Archive for the ‘natural science’ Category

Fossil shark tooth, revisited

June 10, 2022

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.

Fossil shark tooth

June 3, 2022

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.

Happy summer!

June 1, 2022

01 June is the first day of summer. What? Perhaps you’re thinking, no that’s incorrect — the first day of summer is on the day of the June Solstice that occurs annually around 21 June. Well, as it turns out both of us are correct.

Atmospheric scientists, including climatologists and meteorologists, define summer as the three-month time period that includes June, July, and August. Astronomers define summer as the three-month time period from the June Solstice to the September Equinox.

Now you know. Again I say, Happy summer!

Related Resource: The Seasons, the Equinox, and the Soltices (by the National Weather Service).

Copyright © 2022 Walter Sanford. All rights reserved.

RadarScope app

May 27, 2022

RadarScope, one of my favorite apps for Apple iOS devices, is a full-featured app that provides access to nearly the entire suite of Doppler weather radar products generated by the National Weather Service.

As a wildlife photographer I use RadarScope to make go/no-go decisions for photowalking outings. And when I’m already in the field, I use the app to decide whether it’s time to seek shelter from pop-up thunderstorms.

As a weather enthusiast, RadarScope enables me to track the approach and passing of weather systems such as the line of strong thunderstorms that affected the Washington, D.C. metropolitan region on Friday, 27 May 2022.

Composite Reflectivity

The first image shows “Composite Reflectivity.” This is the same type of weather radar imagery that has been used by TV weathercasters for years. In a nutshell, composite reflectivity shows precipitation intensity within range of a weather radar site, in this case KWLX — the NWS Forecast Office located in Sterling, Virginia.

27 MAY 2022 | 10:29 AM EDT | KWLX Sterling

Notice the line of heavy precipitation, indicated by a narrow band of red radar echoes, just to the west of my location in suburban Washington, D.C. (see blue reticle at the center of the screen). Forecast storm tracks (see incremented white lines) indicate individual storm cells are moving generally from southwest to northeast.

To view storm tracks in RadarScope, tap the settings icon in the lower right of the screen, then choose Layers and turn on the Storm Tracks option. The estimated times of arrival can be seen by touching anywhere along the track. Source Credit: RadarScope: How are Storm Tracks Computed? [Editor’s Note: In my experience, this feature works only when I tap the white circle at the origin of each storm track.]

Storm Relative Velocity

Storm Relative Velocity” shows the wind velocity in a storm minus the forward motion of the storm. Greens show motion toward the weather radar site; reds show motion away from the radar (like car tail lights).

27 MAY 2022 | 11:21 AM EDT | KWLX Sterling

Look closely at the full-size version of the preceding image. Notice the yellow polygon located between Beaverdam and Fredericksburg, Virginia that delineates the boundaries of a severe thunderstorm warning area.

There is a red polygon (located inside the yellow polygon) that represents a tornado warning area. Within the boundaries of the red polygon, notice the juxtaposition of greens and reds — a good indicator of counterclockwise rotation in a storm cell. As it turns out, there were several official reports of a tornado on 27 May 2022 in the same location as indicated by the NWS Doppler weather radar.

It’s important to note that the orientation of side-by-side greens and reds typical of rotating thunderstorm cells varies depending upon the location of the storm cell relative to the weather radar site. In the example shown above the greens are on the right and the reds are on the left because the warning area is located to the southwest of KWLX. In contrast, if the warning area were located to the northeast of the radar site, then the reds would be on the right and the greens on the left.

Related Resources

The following resources from the National Weather Service provide excellent background information about Doppler weather radar.

RadarScope features good in-app documentation, as evidenced by the following screen captures.

RadarScope | Help

RadarScope | User’s Guide

RadarScope | User’s Guide – Velocity Products

The same resources (and more) are available online.

Copyright © 2022 Walter Sanford. All rights reserved.

