Sunday, February 11, 2018

Mystery sand spheres


A fellow geologist recently sent me the following pictures and information about "sand spheres" he found in the general area of the shoreline region of the late Pleistocene Lake Manix, in the Mojave Desert, between Barstow and Baker, southern California. Lake Manix formed by overflow of the Mojave River between 500,000 and 25,000 years ago.


The spheres are all of small size and range from 0.51 to 1.5 cm in diameter (e.g., they are about the size of a U.S. dime). They consist of friable (= fragments come loose from the spheres when rubbed) and angular, coarse-grained material called grus, which results from the granular disintegration (weathering) of granite in an arid climate. The material making up the spheres is slightly cemented by calcium carbonate. 



The above picture is a cross-section of a sliced sphere. Compared to armored mud balls, the "sand spheres" do not have a mud core and are too uniformly of small size. Armored mud balls form when a clump of gooey mud begins to roll around under a flow of water and fragments of rock adhere to the mud surface.



The "sand spheres" shown above, in the background, might have formed in place. The "loose" ones in the foreground are derived from this more concentrated mass of them.




If you "lean in" on this far-away shot, you can make out how numerous the small spheres are (thousands and thousands) among the much larger fragments of angular rock. The "sand spheres" litter the ground sort of like rabbit or deer droppings. 

The "sand spheres" are at an elevation of 563 m, which is slightly above the Pleistocene shoreline, thus they were most likely not formed by a shoreline process. There has not been any lake water at this elevation in 18,000 years. The "sand spheres" look fairly fresh. They are on the surface and although they are not very delicate, thus it is doubtful that they have been around since the Pleistocene. My colleague believes that they might be a product of a local (recent?) downpour. 

Although the nonmarine "sand spheres" of Lake Manix resemble "sand balls" created by small "bubbler" crabs on modern beaches in the tropical ocean waters of the Indo-Pacific, they cannot share the same origin. By the way, if you have the interest you will be amazed and amused by a BBC Blue Planet video (online) that shows how these crabs form the "sand balls."

In closing, we do not know the origin of these Lake Manix spheres and could not find anything in the literature about them. Determining how they formed would be a worthy project. 

Saturday, January 27, 2018

Bursa californica: a fossil and modern-day gastropod

Bursa californica (Hinds, 1843) is a modern-day, shallow-marine gastropod (ocean snail), whose fossil record goes back to the early Pliocene (about 3 million years ago).

Genus Bursa Röding, 1798 belongs to the small family of large sea shells called Bursidae. Their common name is "frog shells" because the intersection of spiral and transverse ribs can result in a strong nodulose pattern of many knobs, producing a "warty" or "frog skin" appearance.

Bursa californica, also known as the "Californian Frog Shell," is characterized by having mostly two protruding ridges (varices) along the left and right margins of the shell. Nevertheless, the warty appearance is not evident on this particular species. 

Bursa californica is found from Monterey, along the central coast of California, to the Gulf of California, mainly in offshore waters. The animal lives mostly on silty-sand bottoms in depths of about 60 to 350 feet. They are active predators and feed on bristle worms (polychaetes), which they anesthetize with acidic saliva. After a storm, some of the shells can wash up on an adjacent beach. The shell is tan-cream in color with a whitish aperture (opening).


Apertural view (front) of a modern specimen
(9 cm height) from Mexico.
Abapertural view (back) of same specimen
Apertural view of a fossil specimen
(8 cm height) from Palos Verdes Sand,
late Pleistocene, Playa del Rey,
 southern California.
Abapertural view of same specimen.




Top view of spire of same specimen.



A growth series (juvenile to adult) of fossi specimens
of Bursa californica from Palos Verdes Peninsula, southern California.
Specimens 2.7, 5 cm, and 8 cm high.


Friday, January 12, 2018

California's Official State Dinosaur

In 2017, the State of California declared its official state dinosaur to be Augustynolophus morrisi Prieto-Márquez et al. (2014), a duck bill of Late Cretaceous age. Duck bills are classified as hadrosaurs.
The generic name, Augustynolophus Prieto-Márquez et al., 2014, is a combination of the Augustyn family, who helped support the Los Angeles County Museum of Natural History, and the suffix “lophus,” in reference to its similarity to Saurolophus, another duckbill, 30 to 40 feet in length, bipedal, and with a battery of flat teeth used for chewing coarse vegetation.  

