Dave Rudkin
LightNews LightNews
banner
art-h-ropod.bsky.social
Dave Rudkin
@art-h-ropod.bsky.social
1.4K followers 750 following 510 posts
Retired palaeontologist and museum curator, admirer of arthropods, and all 'round nature nerd. Fiercely Canadian. Staunchly antifascist. 🇨🇦
Posts Replies Media Videos
art-h-ropod.bsky.social
I've been avoiding bsky because of ... you know, too much angst & shit. But it's #TrilobiteTuesday, so if you're feeling #disarticulated, you're not alone. Scale puzzle of #Isotelusrex (72 cm long!) I cut from ethafoam showing how the calcified dorsal #exoskeleton separated into 12 bits on #death.
A large puzzle in the shape of the giant (72 cm in length) trilobite, Isotelus rex, cut from white 1/2" sheet ethafoam. The left image shows all the individual sclerites of the dorsal exoskeleton in juxtaposition, as in life. The ventral hypostome is not included in this version. The right image shows separation between the free cheeks (librigenae) and the cranidium, and between the tail shield (pygidium) and thorax. In the left image, all the dorsal sclerites, including the 8 thoracic pleurae, are slightly separated, but remain in alignment. This configuration represents a more or less intact carcass, after decay of the arthrodial membranes. On the right, the exoskeletal elements are skewed, as might be seen in a carcass with minor post mortem disturbance. Moult remains -- in which the living trilobite actively shed the old exoskeleton -- typically show inversion and/or rotation of certain elements, often displaced some distance from each other.
June 24, 2025 at 2:44 PM
art-h-ropod.bsky.social
Enrolled Isotelus latus w dorsal pygidium broken away revealing classic isoteline "forked" #hypostome (ventral "mouth plate") disarticulated from cephalic doublure. Beautiful preservation of fingerprint-like #terrace ridges! #Ordovician (~450 MYA), Lindsay Fm, Colborne, #Ontario 🇨🇦 #TrilobiteTuesday
A black & white photo of an enrolled isoteline trilobite. The specimen is viewed from beneath, with the cephalon facing downward -- only a narrow band of the ventral cephalic doublure is exposed at the top of the image, with the median connective suture just visible. The dorsal pygidial shield is broken away, leaving an impression of the ventral doublure as a broad arcuate band with curving parallel terrace ridges. Overlapping thoracic pleurae can be seen on either side of the specimen. Underneath the missing pygidium, the hypostome -- detached from the cephalic doublure -- is revealed from the ventral side. It is of classic isoteline form, with a deep posterior embayment giving a broadly "forked" appearance. Anastomosing terrace ridges are well displayed, running more or less parallel to the lateral margins. The scale bar at the bottom of the image is 20 mm in length.
June 17, 2025 at 1:20 PM
art-h-ropod.bsky.social
On #MolluscMonday: a #fossil #shellbed of the iconic Late #Triassic (~210 MYA) #bivalve, Monotis (Pacimonotis) subcircularis, Pardonet Fm, NE #BritishColumbia 🇨🇦. This subgenus has an extensive circum-Pacific distribution in rocks of similar age.
Large, light grey, semicircular shells of a distinctive pterioid bivalve mollusc are strewn over the surface of a darker grey limestone slab. The thin valves carry well-developed radiating ribs, with sets of finer ribs between more prominent ones. Faint concentric growth lines are also visible. Some valves are more or less complete, while others are fragmentary; there is considerable overlap of individual shells.
June 16, 2025 at 2:33 PM
art-h-ropod.bsky.social
Another archival entry for #Strataday: Coastal monoliths in the Middle #Ordovician (~460 MYA) Mingan Fm, #Mingan #Archipelago #National #Park #Reserve, #Quebec 🇨🇦. Differential erosion of Mingan Fm #limestones has sculpted these striking features. Scanned slide from a 1998 #GAC-MAC field excursion.
