor practically anchored them to the sea floor. Some placoderms were herbivorous, such as
Chondrichthyes - Misplaced Pages Continue
2976-759: The Greek region of Macedonia during the last decades has brought to light documents, among which the first texts written in Macedonian , such as the Pella curse tablet , as Hatzopoulos and other scholars note. Based on the conclusions drawn by several studies and findings such as Pella curse tablet , Emilio Crespo and other scholars suggest that ancient Macedonian was a Northwest Doric dialect , which shares isoglosses with its neighboring Thessalian dialects spoken in northeastern Thessaly . Some have also suggested an Aeolic Greek classification. The Lesbian dialect
3069-562: The Silurian and the Devonian periods . While their endoskeletons are mainly cartilaginous , their head and thorax were covered by articulated armoured plates (hence the name), and the rest of the body was scaled or naked depending on the species . Placoderms were among the first jawed fish (their jaws likely evolved from the first pair of gill arches ), as well as the first vertebrates to have true teeth . They were also
3162-745: The bony fishes , and the clade that includes spiny sharks and early cartilaginous fish . The modern bony fishes, class Osteichthyes , appeared in the late Silurian or early Devonian, about 416 million years ago. The first abundant genus of shark, Cladoselache , appeared in the oceans during the Devonian Period. The first Cartilaginous fishes evolved from Doliodus -like spiny shark ancestors. Zangerl, 1981 [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Ancient Greek language Ancient Greek ( Ἑλληνῐκή , Hellēnikḗ ; [hellɛːnikɛ́ː] ) includes
3255-429: The heart , and a lack of opercula and swim bladders . Within the infraphylum Gnathostomata , cartilaginous fishes are distinct from all other jawed vertebrates. The class is divided into two subclasses: Elasmobranchii ( sharks , rays , skates and sawfish ) and Holocephali ( chimaeras , sometimes called ghost sharks, which are sometimes separated into their own class). Extant chondrichthyans range in size from
3348-508: The hox genes hoxd13, the origin of the mating organs in placoderms most likely relied on different sets of hox genes and were structures that developed further down the body as an extra and independent pair of appendages, but which during development turned into body parts used for reproduction only. Because they were not attached to the pelvic fins, as are the claspers in fish like sharks, they were much more flexible and could probably be rotated forward. A study on Kolymaspis showcases that
3441-501: The present , future , and imperfect are imperfective in aspect; the aorist , present perfect , pluperfect and future perfect are perfective in aspect. Most tenses display all four moods and three voices, although there is no future subjunctive or imperative. Also, there is no imperfect subjunctive, optative or imperative. The infinitives and participles correspond to the finite combinations of tense, aspect, and voice. The indicative of past tenses adds (conceptually, at least)
3534-468: The 10 cm (3.9 in) finless sleeper ray to the over 10 m (33 ft) whale shark . The skeleton is cartilaginous. The notochord is gradually replaced by a vertebral column during development, except in Holocephali , where the notochord stays intact. In some deepwater sharks, the column is reduced. As they do not have bone marrow , red blood cells are produced in the spleen and
3627-1031: The 5th century BC. Ancient pronunciation cannot be reconstructed with certainty, but Greek from the period is well documented, and there is little disagreement among linguists as to the general nature of the sounds that the letters represent. /oː/ raised to [uː] , probably by the 4th century BC. Greek, like all of the older Indo-European languages , is highly inflected. It is highly archaic in its preservation of Proto-Indo-European forms. In ancient Greek, nouns (including proper nouns) have five cases ( nominative , genitive , dative , accusative , and vocative ), three genders ( masculine , feminine , and neuter ), and three numbers (singular, dual , and plural ). Verbs have four moods ( indicative , imperative , subjunctive , and optative ) and three voices (active, middle, and passive ), as well as three persons (first, second, and third) and various other forms. Verbs are conjugated through seven combinations of tenses and aspect (generally simply called "tenses"):
3720-495: The Archaic period of ancient Greek (see Homeric Greek for more details): Μῆνιν ἄειδε, θεά, Πηληϊάδεω Ἀχιλῆος οὐλομένην, ἣ μυρί' Ἀχαιοῖς ἄλγε' ἔθηκε, πολλὰς δ' ἰφθίμους ψυχὰς Ἄϊδι προΐαψεν ἡρώων, αὐτοὺς δὲ ἑλώρια τεῦχε κύνεσσιν οἰωνοῖσί τε πᾶσι· Διὸς δ' ἐτελείετο βουλή· ἐξ οὗ δὴ τὰ πρῶτα διαστήτην ἐρίσαντε Ἀτρεΐδης τε ἄναξ ἀνδρῶν καὶ δῖος Ἀχιλλεύς. The beginning of Apology by Plato exemplifies Attic Greek from
