What is Acanthodii?
Acanthodii (sometimes called spiny sharks) is a class of extinct fishes, having features of both bony fish ( Osteichthyes) and cartilaginous fish ( Chondrichthyes ). They appeared in the early Silurian (430 mya) and lasted until the late Permian (250 mya).
When did the acanthodians live?
The acanthodians’ heyday was during the Devonian period, about 419 million to 359 million years ago, but their fossil record stretches back to the Silurian period (around 440 million years ago).
Is an acanthodian a shark?
However, acanthodians are not true sharks; their close relation to modern cartilaginous fish can lead them to be considered " stem -sharks". Acanthodians had a cartilaginous skeleton, but their fins had a wide, bony base and were reinforced on their anterior margin with a dentine spine.
Where are acanthodian fish found?
Acanthodian have been found in many of the more productive fossil fish localities throughout rhe world. However, their remains tend to be poorly fossilized. Most species are known only from isolated spines and/or pectoral bones.
Are Acanthodii bony fish?
Acanthodii (sometimes called spiny sharks) is a class of extinct fishes, having features of both bony fish (Osteichthyes) and cartilaginous fish (Chondrichthyes).
Is the extinct spiny shark?
spiny shark, also called acanthodian, any of a group of more than 150 species of small extinct fishes traditionally classified in the class Acanthodii and considered by many paleontologists as the earliest known jawed vertebrates (or gnathostomes).
When did Acanthodii go extinct?
One specialized filter-feeding group, the Acanthodiformes, persisted until the end of the Permian period (about 252 million years ago), disappearing in the end-Permian mass extinction.
Are Placoderms extinct?
ExtinctPlacodermi / Extinction statusplacoderm, any member of an extinct group (Placodermi) of primitive jawed fishes known only from fossil remains. Placoderms existed throughout the Devonian Period (about 416 million to 359 million years ago), but only two species persisted into the succeeding Carboniferous Period.
What was the first shark?
CladoselacheCladoselache is regarded as the first "true shark". It lived 380 million years ago and it still retained a few characteristics of its fishy ancestors. It had a fish-like head, seven gills instead of five like most sharks, and its body was longer and less muscular than the sharks we see today.
Did sharks exist before trees?
Fun fact of the day: Sharks are older than trees. The earliest species that we could classify as “tree,” the now-extinct Archaeopteris, lived around 350 million years ago, in forests where the Sahara desert is now.
What did Acanthodii evolve from?
Overall, the acanthodians' jaws are presumed to have evolved from the first gill arch of some ancestral jawless fishes that had a gill skeleton made of pieces of jointed cartilage.
How did sharks evolve?
Most scientists believe that sharks came into existence around 400 million years ago. That's 200 million years before the dinosaurs! It's thought that they descended from a small leaf-shaped fish that had no eyes, fins or bones. These fish then evolved into the 2 main groups of fish seen today.
How ancient are sharks?
450 million years agoWhen did sharks first appear? The earliest fossil evidence for sharks or their ancestors are a few scales dating to 450 million years ago, during the Late Ordovician Period. Emma Bernard, a curator of fossil fish at the Museum, says, 'Shark-like scales from the Late Ordovician have been found, but no teeth.
Do armored fish still exist?
Dunkleosteus is an extinct genus of large armored, jawed fishes that existed during the Late Devonian period, about 382–358 million years ago. It consists of ten species, some of which are among the largest placoderms to have ever lived: D. terrelli, D.
Why did armored fish go extinct?
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.
Why did Dunkleosteus go extinct?
1:444:35What If The Dunkleosteus Didn't Go Extinct? - YouTubeYouTubeStart of suggested clipEnd of suggested clipWell right around the time of its extinction oxygen levels in the ocean dropped significantly a dropMoreWell right around the time of its extinction oxygen levels in the ocean dropped significantly a drop in oxygen means that the big fish that needed that oxygen. Wouldn't be able to survive.
