"Blind" trilobite Itagnostus from Utah

Trilobites like the one shown above are well known to most collectors of fossil invertebrates (animals without backbones). This trilobite, which is 4 cm long, has a cephalon or head (with eyes), a thorax (body with many segments), and a short pygidium ("tail"). This particular specimen is an Elrathia kingi of Middle Cambrian age (see time diagram below) from the Wheeler Shale near Delta, Utah.

Another type of trilobite found alongside E. kingi is Itagnostus interstictus, until recently known as Peronopsis interstrictus, which belongs to one group of so-called "blind" trilobites. Technically speaking, "blind trilobites" were not blind because they never had eyes. Itagnostus is an agnostid trilobite, which are characterized by having a thorax consisting of only two segments and a cephalon and pygidium of approximately the same size.

This is a "cluster" of two specimens of Itagnostus interstices. The largest specimen is nearly 1 cm  long. 

Scaphopod

This post concerns scaphopods, which are mollusks that belong to the same phylum as snails, squids, octopi, etc. Scaphopods are tusk-shaped shells that are partially infaunal, that is to say they burrow into the ocean floor but do not burrow deep enough to cover the top part of their shell.

The drawing shows how the shell projects into the sediment. The mouth is surrounded by feeding tentacles which bring microscopic-sized food to it. The gut is straight. Water is brought down into the shell and also is excreted through a hole at the top of the shell.

This is a fossil scaphopod of the Eocene Dentalium stramineum The specimen is 7 cm long and almost complete. It is from Simi Valley, southern California. Fossil scaphopods are not common. 

This is a modern specimen of Dentalium. If it were not for modern specimens, scientists would probably never have determined that these simple tubes were made by mollusks.

This is another modern specimen of Dentalium.

Molds and casts

This picture shows a specimen of the Eocene Turritella andersoni (height 7.5 cm) from southern California (please see one of my earlier posts if you want more information about this species). If the specimen is removed (i.e., is weathered away or simply fell out), it leaves behind an external mold = an impression of the external surface. This external mold is a negative surface, that is to say, it could literally "hold water." 

This next picture shows the external mold of the original specimen and, to the right, an external cast of this mold. Most collectors commonly do not bother to collect external molds. At some localities, however, that is all you can find, and if you need to identify the genus and species, it will help if you create a latex external cast of the external mold. That way, you can make a "positive" out of a "negative." All you need is some liquid latex, like the kind you can put on the back of a rug to keep it from sliding around on a floor. Carefully pour the liquid latex into the external mold (try not to create any bubbles), and let the latex dry. Removal of the latex cast is easy; just pull it off. A latex external cast is shown above just to the right of the external mold. In some, cases nature creates external casts by filling in the external mold with some foreign substance. In the above, because I used latex to make the external cast, therefore, it is called an artificial-external cast.

The above picture shows an internal cast, which shows the interior of a high-spired gastropod shell (most likely, a Turritella). The 6-cm high shell was hollow, and silt and mud filled the shell after the death of the gastropod. Later, the sediment converted into solid rock, the shell was destroyed, and all that is left is the internal cast. Equivalent terms for an internal cast are endocast, internal "mold," or, my personal favorite, steinkern (= a German word meaning a "rock center or core"). Steinkerns are not very useful for determining genus or species. Some early workers, unfortunately, used them for naming new species. Doing so has caused serious taxonomic (classification) problems for subsequent workers, who commonly refer to such a species as a nomen dubium = a name representing a species that is not identifiable from the original specimen (type) used to describe it.  

This final picture shows the external mold (6 cm wide) of the bivalve Laevicardium californiense. The fossil is of Plio-Pleistocene age and from the Santa Barbara Formation, Santa Barbara, southern California.

fossil pine cones

a fossil pine cone, height 10.5 cm

I have always been intrigued by fossil pine cones, especially the ones that were transported by river currents to a ocean shoreline and ended up being deposited in the shallow-marine environment alongside Turritella shells (see some of my earlier posts) and shark teeth. 

The rare specimen shown above is from float material (weathered out and laying loose on the surface) from the Pico Formation near Newhall, southern California. The formation in this area was deposited in a marine-delta environment. There had to have been pine trees growing in the adjacent, ancient San Gabriel Mountains east of the delta. This pine cone floated down a braided river (full of coarse debris consisting of pebbles and cobbles) and was deposited in fine-grained sandstone near the ancient shoreline. 

another fossil pine cone, height 8.5 cm

The rare specimen shown above is from float material found near Topanga State Beach, southern California. Much less is known about its provenance (origin) than the Pico Formation specimen.

