TERROR BIRDS

The generalized term “terror birds” is the focus of this post. It refers to a group of extinct similar looking birds that could be up to 8 or 10 feet tall and weighing 400 pounds. There were several genera/species, and they make up an extinct group of carnivorous flightless birds, referred to as the phorusrhacids. They were the largest apex predators to live in South America during the Cenozoic Era.

One example of this group is genus Phorusrhacos [pronounced For-us-Rah-koss], of middle Miocene age, about 14 million years ago, from Santa Cruz, southern Argentina. Although it superficially resembles an ostrich, it is not one. The skull of Phorusrhacos is very different. Phorusrhacos was 8 feet tall and weight 300 pounds or more. A model of this genus is shown below. 

The geologic time range of “terror birds” is most of the Cenozoic, from late early Paleocene, late Danian Stage [=62 million years], through the early Pleistocene [=1.8 million years]; an interval of approximately 60 million years. Why did they go extinct? Most likely, it was because of changing habitat (related to changing climate during the Pleistocene Ice Age). Also the Panamanian Land Bridge emerged during the Pleistocene, and South America became connected to North America, and large predatory cats and dogs migrated southward into South America for the first time.

It is interesting to mention that the geologically youngest “terror bird” (Titanis walleri = 8 feet tall and 300 pounds), of early Pliocene to early Pleistocene, lived in Texas and Florida. This shows that at least a “terror birds” migrated northward into North America, but their presence there did not last long.

The geologic history of birds, in general, is a complex subject. They originated during the “time of dinosaurs” during the Jurassic Period, but their diversity increased significantly during Cenozoic time. A very generalized cartoon showing the major different groups of Cenozoic birds is shown below. The “story” of bird evolution is still unfolding.  

I encourage you to “Google” the words “terror birds” or Phorusrhacos. There are MANY online colorful renditions of what this animal and its relatives looked like. 

Wild Turkeys Once Lived in Southern California

 This post is appropriately “published” just prior to Thanksgiving Day, 2021 and gives a nod to the turkey, a bird native to North America. 

The earliest known fossils of turkeys are of early Miocene age (23 million years old). They are from near the small town of Bell, northern Florida in northern Gilchrist County, approximately 30 miles northwest of Gainesville. These fossils belong to the extinct genus Rhegminornis, which was about half the size of the modern genus Meleagris, whose type species is M. galiopavo (also known as the wild turkey). The latter is the largest gallinaceous bird (refers to its order in the classification system of birds) in the New World. It is 3-4 feet tall, 10-40 pounds in weight, and has a wingspan up to 6 feet. These turkeys are very social animals, yet territorial.

Today, M. galiopavo lives in the forests of midwestern and eastern United States and into southeastern Canada. I can verify a Gulf Coast occurrence because I saw a wild turkey in southern Alabama, while I was on a fossil-collecting trip (gastropods and bivalves) many years ago. I can also confirm that this species can fly. The one I saw flew high into a tree top. This wild species is the ancestor of the domestic turkey.

A second living species, M. ocellata, lives in the forests of the Yucatán Peninsula, Mexico.

Another species of Meleagris is the extinct Meleagris californica, which lived in southern California during the Pleistocene Ice Age. Bones of this species represent the second most common fossil found in the Rancho La Brea Tar Pits. The most common fossil is the Golden Eagle. Meleagris californica went extinct about 10,000 years ago.

For more detailed information, I highly recommend that you Google rexmachinablog.com for its excellent blog on “The Wild Turkey: the evolution and history of an American icon.”

If you are interested in detailed information about the Rancho La Brea turkeys, see the following pdf (downloadable, for free):

Bockénski, Z.M. and K.E. Campbell, Jr. 2006. The extinct California turkey, Meleagris californica, from Rancho La Brea: comparative osteology and systematics. Contributions in Science, number 509, 92 pp. Natural History Musem of Los Angeles County, California.

The Silica Tetrahedron

The molecular structure of silica tetrahedron (SiO₄) is the basic building block of the silicate minerals, which make up the vast majority of the minerals in the Earth’s crust.

