Happy Sci-Day, fans! Today, I will be finishing up the Evolutionary History of Dinosaurs blog mini-series with a post about the major lineage of dinosaurs known as the Ornithischians. Now, I know some of you might be wondering why I'm not doing a post about Sauropoda, but I do have a good reason. Since there were no sauropods in the Hell Creek formation, spending a lot of time going into their history and anatomy might give people the wrong idea of what animals will be represented in the game itself.
The Ornithischian-Saurischian split is the earliest divergence in the entire Dinosauria clade. In the Ornithischian lineage, the bones of the pelvic girdle were configured such that both pubis and ischium faced caudally, whereas the Saurischian clade retained the ancestral pelvic bone configuration (though several Saurischian lineages would evolve the same configuration through convergence). Another feature that separates Ornithischians from Saurischians is the presence of an additional bone extending from the dentary, called the predentary. This bone did not bear teeth, and coincides with the premaxilla of the upper jaw to form a beak-like structure that would be useful for eating plants.
The earliest confirmed Ornithischian is a species known as Pisanosaurus mertii, from the Carnian- Norian stages of the Triassic period (between 228 and 216 million years ago) of what is now Argentina (Butler et al., 2008). It was a small, bipedal dinosaur, approximately 1 meter in length and weighing around 2.27-9.1 kilograms (Holtz, 2008), though the incompleteness of the specimen makes such estimates somewhat uncertain. Like all Ornithischians currently known, it was herbivorous.
By the early Jurassic, the major clades of the group had already appeared. One such group is the armored Thyreophorans. This lineage would lead to two very famous lineages - the Stegosaurs and the Ankylosauria. Ankylosauria had extremely thick armor, a low-lying posture, and evidence indicates that they also had thick, muscular tongues (Hill et al., 2015). This group would split into the Nodosaurs and Ankylosaurs. In the Ankylosaurs, the scutes at the tip of the tail fused into a massive, bony club, whereas the prominent feature in Nodosaurs were their spikes. Additionally, the Ankylosaurs had large squamosal plates projecting from the bottom and top of the skull on both sides, a feature absent in Nodosaurs. Both Nodosaurs and Ankylosaurs were represented in the Hell Creek ecosystem, in the forms of Denversaurus (=Edmontonia?) schlessmani and Ankylosaurus magniventris, respectively.
Another of the major groups of Ornithischians was the Ornithopods. This group would lead to the extremely successful Hadrosaurs, or "duck-billed" dinosaurs, as well as several other lineages. One lineage of Ornithopod present in the Hell Creek formation was Thescelosaurus. The popular hadrosaur Edmontosaurus annectens also lived in the area.
Sister to the ornithopods were the marginocephalians. This lineage would split to form the Pachycephalosauria and the Ceratopsia. The former of the two contained famous creatures such as Pachycephalosaurus wyomingensis, whereas the latter contained species like Triceratops horridus. The Pachycephalosaurs were bipedal creatures with thick, bony, skulls varying in shape from round to relatively flat 'domes'. It has recently been proposed that the skull morphology thought to be indicative of different species may actually represent growth stages in a single species (Horner and Goodwin, 2009).
Ceratopsians also had very interesting carnial ornamentation, though it came in the form of large frills and horns of varying shapes and sizes. While the earliest members were bipedal with little to no frill or horns, later species would develop extensive frills and large horns, as well as a quadrupedal gait. Scale impressions are known from several species, including Triceratops, which show large, non-overlapping scales. Like in Pachycephalosaurs, there is evidence of complex cranial ontogeny, with specimens of Triceratops of different ages show significant differences in frill and horn shape. In fact, it has been suggested that Torosaurus latus is not a unique species, rather representing adult Triceratops (Scannella and Horner, 2010). While this assertion is by no means settled, the plasticity of the skull as evidenced by known specimens does not eliminate the possibility.
Well, I hope this Sci-Day has been informative! Be sure to tune in next week to learn more about the amazing creatures that lived on ancient earth!
Acknowledgements:
Butler, Richard J; Upchurch, Paul; Norman, David, B. 2008. The phylogeny of the ornithischian dinosaurs. Journal of Systematic Palaeontology 6 (1): 1-40.
Holtz, Thomas R. Jr. 2008. Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages.
Hill, R. V.; D'Emic, M. D.; Bever, G. D.; Norell, M. A. 2015. A complex hyobranchial apparatus in a Cretaceous dinosaur and the antiquity of avian paraglossalia. Zoological Journal of the Linnean Society 175 (4): n/a.
Horner, J. R.; Goodwin, M. B. 2009. Extreme cranial ontogeny in the Upper Cretaceous Dinosaur Pachycephalosaurus. PLoS ONE, 4 (10): e7626.
Scanella, J; Horner, J. R. 2010. Torosaurus Marsh, 1891, is Triceratops Marsh, 1889 (Ceratopsidae: Chasmosaurinae): synonymy through ontogeny. Journal of Vertebrate Paleontology, 30 (4): 1157-1168.
Friday, February 26, 2016
Tuesday, February 23, 2016
Creature Feature 8
Hope you all had a great weekend! This week, we're going to feature one of the most well-known of all the dinosaurs from Hell Creek, the ornithischian hadrosaur Edmontosaurus annectens!
As a hadrosaur, Edmontosaurus is a bulky animal with a long, laterally compressed tail and a head ending in a wide, duck-like beak (hence the term "duck-bill" often associated with hadrosaurs). The forelimbs were not quite as robust as the hindlimbs, but were sufficiently long to be used when standing or moving.
The dentition of Edmontosaurus was quite interesting. Its teeth were only present in the maxillae and dentaries, and were composed of 6 different types of tissue (Erickson et al., 2012). These teeth grew in large columns of at least six teeth, and the number of columns varied by the size of the animal (Lull and Wright, 1942). As with some other herbivorous dinosaurs (ie Triceratops), these teeth were replaced throughout the lifetime of the animal, each new tooth taking around six months to form (Stanton Thomas and Carlson, 2004).
The feeding habits of Edmontosaurus have been a matter of debate for many years. The most recent simulations based on preserved skulls and soft tissue suggest that Edmontosaurus was a grazer instead of a browser, as the microwear on the teeth was dominated by scratches that would be unlikely in a browsing herbivore (due to eating less abrasive foods). Suggested dietary components include Equisetum and other silica-rich plants, as well as soil accidentally ingested while grazing (Williams et al., 2009). Additionally, the structure of Edmontosaurus teeth suggests that they were capable of both slicing and grinding (Erickson et al., 2012).