 

Jumping spider

March 15, 2022

The following photo shows a tiny spider carcass (~3/16″ long) that was inside an exuvia (~1 3/4” long) from a Common Green Darner dragonfly (Anax junius). The exuvia was collected on 17 June 2021 from a small pond in Prince William County, Virginia USA. I discovered the spider long afterward — too late to save its life.

17 JUN 2021 | PNC. Wm. County, VA | Jumping spider

Thanks to Eva Weiderman and Joseph Girgente — members of the “Odonate Larvae and Exuviae” Facebook group — for their help in identifying the specimen as a jumping spider, Family Saticidae.

Salticidae is one of several families of spiders with eight (8) eyes. My take-away from reading the reference on BugGuide entitled “Spider Eye Arrangements” is identification of this specimen to the genus and species level is challenging at best and impossible at worst.

In contrast, it’s well known that spiders use odonate exuviae for shelter. I wish the jumping spider had come out of its most excellent hidey-hole sooner!

17 JUN 2021 | PNC. Wm. County, VA | Anax junius exuvia

Related Resources

Tech Tips

The tiny jumping spider was photographed using a Panasonic Lumix FZ-300, Raynox DCR-250 close-up filter, Godox X2To/p flash trigger, and Godox TT685F plus Altura flash modifier. Camera settings: ISO 100 | f/7.1 | 1/60 s | 56.9mm (316mm, 35mm equivalent).

Raynox DCR-250 close-up filter” is a blog post in which I provide more information about how I use the Raynox with my Panasonic Lumix superzoom bridge cameras.

Copyright © 2022 Walter Sanford. All rights reserved.

Twin-spotted versus Brown Spiketails

February 8, 2022

Four species of genus Cordulegaster are found in the Commonwealth of Virginia: Brown Spiketail (C. bilineata); Tiger Spiketail (C. erronea); Twin-spotted Spiketail (C. maculata); and Arrowhead Spiketail (C. obliqua).

According to the excellent datasets for the Commonwealth of Virginia by Dr. Steve Roble, Staff Zoologist at the Virginia Department of Conservation and Recreation, Division of Natural Heritage, the adult flight periods for spiketail dragonflies are as follows.

MAR 16 – JUL 10 = Twin-spotted

MAR 28 – AUG 08 = Brown

MAY 11 – JUL 17 = Arrowhead

MAY 28 – AUG 22 = Tiger

As you can see, there’s a lot of overlap between the flight periods for Twin-spotted Spiketail and Brown Spiketail. Also notice the overlap between the flight periods for Arrowhead Spiketail and Tiger Spiketail.

I think we can agree the distinctive arrowhead-shaped yellow markings on the abdomen of Arrowhead Spiketail (shown below) are unmistakeable for any other species of spiketail, including Tiger Spiketail.

07 JUL 2014 | Fairfax County, VA | Arrowhead Spiketail (male)

In the opinion of the author it’s more likely a dark-colored Brown Spiketail, such as the one shown below, might be misidentified as a Twin-spotted Spiketail.

02 MAY 2019 | Fairfax County, VA | Brown Spiketail (male)

Differentiating Twin-spotted versus Brown

Twin-spotted and Brown Spiketail dragonflies can be differentiated by looking closely at the yellow markings on abdominal segments one through three (S1-S3).

07 MAY 2018 | Fairfax County, VA | Twin-spotted Spiketail (male)

The pattern of yellow markings on S1-S3 is simpler for Twin-spotted than Brown, as you can see by looking at the full-size versions of these two photos, shown above and below.

11 MAY 2018 | Fairfax County, VA | Brown Spiketail (male)

Female Twin-spotted versus Brown

Female Twin-spotted Spiketails, such as the one shown below, have a much longer subgenital plate (ovipositor) than female Brown Spiketails.

Photo used with written permission from Mike Boatwright.

The subgenital plate for the following female Brown Spiketail is barely visible.

09 MAY 2013 | Fairfax County, VA | Brown Spiketail (female)

It isn’t a lot easier to see the subgenital plate in a close-up view of the same individual shown above.