Is a dog fish a shark?
dogfish, (order Squaliformes), any of several small sharks making up an order of chondrichthyian fishes composed of the families Centrophoridae (gulper sharks), Dalatiidae, Echinorhinidae, Etmopteridae, Oxynotidae, Somniosidae, and Squalidae.
Can sharks be blue?
Appearance. Blue sharks can get up to 13 feet in length but generally are closer to 10 feet long. They have a deep blue color dorsally, which fades to light blue on the sides and white on the belly. They have slender bodies with large eyes and a cone shaped snout.
Is there really a dogfish?
Atlantic spiny dogfish are small sharks with a long and complex history in U.S. waters. Wielding two venomous spines and growing as long as 4 feet, Atlantic spiny dogfish can often be seen hunting prey in dog-like packs (hence the dog-like name).
How poisonous are dogfish?
Unlike virtually all other shark species, dogfish sharks possess venom which coats their dorsal spines; this venom is mildly toxic to humans and would be harmful if the shark were to be mishandled.
Where is the fossil of Acanthodes?
Fossil of Acanthodes. Exhibit in the National Museum of Nature and Science, Tokyo, Japan.
How big is an acanthode shark?
Compared with other spiny sharks, Acanthodes was relatively large, at 30 centimetres (12 in) long. The genus had no teeth, instead gills. Because of this, it is presumed to have been a filter feeder, filtering plankton from the water. The Acanthodes has been found to have only a couple of skull bones. It was covered in scales that were cubical in shape.
How long ago did A. bronni live?
A. bronni lived about 290 million years ago during the Carboniferous period. Researchers took 138 characteristics of various skulls of A. bronni and compared these with skulls of both chondrichthyans and osteichthyans, and determined that acanthodians are closer to cartilaginous fishes.
How long is an Acanthodes bridgei?
Several specimens of Acanthodes were recovered from an abandoned quarry (Hamilton Quarry) which contained individuals ranging in total length from 54 nm to 410 nm. A. bridgei was one of the species found there. A. bridgei has large orbits, a shorter pre-pectoral region, and shallower insertions of the fin spines.
Is an acanthodian a bony fish?
The scientific classification of acanthodians is still a subject of great dispute, due to the fact that they share qualities of both bony fish ( osteichthyes) and cartilaginous fish ( chondrichthyes ). A recent study has suggested that Acanthodes may have been, or closely related to an early common ancestor to all cartilaginous and bony fish, including humans. Acanthodian internal anatomy is primarily understood by Acanthodes bronni because it remains the only example preserved in substantial detail, central to which is an ostensible osteichthyan braincase. For this reason, Acanthodes has become an indispensable component in early gnathostome phylogenies. Acanthodes is quantifiably closer to chondrichthyans than to osteichthyans. However, phylogenetic analysis places Acanthodes on the osteichthyan stem, as part of a well-resolved tree that also recovers acanthodians as stem chondrichthyans and stem gnathostomes. As such, perceived chondrichthyan features of the Acanthodes cranium represent shared primitive conditions for crown group gnathostomes. There has been increasingly detailed findings of early gnathostome evolution highlights ongoing and profound anatomical reorganization of vertebrate crania after the origin of jaws but before the divergence of living clades.
When did the Acanthodians live?
The acanthodians are a mysterious extinct group of fishes, which lived in the waters of the Palaeozoic era (541 million to 252 million years ago). They are characterized by a superficially shark-like coating of tiny scales, and spines in front of their fins (Fig. 1). The acanthodians’ heyday was during the Devonian period, about 419 million to 359 million years ago, but their fossil record stretches back to the Silurian period (around 440 million years ago). One specialized filter-feeding group, the Acanthodiformes, persisted until the end of the Permian period (about 252 million years ago), disappearing in the end-Permian mass extinction. Acanthodian fossils were first described by the eminent Swiss palaeontologist Louis Agassiz during the nineteenth century, and are today known worldwide; acanthodians from the Lower Devonian Old Red Sandstone of the United Kingdom have been particularly well described (Fig. 2a–d), with extremely well-preserved fossil fishes found in places such as Wayne Herbert Quarry in the Welsh Borders. More recently, many spectacularly preserved fossils have also been described from northwestern Canada, in the Man on the Hill (MOTH) locality; these fossils have had a profound impact on our understanding of vertebrate evolution.