Augustynolophus, like Saurolophus, has a bony, spikelike crest that projects up and back from the top of the skull. This spike is an extension of the nasal bones.

Augustynolophus morrisi is of late Maastrichtian age, about 68 million years old. The geologic time diagram below depicts the recognized intervals of time that constitute the Late Cretaceous. The Maastrichtian was the last stage of the Late Cretaceous. The red star indicates the approximate occurrence of this dinosaur.


















The bones of A. morrisi have been found in the Moreno Formation along the west side of the San Joaquin Valley, Fresno County, central California.

In terms of vertebrate (back-boned) fossils, the Moreno Formation is mainly known for its marine-reptiles (plesiosaurs and mosasaurs). It also contains marine-mollusk fossils (oysters, other bivalves, and gastropods). Augustynolophus morrisi lived in a  marshy, coastal area.

Augustynolophus morrisi is endemic (only found) in California.
For excellent copyrighted pictures of this dinosaur, also known as "Auggie," just "Google" its scientific binomial (two-part) name.

The species name, morrisi, is in honor of the late William J. Morris (1923-2000), a highly respected vertebrate paleontologist who had many dinosaur and other vertebrate-fossil discoveries on the west coast of North America, especially in Baja California, Mexico. His final teaching position was at Occidental College in the Eagle Rock neighborhood of Los Angeles, California. He was also a Research Associate in Vertebrate Paleontology at the Natural History Museum of Los Angeles County.


If you want to see  the entire list of official California names of other geologic entities, go to <en.wikipedia.org>, and click on the associated thumbnail images in order to see larger images. 

Thursday, December 28, 2017

An Eocene crab from southern California

If a collector is fortunate, some localities yield a few fossil crabs. This post is about a species of crab, Orbitoplax weaveri (Rathbun, 1926) which can be found in Eocene (approximately 50 million year old) rocks on the west coast of the United States, from southwestern Washington to southern California.

Orbitoplax weaveri is the updated genus name of this crab. It has been erroneously placed in other genera, thus in the older literature this species was called Plagiolophus weaveri and then Glyphithyreus weaveri.

The main part (carapace) of this recently collected specimen is 22 mm (nearly an inch) wide. There are also parts of three of its legs on the left side of the specimen. The collector who found and photographed the specimen kindly gave it to me.


This is another picture of the carapace of the same specimen, after it was removed from the rock. This picture was taken under low-angle lighting to show the sculptural details.


This is another and larger (main part 25 mm) specimen of O. weaveri, which I collected many years ago from the same locality as the one shown above. Its right pincher is intact. Also, a impression of the claw part of the left pincher is present. The total width (from left to right) of the specimen is 55 mm. 

Complete or nearly complete crabs like the ones shown above are typically found in silty sands, which were deposited under relatively quiet-water conditions. Just down section a few meters, there are storm beds with numerous Turritella gastropods, whose shells display preferred orientation caused by current action.

Monday, December 11, 2017

A 50-million year old chambered nautiloid shell

The living "pearly nautilus," also called the "chambered nautilus," is a favorite seashell of many collectors. Today, the biodiversity (number of species) of these animals is very low, and they are confined to tropical waters in the equatorial region of the western Pacific. As certain times in the geologic past, however, when warm oceans extended north and south of where they are now, chambered shells similar to the "pearly nautilus" had high biodiversity, and their distribution was widespread (cosmopolitan). These chambered shells are commonly referred to as coiled nautiloids.

On August, 2016, I created a post about the "pearly nautilus," and two of my pictures are shown again here for comparative purposes. I encourage you to use the "search box" at the top right-hand side of this blog page to find this post and read it again. I also give some interesting details about the life habits of this animal.

