With Easter coming up in a few days, it seems an appropriate time to feature one of the rarer fossils from Diamond Valley Lake, an eggshell fragment.While bird eggs are largely mineralized (unlike leathery lizard, snake, and turtle eggs), they are of course thin and fragile, as anyone who has dropped a carton of eggs knows. Moreover, if an egg lasts long enough to produce a baby bird, the chick shatters it upon hatching and then tramples the fragments in the nest. All this adds up to fragments of eggs, rather than complete, intact eggs. The fragment shown here is one of the largest recovered from Diamond Valley Lake. The curvature suggests that it may have come from a relatively large egg (chicken-sized, maybe), but there's a good deal of uncertainty involved in such a prediction. Most eggs are not spherical, but are instead, well, egg-shaped, which means that the curvature is different on different parts of the egg.Fossils such as eggshells also serve as a reminder of the effects taphonomic bias has on our knowledge of the fossil record. So far, 17 species of birds have been identified from Diamond Valley Lake deposits, although the actual number of bird species was undoubtedly much higher. Those deposits span tens of thousands of years (maybe as much as 200,000). How many eggs would 17 species of birds lay in 100,000 years? Yet, in the deposits we have more mastodon teeth than eggshell fragments. The eggs were mostly broken into tiny, even dust-sized fragments, and the calcium carbonate-rich shells are susceptible to dissolving in acidic groundwater. Between predators, hatching and trampling, and abiotic processes such as dissolution, what must have originally been many millions of eggs was reduced to just a handful of identifiable fragments. Taphonomic processes will selectively remove certain remains, leaving us a fossil record biased in favor of some organisms and against others. This is something to always keep in mind when examining fossil deposits.
Fossil Friday - quail hand
When studying comparative anatomy, one of the most basic skills is identifying homologous structures - the same bone or organ in different organisms. This can be tricky, as a structure may become hugely modified in the course of evolution as it is co-opted for new purposes. The bird's wing provides a classic example.Birds' wings are modified forelimbs, and as such have the same basic components as any other tetrapod's forelimb, including a wrist and hand. A typical tetrapod hand commonly has five bones called metacarpals, that articulate at the proximal ends with a series of small bones called the carpals (wrist bones). In birds there are only three metacarpals, a trait they inherited from their theropod dinosaur ancestors. Moreover, most of the bird carpals and the metacarpals are fused together into a single structure called the carpometacarpus.At the top of the page is a partial carpometacarpus from the Pleistocene deposits at Diamond Valley Lake. This represents part of the proximal end (the wrist end) of a small right carpometacarpus (the small scale increments are millimeters). The long shaft is the 2nd metacarpal, the hand bone associated with the index finger. Even in such a small fragment several features are visible, such as those indicated below:
The projection marked "1" is the 1st metacarpal, the one associated with the thumb; in birds it it reduced and solidly fused to the carpals. The thumb bone, which is called the alula in birds and supports feathers on the leading edge of the wing, articulates at this point.Number "2" is the broken base of the 3rd metacarpal, the one associated with the middle finger. Birds don't have the 4th and 5th metacarpals, the ones associated with the ring and pinky fingers; these were lost in bird ancestors millions of years before the first birds appear in the fossil record.Number "3" is called the intermetacarpal tuberosity; it's a bony spur of metacarpal 2 that projects into the gap between metacarpals 2 and 3. In this specimen, the tuberosity is very large relative to the size of the metacarpal. That's significant, because such a large tuberosity is generally only present in a group of birds called the Galliformes (turkeys, chickens, quails, and their relatives). The size and shape of this particular bone suggests that belongs to a New World quail from the genus Callipepla.Callipepla is still a common bird in southern California, with two different species considered to be native to the area. Callipepla californica is California's official state bird, and C. gambelii is also common in this area (below is C. gambelii from the North Carolina Zoo) . Two other species of Callipepla are found in the southwestern United States or northern Mexico but not currently in California. With such a fragmentary specimen, any of these closely related species are a possibilities for this Diamond Valley Lake specimen. We have a number of Callipepla bones in the collection, suggesting that, like today, quail were a common component of the Diamond Valley Lake fauna during the Pleistocene.