Currently, evidence points to Edmontosaurus having a diet heavy in gymnosperms (Stanton Thomas and Carlson, 2004), based on enriched carbon isotope values in tooth enamel of multiple specimens. However, it is certainly possible that other factors were also contributing to the observed data, so this is by no means certain.
Emontosaurus walked with a quadrupedal gait, but its anatomy might allow it to run on its rear limbs alone should the need arise (for example, to escape a potential predator). The two fastest simulated gaits thought to be realistic were 15.7 meters per second for a gallop, and 14.0 meters per second for a bipedal run. The study in question found only weak support for bipedal running as the most likely option for a high-speed gait, but the possibility of galloping was not ruled out (Sellers et al., 2009).
There is also significant evidence for gregarious behavior in Edmontosaurus. There are extensive bone beds attributed to the genus, with one such bed estimated to contain the dissociated remains of between 10,000-25,000 Edmontosaurus specimens (Chadwick et al., 2006). While Edmontosaurus lacked the bony crests seen in other hadrosaurs, there is evidence for potential soft tissue structures related to auditory or visual signaling (Hopson, 1975). It has even been proposed that the gracile and robust forms observed in Edmontosaurus represent male and female specimens, but the validity of this claim has not yet been established (Gould et al., 2003).
Well, I hope you enjoyed this week's creature feature! Edmontosaurus was a fascinating creature, and it will be a joy to see it come to life in Dinosaur Battlegrounds!
Acknowledgements:
Bell, P. R.; Fanti, F.; Currie, P. J.; Arbour, V. M. 2013. A Mummified Duck-Billed Dinosaur with a Soft-Tissue Cock's Comb. Current Biology.
Erickson, Gregory M.; Krick, Brandon A.; Hamilton, Matthew; Bourne, Gerald R.; Norell, Mark A.; Lilleodden, Erica, Sawyer, W. Gregory. 2012. Complex dental structure and wear biomechanics in hadrosaurid dinosaurs. Science 338 (6103): 98-101.
Lull, Richard Swann, Wright, Nelda E. 1942. Hadrosaurian Dinosaurs of North America. Geological Society of America Special Paper 40. Geological Society of America. pp. 50-93.
Stanton Thomas, Kathryn J; Carlson, Sandra J. Microscale δ18O and δ13C isotopic analysis of an ontogenetic series of the hadrosaurid dinosaur Edmontosaurus: implications for physiology and ecology. Palaeogeography, Palaeoclimatology, and Palaeoecology 206 (2004): 257-287.
Williams, Vincent S.; Barrett, Paul M.; Purnell, Mark A. 2009. Quantitative analysis of dental microwear in hadrosaurid dinosaurs, and the implications for hypotheses of jaw mechanics and feeding. Proceedings of the National Academy of Sciences 106 (27) 11194-11199.
Sellers, W. I.,; Manning, P. L.; Lyson, T.; Stevens, K; Margetts, L. 2009. Virtual palaeontology: gait reconstruction of extinct vertebrates using high performance computing. Palaeontologia Electronica 12 (3): unpaginated. Retrieved 2016-2-23.
Chadwick, Arthur; Spencer, Lee; Turner, Larry. 2006. Preliminary depositional model for an Upper Cretaceous Edmontosaurus bonebed. Journal of Vertebrate Paleontology 26 (3, suppl.): 49A.
Hopson, James A. 1975. The evolution of cranial display structures in hadrosaurian dinosaurs. Paleobiology 1 (1): 21-43.
Gould, Rebecca; Larson, Robb; Nellermoe, Ron. 2003. An allometric study comparing metatarsal IIs in Emontosaurus from a low-diversity hadrosaur bone bed in Corson Co., SD. Journal of Vertebrate Paleontology 23 (3, suppl.): 56A-57A.
Model of Edmontosaurus annectens.
Edmontosaurus was one of the largest hadrosaurs known, reaching approximately 12 meters in length and weighing in at an estimated 4.0 metric tons. It is also known from a few exceptionally preserved specimens displaying soft tissues such as scale impressions and possibly gut contents (Bell et al., 2013)!As a hadrosaur, Edmontosaurus is a bulky animal with a long, laterally compressed tail and a head ending in a wide, duck-like beak (hence the term "duck-bill" often associated with hadrosaurs). The forelimbs were not quite as robust as the hindlimbs, but were sufficiently long to be used when standing or moving.
The dentition of Edmontosaurus was quite interesting. Its teeth were only present in the maxillae and dentaries, and were composed of 6 different types of tissue (Erickson et al., 2012). These teeth grew in large columns of at least six teeth, and the number of columns varied by the size of the animal (Lull and Wright, 1942). As with some other herbivorous dinosaurs (ie Triceratops), these teeth were replaced throughout the lifetime of the animal, each new tooth taking around six months to form (Stanton Thomas and Carlson, 2004).
The feeding habits of Edmontosaurus have been a matter of debate for many years. The most recent simulations based on preserved skulls and soft tissue suggest that Edmontosaurus was a grazer instead of a browser, as the microwear on the teeth was dominated by scratches that would be unlikely in a browsing herbivore (due to eating less abrasive foods). Suggested dietary components include Equisetum and other silica-rich plants, as well as soil accidentally ingested while grazing (Williams et al., 2009). Additionally, the structure of Edmontosaurus teeth suggests that they were capable of both slicing and grinding (Erickson et al., 2012).
Currently, evidence points to Edmontosaurus having a diet heavy in gymnosperms (Stanton Thomas and Carlson, 2004), based on enriched carbon isotope values in tooth enamel of multiple specimens. However, it is certainly possible that other factors were also contributing to the observed data, so this is by no means certain.
Emontosaurus walked with a quadrupedal gait, but its anatomy might allow it to run on its rear limbs alone should the need arise (for example, to escape a potential predator). The two fastest simulated gaits thought to be realistic were 15.7 meters per second for a gallop, and 14.0 meters per second for a bipedal run. The study in question found only weak support for bipedal running as the most likely option for a high-speed gait, but the possibility of galloping was not ruled out (Sellers et al., 2009).
There is also significant evidence for gregarious behavior in Edmontosaurus. There are extensive bone beds attributed to the genus, with one such bed estimated to contain the dissociated remains of between 10,000-25,000 Edmontosaurus specimens (Chadwick et al., 2006). While Edmontosaurus lacked the bony crests seen in other hadrosaurs, there is evidence for potential soft tissue structures related to auditory or visual signaling (Hopson, 1975). It has even been proposed that the gracile and robust forms observed in Edmontosaurus represent male and female specimens, but the validity of this claim has not yet been established (Gould et al., 2003).
Well, I hope you enjoyed this week's creature feature! Edmontosaurus was a fascinating creature, and it will be a joy to see it come to life in Dinosaur Battlegrounds!