Exterior of a modern-day "pearly nautilus."
            Maximum diameter is 14 cm


Interior of same specimen shown above 

This present post concerns one of these ancient widespread groups of coiled nautiloids, namely, an extinct genus belonging to genus Aturia Bronn, 1838.  It was widespread (cosmopolitan) and its geologic time range was Paleocene to Miocene (approximately 40 million years long).

In particular, this post is about Aturia myrlae Hanna, 1927, an early to middle Eocene species of genus Aturia. The ancient geographic distribution of this species covered an area now referred to as central California, southern California (including Ventura, Los Angeles, and San Diego counties), and Baja California Sur, Mexico. Aturia lived in subtropical to tropical ancient environments. So, if you are lucky enough to find one of these fossils, you can be certain that it represents a warm-water ancient environment. Specimens are not that common because, like other coiled nautiloids, Aturia was a predator, thus, their numbers were few.

The next three pictures show a partial specimen of Aturia myrlae from Simi Valley, southern California. The widest dimension (diameter) of this incomplete specimen is 14 cm. 


Side view showing the complex outlines (septal pattern or suture pattern) of the chamber walls (septa). The suture pattern of Aturia is a very distinctive character of this genus and is in sharp contrast to the simple-curved suture pattern of the "pearly nautilus," which belongs to genus Nautilus.

Back side view of the same specimen. 

Front view of the same specimen. Notice the presence of the siphuncle (see a reference picture at the beginning of this post), which was a hollow tube that connected all the empty chambers and allowed for nitrogen gas to be dispersed to all the chambers. In so doing, the shell achieved buoyancy when the gas was pumped in, and the shell sank when the gas was pumped out. The shell could, therefore, move up and down in the water column.

Monday, November 27, 2017

Colors of scallops

If you have been reading my latest posts, you will know that I have been focusing on colors in certain minerals. In this present post, I shall discuss colors of certain clams called scallops, which belong to the family Pectinidae. The family is comprised of many genera.  Those belonging to genus Pecten are called pectens (not: pectins, which refers a group of colloidal substances used to jell various foods or cosmetics). 

Pectinids are especially abundant as fossils, if found in the right environment. Their geologic time range is Triassic to modern day. Along the west coast of the USA, fossil pectinids are  common in sediments of Miocene and Pliocene age (20 million to about 3 million years ago). Today, the strong muscle that holds the two valves together is a popular seafood delicacy. 


The two valves of a pectinid are referred to as the left and right valves. 

In addition to the primary (radial) ribs, important morphologic parts of a pectinid are the auricles ("ears") along the hinge line. As shown above, on the right valve, the anterior auricle is the most elongate. On some pectinids a byssal notch is located directly below the elongate anterior auricle. This notch is where the byssus (a bundle of hairlike material used for attachment) exits the shell.


Today, there are approximately 250 species of pectinids. Some have shells which are bright orange, yellow, red, blue, purple, brown, white, or combinations thereof. This color variation comes mainly from heredity although environment can play a role (e.g., some muddy-bottom pectinids have darker color than sandy-bottom pectinids.


The four colored specimens (each one is about 5 cm width) shown above are of species of the pectinid Chlamys, and they show some of the variation in the color. Some people think that they are hand painted, but the colors of these specimens occur naturally. Chlamys lives by having its byssus attached to a rock, shell, or other hard surface.


These are the right (= the specimen on the left side of this image) and left valves of a modern specimen of Chlamys hastata (2.7 cm wide), dredged from 210 feet depth, at the shelf break just south of Long Beach, southern California.

Nodipecten subnodosus, 15 cm wide, exterior and interior of a right valve. This species is most commonly found in modern waters in the Gulf of California, Mexico.

Nodipecten has been observed anchored by a byssus to hard substrates, but they have been observed also to have the ability to swim for short distances. At least temporarily, therefore, they are not anchored by a byssus. Thus, its byssal notch is not well developed. Nodipecten swims by pulsatory clapping together of their valves. This swimming action is exhausting and cannot be sustained for very long; it is normally used only to escape from predators (e.g., sea stars).


