extinct species grew length resembled modern shrimp morphology habit large body terminating pair tail flaps active swimmer feeding organic particles substrate oldest animals direct evidence brood care based number individuals abundant thousands specimens collected fossils found american described named mountains near discovery site mount species classified genus bears remarkable resemblance modern crustaceans taxonomic remain unclear currently classified stem group tentatively included clade description maximum body length centimetres thin easily distorted possessed large narrow wide posterior margins covered short body segments pairs small poorly preserved feeding single pair long slender antennae present segments relatively elongated probably sensory organs segments possessing small pair short structures possible present position corresponding location second pair antennae modern day crustaceans small triangular plate narrow sharp central ridge developed compound eyes striking morphological similarities eyes extant likely capable producing true visual images sensitive motion median eye present nervous tissue including brain identified divided groups anterior group composed developed walking limbs lengths extend past margins morphological details preserved segments appear possess multitude small spines unknown limbs assumed inner branches leg outer branches absent preserved posterior group possessing pair long multi segments longer near body flexible segments extending past bear fringe long slender directed middle body characteristic shared extant crustaceans usually blade like shapes process slender cylindrical tubes animal alive segment believed functioned gills swimming limbs possibly specimens showing traces small bases abdomen composed lack facing margins bear small spines larger spines abdominal pair flattened function tail fan caudal addition body swimming quick flick tail fan rapidly propel animal backwards functioned means escaping predators like modern shrimp traces fused segments evident faint lines dividing lobe tail fan long present end body traces rounded stomach small digestive terminates tiny anal opening observed specimens discovery fossils discovered august rough sketch present diary august alongside sketches formal description species published species named mountains connected containing locality british_columbia canada comes nation word meaning running water named american telecommunications pioneer specimens recovered dates period million years ago locality underwater located warm shallow tropical sea adjacent submarine limestone cliff landslides caused collapse parts limestone cliff periodically bury organisms area organisms carried landslides fine mud later based number individuals constitutes total number organisms recovered greater bed makes abundant houses thousand specimens species found parts remaining close proximity possible specimens recovered member utah taxonomy species accepted genus classified family established order established tentatively clade early erroneously depicted primitive shrimp modern consider unknown uncertain taxonomic placement authors suggested allied crustaceans like preserved making impossible reliably classify crown group propose related crustaceans member stem group crustaceans despite species recovered abundant fossils depth work morphology apparently similar species described million years ago china originally placed genus reclassified new genus additional discoveries complete specimens resemblance apparent like median ridge pair caudal single pair antennae eyes tentatively transferred genus abdominal contrast limbs unlike authors deemed differences separate genus second similar species recovered formation northern greenland identified possible like abdominal like poor preservation specimens particularly head difficult taxonomic placement difficulty compounded evidence fossils fact actual animal ecology addition striking superficial similarity contemporary shrimp shrimp like habits dwelling deposit lack strong feeding indicates likely feed sea edible organic particles tails feather like posterior imply active swimmers egg identified specimens clutch sizes small containing eggs egg relatively large average diameter inside attached inner surface million years older eggs preserved inside constitute oldest direct evidence brood care selection animals indicates probably lived environment required special measures ensure survival young
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