An offshore view, taken from a small boat in choppy seas, of deeply eroded coastal monoliths (or sea stacks) composed of distinctly layered Middle Ordovician carbonate rocks. The overall tone of the image is grey-blue, from the rough waters in the foreground, to the shoreline rock exposures in mid-right view, to the uniformly overcast skies in the background. Above the barren wave-swept shoreline, a forest of wind-blown spruce trees encroaches from the right.
June 14, 2025 at 3:31 PM
art-h-ropod.bsky.social
Current events call for a "don't let the bastards grind you down" kind of post. These #Ordovician #bryozoans, #brachiopods & #gastropods entered the #fossilrecord ~450 MYA only to be scoured by a Pleistocene glacier. Be like these #fossils - endure! Verulam Fm, Ramara Tp, #Ontario 🇨🇦 #FossilFriday
A small, irregularly shaped slab of limestone is being held by hand in the raking sunlight. The flat surface, stained pale orange by iron minerals, shows a series of straight parallel grooves or scratches -- these are glacial striations cut by the passage of abrasive rock fragments and mineral grains embedded in the sole of the glacier. Numerous fossil fragments are seen on the slab surface. Some of these have been ground through at various angles and show as complete or partial cross sections. Other fragments (lower left and far right) have escaped glacial sectioning and still stand in relief. Close up of the glacially polished slab surface showing several medium- and high-spired gastropods in section, as well as the outlines of rhynchonellid brachiopods. More of the same surface with sections through trepostome bryozoans and a planispiral gastropod.
June 13, 2025 at 8:04 PM
art-h-ropod.bsky.social
Something #fossiliferous for #ThinSectionThursday: traverse slice thru a #Devonian (~ 393 MYA) colonial rugosan #coral. Astreoid/thamnasteroid growth w individual corallites showing zigzag carinate septa. Billingsastraea sp. cf. B. verneuili, Kwataboahegan Fm, Mattagami River, #Ontario 🇨🇦 Scale=3 cm
A translucent cross-sectional slice through a fossil colonial rugosan coral, roughly triangular in outline, showing seven complete corallites along with three partials. The pale tan colour of the preserved structures contrasts sharply with the black background. Each corallite displays many radiating septa, with numerous short zigzag cross-arms (carinae). A white scale bar beneath the section is 3 cm long. One of many such thin sections in the Invertebrate Palaeontology collections of the Royal Ontario Museum. It was made during an extensive 1950's study of Devonian fossil corals of the Hudson Bay Lowlands in Ontario.
June 12, 2025 at 7:41 PM
art-h-ropod.bsky.social
A face from the deep past: #cephalon (head shield) of Hibbertia ottawaensis, a classic harpetid #trilobite. The exact function of the extraordinary pitted "brim" is unknown w hypotheses varying from sensory, to "snowshoe effect", to filter feeding. #Ordovician (~450 MYA) #Quebec 🇨🇦 #TrilobiteTuesday
A striking trilobite head shield is reminiscent of a face or mask. The arcuate outline is extended as a flattened "brim" bearing hundreds of tiny pits between an upturned rim and the elevated central region. A prominent nose-like glabella is flanked by a pair of raised, kidney-shaped "cheeks" on which are located the small prominent eye lobes. The brim extends back into genal prolongations, the right one of which has been broken away. The dark exoskeletal remains stand in contrast against the pale grey of the limestone matrix. Length as preserved = 6 cm. Specimen is in the Invertebrate Palaeontology collections of the Royal Ontario Museum.
June 10, 2025 at 1:07 PM
art-h-ropod.bsky.social
In the face of gut-churning events everywhere, I turn again to the pre-human #fossilrecord for a moment of peace. This is Cyrenopsis meeki, a #bivalve #mollusc showing precious opal replacement of original shell material. Early #Cretaceous (~118 MYA), Coober Pedy, #SouthAustralia #MolluscMonday
A small fossil bivalve mollusc, measuring about 2.5 cm in width, is seen from the left side. It has been slightly polished to reveal a fresh surface of precious opal, which replaced the original aragonitic shell material and internal cast subsequent to initial fossilization. The typical opal iridescent "play-of-colour" can be seen in small patches of blue, green, and orange. Specimen catalogued in the Invertebrate Palaeontology collections of the Royal Ontario Museum.
