Ladies and gentlemen, children of all ages. It’s time for another exciting episode of “What is it?”
If you think you know what is shown in these photos, then please leave a comment. The answer will be revealed in a post update.
Copyright © 2022 Walter Sanford. All rights reserved.
This blog post features a photo of a fossil shark tooth that I collected from the Lee Creek Phosphate Mine in Aurora, North Carolina. I didn’t record the exact date when I collected this specimen, but it was sometime between 1984 and 1989. The mine is currently open for phosphate mining, but it’s closed to the public for fossil collecting.
At the time I collected the tooth, the species of shark was called Carcharodon megalodon. Subsequently, the scientific name was changed to Carcharocles megalodon.
C. megalodon lived in “shallow” seas approximately 10 million years ago. 10 million years seems like a long time on the human time scale, but isn’t long ago on the Geologic Time Scale.
Size and jaw placement
The following annotated image shows one method for measuring the size of a fossil shark tooth. The “slant height” of the tooth is approximately four and one-quarter inches (~4 1/4″) long, as measured along the straighter edge of the tooth (lower edge, relative to the photo).
According to Gareth Williams, a member of the Megalodon Maniacs Facebook group, the tooth is from the upper jaw (lateral).
Lee Creek Phosphate Mine | C. megalodon (lingual side)
Photoblog post flashback
On 11 May 2020 I published a blog post entitled “Focus bracketing using Fujifilm X-T3” that features the same ruler shown in the preceding photo.
The 7″ plastic ruler is from the Calvert Marine Museum. Do you know why the small ruler is 7″ long rather than the more common 6″ length? Please leave a comment if you know the correct answer. Source Credit: Focus bracketing using Fujifilm X-T3.
The reason the ruler is 7″ inches long is because that’s the length of the largest fossil shark teeth ever collected — the holy grail for fossil hunters!
Tech Tips
The Adobe Photoshop “Ruler Tool” can be used to measure the number of pixels between any two points along the ruler shown in the preceding annotated image.
60s ‘shop: Using the ruler tool to measure distances in Photoshop CC, by Photoshop for the Scientist (1:00) provides a clear and concise explanation of how it’s done.
The resulting value (in pixels) can be used to set a custom scale in Photoshop in order to make other measurements of the tooth virtually.
Related Resources
Copyright © 2022 Walter Sanford. All rights reserved.
Sometimes I start working on a blog post by shooting some quick-and-dirty test shots of the subject, such as the following photos of a fossil shark tooth taken using the “Camera” app on my Apple iPad mini 6. Both photos featured in this post are unedited, that is, they are the original JPGs straight from the “Photos” app on the iPad.
Labial side
The first photo was taken with the built-in camera flash turned on. In my opinion, the light is a little too “harsh.”
The photo shows the side of the tooth that faces outward from the mouth of the shark. Notice the tooth edges are serrated.
There are at least two ways to measure the size of a fossil shark tooth. (More about how to measure shark teeth in a follow-up blog post.) This tooth is approximately four and one-quarter inches (~4 1/4″), as measured along the straighter edge of the tooth (right side, relative to the photo).
Lingual side
The last photo was taken was taken using a small LED light and the flash turned off. The LED lighting is better than the flash light, but the specular reflection located near the upper-middle of the tooth enamel is a little distracting.
The photo shows the side of the tooth that faces inward. Three prominent parts of the tooth are easy to identify in the following photo, including the crown/enamel (top), bourlette (middle), and root (bottom).
In the opinion of the author, the lingual side of a shark tooth is often displayed because it is more visually appealing than the labial side.
What’s next?
I plan to shoot better photos, of course, and annotate some of them in order to make it easier to identify the parts of the tooth.
I will describe when and where I collected the fossil shark tooth, identify the species of shark, and provide an estimate of its approximate age on the Geologic Time Scale.
Finally I will explain how to measure the size of a fossil shark tooth, and how to determine whether the tooth is from the upper- or lower jaw, including its approximate position along the jaw line.
Related Resource: Fossil shark tooth, revisited.
Copyright © 2022 Walter Sanford. All rights reserved.
I spotted an emergent Uhler’s Sundragon (Helocordulia uhleri) during a photowalk along a mid-size stream at an undisclosed location in Prince William County, Virginia USA. The following photograph shows the exuvia from which the teneral adult emerged.
13 APR 2021 | PNC. Wm. County, VA | Uhler’s Sundragon | exuvia (ventral)
In the opinion of the author, larvae (nymphs)/exuviae from Family Corduliidae (Emeralds) and Family Libellulidae (Skimmers) can be challenging to differentiate and identify to the family level.
One way to differentiate Emerald from Skimmer larvae/exuvia is to look for a “ventromedial groove” in the prementum: it’s probably Corduliidae (Emeralds) if there is a ventromedial groove; it’s probably Libellulidae if there isn’t.