Acknowledgements:
Bell, P. R.; Fanti, F.; Currie, P. J.; Arbour, V. M. 2013. A Mummified Duck-Billed Dinosaur with a Soft-Tissue Cock's Comb. Current Biology.
Erickson, Gregory M.; Krick, Brandon A.; Hamilton, Matthew; Bourne, Gerald R.; Norell, Mark A.; Lilleodden, Erica, Sawyer, W. Gregory. 2012. Complex dental structure and wear biomechanics in hadrosaurid dinosaurs. Science 338 (6103): 98-101.
Lull, Richard Swann, Wright, Nelda E. 1942. Hadrosaurian Dinosaurs of North America. Geological Society of America Special Paper 40. Geological Society of America. pp. 50-93.
Stanton Thomas, Kathryn J; Carlson, Sandra J. Microscale δ18O and δ13C isotopic analysis of an ontogenetic series of the hadrosaurid dinosaur Edmontosaurus: implications for physiology and ecology. Palaeogeography, Palaeoclimatology, and Palaeoecology 206 (2004): 257-287.
Williams, Vincent S.; Barrett, Paul M.; Purnell, Mark A. 2009. Quantitative analysis of dental microwear in hadrosaurid dinosaurs, and the implications for hypotheses of jaw mechanics and feeding. Proceedings of the National Academy of Sciences 106 (27) 11194-11199.
Sellers, W. I.,; Manning, P. L.; Lyson, T.; Stevens, K; Margetts, L. 2009. Virtual palaeontology: gait reconstruction of extinct vertebrates using high performance computing. Palaeontologia Electronica 12 (3): unpaginated. Retrieved 2016-2-23.
Chadwick, Arthur; Spencer, Lee; Turner, Larry. 2006. Preliminary depositional model for an Upper Cretaceous Edmontosaurus bonebed. Journal of Vertebrate Paleontology 26 (3, suppl.): 49A.
Hopson, James A. 1975. The evolution of cranial display structures in hadrosaurian dinosaurs. Paleobiology 1 (1): 21-43.
Gould, Rebecca; Larson, Robb; Nellermoe, Ron. 2003. An allometric study comparing metatarsal IIs in Emontosaurus from a low-diversity hadrosaur bone bed in Corson Co., SD. Journal of Vertebrate Paleontology 23 (3, suppl.): 56A-57A.
Friday, February 19, 2016
Sci-Day 7: Evolutionary History of Dinosaurs, part 3: Theropoda
Happy Sci-Day, fans! This week, I'm going to talk a bit about the only clade of dinosaurs with extant members - Theropoda.
I already said some of the basics about the group in last week's post, so I won't repeat those points. The theropods are an incredibly diverse group - they range in size from the monstrous Spinosaurus, weighing in at 12 to 20.9 metric tons (Therrien and Henderson, 2007) and over 15 meters long (Ibrahim et al., 2014) to the minute Mesigulla helenae, at only 5-6cm in length and weighing around 2 grams (Del Hoyo and Sargatal, 1999).
Theropods really came into their own at the dawn of the Jurassic - these early creatures were the Neotheropoda (though Coelohysoids existed at the close of the Triassic, Neotheropoda really cranked out some species when the Jurassic came around). These early Neotheropods include the Coelophysoidea and the Dilophosauridae. The forelimbs in these groups were relatively well-developed and robust, with four digits (though at least in some species such as Coelophysis bauri, only 3 were functional (Rinehart et al., 2007)) in contrast to many more derived groups that showed digit reduction (such as the Avialans), overall size reduction (taken to an extreme in some of the most derived Abelisaurs), or both (like in Tyrannosauroids).
The split in the Neotheropoda that led to Dilophosauridae also led to the Averostra - all members of this group have a promaxillary fenestra; this group is composed of the last common ancestor of Ceratosaurus nasicornis and Allosaurus fragilis, and all its descendants (Ezucrra and Cuny, 2007). This group split up into the Ceratosauria and the Tetanurae. The former of the two includes the Abelisaurs, and were the dominant dinosaur lineage on the Southern landmasses at the close of the Mesozoic. The Tetanurae would split again to form the Megalosauroidea (a group including the Spinosaurs), and the Avetheropoda.
The Avetheropoda split into the Allosauroidea and the Coelurosauria - the former of the two lasted until roughly 93 million years ago in South America (Coria and Currie, 2006), though if Megaraptorans are in the group that would mean they lasted to the close of the Mesozoic [though it is currently thought that Megaraptorans are actually tyrannosauroids (Porfiri et al., 2014)]. The Coelurosaurs, on the other hand, still live on today in the form of birds.
Coelurosaurs are an incredibly fascinating group of dinosaurs - this is the group that contains creatures as vastly different as Tyrannosaurus rex and Microraptor. Interestingly, most dinosaurs found with preserved feathers are Coelurosaurs, and it has been suggested that feathers were a shared character between all species in the group (Currie, 2005). The Coelurosaurs came to dominate the northern continents in the end of the Cretaceous, with Tyrannosaurs being the largest terrestrial carnivores. However, it was another Coelurosaur group, the Maniraptorans, that would survive through the K-T extinction in the form of the Avialae. If that name sounds familiar, then you've been paying attention - that is the clade that consists of all extant birds!
Well, I hope you enjoyed this week's Sci-Day! I did not go too in-depth on most of the groups, because I wanted to pay particular attention to those groups that were represented in the Hell Creek formation. As far as I know, the only theropods from Hell Creek were Coelurosaurs, with Tyrannosaurus, a few Oviraptorsaurs, some Ornithomimids, and a bunch of Maniraptorans of several affinities. I could go a bit more into those subgroups, but I also want to get a chance to cover other subjects in future Sci-Day posts. If you would like to learn more about the groups, I'd encourage you to search on the Internet for some information, there are plenty of great places to look! :)
Acknowledgements:
Therrien, F; Henderson, D.M. 2007. My theropod is bigger than yours... or not: estimating body size from skull length in theropods. Journal of Vertebrate Paleontology 27 (1): 108-115.
Ibrahim, N.; Sereno, P. C.; Dal Sasso, C.; Maganuco, S; Fabbri, M.; Martill, D. M.; Zourhi, S.; Myhrvold, N.; Iurino, D. A. 2014. Semiaquatic adaptations in a giant predatory dinosaur. Science 345 (6204): 1613-1616.
Del Hoyo, J. Elliott, A. and Sargatal, J. 1999. Handbook of the Birds of the World Volume 5: Barn-owls to Hummingbirds. Lynx Edicions, Barcelona.
