Mongolarachne

Name: Mongolarachne ‭(‬Mongolia spider‭)‬.
Phonetic: Mon-go-lah-rak-ne.
Named By: P.‭ ‬A.‭ ‬Seldon,‭ ‬C.‭ ‬K.‭ ‬Shih‭ & ‬D.‭ ‬Ren‭ ‬-‭ ‬2013.
Synonyms: Nephila jurassica.
Classification: Arthropoda,‭ ‬Arachnida,‭ ‬Araneae,‭ ‬Araneomorphae,‭ ‬Mongolarachnidae.
Species: M.‭ ‬jurassica‭ (‬type‭)‬.
Diet: Carnivore.
Size: Female total body length estimated at‭ ‬24.6‭ ‬millimeters long,‭ ‬with forwards length‭ ‬56.5‭ ‬millimetres long.‭ ‬Male total body length‭ ‬16.54‭ ‬millimetres long.
Known locations: Inner Mongolia‭ ‬-‭ ‬Jiulongshan Formation.
Time period: Mid Jurassic.
Fossil representation: Partial female and male specimens.

       Mongolarachne was originally described in‭ ‬2011‭ ‬as Nephila jurassica,‭ ‬a prehistoric species of the Nephila genus of orb weaving spiders that we know today.‭ ‬Nephila jurassica made headlines at the time because it was the largest known spider in the fossil record,‭ ‬though comparable in size to modern golden orb weaver spiders that are alive today.‭ ‬It was also credited as being the oldest known species of the Nephila genus,‭ ‬extended the temporal range of the genus back one hundred and thirty million years.
       Then two years later a new study by Kuntner et al cast serious doubt upon the fossil spider‭’‬s inclusion into the Nephila genus.‭ ‬The main argument against the fossil inclusion into the Nephila genus was that it appeared to be a cribellate spider while known members of the Nephila genus are ecribellate.‭ ‬The difference is that ecribellate spiders spin a sticky silk out of their spinnerets to snare prey like insects.‭ ‬Cribellate spiders have a Cribellum organ different to other spinnerets in that instead of weaving sticky silk,‭ ‬it produces a woolly silk which has a super fine series of fibres that are very effective at trapping insects.
       The suggestion that the spider fossils in question were of a cribellate spider lead to new analysis of the specimens with study of a male individual.‭ ‬When the pedipalps‭ (‬appendages between the fore legs and fangs‭) ‬of the male specimen were studied they were found to actually have a very different construction to known males of the Nephila genus,‭ ‬and this combined with the identification of the fossils being of a cribellate spider led to only one possible conclusion:‭ ‬the fossils did not represent a species of Nephila.‭ ‬This led to the creation of the Mongolarachne genus,‭ ‬and since normal practice when establishing a genus from a species is to retain the old species name,‭ ‬Nephila jurassica became Mongolarachne jurassica.
       At the time of its description‭ (‬and time of writing‭) ‬Mongolarachne jurassica represents the largest fossil spider known to us,‭ ‬and although now known to not be related females of Mongolarachne‭ ‬jurassica are known to comparatively equal to the females of the Nephila genus in size.‭ ‬Like in most spider species,‭ ‬the males of Mongolarachne jurassica are much smaller than the females,‭ ‬and just like with modern spiders,‭ ‬the males may have occasionally been eaten by females when they approached to court them.
       When described as Nephila jurassica,‭ ‬Mongolarachne was often‭ ‬reconstructed as sitting within a broad spider web like other orb weaving spiders,‭ ‬though as a cribellate spider such a web construction would be highly unlikely do to the type of silk spun by the spider.‭ ‬Some cribellate spiders don’t spin silk for prey capture,‭ ‬instead preferring to chase prey down,‭ ‬while others spin tangle webs to ensnare passing insects,‭ ‬while other still use he silk to reinforce a burrow so that they can leap out at passing insects that pass a sensory silk line‭ (‬usually monitored by the spider keeping a foot on the line so it can feel vibrations along it‭)‬.‭
       Some cribellate spiders however have a very elaborate method of prey capture,‭ ‬spinning a net like web and casting it over their prey.‭ ‬This might be a plausible method of hunting for Mongolarachne since it is morphological similar to these‭ ‘‬net casting‭’ ‬spiders.‭ ‬Woolly silk stretches well and when allowed to shrink back to size will trap and snare almost anything that is within it.‭ ‬Some spiders will stretch this net over their prey and allow it to collapse while others will stretch it out between their legs,‭ ‬scoop up their prey into the net and then bring their legs in to trap the prey in the net.‭
       It is impossible to say if this was the hunting method for Mongolarachne as it is impossible for us to see one hunting in the wild,‭ ‬but as a cribellate spider,‭ ‬we can at least have a better idea about it.‭ ‬In addition,‭ ‬most cribellate spiders seem to be either nocturnal,‭ ‬or preferring to reside in dark areas such as caves and cervices in trees or amongst rocks.‭ ‬This would mean that Mongolarachne were probably hidden away from potential predators such as small dinosaurs during the day.


Further reading
-‭ ‬A golden orb-weaver spider‭ (‬Araneae:‭ ‬Nephilidae:‭ ‬Nephila‭) ‬from the Middle Jurassic of China.‭ ‬Biology Letters‭ ‬7‭ (‬5‭)‬:‭ ‬775‭–‬8‭ ‬-‭ ‬P.‭ ‬A.‭ ‬Seldon,‭ ‬C.‭ ‬K.‭ ‬Shih‭ & ‬D.‭ ‬Ren‭ ‬-‭ ‬2011.
-‭ ‬A molecular phylogeny of nephilid spiders:‭ ‬Evolutionary history of a model lineage‭"‬.‭ ‬Molecular Phylogenetics and Evolution‭ ‬69‭ (‬3‭)‬:‭ ‬961‭–‬979‭ ‬-‭ ‬M.‭ ‬Kuntner,‭ ‬M.‭ ‬A.‭ ‬Arnedo,‭ ‬P.‭ ‬Trontelj,‭ ‬T.‭ ‬Lokovše‭ & ‬I.Agnarsson‭ ‬-‭ ‬2013.
-‭ ‬A giant spider from the Jurassic of China reveals greater diversity of the orbicularian stem group.‭ ‬Naturwissenschaften‭ ‬100‭ (‬12‭)‬:‭ ‬1171‭–‬1181‭ ‬-‭ ‬P.‭ ‬A.‭ ‬Seldon,‭ ‬C.‭ ‬K.‭ ‬Shih‭ & ‬D.‭ ‬Ren‭ ‬-‭ ‬2013.



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