3813-660: The Classical period of ancient Greek. (The second line is the IPA , the third is transliterated into the Latin alphabet using a modern version of the Erasmian scheme .) Ὅτι [hóti Hóti μὲν men mèn ὑμεῖς, hyːmêːs hūmeîs, Placoderms Placoderms (from Greek πλάξ ( plax , plakos ) ' plate ' and δέρμα ( derma ) 'skin') are vertebrate animals of the class Placodermi , an extinct group of prehistoric fish known from Paleozoic fossils during
Chondrichthyes - Misplaced Pages Continue
3906-499: The Middle Devonian of Australia, suggesting that the basipterygia were used in copulation. The placoderm claspers are not homologous with the claspers in cartilaginous fishes . The similarities between the structures has been revealed to be an example of convergent evolution . While the claspers in cartilaginous fishes are specialized parts of their paired pelvic fins that have been modified for copulation due to changes in
3999-512: The Middle to Late Devonian arthrodire Holonema , and some were planktivores , such as the gigantic arthrodire Titanichthys , various members of Homostiidae , and Heterosteus . Extraordinary evidence of internal fertilization in a placoderm was afforded by the discovery in the Gogo Formation, near Fitzroy Crossing , Kimberley , Western Australia, of a small female placoderm, about 25 cm (10 in) in length, which died in
4092-418: The anatomy of their skulls, and due to patterns on the skull plates and thoracic plates that are unique to this order. From what can be inferred from the mouthplates of fossil specimens, acanthothoracids were shellfish hunters ecologically similar to modern-day chimaeras. Competition with their relatives, the ptyctodont placoderms, may have been one of the main reasons for the acanthothoracids' extinction prior to
4185-448: The antiarchs, with their highly modified, jointed bony pectoral fins, were highly successful inhabitants of Middle-Late Devonian freshwater and shallow marine habitats, with the Middle to Late Devonian genus , Bothriolepis , known from over 100 valid species. The vast majority of placoderms were predators , many of which lived at or near the substrate . Many, primarily the arthrodires , were active, nektonic predators that dwelled in
4278-550: The aorist. Following Homer 's practice, the augment is sometimes not made in poetry , especially epic poetry. The augment sometimes substitutes for reduplication; see below. Almost all forms of the perfect, pluperfect, and future perfect reduplicate the initial syllable of the verb stem. (A few irregular forms of perfect do not reduplicate, whereas a handful of irregular aorists reduplicate.) The three types of reduplication are: Irregular duplication can be understood diachronically. For example, lambanō (root lab ) has
4371-419: The augment when it was word-initial. In verbs with a preposition as a prefix, the augment is placed not at the start of the word, but between the preposition and the original verb. For example, προσ(-)βάλλω (I attack) goes to προσ έ βαλoν in the aorist. However compound verbs consisting of a prefix that is not a preposition retain the augment at the start of the word: αὐτο(-)μολῶ goes to ηὐ τομόλησα in
4464-438: The center of Greek scholarship, this division of people and language is quite similar to the results of modern archaeological-linguistic investigation. One standard formulation for the dialects is: West vs. non-West Greek is the strongest-marked and earliest division, with non-West in subsets of Ionic-Attic (or Attic-Ionic) and Aeolic vs. Arcadocypriot, or Aeolic and Arcado-Cypriot vs. Ionic-Attic. Often non-West
4557-473: The date of first viviparity back some 200 million years earlier than had been previously known. Specimens of the arthrodire Incisoscutum ritchei , also from the Gogo Formation, have been found with embryos inside them indicating this group also had live bearing ability. The males reproduced by inserting a long clasper into the female. Elongated basipterygia are also found on the phyllolepid placoderms, such as Austrophyllolepis and Cowralepis , both from
4650-615: The dialect of Sparta ), and Northern Peloponnesus Doric (including Corinthian ). All the groups were represented by colonies beyond Greece proper as well, and these colonies generally developed local characteristics, often under the influence of settlers or neighbors speaking different Greek dialects. After the conquests of Alexander the Great in the late 4th century BC, a new international dialect known as Koine or Common Greek developed, largely based on Attic Greek , but with influence from other dialects. This dialect slowly replaced most of