Rinehart, Larry F.; Lucas, Spencer G.; Hunt, Adrian P. 2007. Furculae in the Late Triassic theropod dinosaur Coelophysis bauri. Paläontologische Zeitschrift 81 (2): 174-180.
Ezcurra M.D., Cuny, G., 2007. The coelophysoid Lophostropheus airelensis, gen. nov.: A review of the systematics of "Liliensternus" airelensis from the Triassic-Jurassic outcrops of Normandy (France). Journal of Vertebrate Paleontology 27 (1): 73-86.
Coria, R.A., Currie, P. J. 2006. A new carcharodontosaurid (Dinosauria, Theropoda) from the Upper Cretaceous of Argentina. Geodiversitas 28 (1): 71-118.
Porfiri, J.D., Novas, F.E., Calvo, J.O., Agnolin, F.L., Ezcurra, M.D., Cerda, I. A. 2014. Juvenile specimen of Megaraptor (Dinosauria, Theropoda) sheds light about tyrannosauroid radiation. Cretaceous Research 51: 35-55.
Currie, Philip J. 2005. Dinosaur Provincial Park: A Spectacular Ancient Ecosystem Revealed. Indiana University Press. p. 368
I already said some of the basics about the group in last week's post, so I won't repeat those points. The theropods are an incredibly diverse group - they range in size from the monstrous Spinosaurus, weighing in at 12 to 20.9 metric tons (Therrien and Henderson, 2007) and over 15 meters long (Ibrahim et al., 2014) to the minute Mesigulla helenae, at only 5-6cm in length and weighing around 2 grams (Del Hoyo and Sargatal, 1999).
Theropods really came into their own at the dawn of the Jurassic - these early creatures were the Neotheropoda (though Coelohysoids existed at the close of the Triassic, Neotheropoda really cranked out some species when the Jurassic came around). These early Neotheropods include the Coelophysoidea and the Dilophosauridae. The forelimbs in these groups were relatively well-developed and robust, with four digits (though at least in some species such as Coelophysis bauri, only 3 were functional (Rinehart et al., 2007)) in contrast to many more derived groups that showed digit reduction (such as the Avialans), overall size reduction (taken to an extreme in some of the most derived Abelisaurs), or both (like in Tyrannosauroids).
The split in the Neotheropoda that led to Dilophosauridae also led to the Averostra - all members of this group have a promaxillary fenestra; this group is composed of the last common ancestor of Ceratosaurus nasicornis and Allosaurus fragilis, and all its descendants (Ezucrra and Cuny, 2007). This group split up into the Ceratosauria and the Tetanurae. The former of the two includes the Abelisaurs, and were the dominant dinosaur lineage on the Southern landmasses at the close of the Mesozoic. The Tetanurae would split again to form the Megalosauroidea (a group including the Spinosaurs), and the Avetheropoda.
The Avetheropoda split into the Allosauroidea and the Coelurosauria - the former of the two lasted until roughly 93 million years ago in South America (Coria and Currie, 2006), though if Megaraptorans are in the group that would mean they lasted to the close of the Mesozoic [though it is currently thought that Megaraptorans are actually tyrannosauroids (Porfiri et al., 2014)]. The Coelurosaurs, on the other hand, still live on today in the form of birds.
Coelurosaurs are an incredibly fascinating group of dinosaurs - this is the group that contains creatures as vastly different as Tyrannosaurus rex and Microraptor. Interestingly, most dinosaurs found with preserved feathers are Coelurosaurs, and it has been suggested that feathers were a shared character between all species in the group (Currie, 2005). The Coelurosaurs came to dominate the northern continents in the end of the Cretaceous, with Tyrannosaurs being the largest terrestrial carnivores. However, it was another Coelurosaur group, the Maniraptorans, that would survive through the K-T extinction in the form of the Avialae. If that name sounds familiar, then you've been paying attention - that is the clade that consists of all extant birds!
Well, I hope you enjoyed this week's Sci-Day! I did not go too in-depth on most of the groups, because I wanted to pay particular attention to those groups that were represented in the Hell Creek formation. As far as I know, the only theropods from Hell Creek were Coelurosaurs, with Tyrannosaurus, a few Oviraptorsaurs, some Ornithomimids, and a bunch of Maniraptorans of several affinities. I could go a bit more into those subgroups, but I also want to get a chance to cover other subjects in future Sci-Day posts. If you would like to learn more about the groups, I'd encourage you to search on the Internet for some information, there are plenty of great places to look! :)
Acknowledgements:
Therrien, F; Henderson, D.M. 2007. My theropod is bigger than yours... or not: estimating body size from skull length in theropods. Journal of Vertebrate Paleontology 27 (1): 108-115.
Ibrahim, N.; Sereno, P. C.; Dal Sasso, C.; Maganuco, S; Fabbri, M.; Martill, D. M.; Zourhi, S.; Myhrvold, N.; Iurino, D. A. 2014. Semiaquatic adaptations in a giant predatory dinosaur. Science 345 (6204): 1613-1616.
Del Hoyo, J. Elliott, A. and Sargatal, J. 1999. Handbook of the Birds of the World Volume 5: Barn-owls to Hummingbirds. Lynx Edicions, Barcelona.
Rinehart, Larry F.; Lucas, Spencer G.; Hunt, Adrian P. 2007. Furculae in the Late Triassic theropod dinosaur Coelophysis bauri. Paläontologische Zeitschrift 81 (2): 174-180.
Ezcurra M.D., Cuny, G., 2007. The coelophysoid Lophostropheus airelensis, gen. nov.: A review of the systematics of "Liliensternus" airelensis from the Triassic-Jurassic outcrops of Normandy (France). Journal of Vertebrate Paleontology 27 (1): 73-86.
Coria, R.A., Currie, P. J. 2006. A new carcharodontosaurid (Dinosauria, Theropoda) from the Upper Cretaceous of Argentina. Geodiversitas 28 (1): 71-118.
Porfiri, J.D., Novas, F.E., Calvo, J.O., Agnolin, F.L., Ezcurra, M.D., Cerda, I. A. 2014. Juvenile specimen of Megaraptor (Dinosauria, Theropoda) sheds light about tyrannosauroid radiation. Cretaceous Research 51: 35-55.
Currie, Philip J. 2005. Dinosaur Provincial Park: A Spectacular Ancient Ecosystem Revealed. Indiana University Press. p. 368
Tuesday, February 16, 2016
Creature Feature 7
I hope everyone had a great weekend, and I hope you are all ready for this week's Creature Feature!
This week, I will be talking about Champsosaurus natator.
