Teratornis merriami, Miller, 1909
|
publication ID |
https://doi.org/ 10.26879/1191 |
|
persistent identifier |
https://treatment.plazi.org/id/03BD87C3-FFE4-FF9B-5A15-FBF6FBBEA092 |
|
treatment provided by |
Felipe |
|
scientific name |
Teratornis merriami |
| status |
|
( Figure 5 View FIGURE 5 )
Appearance. The avifauna of Rancho La Brea is understudied compared to the mammalian megafauna and deserves a detailed, modern revision. Probably the best known of Rancho La Brea’s birds though is the teratorn ( Teratornis merriami ), a large condor-like bird with a wingspan of 3–4 m and a mass of 13.7 kg (Campbell, K.E., Jr. and Tonni, 1983). With Teratornithidae perhaps sister to Cathartidae , the teratorn closely resembled New World vultures in postcranial appearance (Mayr, 2009). “Consequently, all reconstructions of teratorns have pictured them as slightly larger versions of condors, usually sitting in a tree waiting for a trapped animal to die, or feeding in groups on large carcasses as vultures are wont to do.” (Campbell, K.E., Jr. and Tonni, 1981, p. 265). The large number of teratorn skeletons found in the tar pits supported this inference that they fell into the asphalt while greedily devouring the carcasses of large mammals that had already become stuck (Howard, 1930).
This vulture-like reconstruction is featured in Knight’s iconic mural ( Figure 2A View FIGURE 2 ) and several other pieces of paleoart at the Museum. It prevailed until two papers by Campbell, K.E., Jr. and Tonni (1981; 1983) argued that teratorns were morphologically incapable of vulture-like scavenging and were instead active terrestrial predators of small mammals. This ecology is displayed in Mark Hallett’s 1988 reconstruction at middle right of Figure 2B View FIGURE 2 . Rather than the naked-headed condor with brown/ black plumage, Campbell, K.E., Jr. and Tonni promoted a reconstruction of teratorns analogous to secretarybirds with greyish wings and white countershading. The coloring was speculative but Campbell, K.E., Jr. reasonably believed that countershading and a white head would help camouflage a stalking bird from the view of small prey looking upward towards their demise (Campbell, K.E., Jr., personal commun., 2019). This coloring didn’t appear in Hallett’s mural ( Figure 2B View FIGURE 2 ) but was adopted for several more recent pieces of paleoart at the Museum including a life size teratorn puppet.
The active terrestrial predator reconstruction focused on analysis of the teratorn’s skull (Campbell, K.E., Jr. and Tonni, 1981) and hind limbs (Campbell, K.E., Jr. and Tonni, 1983). Campbell, K.E., Jr. and Tonni (1983) agreed with previous research that the postcranial skeleton of teratorns closely resembled that of the California condor ( Gymnogyps californianus ) except for the teratorn’s larger overall size and proportionally much larger sternum ( Fisher, 1945). The body mass of the teratorn was ~33% larger than that of the California condor but its pectoral musculature would have been about ~200% greater (Chatterjee et al., 2007). Campbell, K.E., Jr. and Tonni (1983) disputed Fisher’s (1945) analysis that this likely gave teratorns pelican-like flapping abilities but agreed the teratorn could have soared much like a California condor and likely faced similar constraints getting aloft.
Early researchers noted the interesting mix of vulturine and aquiline features of the teratorn’s skull (Stock, 1930). Quantitative (Hertel, 1995) and qualitative analyses (Campbell, K.E., Jr. and Tonni, 1981) showed that it had many features in common with piscivorous birds like albatrosses or cormorants that use their hooked bills to actively catch prey. However, stable isotopes show that teratorns fed exclusively from the terrestrial realm on a mix of grazers and browsers (Fox-Dobbs et al., 2006). Based on the high kinesis of the skull and several features of the mandible and maxilla, Campbell, K.E., Jr. and Tonni (1981) concluded that teratorns could not be scavengers. They also hypothesized that a predentary bone was present, a feature unknown in extant birds. Regardless of what they ate, it is clear that teratorns’ skulls don’t fit neatly into any extant morphology.
Campbell, K.E., Jr. and Tonni (1983) disputed Fisher’s (1945) conclusion that teratorns would have been slow and awkward on the ground by noting that the angle of the pelvis more closely matches walking birds like storks. However, they acknowledged that their legs were still short and probably incapable of running or grasping prey. They imagined teratorns actively stalking through a savannah habitat, surprising small prey, hooking it with their beaks, and eating it whole.