4743-541: The early Silurian ( Aeronian ) of Guizhou , China around 439 million years ago, which are also the oldest unambiguous remains of any jawed vertebrates. Shenacanthus vermiformis , which lived 436 million years ago, had thoracic armour plates resembling those of placoderms. By the start of the Early Devonian, 419 million years ago, jawed fishes had divided into three distinct groups: the now extinct placoderms (a paraphyletic assemblage of ancient armoured fishes),
SECTION 50
#17327717648524836-474: The environmental catastrophes of the Late Devonian and end-Devonian extinctions . The earliest identifiable placoderm fossils are of Chinese origin and date to the early Silurian . At that time, they were already differentiated into antiarchs and arthrodires , as well as other, more primitive, groups. Earlier fossils of basal placoderms have not yet been discovered. The Silurian fossil record of
4929-596: The epigonal organ (special tissue around the gonads , which is also thought to play a role in the immune system). They are also produced in the Leydig's organ , which is only found in certain cartilaginous fishes. The subclass Holocephali , which is a very specialized group, lacks both the Leydig's and epigonal organs. Apart from electric rays , which have a thick and flabby body, with soft, loose skin, chondrichthyans have tough skin covered with dermal teeth (again, Holocephali
5022-521: The equally enigmatic Pseudopetalichthyida . These orders are considered to be basal or primitive groups within Placodermi, though their precise placement within the class remains unsure. Fossils of both are currently known only from the Hunsruck lagerstatten . Arthrodira ("jointed neck") were the most diverse and numerically successful of the placoderm orders, occupying roles from giant apex predators to detritus -nibbling bottom dwellers . They had
5115-449: The exquisitely preserved placoderm fossils from Gogo reef changed the picture again. They showed that placoderms shared anatomical features not only with chondrichthyans but with other gnathostome groups as well. For example, Gogo placoderms show separate bones for the nasal capsules as in gnathostomes; in both sharks and bony fish those bones are incorporated into the braincase. Placoderms also share certain anatomical features only with
5208-489: The extinct and related acanthothoracids , and the living and unrelated holocephalians, most of the ptyctodontids are thought to have lived near the sea bottom and preyed on shellfish . On account of their lack of armour, some paleontologists have suggested that the Ptyctodontida were not placoderms, but holocephalians or the ancestors of holocephalians. Anatomical examinations of whole fossil specimens have shown that
5301-756: The extinction event at the Frasnian – Famennian boundary, the Late Devonian extinctions. The remaining species then died out during the end-Devonian extinction; not a single placoderm species has been confirmed to have survived into the Carboniferous . The earliest studies of placoderms were published by Louis Agassiz , in his five volumes on fossil fishes, 1833–1843. In those days, placoderms were thought to be shelled jawless fish akin to ostracoderms . Some naturalists even suggested that they were shelled invertebrates or even turtle -like vertebrates. In
5394-544: The first fish clade to develop pelvic fins , the second set of paired fins and the homologous precursor to hindlimbs in tetrapods . 380-million-year-old fossils of three other genera, Incisoscutum , Materpiscis and Austroptyctodus , represent the oldest known examples of live birth . Placoderms are thought to be paraphyletic , consisting of several distinct outgroups or sister taxa to all living jawed vertebrates , which originated among their ranks. In contrast, one 2016 analysis concluded that Placodermi
5487-399: The forebrain not greatly enlarged. The structure and formation of myelin in their nervous systems are nearly identical to that of tetrapods, which has led evolutionary biologists to believe that Chondrichthyes were a cornerstone group in the evolutionary timeline of myelin development. Like all other jawed vertebrates, members of Chondrichthyes have an adaptive immune system . Fertilization
5580-673: The forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek ( c. 1400–1200 BC ), Dark Ages ( c. 1200–800 BC ), the Archaic or Epic period ( c. 800–500 BC ), and the Classical period ( c. 500–300 BC ). Ancient Greek was the language of Homer and of fifth-century Athenian historians, playwrights, and philosophers . It has contributed many words to English vocabulary and has been
5673-561: The historical Dorians . The invasion is known to have displaced population to the later Attic-Ionic regions, who regarded themselves as descendants of the population displaced by or contending with the Dorians. The Greeks of this period believed there were three major divisions of all Greek people – Dorians, Aeolians, and Ionians (including Athenians), each with their own defining and distinctive dialects. Allowing for their oversight of Arcadian, an obscure mountain dialect, and Cypriot, far from