09 MAY 2013 | Fairfax County, VA | Brown Spiketail (female)

Coach’s Corner

Thanks to Mike Boatwright, founder and administrator of the Virginia Odonata Facebook group, for coaching me up on how to differentiate Twin-spotted Spiketail from Brown Spiketail, including both males and females.

Look for yellow markings on the side of abdominal segments one through three (S1-S3): green arrows show the lack of yellow markings on S1-S3 for Twin-spotted; red arrows show yellow markings on the sides of S1-S3 for Brown.

Set 1

Twin-spotted Spiketail | male (dorsal view)

Photo used with written permission from Mike Boatwright.

Brown Spiketail | male (dorsal view)

Photo used with written permission from Mike Boatwright.

Set 2

Twin-spotted Spiketail | male (dorso-lateral view)

Photo used with written permission from Mike Boatwright.

Brown Spiketail | male (dorso-lateral view)

Photo used with written permission from Mike Boatwright.

What are the take-aways?

Remember the odonate hunter’s credo: Shoot first (photographs, that is); ask questions later. (Repeat it like a mantra.) Get a shot, any shot; refine the shot gradually.

Please don’t waste precious time in the field! You can study the photos when you return home in order to identify the subject(s) you shot as either Twin-spotted Spiketail or Brown Spiketail.

Copyright © 2022 Walter Sanford. All rights reserved.

Twin-spotted Spiketail (terminal appendages)

January 25, 2022

Male

All male dragonflies have three terminal appendages, collectively called “claspers,” that are used to grab and hold female dragonflies during mating: an upper pair of cerci (“superior appendages”) and a lower unpaired epiproct (“inferior appendage”).

Male members of the Family Cordulegastridae (Spiketails), including male Twin-spotted Spiketail dragonflies (Cordulegaster maculata), have relatively small cerci (terminal appendages) that can be mistaken for female cerci.

07 MAY 2018 | Fairfax County, VA | Twin-spotted Spiketail (male)

Male dragonfly secondary genitalia, called hamules, are located below abdominal segments two and three (S2 and S3), as shown in the following annotated image. Hamules come in a variety of sizes and shapes, but their function is identical for all species of odonates.

07 MAY 2018 | Fairfax County, VA | Twin-spotted Spiketail (male)

Female

As far as I know I have never seen a female Twin-Spotted Spiketail. (I have seen several individuals that I was unable to photograph.) No problem. Mike Boatwright kindly allowed me to annotate a couple of his photographs.

Photo used with written permission from Mike Boatwright.

These individuals are female, as indicated by their rounded hind wings, terminal appendages, and prominent subgenital plate (ovipositor) at the tip of their abdomen.

Photo used with written permission from Mike Boatwright.

Copyright © 2022 Walter Sanford. All rights reserved.

Arrowhead Spiketail (terminal appendages)

January 21, 2022

Arrowhead Spiketail dragonflies (Cordulegaster obliqua) were spotted along small streams at undisclosed locations in Fairfax County and Prince William County, Virginia USA.

Male and female Arrowhead Spiketails are similar in appearance. They can be differentiated based upon several field marks.

Male

This individual is a male, as indicated by his “indented” hind wings and terminal appendages.

07 JUL 2014 | Fairfax County | Arrowhead Spiketail (male)

Arrowhead male and female cerci are similar in appearance, and it can be challenging to see the epiproct clearly from some viewpoints. When in doubt whether an individual is male or female, look for indentations at the base of the hind wings of males.

07 JUL 2014 | Fairfax County | Arrowhead Spiketail (male)

Female

This individual is a female, as indicated by her rounded hind wings, terminal appendages, and prominent subgenital plate (ovipositor) at the tip of her abdomen.

21 MAY 2019 | PNC. Wm. County | Arrowhead Spiketail (female)

Although Arrowhead male and female cerci are similar in appearance, there is no mistaking the subgenital plate of female spiketails! It’s easy to see why “Spiketails” is the common name for Family Cordulegastridae.

