Critters Abroad: Alamosaurus

Hey there every peoples!

This post goes out to a little known sauropod who got a boost from a recent paper. I could try to build it up but you already know who it is from the title. Today i want to talk about Alamosaurus and how he pertains to my grandiose ambitions.

Right off the bat, let’s get the common misconception out of the way. Alamosaurus is not named for the Alamo in Texas! It is instead named after a cottonwood tree (in a round about sort of way). The first fossils were discovered in the Ojo Alamo formation of New Mexico in 1922 (dinosaurs come mostly from the Naashoibito member, which many consider part of the Kirtland formation). The dinosaur was named for the formation it was found in, which in turn was named after the Ojo Alamo Trading Post which was in turn named after a cottonwood tree growing next to a nearby spring (Alamo is the local Spanish name for cottonwood trees). It would be a long while after this initial discovery that Alamosaurus would be found in Texas. This dinosaur has so far been restricted to the American southwest, being found in New Mexico, Texas, and Utah (with that last one representing the northernmost extent of Alamosaurus’ range). So far the two most complete specimens are an adult from the North Horn formation of Utah and a juvenile from Big Bend National Park in Texas.

Aside from those 2, many isolated bones have been referred Alamoaurus. How do we know these bones are Alamosaurus? Well for the same reason that Alamosaurus is unique among North American sauropods. Alamosaurus lived at the end of the Cretaceous period, 69 to 65 million years ago. For a long time in paleontology this represented a bit of an enigma. The late Jurassic was the heyday, it seemed, of North America’s giant long necked plant-eaters. But after reaching such a high diversity they all just vanished at the close of the Jurassic period. There was a gap of over 75 million years before the arrival of Alamosaurus into North America. Even though a large crop of early Cretaceous sauropods have been found in Utah (as well as a couple in Texas and Oklahoma) that shows they persisited well into the Cretaceous, they still managed to peter out around 100 million years ago. There wouldn’t be a sauropod in North America until Alamosaurs arrived in the late Cretaceous. Why? Scientists are still working that one that. The currently accepted view is that Alamosaurus migrated north from South America. This idea is supported by the fact that Alamosaurus was a titanosaur, a group of sauropods who thrived throughout the Cretaceous in the southern hemisphere. So far Alamosaurus is the only late Cretaceous sauropod in North America, so scientists can be fairly confident that when they find a sauropod in strata younger than 70 million years it is probably Alamosaurus.

Brian Switek once said “For years, one of the cardinal sins of paleontology illustration was showing a Tyrannosaurus attacking a sauropod dinosaur.” This was largely due to T. rex living tens of millions of years after the last sauropods died out. But a face off between the tyrant lizard king and a lumbering sauropod was declared a possibility when in 2005 a T. rex specimen was found in Utah’s North Horn formation. Since one of the most complete specimens of Alamosaurus was found in the same strata, it is reasonable to assume they lived at the same time and place. Though i find it interesting that few reconstructions of a T. rex attacking Alamosaurus have been rendered, considering that they have both been known from the same areas for some time (The north Horn formation, Utah; Javalina formation, Texas; and New Mexico). Nonetheless, one or two have emerged (though i couldn’t find any to post here).

Recently the big guy got another boost to his public image. Not too long ago paleontologists Denver Fowler (Museum of the Rockies) and Robert Sullivan (State Museum of Pennsylvania) published fragmentary specimens from New Mexico’s San Juan Basin. The fragments proved to be especially large, so the two scientists compared two vertebra fragments ( cervical and caudal) and a distal femur to some dinosaurs from South America, a continent that has produced many contenders for the title of largest dinosaur*. Specifically, they compared Alamosaurus to Puertasaurus and Futalognkosaurus and found that the Alamosauruses from which the three specimens came from (each was found in a different location, ruling out that they came from a single, abnormally large individual) were in the same ballpark in terms of size. Of course, this is all based on fragmentary remains:

Cervical vertebra fragment of Alamosaurus (top, in posterior and right lateral views) compared to cervical vertebra of Puertasaurus (bottom, in anterior and right lateral views). From Fowler and Sullivan, 2011