SECTION 60
#17327717648525766-476: The historical circumstances of the times imply that the overall groups already existed in some form. Scholars assume that major Ancient Greek period dialect groups developed not later than 1120 BC, at the time of the Dorian invasions —and that their first appearances as precise alphabetic writing began in the 8th century BC. The invasion would not be "Dorian" unless the invaders had some cultural relationship to
5859-400: The jawless osteostracans ; because of this, the theory that placoderms are the sister group of chondrichthyans has been replaced by the theory that placoderms are a group of basal gnathostomes. Currently, Placodermi are divided into eight recognized orders . There are two further controversial orders: One is the monotypic Stensioellida, containing the enigmatic Stensioella ; the other is
5952-520: The late 1920s, Dr. Erik Stensiö , at the Swedish Museum of Natural History in Stockholm , established the details of placoderm anatomy and identified them as true jawed fishes related to sharks . He took fossil specimens with well-preserved skulls and ground them away, one tenth of a millimeter at a time. After each layer had been removed, he made an imprint of the next surface in wax . Once
6045-515: The limbs is still not perfectly understood, but most hypothesize that they helped their owners pull themselves across the substrate, as well as allowing their owners to bury themselves into the substrate. Brindabellaspis (" Brindabella's shield") was a long-snouted placoderm from the Early Devonian . When it was first discovered in 1980, it was originally regarded as a weejasperaspid acanthothoracid due to anatomical similarities with
6138-421: The males having pelvic claspers and possibly claspers on the head as well. Rhenanida (" Rhine fish") were flattened, ray-like , bottom-dwelling predators with large, upturned mouths that lived in marine environments. The rhenanids were once presumed to be the most primitive, or at least the closest to the ancestral placoderm, as their armour was made of unfused components—a mosaic of tubercles—as opposed to
6231-533: The massive Dunkleosteus . Various groups of placoderms were diverse and abundant during the Devonian, but all placoderms became extinct at the end-Devonian Hangenberg event 358.9 million years ago, leaving the niches open for the osteichthyan and chondrichthyan survivors who subsequently radiated during the Carboniferous . Many placoderms, particularly the Rhenanida , Petalichthyida , Phyllolepida , and Antiarchi , were bottom-dwellers. In particular,
6324-401: The mid-Devonian extinction event. Petalichthyida ("thin-plated fish") were small, flattened placoderms, typified by their splayed fins and numerous tubercles that decorated all of the plates and scales of their armour. They reached a peak in diversity during the Early Devonian and were found throughout the world. The petalichthids Lunaspis and Wijdeaspis are among the best known. There
6417-450: The middle to upper portions of the water column. A study of the arthrodire Compagopiscis published in 2012 concluded that placoderms (at least this particular genus) likely possessed true teeth contrary to some early studies. The teeth had well defined pulp cavities and were made of both bone and dentine . However, the tooth and jaw development were not as closely integrated as in modern gnathostomes. These teeth were likely homologous to
6510-461: The middle when scapulocoracoid and puboischiadic bars evolved. In rays , the pectoral fins are connected to the head and are very flexible. One of the primary characteristics present in most sharks is the heterocercal tail, which aids in locomotion. Chondrichthyans have tooth-like scales called dermal denticles or placoid scales. Denticles usually provide protection, and in most cases, streamlining. Mucous glands exist in some species, as well. It
6603-508: The older dialects, although the Doric dialect has survived in the Tsakonian language , which is spoken in the region of modern Sparta. Doric has also passed down its aorist terminations into most verbs of Demotic Greek . By about the 6th century AD, the Koine had slowly metamorphosed into Medieval Greek . Phrygian is an extinct Indo-European language of West and Central Anatolia , which
6696-425: The other species found at the same locality. According to Philippe Janvier , anatomical similarities in the brain of Brindabellaspis stensioi and the brain of a jawless fish suggest it is a basal placoderm closest to the ancestral placoderm. Various Early to Middle Devonian placoderm incertae sedis have also been inserted in the order. Phyllolepida ("leaf scales") were flattened placoderms found throughout