The silica tetrahedron is a combination of one silicon and four oxygen atoms that form a four-sided pyramid shape, with the silicon atom in the center and an oxygen at each corner of the pyramid.

This low-tech "marshmallow model"shows the basic design of the silicon tetrahedron.

In a more explicit model of a silica tetrahedron (see below), the element silicon is a cation with a charge of +4. Each oxygen atom is an anion, with a -2 charge; thus four oxygen atoms make a -8 charge. The combination of +4 and -8 makes -4. The silicon tetrahedron molecule has therefore has a net -4 charge, which means it readily combines with other elements besides oxygen in order to balance out the additional -4 negative charge and form a net-zero charge (i.e., nature abhors a molecule with a net negative charge; just like nature “abhors a vacuum”).

There are six main configurations (e.g., rings, chains, frameworks etc.) of linkage among silicon tetrahedra. There are many internet sites that show beautiful reconstructions of these configurations, some of which are quite complicated. One of the most useful sites is: <openeduationalberta.ca/practicalgeology/chapter 3>  You will have to access it yourself because Google no longer allows external links within blogs.

The mineral quartz (SiO₂), which is the most abundant mineral in the Earth’s crust is an  example of the framework configuration known as the tectosilicates. In quartz, in order to neutralize the ionic charge difference, the four oxygen atoms of the silica tetrahedron are “shared” by adjacent silica tetrahedra. Each corner of the pyramidal tetrahedron is bonded to another tetrahedra (with an oxygen shared at each corner of each). As a result, the ratio of silica to oxygen atoms is 1:2, and the atomic charge is neutral (zero). 

A cluster of clear quartz crystals (6.5 cm wide, 6 cm high).

A single crystal of clear quartz (2.4 cm wide, 5.7 cm high).

One of the simplest silicate minerals is olivine, which is made up a single tetrahedron bonded to divalent iron (+2) and/or magnesium (+2), thereby creating Fe₂SiO4 or Mg₂SiO4, or some combination of the two (Fe, Mg)₂SiO4. The combination can occur because both iron and magnesium are divalent (+2) [thus they balance the charge of the silica tetrahedron] and their atomic sizes are similar; thus they can substitute for one another.

The above image is a cluster of tiny olivine crystals (hand specimen 3.6 cm wide, 2.7 cm high).

Terminology Hints

The words silicon and silica, etc., get used a lot in our modern vocabulary. The following list might be of some help to you in understanding these similar terms:

silicon (Si) = the 14^th element on the “Periodic Table of The Elements.”

silica = a solid material made out of SiO₂ (but not necessarily a mineral; e.g., opal---see my previous post on chalcedony).

silica tetrahedron = a combination of one silicon atom and four oxygen atoms that form a tetrahedron (= a four-sided pyramidal shape).

silicate = a mineral that contains a silica tetrahedron or many silica tetrahedra. 

silicone = a flexible synthethic material made up of Si-O chains with added organic molecules.

SMITHSONITE: the blue-green variety

Smithsonite was named in honor of James Smith, founder of the Smithsonian Institution.

This mineral belongs to the carbonate group and consists of zinc carbonate ZnCO3. It effervesces in hydrochloric acid. Its streak is white, and it has silky luster, its specific gravity is 4.4–4.5, its hardness is 4.5. Its crystals belong to the trigonal system, but they are rare. Smithsonite commonly occurs in either a globular (botryoidal) or in a massive (granular) form. 

It has a wide range of colors because of chemical impurities (listed here in brackets): white to gray [no impurities]; blue, blue-green, to apple green [copper]; yellow [cadmium]; pink to purple [cobalt]; and brown to red [iron].

It often forms as a secondary mineral in the upper oxidation zone of zinc-ore deposits within metamorphic rock complexes. It is found in Greece, Spain, Africa, and the USA (one famous example is at the Kelly Mine in New Mexico).

The two images shown above are of the botryoidal form of an encrustation of smithsonite (38 mm length an 9 mm in height) from the Kelly Mine at Magadalena, Socorro County, central New Mexico.