California. A state well known for endlessly perfect sandy beaches, sun, wine, and Arnold Schwarzenegger. Hidden below the surface of this famous American state lies a more complex history that only reveals itself when we look a little closer. Locked within the rocks is a history greater than any Hollywood blockbuster. A history where the Earth really did move. A history where volcanoes violently errupted, mountains slowly, quietly grew, and remarkable creatures lived. The movie of how Hollywood came to be may well be one of the greatest yet.

California has a very complex geological history. The north is dominated by volcanic rocks 25 million years old showing evidence of long lost volcanoes that shook the ground as they spewed out magma and ash. Dominating the east and south east, forming Yosemite National Park and the mountains beyond, are hard, tough, Mesozoic granites. This extremely resistant rock originated around 100 million years ago when old rock was being forced deep down into the Earth: so deep, it melted, resulting in plumes of molten granite rising, slowly pushing it’s way up through the Earths crust. The never ending recycling of rocks is one of the most beautiful wonders of geology.

The rocks we are interested in lie towards the south west of California. Here, something spectacular happened.

A simple geological map of California. The different colours highlight the different rock types. Hidden under this colourful map are huge folds and deep faults that make California a geologically complex area. (Image from USGS, Public Domain).

Marine sediments which settled around 15 million years ago were crumpled into a deep bowl shape as the mountains to the North East formed. More sediments from the sea and rivers built up forming many layers of fine to coarse grained rock. A rock with very high organic content. The organic matter in the coarser grained sediments were trapped with the cap of fine sediments above, and very slowly formed large deposits of oil. Beneath many areas of California lie huge reservoirs of oil. Most are secure underground, tapped by humans and refined. At some places oil has managed to seep to the surface. One place in particular, is the La Brea Tar Pits slap bang in the middle of Los Angles. Here thick, sticky treacle-like asphalt reaches the surface. This semi-solid oil is a death trap. Literally.

Animals have been entombed in this sticky tar for tens of thousands of years, from tiny beetles to enormous mammoths. Staff at the Page Museum have painstakingly cleaned, and carefully recovered 650 different species with an incredible amount of entire skeletons. The amazing story of Los Angles between 40,000 and 10,000 years ago is being pieced back together with awesome animals from the Pleistocene illustrating a beautiful, diverse ecosystem. With large herbivores, like mammoths and ground sloths, getting trapped in the tar pits they inevitably attracted a lot of predators who sniffed out an easy meal. Hundreds of Smilodon fossils and thousands of Dire Wolves have been recovered after they met their fate in a ‘Red Wedding’ style event, where the diners were completely unexpectedly killed off whilst enjoying a little food. Only this Red Wedding spanned for thousands of years. These are the predators that make it into Sinbad and the Eye of the Tiger, or A Game of Thrones. But there is another beast from the La Brea Tar Pits that equally deserves air time. And this would give Big Bird a run for its money.

Incredible display of hundreds of Dire Wolf skulls atthe Page Museum, La Brea Tar Pits. (Image by Pyry Matikainen, from here)

Towards the end of the Pleistocene, there was a giant bird gliding on the air currents. A bird bigger than the largest North American land bird, the California Condor. It was Teratornis merriami. This was a bird you wouldn’t want to see in your back garden. It was huge. Some reconstructions have created a cross between a vulture and a Condor. The wingspan was between 3.2 and 3.8 meters long (that’s about one and a half times as long as me!). Standing, it would have reached my tummy, at 75cm tall. Its sharp, curved beak was made for one thing; slicing and gulping down meat. This was a big beak: large enough to swallow a rabbit whole. It is no wonder this beast belongs to the Teratornithidae Family: which literally means ‘monster bird’.

The incredible skull of Teratornis merriami.  (Image by Wiki User Esv, from here)

Teratornithidae (or Teratorns) were first found at La Brea Tar Pits in 1909 with Teratornis woodburnensis as the species describing the new Family. Since then five different species have been discovered. With only a handful of species, the affinities of this group have only recently been agreed upon. They were originally thought to belong to the Family of Vultures (Cathartidae) when they were first discovered due to similarities in their beak and skeleton. They have been thought of belonging to the Order Ciconiiformes, which includes storks and New World Vultures. However, more recent research has brought them back to where they originally began, and are now placed back in the Order Cathartiformes, where the teratorns sit alongside the New World Vulture. Working out the taxonomy of extinct animals can be tricky business!

The Tar Pits are unique: the preservation of the bones at this site is perfect, and more often than not, the entire skeleton is preserved. This rare double dose of preservation provides an enormous amount of information for researchers. Around 100 individuals of T. merriami have been excavated so far, making this the best known of the Teratorns. But there is still a lot we don’t know.

