Hone and Holtz review spinosaurids

It’s always good to have a clade reviewed now and then.
Reviews form ready references for those just diving into a subject for the first time, or need to get ‘brushed up’ on all the latest literature. However…

You know you’re in a wee bit of trouble
when authors Dr. David Hone and Dr. Thom Holtz open their abstract with “The spinosaurids represent an enigmatic and highly unusual form of large tetanuren theropods.” In this day and age, after two decades of phylogenetic analysis, there is no longer ANY excuse for labeling ANY taxon or clade enigmatic” or “highly unusual.” Every taxon should be phylogenetically ‘buttoned down’ by now. And this one is, more or less…

Everyone agrees
that spinosaurs nest with megalosaurs… but which ones? This is where avoiding suprageneric taxa pays off. And spinosaurs are not all that weird, especially the early ones. Most of their parts (bones) have readily recognizable counterparts in more typical (non-spinosaurid) theropods.

ALL phylogenetic analyses nest EVERY included taxon.
So, there is always a closest known sister taxon, but you have to do the work and not just repeat old adages or promote old papers…and by all means, avoid suprageneric taxa!

Figure 1. Aquatic Spinosaurus to scale with contemporary Early Cretaceous giant fish.

Figure 1. Aquatic Spinosaurus to scale with contemporary Early Cretaceous giant fish.

The authors recover only one suprageneric outgroup taxon
in their tiny six taxon cladogram. Unfortunately, this provides no clue as to the origins of the Spinosauridae other than somewhere within the suprageneric “Megalosauridae”. Hone and Holtz report, “The origins of the Spinosauridae remain somewhat obscure. There is a seemingly undocumented phase of the spinosaurid lineage from 170 until 130 mya.”

Unfortunately,
we’ve seen Dr. Hone punt and sidestep on clade origins before. This habit not only leads to disappointing reading, but feeds into traditional “enigmatic and highly unusual” paradigms that were answered a year ago here (Fig. 1) and should have been answered seven and five years ago by Benson (2010) and by Carrano, Benson & Sampson (2012). Sinocalliopteryx entered the literature in 2007, but was mislabeled a ‘compsognathid.’ There is no longer any value in keeping the sacred vaults of paleontology full of mysteries. To do so runs the risk of permitting amateurs and bloggers to make discoveries that should clearly be in the province of the PhDs. Unless they don’t want to do the work.

Figure 1. The LRT nests spinosaurids with Sinocalliopteryx and other taxa not mentioned in Hone and Holtz 2017.

Figure 1. The LRT nests spinosaurids with Sinocalliopteryx and other taxa not mentioned in Hone and Holtz 2017. All clade members are long-snouted theropods.

Here
at the large reptile tree (LRT, 1033 taxa, subset Fig.1) the following taxa nest with Spinosaurus and Suchomimus.

  1. Sinocalliopteryx – 125 mya
  2. Xiongguanlong – 112 mya
  3. Deinocheirus – 70 mya
  4. Proceratosaurus – 165 mya

Obviously all these taxa
had earlier origins and radiations, based on their late appearances in the fossil record and nesting in the cladogram.

Here’s an OPTION for all paleontologists struggling with a phylogenetic enigma:
Just take a look at the LRT, where every taxon is comfortably nested…(even spinosaurs!), request the .nex file, add your taxon to it, review for errors, then report your results. Or keep the results a secret and perform your own analysis while including all pertinent taxa, and then reporting your own results. The days of enigmatic taxa should be over, though I’m sure we’ll keep seeing moderately unusual taxa. The highly unusual ones are getting to be more commonplace and easier to handle given the large gamut already in our vaults. And the biggest benefit: you won’t have bloggers chiding you for taxon exclusion.

References
Benson RBJ 2010. A description of Megalosaurus bucklandii (Dinosauria: Theropoda) from the Bathonian of the UK and the relationships of Middle Jurassic theropods. Zoological Journal of the Linnean Society 158:882–935.
Carrano MT, Benson RBJ and Sampson SD 2012: The phylogeny of Tetanurae (Dinosauria: Theropoda), Journal of Systematic Palaeontology, 10:2, 211-300.
Hone DWE and Holtz TR Jr. 2017. A century of spinosaurs — a review and revision of the Spinosauridae with comments on their ecology. Acta Geologica Sinica (English edition) 91(3):1120–1132.

 

 

 

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s