Look closely at a version of the preceding photo that was reformatted, rotated, and cropped to show an enlarged view of the prementum. You should notice a ventromedial groove on the basal half of the prementum, indicating this specimen is a member of Family Corduliidae (Emeralds).
13 APR 2021 | PNC. Wm. County, VA | Uhler’s Sundragon | exuvia (ventral)
Three raised structures on the underside of the prementum remind me of the hood ornament on a 1949 Lincoln automobile. (No, I wasn’t alive in 1949!)
Related Resources
Tech Tips
One reason I underexposed the photo is to add definition to the ventromedial groove and avoid overexposing the black background.
I prefer a white background for photographing odonate exuviae. Using a black background proved to be more challenging than I expected. More later in a follow-up blog post.
Copyright © 2021 Walter Sanford. All rights reserved.
My last blog post was a “sketch pad” of test shots of an exuvia from a Comet Darner dragonfly (Anax longipes) collected by Stanley Caveney on 19 July 2021 from a pond at MeadowWoods in West Elgin, Ontario, Canada. All of the shots in that post are unedited JPGs straight from my camera. This post features edited versions of the RAF (raw) files from that photo shoot, including some images with value-added annotations.
Lateral view
I considered annotating the first photo but decided to allow it to stand on its own as the latest addition to my Odonart© Portfolio.
Comet Darner (Anax longipes) | exuvia (lateral)
Ventral view
I used Adobe Photoshop to create a composite image that features the best parts of two photos from the sketch pad.
This specimen is from a male Comet Darner, as indicated by its vestigial primary- and secondary genitalia. The inset photo shows a clear view of the vestigial hamuli (secondary genitalia) that are partially obscured in the background photo.
Comet Darner (Anax longipes) | exuvia (ventral)
Prementum
The last photo shows a closer view of the mentum, a two-segment hinged “jaw” that is used to grab food: the prementum is the segment of the labium closer to the mouth; the postmentum is the segment closer to the base of the head. Only the prementum can be seen in the following photo.
Comet Darner (Anax longipes) | exuvia (prementum)
The preceding annotated image of the prementum includes labels for the moveable hooks (2 of 2) and palpal lobe (1 of 2). Notice that A. longipes palpal lobes are squared off, in contrast with the more rounded shape of the labial palps of Common Green Darner (Anax junius).
Related Resources
Copyright © 2021 Walter Sanford. All rights reserved.
A “horn” on the face-head is a characteristic field mark for odonate larvae/exuviae in the Family Macromiidae (Cruisers).
Look closely at the full-size version of each of the following photos and you should be able to see the horn on the face of a Stream Cruiser dragonfly (Didymops transversa) exuvia that was collected during mid-April 2021.
13 APR 2021 | PNC. William County, VA | Stream Cruiser exuvia (face-head)
It’s easier to see the horn in the next photo…
13 APR 2021 | PNC. William County, VA | Stream Cruiser exuvia (dorsal)
The horn is clearly visible in the last photo. Notice there are three “bumps” located between the eyes of the exuvia: the middle bump is the horn; the antennae bases are located to the left and right of the horn.
13 APR 2021 | PNC. William County, VA | Stream Cruiser exuvia (dorsal)
Related Resources
Copyright © 2021 Walter Sanford. All rights reserved.
I have been working on the prototype for a homemade curved clear plastic tray that is intended for staging subjects against a white background.
My goal for Thursday: Test the prototype stage using a toy mini-lizard as the model for some test shots, and if the proof-of-concept were established, substitute an odonate exuvia for the toy lizard and shoot another set of photos.
16 SEP 2021 | BoG Photo Studio | toy mini-lizard
Well, you know what they say about the best laid plans! First, a line of fairly strong thunderstorms moved through the region where I live so I had to shut down my computer equipment. Second, the Washington Football Team played the New York Giants on Thursday Night Football so I had to watch the game. That’s right, had to watch. Turns out it was time well-spent.
Bottom line: I never finished the test shots of the toy lizard, and of course that means I didn’t shoot any photos of a real scientific specimen.
The curved surface of the clear plastic stage caused reflections from the single external flash that was used to light the subject. I had just figured out a work-around when the thunderstorms rolled in: I took 14 test shots; only the last one (shown above) is usable. I hadn’t intended to create a photo with a pure white background, but it was easy to adjust the image exposure during post-processing.
The Backstory
What’s my motivation? Many macro photographers use insect pins for mounting small subjects like odonate exuviae. I think there’s a big problem with that technique: The position of the pin is permanent. In other words, if the pin is attached to the ventral side of the specimen then it’s challenging at best and impossible at worst to take clean, clear shots of that side of the subject. I don’t want to use insect pins because some of my specimens are one of a kind.