Identification as to the family or genus of pine tree for both of the illustrated specimens is needed. The identification process is not an easy task. Just the presence of pine cones in a sedimentary rock deposit is most helpful, nevertheless, because they indicate that a mountainous area was adjacent to the burial site.

An exceptional trilobite-trace fossil

Trilobites (see the link  http://en.wikipedia.org/wiki/Trilobite ) were Paleozoic arthropods that crawled along the shallow-sea floor. When a trilobite stopped to rest, it made a shallow burrow in the mud or silt. These burrows were commonly filled with sediment and later fossilized as "resting" trace fossils called by the Latin name, Rusophycus. Remember from one of my earlier blogs, a trace fossil shows behavior of a fossil organism.

The above picture is the bottom of a Cambrian Rusophycus from the Inyo Mountains, central California. The burrow is 10 cm in length. Scratch marks made by the trilobites legs are visible on the bottom of the burrow.

These two slabs (both about 11 cm, widest dimension) of slightly metamorphosed Cambrian siltstones from eastern California contain a cluster of Rusophycus. The burrows were probably aligned parallel to an ancient current that brought food to the trilobite. Rusophycus commonly has a bilateral symmetry that was caused by its two rows of legs that moved back and forth in its burrow. This leg action was necessary because its gills were attached to its legs, thus it had to move its legs (even when stationary in its burrows), in order to obtain oxygen from the shallow-sea water.

Ahh, finally we get to a truly exceptional specimen of Rusophycus. It is undoubtedly the best specimen I have ever seen. It is preserved three-dimensionally (8.5 cm long, 3.5 inches) and is of Cambrian age from the Salt Spring Hills, eastern California. The above picture is the bottom view, which shows the scratches made by the legs of the trilobite. The specimen is a plaster replica of the actual specimen, which is now in a museum collection. I painted the plaster replica so as to make it look more like the actual specimen.

This is a side view of the same specimen shown above. The bottom of the burrow is at the top of the picture. I painted the antennae red, so you can readily see them. The fact that the antennae are visible indicates that the remains of the trilobite that made this resting trace are within the burrow, thereby proving the trilobite made this burrow. In situ (in place) specimens of trilobites in their burrows are very rare.

Fossil whale ear bone

Fossil whale ear bones are among some of the most unusual fossils that a collector can find. Whales do not have external-ear structures. Instead, they use the lower jawbone for transmitting sound vibrations to their interiorly located ear structures. They have well developed middle and internal ears and a good sense of hearing.

Their middle ear is enclosed by a bowl-shaped bony structure called the tympanic bulla, which can be fossilized. A fossil bulla is illustrated below.

fossil whale ear bone (bulla), 7 cm wide; Neogene age (Miocene?), California?

Whale ear bones occur in pairs, and the following pictures show replicas of a pair of ear bones from a modern melon-head whale.

models of modern melon-head whale bullae; each one is 3 cm wide

For an interesting article on whale ear bones, including fossil ones, the link is http://vmnhpaleontology.wordpress.com/2007/12/19/in-the-news–whale-ancestors-and-more-ear-bones/

This link provides information on how fossil whale-ear bones help support the evolutionary concept that whales have an ancestry with artiodactyls (modern ones are cows, deer, pigs, etc.).

Pholad boreholes

In the first pictures of my last blog, I showed boreholes made by pholad clams (bivalves) in relatively soft sediment. I decided to expand somewhat on the topic and show pholad boreholes made in harder substrate. Pholad boreholes are trace fossils made by highly specialized clams belonging to the family Pholadidae (pholad, for short) that bore into hard substrate consisting of mud, rock (including cement-covered pilings), coral, shell, and wood. 

The pholads shown below all bored into hard rock and are representative of pholad boreholes commonly found along rocky shorelines of ancient and modern oceans.

Boring is done by the rough file-like anterior of the shell, which is twisted back and forth by the clam, which, as a juvenile, enters a small hole in the rock. As the clam grows larger, it enlarges the borehole to accommodate its growing shell. The borehole is periodically cleaned of debris by jets of water emanating from inside the clam.

These pholad boreholes were made in solid, hard rock (8 cm in width). The middle borehole has both valves of the actual clam, which is in its living position.

A transported clast (eroded rock material) of pholad boreholes in an upper Pliocene, shoreline deposit, Simi Valley, southern California.  Other fossils are fragments of pectinid clams. The blue-colored part of the rock handle is 18 cm long.

Rocky shoreline large cobble containing several empty pholad boreholes. The large cobble has a maximum width of 15 cm.

Sand fillings (casts) of a cluster of pholad boreholes (the rock that once surrounded these boreholes is missing). The rock is 5 cm in width.