Deep L.A. History at the Tar Pits

March 1, 2016

Today let's reflect on the biodiversity of Los Angeles from a deep time perspective. Los Angeles has a unique resource for tracing the legacy of many of the animals that we still see around in this region: the celebrated Tar Pits. Mired in sticky asphalt seeping up to the surface through cracks deep underground, the remains of countless creatures are found at this site in the heart of our city. The gruesome deaths endured by saber-toothed cats, dire wolves, and giant ground sloths as they starved fighting to free themselves from their gooey trap are nearly unimaginable. However, such carnage has left us with the most vivid image of Ice Age L.A., a fossil record that, in addition to various large mammals, includes a myriad of tiny animals. There are also plant remains—branches of all sizes, seeds, and even pollen—which, together with the spectacular record of the animals that once lived in and around what’s today Hancock Park, provide us with unparalleled evidence of the environmental history of Los Angeles over the last 50,000 years.

Thousands of fossils like these have been found at the Tar Pits, in the heart of L.A.   For most people the Tar Pits conjure images of extinct mammoths and saber-toothed cats, but the surprising fact is that 90% of the species recorded in the Tar Pits are still alive today. In some ways, the Tar Pits are far more about the present than about the past! For decades, research has focused on a limited number of extinct species that have rightfully captured our imagination. Who wouldn’t daydream of a time when 10-ton mammoths walked the Miracle Mile next to herds of giant camels and huge bison as they were stalked by big cats and the piercing eyes of 10-foot-winged teratorns high in the sky? Just 12,000 years ago, when our ancestors were experimenting with domestication and toying with agriculture, we had a sort of African drama right in our backyard. But as I mentioned above, the Tar Pits have an important role to play in understanding our time and what we will face in the future. The countless fossils of insects and tiny mollusks, small mammals, lizards, fish, and plant remains—collectively known as microfossils—carry critical information about how the environment changes over time around the last glaciation that blanketed much of North America in ice and paved the road for the arrival of humans to this continent and into Southern California. Understanding the ecological transformations of this time is critical for understanding the environmental change we are experiencing today, for such a knowledge places our time into a historical context and give us baselines against which we can compare the present. As such, the Tar Pits are much more than a window into a fascinating past; they stand as an unparalleled resource for framing environmental change in deep time.  

One of the many insect microfossils found in the Tar Pits Lately, as I see this tremendous resource waiting to be fully tapped, I have come to think of the Tar Pits as a paleontological metaphor for the Roman god Janus. Citizens of this famed empire used to place sculptures of this two-faced god along the roads, milestones looking both backwards and ahead. Our beloved Tar Pits are in many ways a Janus: one face gazes into a fascinating time, when bygone animals roamed our city, while the other provides an insightful look into today and the future, the road to come.   

(Posted by: Luis Chiappe)

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Ant-decapitating Fly Found in Glendale!

November 18, 2013

I just found out we have ant-decapitating flies here in Los Angeles! Dr. Brian Brown, the Museum's Curator of Entomology and one of the world's foremost experts on flies, made a chance discovery by looking right under the nose of an unsuspecting USC student. It all started last Friday, while we were enjoying a nice stroll through the Nature Gardens. First, we checked out the Malaise trap that Brian and his staff set up as part of the BioSCAN project, which aims to survey the insect biodiversity here in Los Angeles. Then, we headed into the Nature Lab to see insects from this trap, and the 25 others that have been placed all over Los Angeles, being sorted.

As we got close to the demo table, Brian was suddenly transfixed. He'd seen something interesting on the screen that shows visitors the insects our scientists are sorting under the microscope. By some amazing coincidence, the USC student who was sorting a sample collected in Glendale, just happened to be looking at a phorid fly. Phorids, aka humpbacked flies, are the group of flies that Brian studies, and according to him, they are a mega-diverse family. How mega, you might ask? Apparently, there are estimated to be 40,000-50,000 species of phorid flies, and only 4,000 have been described by scientists so far. Wow!

But, it wasn't just any phorid fly. After taking a look through the microscope himself, Brian nonchalantly walks back over to me and said, "Yep, it's an ant decapitating fly." Whoa, what? I had no idea we had ant-decapitating flies (ADFs) here in L.A.! How could he have neglected to mention this exciting fact during all of our insect musings? Sure he's regaled me with stories of ADFs from Costa Rica and Brazil, always with devilish decapitating detail. But, he never mentioned we have phorids in the genus Pseudacteon, also known as fire ant decapitating flies, here in L.A. Fire ant decapitating flies do just as their name implies. When a female is ready to lay an egg, she locates an unsuspecting worker ant and injects her egg into the thorax. As the larva develops it migrates into the head capsule and molts a number of times. Through this entire process the ant behaves normally. However, just before pupation, the maggot begins to consume the tissue inside the ant's head, which causes the ant to act oddly, and soon after, to expire. The head falls off and the mouth parts are pushed out, so the oral cavity is clear. As the larva pupates, the adult fly emerges from the now-clear oral cavity of the ant. How's that for an alien ant birth? Later that day, Brian wrote an e-mail to the homeowner where the trap was located in Glendale: "Your backyard trap got something unusual- a phorid fly (the group of insects I study) of the genus Pseudacteon. The flies in this genus are all ant parasites, developing in the ant's head, and are referred to as 'ant-decapitating flies.' Usually, in suburban areas, the ant hosts of Pseudacteon are eliminated by the introduced Argentine ant, but you must have (or be close to) a healthy native ant fauna!" This, as Dr. Luis Chiappe, Vice President of the Museum's Research and Collections Department, put it, "is the power of science!" The presence of this parasite, allowed Brian to infer the presence of the host. If we went out to Glendale today, we'd likely be able to find native fire ants somewhere close by! And I know you all dying to join me on that adventure.    

(Posted by: Lila Higgins)

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