Which fossils are acanthodians?
Redescription of important acanthodian fossils, including Ptomacanthus and Acanthodes, demonstrates that acanthodians have a less osteichthyan-like braincase than was previously thought. Fossils are also being described that blur the line between what we know about the anatomy of chondrichthyans and acanthodians, such as Kathemacanthus with its chondrichthyan-like scales, as well as early sharks such as Doliodus that have acanthodian-like paired fin spines. Furthermore, there is building evidence suggesting that the common ancestor of bony and cartilaginous fishes had large dermal plates rather than small, acanthodian-like scales. This would make micromeric dermal armour a shared character that unites traditional chondrichthyans and acanthodians.
What is the anatomy of an acanthodian?
Because of their generally poor fossilization, the internal anatomy of acanthodians is known chiefly from a single fossil species of acanthodiform, Acanthodes bronni, which has a skeleton that was at least partly made from bone. Acanthodes preserves details of the backbone, the fin skeleton and the braincase (the part of the skull housing the brain). The last of these features is perhaps the most interesting, because it reveals a great many anatomical characters that can be compared to those of other groups of early vertebrates. Indeed, the braincase of Acanthodes displays an unusual combination of traditionally chondrichthyan and osteichthyan characteristics (Fig. 4a–d). Features such as a dorsal (top) ridge at the rear of the braincase are shared with chondrichthyans, whereas the braincase’s overall shape and bony nature are more typical of osteichthyans. Still other features, such as the otico-occipital fissure separating the rear of the braincase from the main part, are shared with both early chondrichthyans and osteichthyans. The only other acanthodian braincase that is known in any detail is that of Ptomacanthus anglicus, an Early Devonian acanthodian from the Welsh Borders (Fig. 4e–h). It shows a very different anatomical makeup to that of Acanthodes, sharing some features, such as the arrangement of the entrances for the internal carotid arteries, with placoderms — extinct, heavily armoured fishes that lived during the Silurian and Devonian. The disparity in the two known acanthodian braincases hints at a more complex pattern of relationships than superficial similarities in spines and scales would suggest.
Why are acanthodians important?
Acanthodians are important to evolutionary biologists and palaeontologists because they can shed light on the early evolution of jawed vertebrates. The jawed vertebrates make up the vast majority of vertebrates alive today; their jawless cousins, the hagfishes and lampreys, are much less diverse and have highly specialized lifestyles. Consequently, the evolution of jawed vertebrates is particularly intriguing: how and why did the jawed vertebrates become so successful? It seems likely that their success was built on key evolutionary innovations such as jaws, a bony skeleton and paired fins: all features that are unique to the jawed vertebrates. So, to understand their success, we first need to get to grips with how these innovations arose.
How long have jawed vertebrates been separated?
The difficulty with studying the evolution of the jawed-vertebrate body plan is that the two modern groups, chondrichthyans and osteichthyans, are separated by at least 420 million years of evolution. This has proved to be plenty of time for each group to become so specialized that it is no longer of much use for working out the early stages of its own evolutionary history. Fortunately, the fossil record provides windows into the past, showing us the morphologies of organisms spanning this critical period, and allowing us to work out how the body plans of modern groups were assembled. This makes the anatomy of groups such as the acanthodians, and other early jawed fishes like the placoderms, crucial to reconstructing the evolution of jawed vertebrates. However, to be able to interpret the information that these groups provide, we must first understand their evolutionary relationships to the other jawed vertebrates: we need to fit the acanthodians into the vertebrate family tree.
What are the three types of acanthodians?
Figure 1 — Reconstructions of three different acanthodians, showing ‘typical’ anatomy: (a) Ptomacanthus, a climatiiform from the Devonian of the United Kingdom; (b) Howittacanthus, an acanthodiform from the Devonian of Australia ; (c) the scale of the acanthodiform Acanthodes bronni, showing ‘typical’ acanthodian onion-like scale growth; and (d) Ischnacanthus, an ischnacanthiform from the Devonian of the United Kingdom. (a) modified from Brazeau ( 2012 ); (b) and (d) redrawn from Long ( 1986) and Watson ( 1937) respectively; (c) modified from Denison ( 1979 ).
