STATISTICAL ANALYSIS OF EVOLUTIONARY TRENDS

 

Introduction

Our Approach

Histological Analysis

Growth Curve Reconstruction and Developmental Mass Extrapolation

Statistical Analysis of Evolutionary Trends

Qualifications and Research Roles of the PI's

Disclosure of findings and contributions to human resources

References

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Evolutionary Trends in Growth Rates

We use several empirical methods that optimize calculated growth rates and histological patterns on existing phylogenetic hypothesis. These methods allow us to test hypotheses regarding where advance growth rates first appear in the coelurosaur family tree and whether avialan growth rate increase occurred via a single event, multiple events, or spanned several phylogenetic nodes. Three main approaches exist among all available methods to optimize quantitative data, such as growth rates, on a phylogenetic tree: linear parsimony (Farris, 1970; Swofford and Maddison, 1987), squared-change parsimony (Huey and Bennet 1987, Maddison, 1991, McArdle and Rodrigo 1994), and model based methods (Martins and Hansen 1997, Schluter et al. 1997). These methods differ both on the assumptions and on the information that can be retrieved from them. We employ linear parsimony and squared-change parsimony since because they have been thoroughly tested.

Findings to Date

Our studies are demonstrating that histological assessments of longevity coupled with DME derived body mass quantification can be used to accurately reconstruct growth curves from the fossilized remains of dinosaurs (Erickson and Tumanova 2000, Erickson et al. 2001; Fig. 6). From these curves the temporal length of the lag, exponential, and stationary stages of development can be elucidated, and exponential stage growth rates and ages at attainment of somatic maturity can be quantified.

Growth curves for non-avian dinosaurs

Figure 6. Growth curves for non-avian dinosaurs assessed from femoral histology and DME (From Erickson, Curry Rogers, and Yerby 2001). Our analysis revealed that sigmoidal equations accurately described the growth data for the six dinosaurs we tested (r 2 = 0.885 - 1.0). Exponential stage growth rates ranged from 3.4 to 14,460 g/day with values positively correlating with increased adult mass. No taxon substantially deviated from the general dinosaurian trend (r2 = 0.96). The length of the exponential growth stages ranged from approximately one to six years. The onset of somatic maturity occurred between the ages of three and thirteen with values positively correlating with increased body size.
Our sample of phylogenetically disparate dinosaurs have shown that all exhibited exponential stage growth rates higher than those found in traditional "reptile" groups. In addition, a unique general "dinosaurian" growth pattern has been discovered (Erickson et al. 2001, Fig. 7). Our testing of close outgroups to birds is showing rates typical of non-avian dinosaurs and no-where near as high as those in living birds. Hence we have evidence that nearly the entire evolution to rapid precocial rates occurred in taxa closer to the Avialae or after the evolution of birds.

Exponential growth of non-avian dinosaurs compared with data for living vertebrate groups

Figure 7. Exponential growth of non-avian dinosaurs compared with data for living vertebrate groups (from Erickson et al., 2001). The smallest dinosaurs (<1.0 kg) are predicted to have growth rates 5-8 times less than the more rapid rates for precocial avialans. DME assessments for dinosaurs from new histological data of Erickson et al. (2001); Chinsamy (1990, 1993); Erickson and Tumanova (2000); Curry (1999); and Horner et al. (2000). Data for extant taxa from compilations by Case (1978), Calder (1984). Progressing smallest to largest: S = Shuvuuia, P = Psittacosaurus, S = Syntarsus, M = Massospondylus, M = Maiasaura, A = Apatosaurus. The regression line extends to the range of size for non-avian dinosaurs (0.2 kg - 100,000 kg).
   
Recently processed specimens:
   

Byronosaurus femur-Hatchling

Byronosaurus  femur-Hatchling

 

   

Conchoraptor fibula

Conchoraptor fibula

 

   

Conchoraptor hatchling fibula

Conchoraptor hatchling fibula

 

   

Deinonychus gastralia

<i>Deinonychus</i> gastralia

 

   

Citpati femur

Citpati femur

 

   

Shuvuuia femur

Shuvuuia femur

 

   

Tyrannosaurus rex rib

Tyrannosaurus rex rib

 

   

Gorgosaurus rib

Gorgosaurus rib

 

   

Velociraptor fibula

Velociraptor fibula

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