A new hypothesis of dinosaur relationships and early dinosaur evolution

Abstract

Further discussion of the main phylogenetic analysesTrees were produced and analysed in TNT 1.5-beta (Goloboff et al. 2008). In total 74 taxa were scored for 457 characters. Using the new technology search function, with ratchet and drift set to their defaults (10 iterations and 10 cycles respectively) and with 100 random additional sequences, our data produced 93 MPTs of length 1734. Bremer supports were also calculated using TNT 1.5-beta.The following characters were treated as ordered: 24, 35, 39, 60, 68, 71, 117, 145, 167, 169, 174, 180, 197, 199, 206, 214, 215, 222, 251, 269, 272, 286, 289, 303, 305, 307, 313, 322, 333, 334, 338, 353, 360, 376, 378, 387, 393, 442, 446 Our characters were drawn and modified from a number of previous studies and supplemented with an additional 63 novel characters. The main sources of our characters were Gauthier (1986), Sereno (1991), Langer and Benton (2006), Yates (2007), Butler et al. (2008), , Nesbitt (2011) and Pol et al. (2011).Our investigations and analyses showed that a number of characters previously thought only to appear in theropods or sauropodomorphs (or both) can also found in a several ornithischian taxa and, conversely, a number of features traditionally associated with basal ornithischian taxa are also present in basal theropods and, in some instances, sauropodomorphs. Furthermore, many other characters that are more traditionally associated with only one or two dinosauriform groups were found to have a wider and/or more complex distribution than other studies have previously proposed, e.g. a mediolaterally oriented scar on the anterior face of the distal femur -present in Dromomeron (Nesbitt et al. 2009a), is also found in some herrerasaurids (PVSJ 373). We tried, as objectively as possible, to capture all these similarities, as well as notable differences, between the basal members of each of the major dinosaurian lineages using our newly composed set of characters.Critically, a large number of character states were found to be present in ornithischians and theropods only (see below). Additionally, a number of other character states were found that are present only in sauropodomorphs and herrerasaurids. Some previously proposed dinosaur synapomorphies were also found to be absent from a few important early dinosaur taxa. In most of these cases, our finds changed the optimisations of important characters within the tree, often leading to changes in the structure of the tree itself, as well as our interpretation of the basal dinosaur interrelationships that the distributions of these character states imply.A number of novel clades were recovered by our analysis. Of these, Ornithoscelida is the most strikingly different from previous systems of grouping and classification. A full list of synapomorphies for each of the major clades that we have recovered is given later in this Supplement (Section 3.4). A discussion of a few of the other important finds of our analysis follows here.A constraint tree was also produced in TNT 1.5-beta in order to test how man...

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