These Monster Birds are full of very cool features to help them fly, scavenge and hunt. For such a big bird to fly, the skeleton was, like all flying birds, very light. The finger bones are all fused, but the index finger has a wide, flat shelf of bone: a shelf to hold large, long feathers that are attached to the hand (the primaries). The extra shelf of bone supports these larger than life feathers to assist in these giants soaring. Originally viewed as of scavenging birds, the leg bones reveal something slightly more terrifying. Compared to Eagles and Condors, the feet were not sharp for grabbing and holding on to prey animals: instead, they could hold down prey which tearing off pieces. This indicates that this bird didn’t hunt on the wing. With longer and stockier legs, it has been suggested that Teratorns would have hunted animals on the ground. It has also been proposed that these animals may have hunted similiarly to an Osprey, by catching fish from rivers. Clearly, as attested by the hundred individuals at La Brea Tar Pits, they were also partial to a little scavenging when the opportunity presented itself.

A classic illustration of La Brea Tar Pits, and one of my favorites with a Charles Knight feel to it. It shows two dire wolves and a Smilodon on top of a Mastodon carcass. Look up and there are several large birds circling and one sat on a branch. These may be the Condor, but I like to think that these are Teratornis merriami soaring those hot air currents. (Illustration by Robert Bruce Horsfall, 1911, from here)

The giant Teratornis merriami was not just restricted to soaring over the warm thermals of California. Fossils have also been found in Arizona, Florida, New Mexico and Mexico. In 1970, Paul Martin, the advocate for the overkill theory, was examining Stanton’s Cave, Arizona for pack rat middens. (Pack rats are cute little rodents that like to grab vegetation from the surrounding area to make their cosy middens. These middens have survived for over 50,000 years, preserving with them the evidence of the flora of the surrounding area, giving vital information about the climate at that time.) Digging back inside Stanton’s Cave, Martin and two colleagues discovered a huge bird humerus bone. It was from T. merriami and radiocarbon dated to around 15,000 years ago.

Other avian species are present alongside the Monster Bird. Raven, eagles, vultures, and Condors were around at the same as these giants. Bones from the ancestor of the modern California Condor have been recovered from the Tar Pits. Looking at the skull and beak shapes, it appears that Condors are not made to tear open big carcasses. But this was not a problem to T. merriami. Paul Martin postulates that the large, sharp beak of T. merriami could have easily ripped open carcasses of Pleistocene giants. After they had their fill, the less powerful scavengers, like the Condor could have simply tucked in. Which obviously begs the question, when Teratornis merriami became extinct, why didn’t the Condor?

Along with the extinction of the American mega-fauna, our beast also succumbed. Condors are scavengers, but more opportunistic and can survive on a larger variety of food than the Monster Bird could have, but there may be more. The climate was undergoing drastic changes which led to changes in rainfall, and consequently changes in food sources. Hunting on the ground may not been as efficient on smaller prey animals compared to other birds of prey who swoop down from the sky. There is also evidence at the Tar Pits of human presence. Extinctions are extremely complex and very rarely the sole cause of one event. As with many species throughout geological time, it may have just been unlucky. We may never know the true cause for the loss of this incredible bird. With the exceptional preservation at the La Brea Tar Pits, we are lucky to have a record of this truly magnificent bird. And we know that Monster Birds really did roam the planet.

Written by Jan Freedman (@JanFreedman)

Further reading:

Campbell, K. E. & Tonni, E. P, (1983), ‘Size and locomotion in teratorns’, Auk.  100(2). pp.390-403. [Full article]

Campbell, K. E, Scott, E, & Springer, K. B, (1999), ‘A new genus for the Incredible Teratorn  (Aves: Teratornithidae)’, Smithsonian Contributions to Paleobiology. 89. pp.169-175. [Full article]

Campbell, K. E, & Stenger, A. T, (2002), ‘A new Teratorn  (Aves: Teratornithidae) from teh upper Plesitocene of Oregon, USA.’ In Zhou, Z & Zhang, F. Proceedings of the 5th Symposium of the Society of Avian Paleontology and Evolution Beijing. 1-4 June 2000. China Science Press, Beijing. [Full article]

Chatterjee, S, et al. (2007), ‘The aerodynamics of Argentavis, the worlds largest flying bird from the Miocene of Argentina’,  Ameginiana. 104(30). pp.12398-12403. [Full article]

Fisher, H. L, (1944), ‘The skulls of Cathartid vultures’, Condor. 46(6). pp.272-296. [Full article]

Howard, H, (1947), ‘A preliminary survey of trends in avian evolution from Pleistocene to recent time’, Condor. 49(1). pp.10-13. [Full article]

Howard, H, (1952), ‘The prehistoric avifauna of Smith Creek Cave, Nervada, with a description of a new gigantic raptor’, Bulletin of the South California Acadamy of Sciences. 51. pp.50-54. [Full article]

Howard, H, (1962), ‘Bird remains from a preistoric cave deposit in Grant County, New Mexico’, Condor, 64(3). pp.241-242. [Full article]

Martin, P. S. (2007), Twilight of the Mammoths. University of California Press. [Book]

Miller, L. H, (1909), ‘Teratornis, a new avian genus from Rancho La Brea’, University of California Publications, Bulletin of the Department of Geology. 5.  pp.305-317.

Miller, L, (1960), ‘Condor remains from Rampart Cave, Arizona’, Condor. 62(1). pp.70. [Full article]