Without disputing any of the individual findings of Campbell, K.E., Jr. and Tonni’s (1981; 1983) detailed analyses, we find their reconstruction of the teratorn as an active terrestrial predator problematic. Imagine the ecology of a bird that flies like a condor yet hunts small mammals and herps on the ground. The teratorn wakes up from its presumably elevated roost. It soars to high altitudes on thermals, covering large areas looking for prey. Once it spots a mouse, it swoops down to a nearby area as it cannot catch the prey immediately with its feet like a raptor. It folds up its 4 m wings, then quietly stalks up on the mouse, catching it, and swallowing it whole. It cannot chase prey into the shrubs common in the chaparral landscape around the tar pits because it would risk entangling its large wings and getting eaten by one of the many mammalian predators in the area (Campbell, K.E., Jr. and Tonni, 1983). Thus, it likely takes back to the air after only a few hunting attempts. What other bird lives like this? Terrestrial avian predators like caracaras or secretarybirds have clear cursorial adaptations in their hind limbs. The teratorn had shorter legs than the Andean condor ( Vultur gryphus ), hardly a species considered fleet footed on the ground (Campbell, K.E., Jr. and Tonni, 1983). Condor-like soaring makes more sense for spatially rare, high reward resources like predator kills, not small mammals. Metabolic scaling analyses of the much larger teratornithid Argentavis magnificens also showed that its presumed life history traits make much more sense if the bird was a soaring scavenger rather than an active predator (Palmqvist and Vizcaíno, 2003). The skull of the teratorn was different than condors but Campbell, K.E., Jr. and Tonni’s (1983, p. 390) assertion that “They were functionally incapable of feeding by tearing pieces of flesh from carcasses as vultures do.” seems overstated. Many birds like eagles and corvids that do not have vulture-like beaks feed regularly on carrion. Lastly, reconstructing the teratorn as something other than a specialist of large mammal carcasses begs the question of why this species went extinct at the end of the Pleistocene at the same time as the megafauna (Campbell, K.E., Jr. and Tonni, 1983).
The taphonomic evidence for teratorns feeding on large mammal carcasses (their high abundance in the predator trap tar pits) is admittedly muddled, though. Nine of the ten most common birds found in Rancho La Brea’s early excavations are (or likely were) carnivorous (Howard, 1930). But of predatory birds found in the asphalt, only one half of individuals are from species that are (or likely were) obligate carrion feeders (Howard, 1930). The second most common species with 517 individuals, the extinct California turkey (Parapavo californicus), was likely omnivorous like extant turkeys and may have become stuck in asphalt in such high numbers due to its large mass, gregariousness, and foraging habit of scratching away ground litter, thus exposing the underlying sticky goo (Howard, 1930; Bocheński and Campbell, K.E., Jr., 2006). Bocheński and Campbell, K.E., Jr. (2006) hypothesized that the most common bird, the golden eagle (Aquila chyrsaetos), with 880 individuals (Howard, 1930) may have become stuck predating the second most common bird, the aforementioned California turkey. High speed aerial attack dives were likely hard to recover from when the prey was glued in place. Golden eagles are also common opportunistic scavengers, though and this likely explains some of their overabundance (Wilmers et al., 2003). The bird found at La Brea whose foraging most closely resembles Campbell, K.E., Jr. and Tonni’s (1983) terrestrial hunting teratorn is the caracara (either the extant Caracara cheriway or a similar extinct form), at 251 individuals, the third most common bird preserved (Howard, 1930). What this means for the habits of the teratorn (tenth most common with 108 individuals) is unclear (Howard, 1930). But the fact that the remains of two terrestrial opportunistic generalists (with varying degrees of carnivory) are more abundant than Rancho La Brea’s vultures ( Coragyps occidentalis , Neophrontops americanus ), condors ( Gymnogyps californianus ), and bald eagles (Haliaeetus leucocephalus), all obligate or common carrion feeders, shows that Knight’s iconic image of scavengers fluttering down to feast on the carcasses of megafauna entrapped in asphalt ( Figure 2A View FIGURE 2 ) was apparently not the only way, or even the most common way, for birds to enter the fossil record at Rancho La Brea (Howard, 1930; Wilmers et al., 2003). More research needs to be done comparing the fossil bird assemblage at Rancho La Brea to actualistic predator kills like has been carried out with mammals (Carbone et al., 2009). And the life habits of the iconic teratorn are due for reanalysis using all the modern techniques now at our disposal.
Reconstructing the general body contours and bone placement of teratorns, we followed two mounted skeletons from our Museum posed in both perching and soaring positions (Scott, 1988) and a reconstruction by Scott Hartman (2013) showing a teratorn walking. Given the controversial reconstructions of teratorns, we decided to hedge our bets on its external appearance. We followed the white and grey coloration of several recent reconstructions in the Museum but deliberately left the neck narrower than would be expected with full plumage ( Figure 5 View FIGURE 5 ). This will allow us to draw a new texture to wrap around the mesh that reconstructs the teratorn with a more condor-like naked head should we choose to do so in the future.
Behavior. We created both walking and soaring behaviors closely following the movements of California condors. We will likely display teratorns both eating carrion and actively walking around the tar pits to reflect their uncertain status as scavengers.
Dwarf Pronghorn
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.