Patinopecten caurinus (Gould, 1850), 16.5 cm wide, exterior of a large right valve modern-day specimen from Skagway, Alaska. Patinopecten has a well developed byssal notch, therefore, it lived by attaching to hard surfaces. 


Patinopecten caurinus, 16 cm wide, exterior of a large right valve fossil specimen from a late Pliocene (3 million years old) bed found between Goleta and Santa Barbara, California. If you look carefully, you can see the minute daily growth lines of this shell.

Saturday, November 11, 2017

Barnacles make interesting fossils

Barnacles are classified as cirriped crustaceans and belong to phylum Arthropoda (a large group that also includes trilobites, crabs, insects, etc.). The name "cirriped" (cirri, curl; ped, foot) refers to the six pairs of delicate appendages which are used for filter feeding.

Barnacles are not very different from other arthropods in that they hatch as an egg, have a short existence as free-swimming larval forms, and molt (shed) to grow larger. In adult life, however, barnacles do not resemble other arthropods at all. With a shelly (calcareous) covering of many plates enclosing their shrimp-like body, most barnacles grow attached to hard substrate. Genus Megabalanus Hoek, 1913one of the so-called “acorn" barnacles, is common in the fossil and modern-day record of the eastern Pacific. 

Few people know that Charles Darwin, yes, that Charles Darwin, was an expert on barnacles. He derived some of his concepts about evolution based on his detailed studies of them.

bivalve shell is 3.4 cm in diameter
A bivalve shell (the "jingle" shell Anomia) with a large Megabalanus base (circular) at the top of the shell and 15 Megabalanus shells elsewhere on the shell. These fossils are of late Pleistocene age from the vicinity of Long Beach, Los Angeles County, southern California.

large barnacle is 1.5 cm high 
Megabalanus shell encrusting a shallow-marine gastropod shell, and a small Balanus shell encrusting the larger Megabalanus shell. All of these fossils are of late Pleistocene age from the same locality as those shown in the previous image.

acorn-barnacle operculum: smaller parts are 4.5 mm length;
 larger parts are approximately 5.5 mm length
Covering the top of an acorn-barnacle shell is a calcareous structure consisting of four interlocking plates. These two pairs of plates close together, just like a tight-fitting “lid,” used when the barnacle is not feeding or when it is disturbed. The opercular plates, which show continuous growth records (like tree rings) and are not shed during molting. Upon death of the animal, these plates eventually fall apart, thus they are mostly missing on fossil barnacles. The pair of plates shown (above) on the left are called terga, and those on the right are called scuta.

cluster is 2.2 cm wide
 The image shown above is a small cluster of modern-day barnacles with their opercular plates in life position. These are specimens of Balanus amphitrite saltonensis Rogers, 1949 from the Salton "Sea," an inland lake with very salty waters in southeastern California. This lake was created by accident in the early 1900's, when an aqueduct overflowed. This subspecies of barnacle, which is closely allied to the globally widespread B. a. amphitrite Darwin, 1854, was  introduced into the lake. This introduction was most likely via  migratory water birds.

cluster is 21 cm in maximum dimension
A cluster of five large-sized Tamiosoma gregarious from Pliocene rocks in the central San Joaquin Valley of central California.



each component is 2.8 cm length
These four images above show the exterior (above) and the interior (below) of two scuta of Tamiosoma gregarious found in Pliocene beds in the central San Joaquin Valley of central California. These are unusual finds.

2.6 cm height
This is the side view of a modern-day "gooseneck" barnacle (Pollicipes polymers) from a rocky intertidal zone in the vicinity of Goleta, Santa Barbara County, California. Notice the leathery stalk (pedicle) which is used by the barnacle to attach to rock. The stalk does not get preserved, thus, in the fossil record all one can find are the individual calcareous plates that make up the upper part of the animal.

The geologic time range of barnacles is Paleozoic (Silurian) to Holocene [= modern day]. Gooseneck barnacles evolved first. "Acorn" barnacles did not appear until the early Cenozoic.

3.5 cm maximum diameter
Lastly, I show an image of the barnacle genus Chelonibia, which attaches to the carapaces of sea turtles. This modern-day specimen is from Baja California Sur, Mexico.