Champsosaurus may look like a cross between a lizard and a crocodile, but it is not closely related to either. In fact, Champsosaurus was neither a squamate nor an archosaur - it was a member of the now-extinct sauropsid lineage called Choristodera. While the phylogenetic positioning of this group is still uncertain, most recent analyses place it within Archosauromorpha (Lee, 2013).
While it is not closely related to crocodilians, its superficial resemblance to the modern gharial is due to convergent evolution - this creature was highly aquatic, using its long, narrow jaws to catch fish that shared its environment, though in early life it likely fed on arthropods, amphibians, and slow-swimming fish (Katsura, 2010). It is thought that this creature swam much like modern crocodilians or Amblyrhynchus cristatus, using its tail to propel itself forward while pinning its arms close to its body to minimize drag. The jaws widened significantly at the base, where strong jaw muscles attached (Lambert et al., 2001).
Champsosaurus had a flexible neck and long nasal passages, with external openings at the tip of the snout [as opposed to crocodilians, with external nares on the dorsal ends of the rostrum) - this, combined with a well-developed secondary palate, is thought to be indicative of a 'snorkeling'-esque resting posture. In other words, unlike crocodilians, where the head lies parallel to the surface with the nares and eyes just above the surface and the body sinking down, Champsosaurus would rest on the bottom, angling its snout towards the surface so it could breathe (Katsura, 2010).
Champsosaurus was specialized for its aquatic lifestyle to the point where the only part of its life cycle that still required land was reproduction. In fact, it is thought that males were unable to walk on land at all; it is thought that the specimens with fused sacral vertebrae and more robust limbs represent females, with features allowing them to come to land for the purpose of laying their eggs (Katsura, 2007).
Well, I hope this has given you a bit more information on the fascinating Champsosaurus! It's a pity that this fascinating lineage of creatures went extinct - I would've loved to see these creatures in the wild!
Acknowledgements:
Lee, M. S. Y. 2013. Turtle origins: Insights from phylogenetic retrofitting and molecular scaffolds. Journal of Evolutionary Biology 26 (12): 2729.
Katsura, Y. 2010. Ontogenetic change of bone microstructures and its ethological implication in Champsosaurus (Diapsida, Choristodera). Historical Biology, 22 (4), 380-386.
D. Lambert, D.Naish, E.Wyse. 2001. Encyclopedia of Dinosaurs and prehistoric life. Dorling Kindersley Limited, London. p. 77.
Katsura, Y. 2007. Fusion of sacrals and anatomy in Champsosaurus (Diapsida, Choristodera). Historical Biology, 19 (3), 263-271.
This week, I will be talking about Champsosaurus natator.
While it is not closely related to crocodilians, its superficial resemblance to the modern gharial is due to convergent evolution - this creature was highly aquatic, using its long, narrow jaws to catch fish that shared its environment, though in early life it likely fed on arthropods, amphibians, and slow-swimming fish (Katsura, 2010). It is thought that this creature swam much like modern crocodilians or Amblyrhynchus cristatus, using its tail to propel itself forward while pinning its arms close to its body to minimize drag. The jaws widened significantly at the base, where strong jaw muscles attached (Lambert et al., 2001).
Champsosaurus had a flexible neck and long nasal passages, with external openings at the tip of the snout [as opposed to crocodilians, with external nares on the dorsal ends of the rostrum) - this, combined with a well-developed secondary palate, is thought to be indicative of a 'snorkeling'-esque resting posture. In other words, unlike crocodilians, where the head lies parallel to the surface with the nares and eyes just above the surface and the body sinking down, Champsosaurus would rest on the bottom, angling its snout towards the surface so it could breathe (Katsura, 2010).
Champsosaurus was specialized for its aquatic lifestyle to the point where the only part of its life cycle that still required land was reproduction. In fact, it is thought that males were unable to walk on land at all; it is thought that the specimens with fused sacral vertebrae and more robust limbs represent females, with features allowing them to come to land for the purpose of laying their eggs (Katsura, 2007).
Well, I hope this has given you a bit more information on the fascinating Champsosaurus! It's a pity that this fascinating lineage of creatures went extinct - I would've loved to see these creatures in the wild!
Acknowledgements:
Lee, M. S. Y. 2013. Turtle origins: Insights from phylogenetic retrofitting and molecular scaffolds. Journal of Evolutionary Biology 26 (12): 2729.
Katsura, Y. 2010. Ontogenetic change of bone microstructures and its ethological implication in Champsosaurus (Diapsida, Choristodera). Historical Biology, 22 (4), 380-386.
D. Lambert, D.Naish, E.Wyse. 2001. Encyclopedia of Dinosaurs and prehistoric life. Dorling Kindersley Limited, London. p. 77.
Katsura, Y. 2007. Fusion of sacrals and anatomy in Champsosaurus (Diapsida, Choristodera). Historical Biology, 19 (3), 263-271.
Friday, February 12, 2016
Sci-Day 6: Evolutionary History of Dinosaurs, part 2: Evolution and Diversification of Dinosauria
In last week's Sci-Day, I did an overview on the origin of Dinosauria - what they branched off from, and a few of the characters that are indicative of that ancestry. This week, I will be continuing from where we left off - the dinosaurs just appeared, and we're going to look at what happened in the next ~180 million years. If you have not read the last Sci-Day post, I would recommend that you do so now.
As I said before, the earliest true dinosaurs known date from the Carnian stage of the Late Triassic. In this time, Dinosauria diverged into two lineages. These two lineages, Ornithischia and Saurischia, can be identified by the position of the pubis and ischium. In Saurischians, the ischium points backwards while the pubis points forward; in Ornithischians, both pubis and ischium point backwards (as in modern birds). However, the similarity between the hips of birds and those of Ornithischian dinosaurs is not indicative of shared ancestry, but rather is a result of convergent evolution.
After this split between the aforementioned lineages, Saurischia diverged into another two lineages - Theropoda and Sauropodomorpha. Theropoda is composed of bipedal (with the possible exception of Spinosaurus (Ibrahim et al., 2014)) dinosaurs - many lineages were carnivorous, though there were several groups that evolved omnivorous and herbivorous diets such as Therizinosaurs and some Maniraptorans (Longrich and Currie, 2009). Modern birds are the only living descendants of this group.
Sauropodomorpha consisted of bipedal and quadrupedal herbivorous dinosaurs with long necks, proportionally small heads, and long tails for counterbalance. The synapomorphies for this clade can be found in Martin, 2006. While the earliest members of this lineage were relatively small (Langer et al., 1999), through time they would grow to be the largest animals to ever walk the planet - the largest known sauropod, Argentinosaurus huinculensis, has been estimated to be up to 30 meters (98 feet) long (Carpenter, 2006) and weighed up to 83.2 tonnes (91.7 tons) (Sellers et al., 2013)!
