Batomorphi
The 5th edition of Fishes of the World classifies Batomorphi as a division within cartilaginous fishes. These creatures possess boneless skeletons made from tough, elastic cartilage instead of rigid bone. Most batomorphs display dorsoventrally flattened bodies that resemble a mantle or disc shape. This flattened form contrasts sharply with the spindle-shaped bodies typical of sharks. Their pectoral fins have evolved into broad appendages often called wings to aid in movement. The anal fin is absent from their anatomy entirely. Eyes and spiracles sit on top of the head for bottom-dwelling species. Water enters through these spiracles rather than the mouth for breathing purposes. Gill slits lie under the pectoral fins on the underside of the body. Most batomorphs carry five ventral gill slits while Hexatrygonidae species hold six. A ventrally located mouth allows them to capture prey effectively. Many species can protrude their upper jaw away from the cranium to feed. Heavy rounded teeth help crush shells of snails, clams, oysters, crustaceans, and some fish. Manta rays utilize dense gill rakers to filter plankton from the water column.
Fossil denticles resembling those of modern chondrichthyans date back to at least the Ordovician period. The oldest unambiguous fossils of cartilaginous fish appear from the middle Devonian era. A clade known as Neoselachii emerged by the Triassic period. Best-understood neoselachian fossils originate from the Jurassic epoch. Antiquaobatis stands as the oldest confirmed ray fossil found in Germany during the Pliensbachian stage. Early Eocene fossils like Heliobatis radians provide evidence of ancient whipray lineages. These findings trace the lineage of sharks, sawfishes, rays, and skates through deep time. The Mesozoic Sclerorhynchoidea were long considered basal or incertae sedis in classification systems. They show features of Rajiformes but possess snouts resembling sawfishes. Modern analysis now considers them true skates within the Rajiformes order. This evolutionary history spans hundreds of millions of years of adaptation and survival.
Molecular evidence refutes the hypothesis that skates and rays are derived directly from sharks. The monophyly of skates, stingrays, and electric rays has been generally accepted for a long time. Nelson's 2006 Fishes of the World lists four traditionally accepted major batomorph lineages. Rhinopristiformes joins these three groups to form the traditional classification framework. A 2011 study significantly reevaluated the phylogeny using nuclear and mitochondrial DNA from 37 taxa. This sample set represented almost all recognized families and all traditional four major lineages. The study strongly confirmed the internal monophyly of skates, stingrays, and electric rays. It recovered panrays as sister to the stingrays as older morphological analyses had suggested. However, it found Rhinopristiformes to be paraphyletic comprising two distinct clades. These new groups were referred to as Guitarfishes 1 and Guitarfishes 2. Guitarfishes 1 contains only Trygonorrhinidae while Guitarfishes 2 holds the remainder of Rhinopristiformes. A polytomy between skates, electric rays, and thornbacks appears at the base of Batomorphi in newer analyses. Weak support suggests skates may be the actual most basal lineage followed by a clade uniting electric rays and thornbacks.
Batomorphs undergo internal fertilization characteristic of elasmobranchs. Internal fertilization conserves sperm and does not expose eggs to consumption by predators. All energy involved in reproduction is retained rather than lost to the environment. All skates and some rays are oviparous meaning they lay eggs. Other rays are ovoviviparous giving birth to young that develop in a womb without placental involvement. The eggs of oviparous skates are laid in leathery egg cases known as mermaid's purses. These empty cases often wash up on beaches where skates are common. Capture-induced premature birth occurs frequently when sharks and rays are fished. This phenomenon collectively called capture-induced parturition happens in at least 12% of live bearing species. Eighty-eight species have been documented exhibiting this response so far. Fisheries management rarely considers this occurrence despite its prevalence among captured populations.
Most batomorph species live on the sea floor across various geographical regions. They inhabit coastal waters though some dwell in deep waters reaching depths of at least 3000 meters. A cosmopolitan distribution characterizes most batomorphs preferring tropical and subtropical marine environments. Temperate and cold-water species exist alongside these tropical populations. Only a few species like manta rays live in the open ocean. Very few batomorphs reside in freshwater habitats while others survive in brackish bays and estuaries. The Mediterranean Sea hosts numerous species but faces severe population pressures from unregulated fishing activities. Recent surveys indicate only 38 species of rays and skates still subsist there today. This geographic spread demonstrates their adaptability to diverse aquatic conditions worldwide.
A 2021 study published in Nature documents a global decline of 71% in oceanic sharks and rays over fifty years. This drop jeopardizes the health of entire ocean ecosystems as well as food security for poor countries. Overfishing has increased extinction risk so that three-quarters of these species are now threatened with extinction. The Mediterranean Sea remains the most impacted region by unregulated fishing practices globally. An international survey by the Mediterranean Science Commission found only 38 species of rays and skates remaining there. Guide of Mediterranean Skates and Rays published in October 2022 confirms this critical status. Conservation efforts must address these rapid declines to prevent further ecosystem collapse. The scale of loss threatens both biodiversity and human livelihoods dependent on marine resources.
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Common questions
What is Batomorphi according to the 5th edition of Fishes of the World?
The 5th edition of Fishes of the World classifies Batomorphi as a division within cartilaginous fishes. These creatures possess boneless skeletons made from tough, elastic cartilage instead of rigid bone.
When did the oldest confirmed ray fossil Antiquaobatis appear in Germany?
Antiquaobatis stands as the oldest confirmed ray fossil found in Germany during the Pliensbachian stage of the Jurassic epoch. This finding contributes to the lineage history tracing back through deep time alongside other early fossils like Heliobatis radians from the Early Eocene.
How many gill slits do Hexatrygonidae species have compared to most batomorphs?
Most batomorphs carry five ventral gill slits while Hexatrygonidae species hold six. Gill slits lie under the pectoral fins on the underside of the body for breathing purposes.
Why are skates and rays considered distinct from sharks based on molecular evidence?
Molecular evidence refutes the hypothesis that skates and rays are derived directly from sharks. A 2011 study significantly reevaluated the phylogeny using nuclear and mitochondrial DNA from 37 taxa to confirm these relationships.
What percentage of oceanic sharks and rays declined over fifty years according to a 2021 Nature study?
A 2021 study published in Nature documents a global decline of 71% in oceanic sharks and rays over fifty years. Overfishing has increased extinction risk so that three-quarters of these species are now threatened with extinction.