21 MAY 2019 | PNC. Wm. County | Arrowhead Spiketail (female)

So the take-away is simple: If you see a subgenital plate then the individual is definitely female; if not, then it’s probably a male.

Copyright © 2022 Walter Sanford. All rights reserved.

The time is now!

January 4, 2022

Happy New Year! Let the yearning begin. Wait, what? Yep, I’m fighting feeling like I can’t wait for the start of the new odonate hunting season.

Realistically it will be a few months before adult dragonflies and damselflies are flying again, but that’s a good thing. Wait, did I just say that? Yes, and here’s why.

The odonate hunting “off season” provides a good opportunity to plan for the next campaign by making a list of target species and laying out when and where to look for them.

Why is it important to make a plan? Because the season starts slowly but explodes quickly. To illustrate my point, take a look at my Odonate Calendar for adult flight dates of dragonfly species for the month of February (shown below). Not much happening until the end of the month, right?

Dragonflies (VA Flight Dates) | February 2022

Now look at March (shown below). There’s an explosion of species beginning around the second week in March. The boom continues into July before slowing down noticeably in August.

Dragonflies (VA Flight Dates) | March 2022

Also notice many of the spring species of dragonflies are habitat specialists that require extra time and effort to find. So my advice is start planning now for a more productive and satisfying season of odonate hunting.

Related Resources

Both of the following resources feature online, interactive calendars for dragonflies and damselflies based upon Dr. Steve Roble’s excellent datasets for the Commonwealth of Virginia.

Copyright © 2022 Walter Sanford. All rights reserved.

New Life List additions in 2021

December 21, 2021

The anticipation of the hunt and the thrill of discovery — the adrenalin rush from finding new species of odonates is ever more elusive as one gains experience and expertise. Accordingly, the number of additions to my Life List is fewer year after year.

Selys’s Sundragon (Helocordulia selysii)

Selys’ Sundragon dragonfly (Helocordulia selysii) was spotted during a photowalk along a mid-size stream at an undisclosed location in Prince William County, Virginia USA.

This individual is a male with a malformed abdomen. Selys’s Sundragon is a new species for both my Life List of odonates and for Prince William County, VA.

13 APR 2021 | Prince William County, VA | Selys’s Sundragon (male)

Uhler’s Sundragon (Helocordulia uhleri) and Selys’s Sundragon are colocated at many sites — find one species and you should find the other. I’ve been on the lookout for Selys’s since Uhler’s was found several years ago near the site where this Selys’s was spotted.

Yellow-sided Skimmer (Libellula flavida)

Yellow-sided Skimmer dragonflies (Libellula flavida) were spotted around a small pond at an undisclosed location in Prince William County, Virginia USA.

The first individual is a female, as indicated by her terminal appendages.

17 JUN 2021 | PNC. Wm. County | Yellow-sided Skimmer (female)

The last individual is a male, as indicated by his blue coloration and terminal appendages.

17 JUN 2021 | PNC. Wm. County | Yellow-sided Skimmer (male)

Many species of dragonflies in the Family Libellulidae (Skimmers) are habitat generalists and relatively easy to find almost anywhere there is water. In contrast, Yellow-sided Skimmer is a habitat specialist that is challenging to find.

Tiger Spiketail (Cordulegaster erronea)

Tiger Spiketail dragonfly (Cordulegaster erronea) was captured along a small stream at an undisclosed location in Prince William County, Virginia USA. The specimen was photographed and released unharmed.

05 AUG 2021 | Prince William County, VA | Tiger Spiketail (male)

This individual is a male, as indicated by his hamules, “indented” hind wings, and terminal appendages.

05 AUG 2021 | Prince William County, VA | Tiger Spiketail (male)

“Sight records are insufficient” is one of many “Walterisms.” In other words, I don’t add a species to my Life List until I have photographed it. And so it is with Tiger Spiketail. I have seen several Tiger Spiketail dragonflies during the past few years (at several locations) but had no photos to show for my efforts because they are fliers rather than perchers.

Copyright © 2021 Walter Sanford. All rights reserved.


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