Thursday, January 28, 2010

Haplocheirus, the (or one of the?) Jurassic alvarezsaur(s)

Above: Illustration of Haplocheirus, from Stone 2010 (intro article published in Science)

Those coelurosaur ghost lineages just keep getting filled in lately. Today sees the publication of Haplocheirus sollers, the first Jurassic alverezsaur. Unlike its later brethren, this doesn't look very alvarezsaurian at first glance, more like you're typical generic coelurosaur. As Tom Holtz said o the DML, this is the first alvarezsaur that "looks normal"!

However, telltale signs (such as downward-flared basipterygoid processes on the skull) and a phylogenetic analysis shows that this is the earliest and most primitive member of the group. It comes from the Late Jurassic of China, and falls out as a basal maniraptoran, which jibes with the placement of alvarezsaurs in many recent studies, not avialan or ornithomimosaur as previously suspected by some. Interestingly, the teeth are heterodont, which seems to me to give weight to the reent hypothesis that all maniraptorans are ancestrally omnivorous. It's also the largest nkown alvarezsaurid known from good material, indicating that these guys may have started out fairly big and later shrunk to the diminutive sizes seen in the likes of Parvicursor.

But, is this really the earliest alvarezsaur on the radar? Some goss fans may have heard of a supposed alvarezsaur from the Tiaojishan Formation, preserved with feathers, mentioned at last year's SVP. That ain't this, though it would be from roughly the same time period (about 60 Ma ago). Depending on how similar the two species are, we might be looking at a ghost lineage that goes even further back than before, rther than being clipped to the mid-Jurassic. Time will tell.

9 comments:

  1. Oh, boy, oh, boy! It's that (one of those?) Jurassic alvarezsaurids I was so anticipating. We finally get a look at what really basal alvarezsaurids look like!

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  2. I think you mean 160 mya, right?

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  3. Don't be too quick to assume it's a maniraptor: http://theropoddatabase.blogspot.com/2010/01/haplocheirus-jurassic-alvarezsaur-is.html

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  4. Oh, wait a moment. It's not an alvarezsaurid as I supposed is it? It's an alvarezsauroid!

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  5. Albertonykus: Actually, it's kinda both. Most definitons of Alvarezsauridae are branch based, (Mononykus > Passer). The new paper names that group Alvarezsauroidea, and restricts Alvarezsauridae to (Alvarezsaurus + Mononykus). So in the traditoonal sense, it's an Alvarezsaurid, but the paper isn't using traditional terms. Kinda like how the Neovenatorids would be a sub-group of Carcharodontosauridae in traditional definitions, but the paper describing them re-named the traditional Carcharodontosauridae to Carcharodontosauria. Jeez, where's phylocode when you need it?

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  6. Damn, Mike beat me to the punch on linking Mickey's post. :)

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  7. The first phylogenetic definition of Alvarezsauridae is Novas's (1996) = "Mononykus + Alvarezsaurus" and not Sereno's one.

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  9. I always like Jurassic events and shows. The pre historic creatures attracts me a lot. Especially the dinosaurs. I have watched the movie "Jurassic Park" no less than 15 times.

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