Fossil Friday - eagle talon (or, a Pleistocene dinosaur)
With the release of Jurassic World, we've been getting some inquiries from the media about what dinosaurs the Western Science Center has in our collections. While we have a small number of isolated bones and teeth from the Cretaceous Hell Creek Formation in Montana, the answer that they really don't like to hear is that we have lots of dinosaurs, because we have lots of birds.In general, the paleontological community's reaction to Jurassic World has been disappointment at best (disclosure: I haven't seen the movie, and have no immediate plans to do so). The problem is that, while the original Jurassic Park movie had a lot of errors, it did a pretty good job of portraying dinosaurs based on our scientific knowledge at the time. But we've learned a lot more in the 20+ years since, and Jurassic World doesn't reflect that; in fact, in some ways it seems to be a huge step backwards even relative to Jurassic Park. One of the key points where Jurassic World fails is in it's failure to use birds as a model for reconstructing dinosaurs. Whether or not the Jurassic World designers like to admit it, birds are the last surviving branch of dinosaurs. They also happen to be a highly successful branch; there are roughly twice as many modern species of birds as there are of mammals. Even though birds have a relatively low preservation potential due to their fragile bones, with such a successful and widespread group we would expect them to show up fairly commonly as fossils. In fact, we have quite a few species of Pleistocene birds represented in the Diamond Valley Lake fauna. These are almost all based on isolated bones, such as the eagle talon shown at the top of the page. I'm not sure what species this talon represents, but a good possibility is a golden eagle, Aqulia chrysaetos (modern example below from the Nashville Zoo): 
Golden eagles were widespread in California during the Pleistocene; in fact, they are the most common animal at the Pleistocene tar pits at Rancho la Brea, and there are several specimens in the Diamond Valley Lake fauna. So, Jurassic World aside, California dinosaurs are alive and well!
Fossil Friday - turkey
It's the day after Thanksgiving in the US, so for today's Fossil Friday we have a probable turkey bone from south of Diamond Valley Lake.I found this bone by accident last week while looking for good examples of packrat teeth. While this fragment isn't much to look at, we have almost no other fossil turkeys in the WSC collection.This fragment is part of the distal end of the tarsometatarsus. This is a structure unique to birds and certain other dinosaurs, in which the ankle bones (the tarsals) and the foot bones (the metatarsals) are fused into a single unit. The proximal end articulates with the shin bone (tibiotarsus in birds), while the distal end has structures called trochlea that articulate with the toes. Most birds have three toes, and so have three trochlea at the end of the tarsometatarsus, as can be seen in the examples from modern turkeys shown below (from Thornton et al. 2012):
The WSC fragment is one of the trochlea, I think for either the second or third digit (the inside or middle toe). I'll need to compare it to a modern turkey bone to confirm which one, and unfortunately the turkeys you buy at the grocery store don't typically include the tarsometatarsus!Judging by their near-absence in our collection, it would seem that turkeys were relatively rare in the valley during the Pleistocene. This is a little surprising since vast numbers of turkey bones have been recovered from Rancho la Brea, which is only about 80 miles away from Hemet (more than 11,000 turkey bones have been found there, according to Bocheński and Campbell, 2006). The Rancho la Brea turkey was long considered to be its own genus, Parapava, but was reassigned to the same genus as the extant turkey as Meleagris californica by Steadman (1980). (Below is a reconstructed skeleton of M. californica on display at the George C. Page Museum.)
It's possible that turkeys may have breeding at Rancho la Brea, and there are reasons to think that they may have been particularly susceptible to being trapped in tar (Bocheński and Campbell, 2006). It's also not clear that the turkey in the WSC collection is M. californica; it could be the modern wild turkey M. gallopavo or some other species. Even so, it's remarkable that turkeys were seemingly quite rare such a short distance away from Rancho la Brea, and may have interesting implications for different environmental conditions across California during the Pleistocene.References:Bocheński, 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, Natural History Museum of Los Angeles County, No. 509:1-92.Steadman, D. W., 1980. A review of the osteology and paleontology of turkeys (Aves: Meleagridinae). Contributions in Science, Natural History Museum of Los Angeles County, No. 330:131-207.Thornton, E. K., K. F. Emery, D. W. Steadman, C. Speller, R. Matheny, and D. Yang, 2012. Earliest Mexican Turkeys (Meleagris gallopavo) in the Maya Region: Implications for Pre-Hispanic Animal Trade and the Timing of Turkey Domestication. PLoS ONE 7(8): e42630. doi:10.1371/journal.pone.0042630