For quite some time, I’ve been experimenting with the use of flat clear plastic stages as a solution for this problem. I think a curved stage might be a breakthrough, but more testing is required to be sure.
For example, notice the color fringing near the tip of the lizard’s tail — I’m not sure what caused that problem in only one part of the photo, therefore I don’t know how to fix it. Yet.
To be continued. Please stay tuned.
Copyright © 2021 Walter Sanford. All rights reserved.
The following photograph shows the relative size of odonate exuviae from two species in the Genus Anax: junius; and longipes. Both specimens are from the Family Aeshnidae (Darners).
Relative size of exuviae from Anax junius versus Anax longipes.
The Common Green Darner dragonfly (Anax junius) exuvia was collected on 17 June 2021 from a small pond at an undisclosed location in Prince William County, Virginia USA.
The Comet Darner dragonfly (Anax longipes) exuvia was collected by Stanley Caveney on 19 July 2021 from a pond at MeadowWoods in West Elgin, Ontario, Canada.
Taxonomy
There are five species of dragonflies in the Genus Anax for the United States and Canada: Amazon Darner (Anax amazili); Common Green Darner (Anax junius); Comet Darner (Anax longipes); Giant Darner (Anax walsinghami); and Blue-spotted Comet (Anax concolor).
Common Green Darner and Comet Darner are the only species from the Genus Anax found where I live in Northern Virginia USA.
Related Resources
Copyright © 2021 Walter Sanford. All rights reserved.
An odonate exuvia from a Comet Darner dragonfly (Anax longipes) was collected by Stanley Caveney on 19 July 2021 at MeadowWoods in West Elgin, Ontario, Canada.
This specimen is from Family Aeshnidae (Darners), as indicated by the following field marks: the exuvia has a flat labium that doesn’t cover the face (not mask-like); the antennae are thin and thread-like (not club-like, as in Gomphidae larvae/exuviae); and the eyes are large relative to the size of the head.
19 JUL 2021 | Ontario, Canada | Comet Darner exuvia (lateral view)
Lateral spines along abdominal segments seven, eight, and nine (S7-9) indicate the genus is Anax; the length of the exuvia indicates longipes (~6 cm, measured as is).
The Backstory
Stanley Caveney is shown in the first of several photos taken by Hugh Casbourn. Stan contacted me for confirmation of his tentative identification of several Comet Darner exuviae that he collected during July 2021. Stan kindly gave one of the exuviae to me.
Photo used with written permission from Hugh Casbourn.
I asked Stan whether he had taken photographs of the Comet Darner exuviae in situ. Stan hadn’t, so he and Hugh revisited a local pond where they searched for and found two more exuviae.
How many exuviae do you see in the next photo? Look closely — both cast skins are shown in the same image.
Photo used with written permission from Hugh Casbourn.
An exuvia from a female Comet Darner appears in the foreground of the preceding photograph…
Photo used with written permission from Hugh Casbourn.
and a male Comet Darner appears in the background.
Photo used with written permission from Hugh Casbourn.
I asked Stan for advice regarding where to look for Comet Darner exuviae.
The six exuviae found to date were mainly at the inner edge of the cattail beds, facing the open water of the pond and where the individual cattail plants were spaced out. Source Credit: Personal communication from Stanley Caveney.
Related Resource: Identification Keys to Northeastern Anisoptera Larvae, compiled by Ken Soltesz. Refer to pp. 21-22.
Editor’s Note: Sincere thanks to Derek Caveney, Stan’s son, for shipping the exuvia to me. The specimen was packed so carefully that it arrived in excellent condition, as you can see in the first photo in this blog post. I’m looking forward to shooting a complete photo set of the exuvia.
Copyright © 2021 Walter Sanford. All rights reserved.
I spotted an odonate exuvia along the shoreline of a small pond at an undisclosed location in Prince William County, Virginia USA that was collected by Mike Powell, my good friend and photowalking buddy.
This specimen is from the Family Aeshnidae (Darners), as indicated by the following field marks: the exuvia has a flat labium that doesn’t cover the face (not mask-like); the antennae are thin and thread-like (not club-like, as in Gomphidae larvae/exuviae); and the eyes are large relative to the size of the head.
17 JUN 2021 | PNC. Wm. County | Anax junius exuvia
Lateral spines along abdominal segments seven, eight, and nine (S7-9) indicate the genus is Anax; the length of the exuvia indicates junius (greater than ~4 cm, measured as is).
Common Green Darner dragonfly (Anax junius) is one of the more common species of Aeshnidae found in Northern Virginia.
Related Resource: What is it?
Copyright © 2021 Walter Sanford. All rights reserved.
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