Now, because there are so many lineages to talk about within the aforementioned 3, I will be using subsequent Sci-Day posts to go into more detail about some of those lineages so I can do them justice. Plus, if I were to write all of it in a single post, it would take a LONG time to read! I hope you have learned something from this post, and I look forward to delving into the history of one of these lineages in the future Sci-Days!
Acknowledgements:
Ibrahim, N.; Sereno, P. C.; Dal Sasso, C.; Maganuco, S; Fabbri, M.; Martill, D. M.; Zourhi, S.; Myhrvold, N.; Iurino, D. A. 2014. Semiaquatic adaptations in a giant predatory dinosaur. Science 345 (6204): 1613-1616.
Longrich, Nicholas R.; Currie, Philip J. 2009. Albertonykus borealis, a new alvarezsaur (Dinosauria: Theropoda) from the Early Maastrichtian of Alberta, Canada: Implications for the systematics and ecology of the Alvarezsauridae. Cretaceous Research 30 (1): 239-252.
Martin, A.J. 2006. Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. pg. 299-300.
Carpenter, Kenneth. 2006. Biggest of the Big: A Critical Re-Evaluation of the Mega-Sauropod Amphicoelias fragillimus Cope, 1878. In Foster, John R.; Lucas, Spencer G. Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin. pp. 131-138.
Langer, M.C., Abdala, F., Richter, M., and Benton, M. 1999. A sauropodomorph dinosaur from the Upper Triassic (Carnian) of southern Brazil. Comptes Rendus de l'Académie des Sciences, 329: 511-517.
Sellers, W. I.; Margetts, L.; Coria, R. A. B; Manning, P. L. 2013. Carrier, David, ed. March of the Titans: The Locomotor Capabilities of Sauropod Dinosaurs. PLoS ONE 8 (10): e78733.
As I said before, the earliest true dinosaurs known date from the Carnian stage of the Late Triassic. In this time, Dinosauria diverged into two lineages. These two lineages, Ornithischia and Saurischia, can be identified by the position of the pubis and ischium. In Saurischians, the ischium points backwards while the pubis points forward; in Ornithischians, both pubis and ischium point backwards (as in modern birds). However, the similarity between the hips of birds and those of Ornithischian dinosaurs is not indicative of shared ancestry, but rather is a result of convergent evolution.
After this split between the aforementioned lineages, Saurischia diverged into another two lineages - Theropoda and Sauropodomorpha. Theropoda is composed of bipedal (with the possible exception of Spinosaurus (Ibrahim et al., 2014)) dinosaurs - many lineages were carnivorous, though there were several groups that evolved omnivorous and herbivorous diets such as Therizinosaurs and some Maniraptorans (Longrich and Currie, 2009). Modern birds are the only living descendants of this group.
Sauropodomorpha consisted of bipedal and quadrupedal herbivorous dinosaurs with long necks, proportionally small heads, and long tails for counterbalance. The synapomorphies for this clade can be found in Martin, 2006. While the earliest members of this lineage were relatively small (Langer et al., 1999), through time they would grow to be the largest animals to ever walk the planet - the largest known sauropod, Argentinosaurus huinculensis, has been estimated to be up to 30 meters (98 feet) long (Carpenter, 2006) and weighed up to 83.2 tonnes (91.7 tons) (Sellers et al., 2013)!
Now, because there are so many lineages to talk about within the aforementioned 3, I will be using subsequent Sci-Day posts to go into more detail about some of those lineages so I can do them justice. Plus, if I were to write all of it in a single post, it would take a LONG time to read! I hope you have learned something from this post, and I look forward to delving into the history of one of these lineages in the future Sci-Days!
Acknowledgements:
Ibrahim, N.; Sereno, P. C.; Dal Sasso, C.; Maganuco, S; Fabbri, M.; Martill, D. M.; Zourhi, S.; Myhrvold, N.; Iurino, D. A. 2014. Semiaquatic adaptations in a giant predatory dinosaur. Science 345 (6204): 1613-1616.
Longrich, Nicholas R.; Currie, Philip J. 2009. Albertonykus borealis, a new alvarezsaur (Dinosauria: Theropoda) from the Early Maastrichtian of Alberta, Canada: Implications for the systematics and ecology of the Alvarezsauridae. Cretaceous Research 30 (1): 239-252.
Martin, A.J. 2006. Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. pg. 299-300.
Carpenter, Kenneth. 2006. Biggest of the Big: A Critical Re-Evaluation of the Mega-Sauropod Amphicoelias fragillimus Cope, 1878. In Foster, John R.; Lucas, Spencer G. Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin. pp. 131-138.
Langer, M.C., Abdala, F., Richter, M., and Benton, M. 1999. A sauropodomorph dinosaur from the Upper Triassic (Carnian) of southern Brazil. Comptes Rendus de l'Académie des Sciences, 329: 511-517.
Sellers, W. I.; Margetts, L.; Coria, R. A. B; Manning, P. L. 2013. Carrier, David, ed. March of the Titans: The Locomotor Capabilities of Sauropod Dinosaurs. PLoS ONE 8 (10): e78733.
Tuesday, February 9, 2016
Creature Feature 6
Hello, everyone! For today's Creature Feature, I've decided to cover the dromaeosaur Acheroraptor temertyorum.
Unfortunately, not much is known in terms of actual remains of this species - the holotype specimen consists of a complete maxilla with a few maxillary teeth (as well as additional isolated teeth), and an additional dentary attributed to the species (Evans et al., 2013).
However, enough information was gleaned from these remains to investigate the phylogenetic position of the species - interestingly, this species falls within the subfamily Velociraptorinae, occupying a relatively basal position in the group. This is particularly interesting because aside from Acheroraptor, all Velociraptorinae species lived in Asia (Evans et al., 2013).
In the original description paper, Evans et al. predicted that Acheroraptor was the only species of dromaeosaur present in the Hell Creek formation, though this would later be disproven with the discovery of Dakotaraptor steini (DePalma et al., 2015). However, Acheroraptor was far smaller than its cousin, being a mid-sized Dromaeosaurid (Evans et al., 2013), whereas Dakotaraptor is second only to Utahraptor in size.
As I pointed out in the first Sci-Day post, phylogenetic trees are extremely important for Dinosaur Battlegrounds, and this species is a great example to illustrate that importance. Without any knowledge of its relations to other dinosaurs, it would be impossible to make any sort of accurate reconstruction based on the fragmentary remains known. Luckily, we do have a good idea of what its closest relatives were, and so we can use that information along with what material is known from the species to make a reliable estimate of what it may have looked like. Hopefully, more complete remains of this species will be found in the future, so that we may be able to have a clearer picture of its anatomy and physiology.