June 9, 2025 at 2:31 PM
art-h-ropod.bsky.social
Another 🇨🇦 #Strataday treasure: Late #Ordovician (~448 MYA) shales & carbonates of the upper Vauréal Fm at #VauréalFalls in #AnticostiNationalPark. Anticosti Island, #Quebec, was inscribed as a UNESCO World Heritage Site 2023 for its exceptional #fossil record across the end-Ordovician #extinctions.
At Vauréal Falls, Vauréal River in full flow plunges 76 metres over a cliff of grey interbedded shales and carbonates of the Upper Vauréal Formation. The river continues to flow away from the viewer down Vauréal Canyon beneath near vertical cliffs on the right. A steep talus slope extends from the base of the cliffs to the river's edge. Above the canyon, dense mixed forest continues to the horizon under grey, overcast skies. Image scanned from a 35 mm slide taken in May 1998.
June 7, 2025 at 5:39 PM
art-h-ropod.bsky.social
#Smoke and #cloud tonight. Caught a quick break and managed a single shot. #Luna #Waxing #Gibbous #YorkRegion 🇨🇦
The waxing gibbous moon is partly obscured by cloud and haze from wildfire smoke. In the upper right, white spruce branches are silhouetted against the faintly illuminated sky. The waxing gibbous moon (~84% illuminated) seen through thin wildfire generated haze in this handheld zoom shot.
June 7, 2025 at 2:35 AM
art-h-ropod.bsky.social
It's #FossilFriday & here's the #star of the show! Promopalaeaster sp. cf. P. bellulus - a lovely little sea star from the #Ordovician (~450 MYA) Neuville Fm, #Quebec 🇨🇦. Intact fossil sea stars are relatively rare, but this one is almost complete & shows 2 folded arm tips #Echinodermata #Asteroidea
A small, nearly complete fossil sea star has been carefully prepared from a dark grey shaly matrix to reveal its complex skeletal framework composed of hundreds of tiny individual calcitic plates and spines. It lies dorsal (aboral) side up, with two arm tips folded over to reveal the ventral (oral) surface and (on the right) part of the ambulacrum ("food groove"). Part of the arm at the at the top of the image is missing, but impressions of the lost plates are visible on the rock surface. This is another fine specimen held in the Invertebrate Palaeontology collections of the Royal Ontario Museum. It was collected and prepared by an expert avocational palaeontologist.
June 6, 2025 at 3:01 PM
art-h-ropod.bsky.social
I'm out of #fossil #sponges so we're back in the #garden for some Thursday "creature comfort". This is Misumena vatia: a Goldenrod Crab #Spider lurking in the serviceberry. She's cleverly chosen a spot close to a batch of aphids, which in turn attract ants & hoverflies -- dinner on the doorstep!
A female Goldenrod Crab Spider in her basic white colour phase is perched amongst the curled leaves of a Canada Serviceberry. She has extended the longer first two pairs of her legs in a typical capture or warning pose. The same spider as seen from the right front. The lower row of four larger eyes is visible as a series of dark dots against a pale yellow crescent-shaped patch. Viewed from above, the difference in leg size is clearly seen. The first two pairs are much longer and more robust than the posterior two pairs. A pair of much smaller pedipalps extend from beneath the front of the nearly circular cephalothorax, and the ovoid abdomen bears a median anterior pit followed by three pairs of pits behind. A human thumb in the foreground provides scale.