6789-487: The perfect stem eilēpha (not * lelēpha ) because it was originally slambanō , with perfect seslēpha , becoming eilēpha through compensatory lengthening. Reduplication is also visible in the present tense stems of certain verbs. These stems add a syllable consisting of the root's initial consonant followed by i . A nasal stop appears after the reduplication in some verbs. The earliest extant examples of ancient Greek writing ( c. 1450 BC ) are in
6882-434: The placoderms is both literally and figuratively fragmented. Until the discovery of Silurolepis (and then, the discoveries of Entelognathus and Qilinyu ), Silurian-aged placoderm specimens consisted of fragments. Some of them have been tentatively identified as antiarch or arthrodire due to histological similarities; and many of them have not yet been formally described or even named. The most commonly cited example of
6975-456: The point of literally resembling a box with eyes, with the sometimes scaled, sometimes naked rear portions often becoming sinuous , particularly with later forms. The pair of pectoral fins were modified into a pair of caliper -like, or arthropod -like limbs. In primitive forms, such as Yunnanolepis , the limbs were thick and short, while in advanced forms, such as Bothriolepis , the limbs were long and had elbow-like joints. The function of
7068-476: The process of giving birth to a 6 cm ( 2 + 1 ⁄ 2 in) offspring and was fossilized with the umbilical cord intact. The fossil, named Materpiscis attenboroughi (after scientist David Attenborough ), had eggs which were fertilized internally, the mother providing nourishment to the embryo and giving birth to live young. With this discovery, the placoderm became the oldest vertebrate known to have given birth to live young (" viviparous "), pushing
7161-565: The scarcity of placoderms in the Silurian fossil record is due to placoderms' living in environments unconducive to fossil preservation, rather than a genuine scarcity. This hypothesis helps to explain the placoderms' seemingly instantaneous appearance and diversity at the very beginning of the Devonian . During the Devonian, placoderms went on to inhabit and dominate almost all known aquatic ecosystems, both freshwater and saltwater . But this diversity ultimately suffered many casualties during
7254-533: The second most successful order of placoderms known, after the Arthrodira . The order's name was coined by Edward Drinker Cope , who, after incorrectly identifying the first fossils as being those of an armored tunicate , mistakenly thought the eye-hole was the mouth, and the opening for the anal siphon was on the other side of the body, as opposed to having both oral and anal siphons together at one end. The front portions of their bodies were heavily armoured, to
7347-561: The similarities between these two groups are superficial. The major differences were that holocephalians have shagreen on their skin, while ptyctodontids do not; the armoured plates and scales of holocephalians are made of dentine , while those of ptyctodontids are made of bone; the craniums of holocephalians are similar to sharks, while those of ptyctodontids are similar to those of other placoderms; and, most importantly, that holocephalians have true teeth, while ptyctodonts have beak-like tooth plates. Ptyctodontids were sexually dimorphic , with
7440-604: The sister group of the Arthrodires + Phyllolepida + Antiarchi trichotomy and the Acanthothoraci + Rhenanida dichotomy . Stensioellida ("[Heintz's] little Stensio ") contains another problematic placoderm of uncertain affinity, known only from the Lower Devonian Hunsrück slates of Germany. Stensioella was a thin fish that, when alive, looked vaguely like an elongated ratfish , or
7533-450: The solidified plates of "advanced" placoderms, such as antiarchs and arthrodires . However, through comparisons of skull anatomies, rhenanids are now considered to be the sister group of the antiarchs. When rhenanids die, their "mosaics" come apart, and it has been suggested that the rarity of rhenanids in the fossil record reflects postmortem disassociation, and is not an actual rarity of the species. Acanthothoraci ("spine chests") were
7626-649: The species , click here . The fossil record of the Holocephali starts in the Devonian period. The record is extensive, but most fossils are teeth, and the body forms of numerous species are not known, or at best poorly understood. * position uncertain Cartilaginous fish are considered to have evolved from acanthodians . The discovery of Entelognathus and several examinations of acanthodian characteristics indicate that bony fish evolved directly from placoderm like ancestors, while acanthodians represent
