ZEBRAS: A GRADATIONAL GENETIC CONCEPT

Zebras are highly recognizable because of their stripes. These animals are perissodactyl equines native to southern Africa, in regions other than deserts and rainforests. They all belong to genus Equus, which includes horses, donkeys, zebras, and asses. Zebras have excellent hearing and eyesight, and they are highly social animals; thus, they have sophisticated communication sounds. If necessary, they can run at speeds about 35 to 40 miles per hour. They are constantly on-the-move to find fresh grass and water, and sometimes, they gather in huge herds of thousands of individuals. Their lifespan in the wild is about 20 years, but, in captivity, they can live up to 40 years (Wikipedia).

During the Pleistocene, enormous herds of horses once lived in Europe, Asia, Africa, and North and South America. Those in the America’s and in Europe eventually died out, leaving abundant zebras only on the plains of Africa, plus some rare forms in Asia, e.g., the Asiatic onager (Fenton and Fenton, 1989, p. 579). Until recent years, it has been reported that there are three living species of zebras. Equus quagga, also called the “plains zebra,” is the most common and widespread. According to Pedersen et al. (2018), at least 600,000 plains zebras currently inhabit the African savannahs. These animals can be up 880 pounds. This species has also been referred to as burchellii, but the name quagga has taxonomic priority.

Equus quagga displayed in the Age of Mammals Exhibit Hall at the Natural History Museum of Los Angeles County, southern California (nhm.org). Image taken by the author.

The other two “species” of zebra are Equus zebra, also called the “mountain zebra,” is only up to 620 pounds and lives only in southwest Africa; and Equus grevyi, which is the rarest and weighs the most (up to 990 pounds). It is restricted today to a very small area in south-central Africa.

Early classifications of zebras were based on features, such as skull dimensions, presence or absence of a mane, and stripe pattern. These early classifications resulted in various numbers of species ± various numbers of subspecies. A modern-day DNA study (Pederson et al., 2018), however, supports variations in zebra populations being clines rather than species or subspecies. In biology, a cline is a measurable gradient in a single characteristic biological trait of a species across its geographical range. Clines can be smooth, continuous gradation, or more abrupt changes from one geographic region to the next. Thus, clines do not equal taxonomic recognition in the way species or subspecies do. This 2018 DNA study shows, furthermore, that there are nine populations of zebras, and only two of these overlap with traditional categorizations (one of which is the quagga population = the largest population and most distinct population, which originated in South Africa around 370,000 years ago). The population genetic structure does not mirror the traditionally reported, morphological-based subspecies delineations. 

References Cited: 

Casper–Emil, T. Pedersen and seven others. 2018. A southern Africa origin and cryptic structure in the highly mobile plains zebra. Nature Ecology and Evolution, v. 2, pp. 491–498. (pdf available online for free)

Fenton, C.L. and M.A. Fenton. 1989. The fossil book-a record of prehistoric life. Doubleday, New York, 740 pp.

Wikipedia.org

A REMARKABLE EXAMPLE OF A SPECIES PAIR

Species pairs are two species that closely resemble one another in morphology and are similar in geologic age, yet these species can have lived in geographically far-apart areas.

An excellent example of a species pair are two species of the cassid warm-water, shallow-marine gastropod Galeodea. This genus lived only during the early through middle Eocene time. One species (shown on the right side of the following diagram) is Galeodea turneri Gardner, 1939, which lived during the early Eocene in eastern Texas. The other species (shown on the left) is Galeodea sutterensis Dickerson, 1916, which lived during middle Eocene (approximately 50 million years ago) in California. 

Comparison of the close morphology of the front and back views of the east Texas G. turneri versus similar views of the California G. sutterensis.

The presence of these two species is indicative that the waters where they lived were once connected. During the time that they lived, there was an open connection between Texas and southern California. In addition, this connection extended up along the eastern seaboard area of North America, across the then much narrower Atlantic Ocean, and eastward into the Tethys Sea, including southern England and the Paris Basin, France. The Tethys Sea closed up following Eocene time when Africa and India collided with Eurasia. 

Reference Cited:

Squires, R.L. 2019. Revision of Eocene warm-water cassis gastropods from coastal southwestern North America: Implications for paleobiogeographic distribution and faunal turnover. PaleoBios 36L1-22, figs. 1-5.

 FAUX DIAMOND CRYSTAL PAPERWEIGTHS

These glass (silica) paperweights are popular in “curio shops” because of their vivid colors and multi-faceted surfaces. One side is flat, and the opposite side is pointed. Most are 5 cm in width (as for the examples shown below), but larger sizes (8 cm width) are available. They have great “eye appeal,” to the consumer. I know this because many years ago I purchased several (normal size) in order to obtain a full range of their colors. I also know that some mineralogists frown on anyone who buys these items.