June 5, 2025 at 9:19 PM
art-h-ropod.bsky.social
Here's yet another #garden goody. A big #ichneumonid #wasp: Therion sp. -- probably T. circumflexum (female) -- ~ 30 mm long. These impressive fliers are parasitoids of lepidopteran larvae. #backyard #biodiversity #native #YorkRegion #Ontario 🇨🇦
A very large, long-legged, thread-waisted ichneumonid wasp is perched on the underside of a leaf. It is predominantly black in colour, but has long red antennae, red and black banded hind legs, a narrow red "waist", and long, heavily veined translucent brown wings folded over over its back. At the tip of her abdomen is a short, sharply pointed ovipositor.
June 5, 2025 at 2:17 AM
art-h-ropod.bsky.social
And while we're in the #garden, here's our first Eastern Forktail (Ischnura verticalis) of the season. Orange colouration with black stripes indicate this is an immature female. #Damselfly #backyard #biodiversity #TYorkRegion #Ontario 🇨🇦
A slender, predominantly orange, narrow-winged damselfly perches at the tip of an Eastern White Cedar branch; it is about 4 cm in length. Seen from the right front, it shows one of the black stripes that run along the "shoulders" of the thorax. The large spherical eyes are a cream colour with a faint darker band and spot on the upper half. The top of the long abdomen is black except for the first two segments. Each of the three pairs of pale legs bears numerous small black spines. Tufts of short light coloured hairs can be seen around the margins of the thorax.
June 4, 2025 at 8:23 PM
art-h-ropod.bsky.social
Bee-n awhile since my last entry in the #garden #Anthophila line-up, so here is another frequent halictid visitor to our yard: a Pure Green Sweat #Bee (Augochlora pura) on Zizea aurea. #backyard #biodiversity #native #YorkRegion #Ontario 🇨🇦
A tiny metallic green bee is feeding on the bright yellow umbelliferous flowers of Golden Alexanders. It is seen from the right and slightly behind, as it stretches between two florets. The same small bee as viewed from the left front. The bright metallic sheen of the head and thorax contrasts with the smoky brown translucent wings. Both the lateral compound eyes and three median ocelli are visible.
June 4, 2025 at 11:31 AM
art-h-ropod.bsky.social
Smoked #moon tonight. #wildfires 🇨🇦
Hand-held telephoto image of tonight's waxing gibbous moon (59.5% illumination). The dull brown tinge is due to smoke from wildfires in northwestern Ontario and Manitoba.
June 4, 2025 at 2:27 AM
art-h-ropod.bsky.social
Just a chip off the old rock ... tiny & not quite complete, but the only one I've ever found in 50 yrs of collecting in this formation: Eomonorachus sp. cf. E. intermedius -- Upper #Ordovician (~450 MYA) Verulam Fm, Ramara Tp #Ontario 🇨🇦 #TrilobiteTuesday
A tiny rectangular chip of dark grey shale sits on a human fingertip. The chip bears an almost complete dorsal exoskeleton of the pterygometopid trilobite, Eomonorachus sp. Only the anteriormost margin of the cephalon is missing. The specimen has been coated with a thin layer of ammonium chloride sublimate to accentuate subtle topographic features. Collected from a road cut in the Upper Ordovician Verulam Formation near Bolsover, Ontario in 1977. Specimen is in the Invertebrate Palaeontology collections of the Royal Ontario Museum. Close-up of the same specimen in isolated view. Specimen is just under 10 mm in length.
June 3, 2025 at 12:49 PM
art-h-ropod.bsky.social
Internal mold (= #steinkern) of an impressively large high-spired #gastropod -- possibly Subulites sp. Bonus points for spotting the 4 #trilobite cephala! Upper #Ordovician (~450 MYA) Verulam Fm, Ramara Tp, #Ontario 🇨🇦. Scale in mm. #MolluscMonday #fossil #snail
A small rectangular slab of tan-coloured limestone bears numerous fossils on the exposed surface. Most conspicuous is a large high-spired gastropod, preserved as a "steinkern". The originally aragonitic shell has been dissolved away leaving only the fine sediment infill as an internal mold. The general form of the fossil suggests it might be assigned to the genus Subulites. Also present on the slab surface are several cephala of the trilobite Calyptaulax, other seal stinkers, bryozoans, and brachiopods.
