Name: Chimerarachne ‭(‬Chimera spider‭)‬.
Phonetic: Ky-me-rah-rak-nee.
Named By: Bo Wang,‭ ‬Jason A.‭ ‬Dunlop,‭ ‬Paul A.‭ ‬Seldon,‭ ‬Russel J.‭ ‬Garwood,‭ ‬William A.‭ ‬Shear,‭ ‬Patrick Müller‭ & ‬Xiaojie‭ ‬Lei‭ ‬-‭ ‬2018.
Classification: Animalia,‭ ‬Arthropoda,‭ ‬Chelicerata,‭ ‬Arachnida,‭ ‬Tetrapulmonata.
Species: C.‭ ‬yingi‭ (‬type‭)‬.
Diet: Insectivore.
Size: Main body length‭ ‬2.5‭ ‬millimetres long,‭ ‬tail about‭ ‬3‭ ‬millimetres.
Known locations: Myanmar.
Time period: Roughly around the Early/late Cretaceous boundary.
Fossil representation: Five individuals preserved in amber,‭ ‬at least four of which are male.

       The easiest way to describe Chimerarachne is as a spider with a tail,‭ ‬a tail similar to those seen in some whip scorpions.‭ ‬However,‭ ‬most researchers agree that while Chimerarachne looks similar to a spider it probably wasn’t a‭ ‘‬true‭’ ‬spider.‭ ‬Instead,‭ ‬Chimerarachne represents group of arachnids that might have had a shared ancestry with true spiders.‭ ‬In the earliest radiation of forms there would have been many spider-like forms,‭ ‬but only one evolutionary line leading to true spiders.‭ ‬How close Chimerarachne is placed to true spiders currently depends more upon interpretation of features between this specific genus and the true spiders as a group.
       The body of Chimerarachne is composed into two segments,‭ ‬cephalothorax and abdomen.‭ ‬The abdomen of‭ ‬Chimerarachne‭ ‬is segmented,‭ ‬a trait seen in many primitive arachnids and spiders,‭ ‬including those of the Mesothelae group of spiders,‭ ‬some of which are still alive today.‭ ‬Chimerarachne had eight legs as well as a pair of pedipalps.‭ ‬At the time of writing four known species of Chimerarachne display palpal bulbs,‭ ‬organs that are used for transferring sperm during mating indicating that these individuals were males.‭ ‬The structure of these palpal bulbs is simpler than those seen in the previously mentioned Mesothelae spiders,‭ ‬with greater similarity to mygalomorph spiders‭ (‬ground dwelling spiders such as tarantulas and trapdoor spiders.‭ ‬Chimerarachne also‭ ‬had fangs,‭ ‬and like those of true spiders,‭ ‬these were hairless.‭ ‬At the time of writing it is impossible to say if Chimerarachne was venomous,‭ ‬and if so how potent the venom,‭ ‬if present,‭ ‬was.

       Of course the standout feature of Chimerarachne is the thin whip-like tail.‭ ‬What this tail was for is unknown,‭ ‬it may simply have been a primitive feature that had been retained from arachnid ancestors hundreds of millions of years before.‭ ‬However,‭ ‬nature has a way of reducing useless unused body parts that serve no practical or display function,‭ ‬so the observation that the tail is still present after so long lends some weight as to the tail once serving some kind of function,‭ ‬even if it was only vestigial by the Cretaceous.
       Chimerarachne also possessed spinnerets,‭ ‬though in a very different arrangement to those seen in true spiders.‭ ‬Two pairs of these are very well developed and similar to those seen in the Mesothelae spiders.‭ ‬There are two additional pairs of stubs that might represent two additional pairs of spinnerets,‭ ‬possibly in the process of being formed.
Chimerarachne would have certainly been a predator of other small invertebrates of similar or smaller size.‭ ‬The fact that all known specimens of Chimerarachne have been found trapped in amber suggests that Chimerarachne may have hunted upon the trunks and branches of trees,‭ ‬either actively searching for prey or maybe lurking within cracks and ambushing creatures as they passed by.

Further reading
-‭ ‬Cretaceous arachnid Chimerarachne yingi gen.‭ ‬et sp.‭ ‬nov.‭ ‬illuminates spider origins.‭ ‬-‭ ‬Nature Ecology‭ & ‬Evolution.‭ ‬2‭ (‬4‭)‬:‭ ‬614‭–‬622.‭ ‬-‭ ‬Bo Wang,‭ ‬Jason A.‭ ‬Dunlop,‭ ‬Paul A.‭ ‬Seldon,‭ ‬Russel J.‭ ‬Garwood,‭ ‬William A.‭ ‬Shear,‭ ‬Patrick Müller‭ & ‬Xiaojie‭ ‬Lei‭ ‬-‭ ‬2018.
-‭ ‬Origin of spiders and their spinning organs illuminated by mid-Cretaceous amber fossils.‭ ‬-‭ ‬Nature Ecology‭ & ‬Evolution.‭ ‬2‭ (‬4‭)‬:‭ ‬623‭–‬627.‭ ‬-‭ ‬Diying Huang,‭ ‬Gustavo Hormiga,‭ ‬Chenyang Cai,‭ ‬Yitong Su,‭ ‬Zongjun Yin,‭ ‬Fangyuan Xia‭ & ‬Gonzalo Gribert‭ ‬-‭ ‬2018.


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