KINGDOM:ANIMALIAKINGDOM:ANIMALIAPHYLUM:CHORDATAPHYLUM:CHORDATA

CLASS:GRAPTOLITHINACLASS:GRAPTOLITHINA

GraptolithinaGraptolithina

Graptolite comes from the Graptolite comes from the GreekGreek graptosgraptos, , meaning "written", and meaning "written", and lithoslithos, meaning , meaning "rock","rock",

are are fossilfossil colonial colonial animalsanimals known chiefly known chiefly from the Upper from the Upper CambrianCambrian through the through the Lower Lower CarboniferousCarboniferous ( (MississippianMississippian). A ). A possible early graptolite, possible early graptolite, ChaunograptusChaunograptus, , is known from the Middle Cambrian. is known from the Middle Cambrian.

TAXONOMYTAXONOMY

The name originates from the genus The name originates from the genus GraptolithusGraptolithus, which , which was used by was used by LinneusLinneus in 1735 for inorganic in 1735 for inorganic mineralizationsmineralizations and crustations which resembled actual and crustations which resembled actual fossils. In 1768, in the 12th volume of fossils. In 1768, in the 12th volume of SystemaSystema NaturaeNaturae, , he included he included G. sagittariusG. sagittarius and and G. scalarisG. scalaris, respectively a , respectively a possible possible plantplant fossil and a possible graptolite. In his 1751 fossil and a possible graptolite. In his 1751 Skånska ResaSkånska Resa, he included a figure of a "fossil or , he included a figure of a "fossil or graptolite of a strange kind" currently thought to be a graptolite of a strange kind" currently thought to be a type of type of ClimacograptusClimacograptus (a (a genusgenus of biserial graptolites). of biserial graptolites). Later workers used the name to refer to a specific group Later workers used the name to refer to a specific group of organisms. of organisms. GraptolithusGraptolithus was officially abandoned in was officially abandoned in 1954 by the 1954 by the ICZNICZN, partly because of its original purpose , partly because of its original purpose as a grouping for inorganic mimicries of fossils.as a grouping for inorganic mimicries of fossils.

Since the 1970s, as a result of advances in Since the 1970s, as a result of advances in electron microscopyelectron microscopy, graptolites have generally , graptolites have generally been thought to be most closely allied to the been thought to be most closely allied to the pterobranchspterobranchs, a rare group of modern marine , a rare group of modern marine animals belonging to the animals belonging to the phylumphylum HemichordataHemichordata ( (hemichordateshemichordates). Comparisons are drawn with ). Comparisons are drawn with the modern hemichordates the modern hemichordates CephalodiscusCephalodiscus and and RhabdopleuraRhabdopleura..[1][1] CephalodiscusCephalodiscus numbers about numbers about 18 species, and was first discovered in 1882. 18 species, and was first discovered in 1882.

Graptolites as Index fossilsGraptolites as Index fossils

Each graptolite colony is known as a Each graptolite colony is known as a rhabdosomerhabdosome and has a and has a variable number of branches (called variable number of branches (called stipesstipes) originating from an initial ) originating from an initial individual (called a individual (called a siculasicula). Each subsequent individual (). Each subsequent individual (zooidzooid) is ) is housed within a tubular or cup-like structure (called a housed within a tubular or cup-like structure (called a thecatheca). ).

Most of the dendritic or many-branched types are classified as Most of the dendritic or many-branched types are classified as dendroid graptolites (order Dendroidea). They appear earlier in the dendroid graptolites (order Dendroidea). They appear earlier in the fossil record (in the Cambrian period), and were generally benthic fossil record (in the Cambrian period), and were generally benthic animals (attached to the sea-floor by a root-like base). Graptolites animals (attached to the sea-floor by a root-like base). Graptolites with relatively few branches were derived from the dendroid with relatively few branches were derived from the dendroid graptolites at the beginning of the graptolites at the beginning of the OrdovicianOrdovician period. This latter type period. This latter type (order Graptoloidea) were pelagic, drifting freely on the surface of (order Graptoloidea) were pelagic, drifting freely on the surface of ancient seas or attached to floating ancient seas or attached to floating seaweedseaweed by means of a slender by means of a slender thread. thread.

MorphologyMorphology

PreservationPreservation

Graptolite fossils are often found in Graptolite fossils are often found in shalesshales and and mud rocks where sea-bed fossils are rare, mud rocks where sea-bed fossils are rare,

Graptolites are also found in Graptolites are also found in limestoneslimestones and and chertscherts

Graptolite fossils are often found flattened along Graptolite fossils are often found flattened along the bedding plane of the rocks in which they the bedding plane of the rocks in which they occur, though may be found in three dimensions occur, though may be found in three dimensions when they are infilled by when they are infilled by ironiron pyritepyrite

Graptolites are normally preserved as a black Graptolites are normally preserved as a black carbonizedcarbonized film on the rock's surface or as light film on the rock's surface or as light grey clay films in grey clay films in tectonicallytectonically distorted rocks distorted rocks

EvolutionEvolution

One of the most compelling facts about One of the most compelling facts about graptolite evolution is the interaction graptolite evolution is the interaction between grade and clade: A similar between grade and clade: A similar gradegrade of organization (of organization (e.ge.g. four stipes) was . four stipes) was reached by more than one clade (line of reached by more than one clade (line of descent) of graptolites, at more or less the descent) of graptolites, at more or less the same time. same time.

ExtinctionExtinction

After a number of marked extinction After a number of marked extinction events which repeated reduced graptoloid events which repeated reduced graptoloid diversity, the diverse graptoloid diversity, the diverse graptoloid assemblage finally disappeared entirely, assemblage finally disappeared entirely, fairly suddenly, for reasons that remain fairly suddenly, for reasons that remain obscure but which coincided with the obscure but which coincided with the spread of fish into the planktonic realm. spread of fish into the planktonic realm.

SystematicsSystematics

For many years, however, graptolite taxa For many years, however, graptolite taxa were simply binned into form genera were simply binned into form genera based on the gross morphology of the based on the gross morphology of the colony – the number of stipes and their colony – the number of stipes and their arrangement, whether or not the stipes arrangement, whether or not the stipes were scandent, the closeness of the were scandent, the closeness of the thecae – rather than the characteristics thecae – rather than the characteristics which, today, are believed to be good which, today, are believed to be good indicators of phylogeny. indicators of phylogeny.

ORDERS OF GRAPTOLITHINAORDERS OF GRAPTOLITHINA

DendroideaDendroidea TuboideaTuboidea CamaroideaCamaroidea Crustoidea Crustoidea Stolonoidea Stolonoidea Graptoloidea Graptoloidea Dithecoidea Dithecoidea