June 2, 2025 at 1:17 PM
art-h-ropod.bsky.social
Down by the bay for #Strataday ... #HudsonBay, that is. Upper #Ordovician (~445 MYA) fossiliferous Churchill River Gp carbonates onlap & incorporate Proterozoic (~1.8 BYA) Churchill "quartzite" (metagreywacke) in a spectacular ancient #rocky boulder-strewn #shoreline. E of #Churchill, #Manitoba 🇨🇦
Aerial view of the Hudson Bay coast line east of Churchill, Manitoba. Looking approximately westward along a rocky ridge of dark coloured Proterozoic metasedimentary rock (Churchill "quartzite") on the right, with light tan coloured, gently shelving, Ordovician carbonate rocks in mid view. On the left, the dark waters of Hudson Bay extend to the horizon. A series of linear waves is breaking along the shoreline. Between the ridge on the right and the shelving Ordovician strata, an extensive boulder field of Churchill "quartzite" has developed. Where the two lithologies meet, the carbonate sediments have incorporated the much older boulders, some of which are very large (up to 12 metres x 4 metres). A ground level view of the boulder field, with pale Ordovician carbonate rocks enveloping much older boulders of dark, deeply weathered metagreywackes in a spectacular ancient rocky shoreline setting. The fog shrouded waters of Hudson Bay lay off in the upper right background. A view across the gently dipping Ordovician tan coloured carbonate rocks of the Churchill River Group, towards a dark ridge of Proterozoic Churchill "quartzite" in the distance. This just east of the main boulder field, and in the middle distance just a few large blocks of metagreywacke can be seen.
May 31, 2025 at 8:05 PM
art-h-ropod.bsky.social
A big #brachiopod dorsal valve for #FossilFriday. This #Devonian (~393 MYA) #strophomenid measures about 8 cm across the straight (=strophic) hinge. Bonus appearance = longitudinal section thru' a solitary rugosan #coral to the right. Kwataboahegan Fm, Kwataboahegan R, #HudsonBayLowland, #Ontario 🇨🇦
An irregularly shaped slab of buff coloured limestone features in the upper left a large, flat dorsal (brachial) valve of a Strophomenida brachiopod. The valve is approximately semicircular in outline and measures about 8 cm wide across the essentially straight hinge line. Low slightly curved ribs radiate from the valve apex to the shall margin. Faint concentric ridges mark the former valve outline at earlier growth stages. To the right of the brachiopod is a lengthwise cross section through a curving solitary rugosan coral. Other fragmentary fossils are present on the same surface. A scale in the lower right is graduated in millimetres.
May 30, 2025 at 11:49 AM
art-h-ropod.bsky.social
Female Black #Swallowtail on Physocarpus. #Butterfly #Garden #Backyard #Biodiversity #YorkRegion 🇨🇦
A large, predominantly black butterfly is perched on an arched, leafy green branch of Ninebark, shown against a deeply shadowed background. The butterfly is facing away from the viewer. Its dark wings are outstretched, displaying the characteristic markings of a female Eastern Black Swallowtail (Papilio polyxenes): two rows of small pale yellow spots bordering the rear margins, four pairs of blue patches near the inner edges between the yellow markings, and one pair of orange-red patches with black "eyes" where the hind wings meet. The rear margins of the hind wings are drawn out into short "tails".
May 29, 2025 at 8:00 PM
art-h-ropod.bsky.social
#Wet #Black&White #WitchHazel
The underside of a Witch Hazel (Hamamelis virginiana) leaf with rain droplets, each of which is acting like a miniature magnifying lens revealing a blow-up view of the net-like vein pattern beneath. The leaf stands in sharp contrast to the dark out-of-focus background.