Why are acanthodians important to palaeontologists?
Acanthodians are of particular interest to palaeontologists because of the insight they provide into the early stages of evolution of the jawed vertebrates. Today, all vertebrates with jaws are separated into two groups: the osteichthyans and the chondrichthyans.
What are the differences between acanthodians and bony fish?
They have notable differences from other bony fish, especially their teeth and their fin spines. Some lost their teeth altogether. Their scales and tails are similar to those sharks.
Which fish has a tapering snout?
One acanthodian, Brochoadmones, is rather atypical in its sharply tapering snout and the only paired prepelvic finlets known in any fish (Hanke, 2006).
Is acanthodian a vertebrate?
If they are a separate class, acanthodians and placoderms would be the only completely extinct vertebrate classes. Their body shape is similar to that of sharks while their scales and the presence ...
What is the last surviving acanthodian?
The last surviving acanthodians belong to the Acanthodiformes. This group, which extends from the Lower Devonian through the Lower Permian, is characterized by a single dorsal spine and fin, absence of dermal bones covering it head and shoulder girdle, lack of teeth and the presence of well-developed gill rackers. Acanthodes is the best known member of this group.
Where did the Acanthodians come from?
Acanthodians are among the earliest jawed vertebrates known. Fragmentary remains have been recovered from as early as the Upper Ordovician of North America and Lower Silurian of China. Their record extends about 160 million years to the Lower Permian. Diversity is greatest from the Upper Silurian through the Devonian.
What are the bones of an acanthodian fish?
Acanthodians are a poorly understood group of extinct jawed fishes that are distinguished by the bony spines projecting in front of their fins and by minute, diamond-shaped scales. Most of them also have relatively large eyes set near the front of their short blunt heads. Like most early fishes, acanthodians had heterocercal caudal fins (tail fins with the top longer that the bottom).
What was the first acanthodian?
The earliest acanthodians were exclusively marine , but freshwater forms predominated during and after the Middle Devonian. Most were small, but some gyracanthids and ischnacanthids could exceed 1 meter in length. Most also had streamlined bodies and were probably good swimmers. The teeth of ischnacanthiforms and many climatiiforms suggest that they were predators, whereas the presence of gill rackers and the absence of teeth suggest that the acanthodiforms were zooplankton feeders. Indeed, the stomach contents of some Late Devonian acanthodids included numerous small crustaceans.
Is the acanthodian group conservative?
Similarities in body shape, scales and spine morphology suggest that they were an evolutionarily conservative group. However, since so little is known about crucial elements of the braincase and gill arches, acanthodian diversity might be greater than is generally recognized.
Do acanthodians have a relationship with sharks?
Opinion has now generally swung back in favor of a closer relationship with ray-fins, but this is not universally accepted.
Is the acanthodian reconstruction copyrighted?
The acanthodian reconstruction at the top and the spindle diagram are copyrighted, © Dennis C. Murphy, 2002. (See Terms of Use .) The reconstructions of Acanthodes, Climatius and Diplacanthus were based on Denison (1979) and Moy-Thomas and Miles (1971).
How big are acanthodes?
Species of Acanthodes grew to be about 30 centimetres (about 12 inches) long and in many respects represent a specialized form, losing many of the traits characteristic of the acanthodians. The spiny shark’s head was small compared with its elongated body, and its eyes were very large.
What is the name of the first jawed vertebrate?
Spiny shark, any of a group of more than 150 species of small extinct fishes traditionally classified in the class Acanthodii and considered by many paleontologists as the earliest known jawed vertebrates. It first appeared in the Silurian Period and lasted into the Permian Period (443.8 to 251.9 million years ago).
When did the jawed vertebrates first appear?