Caudal vertebra of Alamosaurus (first 3: vertebra 2-4 from the North Horn specimen. Fourth: fragment from the San Juan Basin, New Mexico) compared to caudal vertebra of Futalognkosaurus. From Fowler and Sullivan, 2011

*(I define “largest” by mass. It just seems like the best measurement to determine who is bigger than another. For example, a giraffe is much taller than an elephant and yet it is the elephant who is granted the title of largest living land mammal. Another example is the Arctic lion’s mane jellyfish and the blue whale. Even though the jelly fish can grow longer, the whale is considered bigger because it is exponentially heavier. Plain and simple, putting two of any of these animals on a scale against each other, the scale will always tip towards who is heavier. So i think the best definition of largest is by weight)

The Alamosaurus material is all incomplete bones, Puertasaurus is based on four vertebra, and Futalognkosaurus is known from a significant section of the spinal column made up of 3 individuals. These animals have been estimated between 90 and 110 feet long and anywhere between 80 and 100 tons. Since Alamosaurus appears to be of a similar size, that would make it North America’s largest dinosaur, surpassing the two current contenders Supersaurus (108 to 112 ft long and 35 to 40 tons) and Sauroposeidon (~80 ft long, 56 ft tall, and 55-65 tons).  Of course, Alamosaurus and Sauroposeidon are known from very fragmented (and in the case of Sauroposeidon limited) materiel, so knowing just how bulky and proportioned they were is going to take a lot more fossils and study.

While throwing North America back into the ring as far as fossil records go, Denver Fowler apparently had another goal intended with this paper. He wrote in a comment on Dinosaur tracking:

Anyway, the “biggest dinosaur” label is fun, but I was hoping that this paper might drum up some further interest in the New Mexico faunas. We really need to get down there with larger field teams and find more complete specimens of the unique fauna.

Over the past 20 years or so, fieldwork by Bob Sullivan (State Museum PA) and the NMMNH has identified a number of good fossil sites and horizons. I would really like to see the New Mexico Late Cretaceous achieve something similar to the great work the Utah crew have done in the Kaiparowits (and elsewhere, e.g. the early Cretaceous).

To which i replied in the same post:

While not as a result of your paper (well, a little bit), I do have interest in the late cretaceous of New Mexico. I got hooked by the idea of dinosaur provincialism (boosted by the description of Bistahieversor (god, that’s a hard name to spell and pronounce!)) and as such want to build a provincial collection. No one has any idea how much i have been chomping at the bit to go search the Two Medicine, Kaiparowits, and Kirtland formations (and maybe the El Gallo formation in Baja California. Anyone got good relations with Mexico?). I agree that the late Cretaceous of New Mexico does warrant more exploration. Wish i could be out there right now looking for Titanoceratops, Bistahieversor, Kritosaurus, and their countrparts to the north. Unfortunately, i’m just a community college student at the moment and am so far having trouble just looking for fossils in my home county. But at least your paper has given me one more incentive!

As some of you might know, i have a rather unrealistic vision of opening my own museum some day (which i feel like is likely never to happen. I figured i might be better off helping some other museum. We’ll just have to wait and see) and part of that vision is building a provincial collection of dinosaurs. It would consist of: Two Medicine formation in Montana for north; Kirtland formation in New Mexico for south; and the El Gallo formation in Baja California for west. While it would be nice to dig into the Kaiparowits to complete the north-south chain, the El Gallo has priority for me (but if i can’t get search the El Gallo, the Kaiparowits will make a nice back up). As i mentioned above many consider the Ojo Alamo formation to be part of the Kirtland formation. While it doesn’t necessarily fit with the typical idea of dinosaur provincialism, I said i wanted to search the Kirtland formation so that means looking in this member as well. And why not? Finding more of the (possibly) largest dinosaur in North America, finding new species, fleshing out what the south looked like at the end of the Cretaceous (so much has been focused on the north, namely the Hell Creek formation) sounds awfully enticing. This rock preserves the final chapter of North America’s dinosaurs. Considering that so little has been done in the Ojo Alamo formation, it’s sounds like a fantastic place to break new ground (like several other instances in this post, no pun was intended). That’s plenty reason enough for me! So thanks Denver and Robert for giving me another reason to go to New Mexico for my dinosaurs.

Till next time!

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