May 29, 2025 at 4:25 PM
art-h-ropod.bsky.social
Gotta slip in a late-in-the-day #WormWednesday post: Burgessochaeta setigera is a #fossil stem-group #polychaete from the #BurgessShale. Nice reflective setae in this specimen + an infilled gut trace. Approx. 25 mm long - anterior to right. #Cambrian (~508 MYA), #YohoNP, #BritishColumbia 🇨🇦
Close-up image of a small fossil polychaete "bristle worm". The slightly curved body is preserved as a flattened film on a flecked grey mudstone matrix. Small paired bundles of lateral setae show up as silvery reflections along the length of the worm. A dark, slightly reflective ribbon-like trace down the mid-line marks the gut. The "head" of the worm is to the right, and at the rear end a short dark stain is interpreted as gut contents extruded after burial. This is yet another superb specimen in the Invertebrate Palaeontology collections of the Royal Ontario Museum. For more information, see: https://burgess-shale.rom.on.ca/fossils/burgessochaeta-setigera/
May 28, 2025 at 8:34 PM
art-h-ropod.bsky.social
Compound #eye opener for #TrilobiteTuesday! Nice examples of the #holochroal eye condition in 2 diff #trilobite groups. 100's of tiny calcitic lenses packed together & sharing (in life) a continuous calcite corneal cover. Meroperix (L) - a styginid & Chiozoon (R) - a cheirurid. #Silurian (~430 MYA)
Close-up B&W photo of the kidney-shaped compound eye on an isolated left free cheek of the small styginid trilobite, Meroperix aquilonaris. The strongly curved and convex eye surface contains hundreds of tiny individual, calcitic lenses in a close-packing arrangement. Field of view approximately 25 mm across. Attawapiskat Fm, Akimiski Is, Nunavut 🇨🇦 A B&W photo of a right lateral view of a complete, but partly exfoliated, cephalon of the cheirurid trilobite, Chiozoon umisk. The small, bulbous holochroal right eye is located mid-field on the pitted free cheek, just ahead of a sharp curve in the proparian facial suture. The eye comprises hundreds of very small lenses closely packed together across the strongly curved surface. Field of view approximately 40 mm across. Attawapiskat Fm, Akimiski Is, Nunavut 🇨🇦
May 27, 2025 at 1:38 PM
art-h-ropod.bsky.social
Another #mail-in #MolluscMonday: our #philatelic feature is the giant #clam, Tridacna gigas + other species in the genus. These hefty denizens of Indo-pacific reefs house #symbiotic photosynthesizing #algae in their mantle tissues. My 1 & only encounter ... snorkelling on the GB reef #Australia!
A small white envelope with an artist's coloured rendering of a giant clam occupying the left one-third, and two small postage stamps in the upper right corner. The stamps depict a different artistic rendering of a living specimen of Tridanca gigas with a swimming fish and bear the words "Republic of PALAU" over "Giant Clam" and a value of 13 c. The inked cancellation reads: KOROR PALAU 96940 around the periphery of a small circle, with the date: FEB 22 1984 in the centre; four horizontal bars to the right contain in the middle space the words: FIRST DAY OF ISSUE. A printed caption beneath the large artist's rendering reads: "GIANT CLAM These slow moving giants rest on the bottom of tropical waters and live off the algae that grow inside them. FIRST DAY OF ISSUE" A low resolution colour image (scanned from a print) shows an undersea scene on Hardy Reef, off the Whitsunday Islands on Australia's east coast (January 2000). The photo was taken while snorkelling and, in the centre, nestled among abundant corals, is a single large clam in the genus Tridacna. All that can be seen is the dark green-blue mantle edge tracing out a sinuous line along the valve margins. The remainder of the shell is covered by the surrounding coral community. The anchor line of a diving platform runs diagonally across the upper left corner of the image.
May 26, 2025 at 1:08 PM