The next class of fishes to appear was the Acanthodii, containing the earliest known jawed vertebrates, which arose in the Late Silurian, more than 416 million years ago. The acanthodians declined after the Devonian but lasted into the Early Permian, a…
What is an acanthodian fish?
Acanthodians are long-extinct fossil fish that stand close to the divergence of cartilaginous and bony fishes. Their morphology has the potential to reveal much about the early evolution of jawed vertebrates. The problem is that their anatomy is poorly known, most of it confined to Acanthodes, a probably unrepresentative genus that lived in the Permian, late in acanthodian history. Martin Brazeau now presents the first detailed description of the braincase of Ptomacanthus, an acanthodian that lived in the Early Devonian acanthodian heyday, about 415 million years ago. The results show that acanthodians were probably not a natural group: Ptomacanthus was either a very early relative of sharks, or close to the common ancestry of all modern jawed vertebrates.
Where did Miles find the acanthodian fish?
Miles, R. S. Articulated acanthodian fishes from the Old Red Sandstone of England, with a review of the structure and evolution of the acanthodian shoulder-girdle. Bull. Br. Mus. Nat. Hist. (Geol.) 24, 111–213 (1973)
What is the basisphenoid region?
The basisphenoid region is incompletely mineralized at its anterior end, but is delimited anteriorly by the intact tooth row. The anterior margin of this mineralization bears a deep medial notch corresponding to the hypophyseal opening. At the anterolateral margins of the basisphenoid are the articulations for the palatoquadrate. The sphenoid region narrows only slightly anterior to these articulations, suggesting that it continued forward between them to contact the ethmoid. The interorbital portion of the basisphenoid is otherwise very broad and extends only a short way anterior to the articulations compared with Acanthodes 5 and basal osteichthyans 18, 19, in which it forms a narrow, elongate extension between the orbits 5 ( Fig. 2 ). In these aspects, Ptomacanthus resembles some placoderms 7, 20 which have very short ethmosphenoid regions. This is also seen in some early chondrichthyans 9, 21, but even there the pre-hypophysial extension of the sphenoid is comparatively longer than in Ptomacanthus. Flanking either side of the hypophysial opening is a foramen that gives off a posterolaterally directed groove (most clearly visible on the anatomical right side of the specimen). The right groove (left in the figures) appears to continue as far as the lateral margin of the basicranium. These grooves and foramina are here interpreted as having accommodated the internal carotid arteries. This is based on their position near to the hypophysis and the angle of the associated grooves. A smaller but distinct groove extends anteriorly from the foramen for the right internal carotid and possibly carried the efferent pseudobranchial artery as in the arthrodire Buchanosteus 22 and the early osteichthyan braincase assigned to Ligulalepis 23, 24. Unlike basal osteichthyans 18, 19, 24 and Acanthodes 5, the basisphenoid of Ptomacanthus lacks evidence of spiracular grooves, again comparing more closely to chondrichthyans and placoderms.
What era did gnathostomes emerge?
Modern gnathostomes (jawed vertebrates) emerged in the early Palaeozoic era 1 , but this event remains unclear owing to a scant early fossil record. The exclusively Palaeozoic ‘acanthodians’ are possibly the earliest 2, 3 gnathostome group and exhibit a mosaic of shark- and bony fish-like characters that has long given them prominence in discussions of early gnathostome evolution 1. Their relationships with modern gnathostomes have remained mysterious, partly because their un-mineralized endoskeletons rarely fossilized. Here I present the first-known braincase of an Early Devonian (approximately 418–412 Myr bp) acanthodian, Ptomacanthus anglicus 4, and re-evaluate the interrelationships of basal gnathostomes. Acanthodian braincases have previously been represented by a single genus, Acanthodes 5, which occurs more than 100 million years later in the fossil record. The braincase of Ptomacanthus differs radically from the osteichthyan-like braincase of Acanthodes 5 in exhibiting several plesiomorphic features shared with placoderms 6, 7 and some early chondrichthyans 8, 9. Most striking is its extremely short sphenoid region and its jaw suspension, which displays features intermediate between some Palaeozoic chondrichthyans and osteichthyans. Phylogenetic analysis resolves Ptomacanthus as either the most basal chondrichthyan or as the sister group of all living gnathostomes. These new data alter earlier conceptions of basal gnathostome phylogeny and thus help to provide a more detailed picture of the acquisition of early gnathostome characters.