The paperweighs are artificial but look like real crystals. The are made out of melted glass (silica). Some are colorless (these can be referred to as “rock crystal,” but most are solid-colored (e.g, pink, red, yellow, green, blue, purple). I searched online in order to find out how they are manufactured, but I could not find out any details. I also tried to find out where they are made, but this information is very scarce. So my searches were largely futile. I surmised that they are made from melted glass with elements (in powdered form--as oxides) added to create certain colors. I did detect one manufacturer (Pujiana Hongdingwang Houseware Company in Pujiana Country, Zheijiang Province of China), but no information was provided by them in terms of how they make these “crystal diamond” paperweights.

                                         red paperweight

pink paperweight

                                       yellow paperweight

                                          orange paperweight

                                          green paperweight

blue paperweight

                                         purple paperweight

                                                     

                                          clear paperweight

Chemical elements (mostly as oxides) produce which color when added to the melted silica. These elements are summarized below:

Red–add iron, cadmium, or lead.

Yellow Color/Amber–add sulfur or cadium.

Green–add chromium

Blue–add cobalt, iron, or manganese.

Light blue–copper

Purple–manganese, or nickel-cobalt

White–add tin 

 MARBLES

Marbles have been “around” (no pun intended) for centuries, and their colors appeal to both young and old. I played with marbles when I was a child, and, fortunately, I kept a small sack of them, thus “I did not lose all my marbles.”

I know that vintage marbles are worth considerable money, especially if you have rare ones. So I looked at my very small collection and tried to evaluate it. I soon discovered that evaluation is not an easy task. After considerable effort (by viewing several videos on “You Tube”), I am only very tentatively confident about my evaluations. Apparently, I have marbles that were made in the 1950’s, thus they have only moderately low value, but they are still fun to have.

YouTube has some really good videos about how marbles are made. Some of the ones being made today show considerable interior complexity and are time-consuming to make. If you are interested in evaluating your marble collection, good luck and have fun.

Marbles are made from silica sand, mixed with both a flux (e.g., potash) to help the mixture flow more easily at lower temperatures and also a stabilizer (e.g., calcium carbonate) to help chemically stabilize the mixture . The colors, like those found in faux crystals, are created when the artisans that make the marbles add different metals (in powdered form) to the molten glass (e.g., copper imparts a light blue color, chromium imparts an orange color). The interior complexity is all hand-done, while the glass is still very hot.

                          Examples of "solids" in my collection

                                                  "swirls"

                                          "clears" or clearies"

                                                "cats eyes"

                             "unusual" marbles in my collection

If you are are a subscriber to “National Geographic Magazine,” it recently (February, 2024) had a very informative article called “The Class Age.”

To see an informative video about how marbles are made, copy and then paste the following website into your browser:

https://www.youtube.com/watch?v=M4Pe-w9vXhg

VENUS FLOWER BASKET: NOT AN ORDINARY SPONGE

The use of the name “Venus Flower Basket” as used in this blog refers strictly to the living species of Euplectella aspergillum. I had to make this disclaimer because the common name “Venus Flower Basket” sponge has been broadly applied in the published literature to several loosely defined “euplectellid sponges” that encompass a span of geologic time ranging from the Late Ordovician age to present day. 

CLASSIFICATION

Phylum Porifera (= sponges)

Class Hexactinellidae

Family Euplectellidae

Genus Euplectella

Species aspergillum  Owen, 1841

Note: There is no known fossil record of Euplectella aspergillum. The family Euplectellidae (used in the broadest sense) has a sparse record from the Middle Cretaceous onward (Botting et al., 2022). 

HABITAT: 

Deep-marine (100 to 1000 m depth = 330 feet to 3300 feet; commonly below 300 m).

Western Pacific (especially the Philippine Islands and Japan) and also Indian Ocean.

Lives on muddy sediments on the ocean floor.

MORPHOLOGY:

The walls of this sponge are highly porous. Its tubular body (exoskeleton) is made up of numerous small, siliceous six-pointed spicules-interlocking so as to collectively form create a mesh-like vertical structure that allows ocean water to circulate through the walls. Flexible thin glassy fibers (2 to 8 inches long) anchor the sponge to the muddy ocean floor. The top of the tube also has a mesh-like lid.

OTHER:

The tubular body typically houses a pair of breeding “glass-sponge” shrimps. They are unable to leave the cylindrical tube, thus, they live their entire lives inside the sponge. In return, they clean the inside of tube. This is a mutualistic relationship. In Japan, this sponge (with the shrimp inside) is often given as a wedding gift to newlyweds–– as a symbol of undying love. 

The long fibers anchoring the sponges to the ocean floor are of interest to researchers looking for more efficient, low-cost solar cells or considering new materials to be used for other engineering applications.  

References Consulted:

Botting, J.P. et al. 2022. Extraordinary early Venus’ flower basket sponges (Hexactinellidae from the uppermost Ordovician Anji Biota, China. Palaeontology 65, issue 2. (pdf costs $). 

en.wikipedia.org