7719-412: The specimens had been completely ground away (and so destroyed), he made enlarged, three-dimensional models of the skulls to examine the anatomical details more thoroughly. Many other placoderm specialists thought that Stensiö was trying to shoehorn placoderms into a relationship with sharks ; however, as more fossils were found, placoderms were accepted as a sister group of chondrichthyans . Much later,
7812-517: The syllabic script Linear B . Beginning in the 8th century BC, however, the Greek alphabet became standard, albeit with some variation among dialects. Early texts are written in boustrophedon style, but left-to-right became standard during the classic period. Modern editions of ancient Greek texts are usually written with accents and breathing marks , interword spacing , modern punctuation , and sometimes mixed case , but these were all introduced later. The beginning of Homer 's Iliad exemplifies
7905-403: The teeth and the original dermal scales. The old placoderms did not have teeth at all, but had sharp bony plates in their mouth. Thus, it is unknown whether the dermal or oral teeth evolved first. It has even been suggested that the original bony plates of all vertebrates are now gone and that the present scales are just modified teeth, even if both the teeth and body armor had a common origin
7998-516: The teeth of other gnathostomes. One of the largest known arthrodires, Dunkleosteus terrelli , was 3.5–4.1 metres (11–13 ft) long, and is presumed to have had a large distribution, as its remains have been found in Europe, North America and possibly Morocco. Some paleontologists regard it as the world's first vertebrate "superpredator", preying upon other predators. Other, smaller arthrodires, such as Fallacosteus and Rolfosteus , both of
8091-419: The top of their head. The orbits for the eyes were extremely small, suggesting the eyes were vestigial and that the phyllolepids may have been blind. Ptyctodontida ("folded teeth") were lightly armoured placoderms with big heads, big eyes and long bodies. They have a strong but superficial resemblance to modern day chimaeras . Their armour was reduced to a pattern of small plates around the head and neck. Like
8184-455: The vertebrate shoulder girdle evolved from gill arches. It was thought for a time that placoderms became extinct due to competition from the first bony fish and early sharks , given a combination of the supposed inherent superiority of bony fish and the presumed sluggishness of placoderms. With more accurate summaries of prehistoric organisms, it is now thought that they systematically died out as marine and freshwater ecologies suffered from
8277-450: The water around them. Most species have large well-developed eyes. Also, they have very powerful nostrils and olfactory organs. Their inner ears consist of 3 large semicircular canals which aid in balance and orientation. Their sound detecting apparatus has limited range and is typically more powerful at lower frequencies. Some species have electric organs which can be used for defense and predation. They have relatively simple brains with
8370-400: The world. Like other flattened placoderms they were bottom-dwelling predators that ambushed prey. Unlike other flattened placoderms, they were freshwater fish. Their armour was made of whole plates, rather than the numerous tubercles and scales of Petalichthyida. The eyes were on the sides of the head, unlike visual bottom-dwelling predators, such as stargazers or flatfish , which have eyes on
8463-480: Was Aeolic. For example, fragments of the works of the poet Sappho from the island of Lesbos are in Aeolian. Most of the dialect sub-groups listed above had further subdivisions, generally equivalent to a city-state and its surrounding territory, or to an island. Doric notably had several intermediate divisions as well, into Island Doric (including Cretan Doric ), Southern Peloponnesus Doric (including Laconian ,
8556-472: Was an independent diversification event that occurred in what is now Southern China, producing a handful of unique genera that were once placed in their own order, "Quasipetalichthyida", named after the first discovered species there, Quasipetalichthys haikouensis . Soon after the petalichthids' diversification, they went into decline. Because they had compressed body forms, it is supposed they were bottom-dwellers that pursued or ambushed smaller fish. Their diet
8649-440: Was originally considered to be from the late Llandovery , although later study reconsidered its age at Ludfordian . Shimenolepis plates are very similar to the early Devonian yunnanolepid Zhanjilepis , also known from distinctively ornamented plates. In 2022, Xiushanosteus is described from complete fossils from Telychian , late Llandovery of Chongqing , China. Paleontologists and placoderm specialists suspect that
#851148