Fossil Bony Fish Ear Bones

Otoliths ("ear bones") occur in all vertebrates, including humans, whales, and dolphins [see my previous posts: Fossil whale ear bone, August 15, 2014; Fossil dolphin ear bones, Oct. 4, 2015] for these latter two examples) and allow for perception of linear acceleration, both horizontally and vertically. Otoliths are not skeletal components; rather they form as three separate bones (in each ear) within the auditory capsules. Their composition is calcium carbonate (mainly the mineral aragonite). They can also be fossilized and many are microscopic in size. Some, however, can be macroscopic in size.

Otoliths of modern-bony fish (teleosts) can be common in Tertiary freshwater and marine environments. The shapes and proportions of otoliths vary with fish species. Fish from reef or rocky bottom habitats (snappers, groupers) have larger otoliths than open-clean fish (tuna, mackeral). The growth rings in otoliths are similar to tree rings, in that they can be used to estimate the age of fish, as well to determine early life transitions from planktic larvae to benthic juveniles. The stable isotopes of oxygen and carbon found in the otoliths can be used to determine ancient temperatures of their environments. 

Front, side, and back views (in vertical order) of a matched pair of macroscopic left-and-right otoliths (24 mm long and 7 mm thick) from a 1-meter long, 40-pound White Sea Bass from the northern Gulf of California, Mexico.

Glass Sponges

Sponges occupy an “intermediate position” in the classification of living things. They are not quite an animal but also not a fungus nor a plant.

 Although sponges are multicellular, they have no organs. They lack mouths, intestines, and respiratory and circulatory systems. They are made of two layers of cells; between the layers is a gelatinous layer, which contains amoebid cells and spicules (skeletal needles) or fibers. Glass sponges (also referred to as hexactinellids or siliceous sponges) are made of four- and/or six-pointed spicules made of silica (hence the name). 

In some genera of glass sponges, the spicules fuse to form rigid skeletons, which can be anchored in mud by ropy root tuffs (as long as 7 inches) or mats of spicules. The recent Euplectella ("Venus’s flower-basket") is an example of one of these glass sponges. It displays an interesting commensal relation with certain species of spongicolid shrimp-like creatures, closely related to lobsters and crabs. A young male and a young female shrimp enter the central cavity of the sponge, and after growth, are unable to escape. Their entire life is spent inside the sponge, where they feed on plankton brought in by water currents. 

Euplectella aspergillum, 21 cm length, western Pacific.

Glass sponges are common only in the deep sea, especially below 500 m. They can live, however, in relatively shallow waters (35 m depth) in cold waters in Antarctica.

Glass sponges have a long geologic history, ranging from the latest Precambrian and earliest Cambrian to modern day. 

Devonian glass sponge, 10 cm length, Early Paleozoic.

Mud curls that resemble arthropod appendages

In the early 1980's, geologists and paleontologists were excited by the discovery of what appeared to be arthropod appendages (legs) preserved in a slab of upper Precambrian or lower Cambrian silty sandstone found in the Grand Canyon, Arizona. Pictures of the slab were published on the cover of at least one leading journal (I searched the internet but could not find the article).

The slab was put on display at some major universities in the American west. I viewed the slab at Caltech.

A bedding-plane view of the slab is shown below (top image). The slab is about 2 feet in width and seemed to be very heavy. A cross-section view of the slab is shown below (bottom image).

The significance of this slab is that, if it actually contains fossil arthropod appendages, then they were larger and more evolved than previously believed. Although the bedding-plane view seemed to support the idea that the structures were "legs" of some sort, the cross-section view did not support this idea. Cooler heads prevailed eventually, and most experts ruled that these structures are actually "mud curls" or "sun curls," caused by the shrinkage of muddy layers on an ancient shoreline or lake. In summary, the slab contains pseudofossils, not fossils.

Once the geologic community, as a whole, considered the evidence, this slab became relegated to the dark depths of some storage room and was not mentioned again!

It is interesting to mention that *McKee (1932), a Grand Canyon Park naturalist, illustrated slabs similar to the one shown above. He referred to them as "fucoides," a name used by paleontologists then to describe any unusual "biologic?" structure, like algal remains, "worm" burrows, etc.

*McKee, E.D. 1932. Some fucoides from the Grand Canyon. Grand Canyon Nature Notes 7(8): approx. 5 pp.  [pdf available online for free].