What is the basicranial circulation of Ptomacanthus?
The basicranial circulation of Ptomacanthus resembles that in arthrodire placoderms 6, 7. The internal carotid foramina are widely separate from one another on a platybasic neurocranium (see Supplementary Information for a discussion of the chondrichthyan Pucapampella, which Ptomacanthus also resembles). In most chondrichthyans and in Acanthodes 5, the internal carotid arteries share a common medial foramen, usually shared with the hypophyseal opening.
Where is the Ptomacanthus anglicus specimen?
Ptomacanthus anglicus specimen NHM (Natural History Museum, London, UK ) P 24919a ( Fig. 1) was collected from the Wayne Herbert Quarry Lagerstätte 4 in Herefordshire, England, UK. The site is Lochkovian in age (approximately 418–412 Myr bp ), placing Ptomacanthus among the earliest recorded articulated acanthodians. Ptomacanthus is assigned to the ‘Climatiidae’, a division of the ‘Acanthodii’, on the basis of its paired and median fin spine complement, paired pre-pelvic (or intermediate) fin spines and tessellated dermal cranial covering (further taxonomic review is found in the Supplementary Information ). The specimen is a nearly complete, dorsoventrally flattened head and pharynx preserved as a natural mould in fine siltstone that has previously been acid etched and cast in rubber. Part and counterpart are preserved, with one side showing the specimen in palatal view, revealing the partial basicranium, the internal faces of the articulated palatoquadrates, the posterior half of the right Meckelian cartilage and several incomplete branchial arches.
Does the dental arcade of Ptomacanthus show mesia?
Jarvik 19 cited the complete dental arcade of Ptomacanthus ( Fig. 1) as evidence of a palatoquadrate symphysis, as in modern elasmobranchs. However, the palatoquadrates show no evidence of continuing mesially beneath the ethmoid. It is likely that the mesial part of the tooth row was supported on the ethmoid, a condition now considered to be plesiomorphic for chondrichthyans 26.
How big is an acanthode shark?
Compared with other spiny sharks, Acanthodes was relatively large, at 30 centimetres (12 in) long. The genus had no teeth, instead gills. Because of this, it is presumed to have been a filter feeder, filtering plankton from the water. The Acanthodes has been found to have only a couple of skull bones. It was covered in scales that were cubical in shape.
How long is an Acanthodes bridgei?
Several specimens of Acanthodes were recovered from an abandoned quarry (Hamilton Quarry) which contained individuals ranging in total length from 54 nm to 410 nm. A. bridgei was one of the species found there. A. bridgei has large orbits, a shorter pre-pectoral region, and shallower insertions of the fin spines.
How long ago did A. bronni live?
A. bronni lived about 290 million years ago during the Carboniferous period. Researchers took 138 characteristics of various skulls of A. bronni and compared these with skulls of both chondrichthyans and osteichthyans, and determined that acanthodians are closer to cartilaginous fishes.
Is Acanthodes a chondrichthyan?
Acanthodianinternal anatomy is primarily understood by Acanthodes bronni because it remains the only example preserved in substantial detail, central to which is an osensible osteichthyan braincase. For this reason, Acanthodes has become an indispensable component in early gnathostome phylogenies. Acanthodes is quantifiably closer to chondrichthyans than to osteichthyans. However, phylogenetic analysis places Acanthodes on the osteichthyan stem, as part of a well-resolved tree that also recovers acanthodians as stem chondrichthyans and stem gnathostomes. As such, perceived chondrichthyan features of the Acanthodes cranium represent shared primitive conditions for crown group gnathostomes. There has been increasingly detailed findings of early gnathostome evolution highlights ongoing and profound anatomical reorganization of vertebrate crania after the origin of jaws but before the divergence of living clades.