Well, I hope you enjoyed today's Creature Feature! I apologize for its brevity, but unfortunately due to the relatively fragmentary remains of the species combined with the fact that it was only very recently described means that there is not much information to go on.
Acknowledgements:
Evans, D.C.; Larson, D.W.; Currie, P.J. 2013. A new dromaeosaurid (Dinosauria: Theropoda) with Asian affinities from the latest Cretaceous of North America. Naturwissenschaften.
Depalma, Robert A.; Burnham, David A.; Martin, Larry D.; Larson, Peter L.; Bakker, Robert T. 2015. The First Giant Raptor (Theropoda: Dromaeosauridae) from the Hell Creek Formation. Paleontological Contributions (14).
However, enough information was gleaned from these remains to investigate the phylogenetic position of the species - interestingly, this species falls within the subfamily Velociraptorinae, occupying a relatively basal position in the group. This is particularly interesting because aside from Acheroraptor, all Velociraptorinae species lived in Asia (Evans et al., 2013).
In the original description paper, Evans et al. predicted that Acheroraptor was the only species of dromaeosaur present in the Hell Creek formation, though this would later be disproven with the discovery of Dakotaraptor steini (DePalma et al., 2015). However, Acheroraptor was far smaller than its cousin, being a mid-sized Dromaeosaurid (Evans et al., 2013), whereas Dakotaraptor is second only to Utahraptor in size.
As I pointed out in the first Sci-Day post, phylogenetic trees are extremely important for Dinosaur Battlegrounds, and this species is a great example to illustrate that importance. Without any knowledge of its relations to other dinosaurs, it would be impossible to make any sort of accurate reconstruction based on the fragmentary remains known. Luckily, we do have a good idea of what its closest relatives were, and so we can use that information along with what material is known from the species to make a reliable estimate of what it may have looked like. Hopefully, more complete remains of this species will be found in the future, so that we may be able to have a clearer picture of its anatomy and physiology.
Well, I hope you enjoyed today's Creature Feature! I apologize for its brevity, but unfortunately due to the relatively fragmentary remains of the species combined with the fact that it was only very recently described means that there is not much information to go on.
Acknowledgements:
Evans, D.C.; Larson, D.W.; Currie, P.J. 2013. A new dromaeosaurid (Dinosauria: Theropoda) with Asian affinities from the latest Cretaceous of North America. Naturwissenschaften.
Depalma, Robert A.; Burnham, David A.; Martin, Larry D.; Larson, Peter L.; Bakker, Robert T. 2015. The First Giant Raptor (Theropoda: Dromaeosauridae) from the Hell Creek Formation. Paleontological Contributions (14).
Friday, February 5, 2016
Sci-Day 5: Evolutionary History of Dinosaurs, part 1: The Evolutionary Origin of Dinosauria
Happy Sci-Day, everyone! I'll admit it took me a long time to decide what today's topic would be, especially given that it is following the single most important post that I could ever make on any Sci-Day. That said, today I will be trying to give you a bit more info on what we know about the evolutionary history of dinosaurs. I will not be going too in-depth on specific families within dinosauria, though perhaps later sci-day posts will cover that information on lineages that were present in some form in the Hell Creek formation. This will be a two-part blog - today, I will simply cover the origins/roots of the dinosaurs, with the second post covering the evolutionary history of the group itself.
Before I delve in to their origins and evolution, let's answer an important question: what is a dinosaur?
By the middle of the Triassic period, archosauria split into several separate lineages - the largest two were Pseudosuchia (those archosaurs more closely related to modern crocodilians than to birds), and Avemetarsalia (those archosaurs more closely related to birds than to modern crocodilians) (Benton, 1999). The dinosaurs are included in the latter of these two, linked by the structure of their ankle joint. Interestingly, this clade also includes Pterosauria - I think you can guess what prehistoric creatures that lineage led to :)
Dinosauromorpha split into three lineages, with dinosaurs being placed in the aptly-named dinosauriformes. From this clade came Dinosauria (as well as several other taxa, but let's stay on topic here). The earliest true dinosaur known is Eoraptor - a small, bipedal predator that lived approximately 231 million years ago. It is thought that this genus bears resemblance to the common ancestors of all dinosaurs (Sereno, 1999). Throughout the rest of the Triassic, dinosaurs were not the dominant terrestrial animals; that role fell to the archosauromorphs. It is also believed that dinosaurs competed with the pseudosuchians of the time (Brusatte, 2008).
However, towards the end of the Triassic, many of the early archosauromorphs started to disappear, and many lineages went extinct during the Triassic-Jurassic mass extinction event. As the archosauromorphs began to die out (during the Carnian and Norian stages of the Triassic), the early dinosaurs began to diversify - it is hypothesized that this diversification was due to the vacant niches left by the extinct archosauromorphs (Langer et al., 2010).
Hopefully, this has given you a bit more information on how dinosaurs came to be. Check in next week to find out more about the evolution of dinosaurs themselves!
Acknowledgements:
Gower, D.J.; Sennikov, A.G. 2003. Early archosaurs from Russia. In Benton, M.J.; Shishkin, M.A.; and Unwin, D.M. (eds.). The Age of Dinosaurs in Russia and Mongolia. Cambridge: Cambridge University Press. pp. 140-159.
Gareth Dyke, Gary Kaiser, ed. 2011. Living Dinosaurs: The Evolutionary History of Modern Birds. John Wiley & Sons. p. 10.
Khanna, D.R. 2004. Biology Of Reptiles. Discovery Publishing Hourse. pp. 78ff.
Benton, M.J. 1999. Scleromochlus taylori and the origin of dinosaurs and pterosaurs. Philosophical Transactions of the Royal Society of London 354: 1423-1446.
Sereno, P.C. 1999. The evolution of dinosaurs. Science 284 (5423): 2137-2147.
Brusatte, Stephen L. Superiority, Competition, and Opportunism in the Evolutionary Radiation of Dinosaurs. 321 (5895): 1485-1488.
Langer, Max C.; Ezcurra, Martin D.; Bittencourt, Jonathas S.; Novas, Fernando E. 2010. The origin and early evolution of dinosaurs. Biological Reviews 85 (1): 65-66, 82.
Before I delve in to their origins and evolution, let's answer an important question: what is a dinosaur?
A dinosaur is any species within the clade Dinosauria. I have already explained cladistics in my first Sci-Day post, so if you haven't read that, you may want to do so now it will help you understand this a bit easier. There are several characteristics that all members of Dinosauria share - these derived characteristics are what distinguish them from other groups, and are known as synapomorphies. I will not list these here, as they require a deep understanding of skeletal anatomy, but it is important to understand that these characteristics are shared by dinosaurs and are indicative of their shared evolutionary history.
