torosaurus is the closest relative to the triceratops.
torosaurus is the closest relative to the triceratops.
what is the closest relative to the triceratops?
torosaurus
in 2012, longrich investigated the problem by applying the principle of falsification. from any valid scientific hypothesis predictions can be derived by which it can be tested. longrich argued that the "toromorph" hypothesis implied three such predictions. firstly, if "torosaurus" were identical to "triceratops", their fossils should be found in the same locations. in fact, their geographical ranges do not perfectly coincide: in the very north no "torosaurus" fossils have been found, while from the south only "torosaurus utahensis" is known. however, this situation could be an artefact of the relative scarcity of "torosaurus" remains and imperfect sampling. longrich therefore concluded that the hypothesis was corroborated by the first prediction. secondly, the hypothesis predicted that all "torosaurus" specimens would be adults, while no "triceratops" specimens would be very old. according to longrich, this last point had not yet been established. admittedly, in 2011 horner had published an histological study showing that all "triceratops" specimens investigated possessed a subadult bone structure, but the sample had been too small to allow for a valid generalisation to all "triceratops" fossils. to better test the prediction, longrich proposed a list of twenty-four external skull traits, by which specimens could be checked regarding their level of skull element fusion and thus maturation. thirty-six specimens were investigated applying these criteria. it transpired that the fusion typically took place in a certain sequence, providing additional information about their age. indeed, by these criteria most "torosaurus" specimens were very old. however, there were two exceptions. the small individual ansp 15192 was, though adult, still relatively young as shown by the lack of fusion of the snout bones. the youngest specimen was ypm 1831, with an unfused snout, epijugal and occipital condyle; furthermore, it had lost all of its frill osteoderms, apparently because they had not been fused yet, while the frill edge had the external appearance of growing, young, bone. on the other hand, longrich found that ten of the "triceratops" skulls investigated had attained the same level of maturation as the most aged "torosaurus" specimens. longrich concluded that the test of the second prediction refuted the hypothesis. the third prediction was that transitional forms could be found between "torosaurus" and "triceratops". longrich considered the claim that the thin areas on "triceratops" frills were precursors of parietal "fenestrae", as the strongest proof of a transitional phase. however, he pointed out that these structures differed in position: the "triceratops" depressions are partly located on the squamosal while the "torosaurus" holes are fully surrounded by the parietal. furthermore, the depressions are bordered by much thicker bone, while the "torosaurus" holes are surrounded by thin bone. longrich concluded that the hypothesis failed regarding the third prediction. being refuted in two of the three predictions, the hypothesis should be rejected.
torosaurus
david a. krauss and john m. robinson proposed that "tyrannosaurus" could have used a hunting strategy similar in concept to "cow tipping" against "triceratops", where the "tyrannosaurus" would ambush and knock the "triceratops" over to fall on its side. this strategy, according to the krauss and robinson could explain the unique characteristics of "tyrannosaurus". "tyrannosaurus"s small, yet strong arms could have been adapted to grasp onto the back of triceratops while pushing with its pectoral region, its large clawed feet would have given it better traction, its large head could have been used to tip the "triceratops" over and its large mouth and bone piercing teeth would have made bites to the side more efficient and deadly. when the "triceratops" had fallen over to its side, "tyrannosaurus" would then bitten it at the rib cage; killing it. krauss and robinson backed up their proposal through physical analyses; finding that "tyrannosaurus" moving at moderate speed could have generated enough force to topple "triceratops" and would have only taken 2–3 seconds. their study suggested that a "tyrannosaurus" impacting the "triceratops" at a conservative estimated speed of 7.5 meters per second would have enabled it to topple "triceratops" without injuring itself, though there could be some variance depending on the sizes of the animals ("tyrannosaurus" could have attacked a smaller "triceratops"). furthermore, their study noted that "triceratops" would have experienced some difficulty quickly getting back up from being toppled on to its side. according to the study, modern day analogues of "triceratops" such as rhinoceros, camels and large bovids, experience the same kind of difficulty, taking 3–10 seconds to recover. but "triceratops" may have experienced more difficulty due to its frill. according to the study, "tyrannosaurus" arms were adapted for this strategy, pushing the prey with its chest while gripping it with its arms reduced the chance of the prey slipping away while being pushed. the arms, being short yet strong reduced the chance of joint injury during this struggle. also having more of the arm's power concentrated on its flexors instead of the extensors, were ideal since it would have had to flex its arms to keep its prey close. when the "tyrannosaurus" is pressed against the side of "tricieratops", its arms were at the right height to reach the spine of the "triceratops", providing a place to grip on. furthermore, krauss and robinson suggest that this strategy would have been effective against other large ceratopsians and because the attack was done through an ambush, "tyrannosaurus" would not have needed to compete in speed.
feeding behaviour of tyrannosaurus