Given the task definition and input, reply with output. In this task, you are given a text of many news articles seperated by special token "|||||". Your task is to summarize them.

The deciphering of evolutionary trends in nonavian dinosaurs can be impeded by a combination of small sample sizes, low stratigraphic resolution, and lack of ontogenetic (developmental) details for many taxa. Analysis of a large sample (n > 50) of the famous horned dinosaur Triceratops from the Hell Creek Formation of Montana incorporates new stratigraphic and ontogenetic findings to permit the investigation of evolution within this genus. Our research indicates that the two currently recognized species of Triceratops (T. horridus and T. prorsus) are stratigraphically separated and that the evolution of this genus likely incorporated anagenetic (transformational) change. These findings impact interpretations of dinosaur diversity at the end of the Cretaceous and illuminate potential modes of evolution in the Dinosauria. 
  
 Abstract 
  
 The placement of over 50 skulls of the well-known horned dinosaur Triceratops within a stratigraphic framework for the Upper Cretaceous Hell Creek Formation (HCF) of Montana reveals the evolutionary transformation of this genus. Specimens referable to the two recognized morphospecies of Triceratops, T. horridus and T. prorsus, are stratigraphically separated within the HCF with the T. prorsus morphology recovered in the upper third of the formation and T. horridus found lower in the formation. Hypotheses that these morphospecies represent sexual or ontogenetic variation within a single species are thus untenable. Stratigraphic placement of specimens appears to reveal ancestor–descendant relationships. Transitional morphologies are found in the middle unit of the formation, a finding that is consistent with the evolution of Triceratops being characterized by anagenesis, the transformation of a lineage over time. Variation among specimens from this critical stratigraphic zone may indicate a branching event in the Triceratops lineage. Purely cladogenetic interpretations of the HCF dataset imply greater diversity within the formation. These findings underscore the critical role of stratigraphic data in deciphering evolutionary patterns in the Dinosauria. ||||| Story highlights Triceratops didn't always look like the way we picture them 
  
 It took a million years for its horn to evolve 
  
 The researchers spent 15 years to come up with the finding 
  
 Researchers at the Montana State University have breaking news -- one million years in the making. 
  
 Triceratops, the three horned dinosaur, didn't always look like the famous silhouette we know and love. Its signature profile, according to newly published research, took over a million years to develop. 
  
 It took researchers 15 years to come up with this finding. 
  
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 The researchers returned year after year to one area in Montana known as The Hell Creek Formation. 
  
 There, they found enough triceratops specimens to see the development of its facial anatomy. 
  
 John Scannella headed up the project and is the lead author of the paper in the Proceedings of the National Academy of Sciences 
  
 The group compared over 50 skulls. It found that "over one to two million years at the end of the Cretaceous Period, Triceratops went from having a small nasal horn and long beak to having a long nasal horn and shorter beak." 
  
 Although not ferocious in reputation like the Tyrannosaurus Rex, Triceratops was a beast of epic proportions. Thirty feet long, weighing up to 16,000 pounds, the creatures also featured a distinctive bony frill at the back of the head, covering the neck. 
  
 Previously, the group working at Hell Creek found that as an individual creature aged, the shape of its horns and skull changed. 
  
 "The new study finds evidence that not only did Triceratops change shape over the lifetime of an individual, but that the genus transformed over the course of the end of the age of dinosaurs," Scannella said. 
  
 Triceratops roamed the Earth near the end of the Cretaceous Period, a half a million years before the dinosaurs went extinct. 
  
 The first skeleton, found in 1887, was initially mistaken for a buffalo. 
  
 A scientist at Yale gave the creature its name two years later, translating from Greek as "three horned face." |||||

The rhino-like Triceratops, Greek for "three-horned face," didn't always embody its name in way we picture it doing. By comparing 50 skulls collected over a 15-year period from the Hell Creek Formation in Montana, paleontologists have learned that it took between 1 million and 2 million years for the large nasal horn it is famous for today to fully develop, while what started as a long beak shortened over that same time period, the scientists report in the Proceedings of the National Academy of Sciences. Though they've established the evolution, the study's lead author tells USA Today that "it's difficult to say what drove the change." The first Triceratops skeleton was found in 1887, reports CNN, and was at first thought to be that of a (presumably very large) buffalo. Two years later, a Yale scientist named it Triceratops for its impressive three-horned skull, which the scientists had previously learned changes subtly in shape over the course of a single lifetime as well. A half-million years before their extinction, they roamed the Earth in great numbers, reports UPI, which points out that our understanding of the Triceratops has been greatly boosted by the fact that so many fossils of the creature can be found in the Hell Creek Formation. "We went out and looked at where the fossils came from in context of the rock formation," the lead author explains. "The ones found low in the formation look different from the ones found high up." (Click to read about how one relative of Triceratops had wings on its head.)