Now, onto the question at hand - where did dinosaurs come from?
Well, when a mommy and a daddy dinosaur love each other very much.... Oh, whoops, we're talking about where they come from in an EVOLUTIONARY sense! My mistake. ;)
The evolutionary path that would eventually lead to dinosaurs started in either the Permian or Early Triassic, with the first Archosaurs (Gower and Sennikov, 2003). These creatures had several synapomorphies that dinosaurs would also inherit (Dinosauria is placed within Archosauria, which also includes the lineage that consists of modern crocodilians and their extinct relatives) - their teeth were set in sockets, they had two additional openings, or fenestrae, in their skull (antorbital and mandibular, specifically) (Dyke and Kaiser, 2011), and a prominent ridge on the femur called a fourth trochanter (Khanna, 2004). The last of these was particularly important, as it provided a large site for muscle attachments that allowed for an upright gait in these primitive archosaurs.
By the middle of the Triassic period, archosauria split into several separate lineages - the largest two were Pseudosuchia (those archosaurs more closely related to modern crocodilians than to birds), and Avemetarsalia (those archosaurs more closely related to birds than to modern crocodilians) (Benton, 1999). The dinosaurs are included in the latter of these two, linked by the structure of their ankle joint. Interestingly, this clade also includes Pterosauria - I think you can guess what prehistoric creatures that lineage led to :)
Dinosauromorpha split into three lineages, with dinosaurs being placed in the aptly-named dinosauriformes. From this clade came Dinosauria (as well as several other taxa, but let's stay on topic here). The earliest true dinosaur known is Eoraptor - a small, bipedal predator that lived approximately 231 million years ago. It is thought that this genus bears resemblance to the common ancestors of all dinosaurs (Sereno, 1999). Throughout the rest of the Triassic, dinosaurs were not the dominant terrestrial animals; that role fell to the archosauromorphs. It is also believed that dinosaurs competed with the pseudosuchians of the time (Brusatte, 2008).
However, towards the end of the Triassic, many of the early archosauromorphs started to disappear, and many lineages went extinct during the Triassic-Jurassic mass extinction event. As the archosauromorphs began to die out (during the Carnian and Norian stages of the Triassic), the early dinosaurs began to diversify - it is hypothesized that this diversification was due to the vacant niches left by the extinct archosauromorphs (Langer et al., 2010).
Hopefully, this has given you a bit more information on how dinosaurs came to be. Check in next week to find out more about the evolution of dinosaurs themselves!
Acknowledgements:
Gower, D.J.; Sennikov, A.G. 2003. Early archosaurs from Russia. In Benton, M.J.; Shishkin, M.A.; and Unwin, D.M. (eds.). The Age of Dinosaurs in Russia and Mongolia. Cambridge: Cambridge University Press. pp. 140-159.
Gareth Dyke, Gary Kaiser, ed. 2011. Living Dinosaurs: The Evolutionary History of Modern Birds. John Wiley & Sons. p. 10.
Khanna, D.R. 2004. Biology Of Reptiles. Discovery Publishing Hourse. pp. 78ff.
Benton, M.J. 1999. Scleromochlus taylori and the origin of dinosaurs and pterosaurs. Philosophical Transactions of the Royal Society of London 354: 1423-1446.
Sereno, P.C. 1999. The evolution of dinosaurs. Science 284 (5423): 2137-2147.
Brusatte, Stephen L. Superiority, Competition, and Opportunism in the Evolutionary Radiation of Dinosaurs. 321 (5895): 1485-1488.
Langer, Max C.; Ezcurra, Martin D.; Bittencourt, Jonathas S.; Novas, Fernando E. 2010. The origin and early evolution of dinosaurs. Biological Reviews 85 (1): 65-66, 82.
Tuesday, February 2, 2016
Creature Feature 5
For today's Creature Feature, I'd like to cover one of the non-dinosaurian animals from Hell Creek - the alligatoroid Brachychampsa montana.
Brachychampsa montana existed from the late Campanian stage of the Cretaceous and even through the first few million years of the Paleocene (after the K-T extinction)... Yes, that means this resilient creature survived the massive catastrophe that spelled the end for the non-avian dinosaurs!
Since its description was published by Charles Gilmore in 1911, the exact relationships of B. montana have been debated and changed multiple times. Originally, it was placed within the family Alligatoridae (Gilmore, 1911), and this was then placed within the subfamily Alligatorinae (Estes,19 64). However, in 1994 new remains and data subsequently placed it outside Alligatoridae, but still within Alligatoroidea (Norell and Clark, 1994).
Brachychampsa is particularly interesting due to its heterodont dentition - this means that, unlike most reptiles, it has differently-shaped teeth in different areas of the jaw. In the anterior portion of the jaw, the teeth are narrow and conical, whereas the posterior teeth are bulbous. This has led some to postulate a diet mainly consisting of turtles (Carpenter and Lindsay, 1980), but the current thought is that it had a more generalist diet. This is based on the fact that modern alligators consume turtles despite a lack of bulbous posterior teeth, and the fact that dietary preferences in crocodylians change with age. While turtles would have provided a bountiful food source for any crocodylians in the Late Cretaceous based on their relative abundance and co-occurrence, it is likely that these creatures were generalists and would include other prey in their diet (Sullivan and Lucas, 2003).
Well, I hope this Creature Feature has given you a bit more knowledge about Brachychampsa montana, and perhaps will get you a bit more interested in the non-dinosaurian fauna of Hell Creek!
Acknowledgements:
Gilmore, Charles W. 1911. A new fossil alligator from the Hell Creek Beds of Montana. Proceedings of the United States National Museum 41: 297-302.
Estes, R. 1964. Fossil vertebrates from the Late Cretaceous Lance Formation, eastern Wyoming. University of California Publications in Geological Sciences 49: 1-180.
Norell, M. A.; Clark, J. M.; Hutchison, J. H. 1994. The Late Cretaceous alligatoroid Brachychampsa montana (Crocodylia): new material and putative relationships. American Museum Novitates 3116: 1-26.
Carpenter, K. and D. Lindsey. 1980. The dentary of Brachychampsa montana Gilmore (Alligatorinae; Crocodylidae), a Late Cretaceous turtle-eating alligator. Journal of Paleontology 54:1213–1217
Sullivan, Robert M.; Lucas, Spencer G. 2003. Brachychampsa montana Gilmore (Crocodylia, Alligatoroidea) from the Kirtland Formation (upper Campanian), San Juan Basin, New Mexico. Journal of Vertebrate Paleontology 23 (4): 832-841.
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