Theropoda
Theropoda | |
---|---|
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | Saurischia |
Clade: | Eusaurischia
|
Clade: | Theropoda Marsh, 1881 |
Subgroups[1] | |
Theropoda (
Biology
Diet and teeth
Theropods exhibit a wide range of diets, from insectivores to herbivores and carnivores. Strict carnivory has always been considered the ancestral diet for theropods as a group, and a wider variety of diets was historically considered a characteristic exclusive to the avian theropods (birds). However, discoveries in the late 20th and early 21st centuries showed that a variety of diets existed even in more basal lineages.
The first confirmed non-carnivorous fossil theropods found were the
Diet is largely deduced by the tooth morphology,[7] tooth marks on bones of the prey, and gut contents. Some theropods, such as Baryonyx, Lourinhanosaurus, ornithomimosaurs, and birds, are known to use gastroliths, or gizzard-stones.
The majority of theropod teeth are blade-like, with serration on the edges,[8] called ziphodont. Others are pachydont or folidont depending on the shape of the tooth or denticles.[8] The morphology of the teeth is distinct enough to tell the major families apart,[7] which indicate different diet strategies. An investigation in July 2015 discovered that what appeared to be "cracks" in their teeth were actually folds that helped to prevent tooth breakage by strengthening individual serrations as they attacked their prey.[9] The folds helped the teeth stay in place longer, especially as theropods evolved into larger sizes and had more force in their bite.[10][11]
Integument (skin, scales and feathers)
The coelurosaur lineages most distant from birds had feathers that were relatively short and composed of simple, possibly branching filaments.
Based on a relationships between tooth size and skull length and also a comparison of the degree of wear of the teeth of non-avian theropods and modern lepidosaurs, it is concluded that theropods had lips that protected their teeth from the outside. Visually, the snouts of such theropods as Daspletosaurus had more similarities with lizards than crocodilians, which lack lips.[17]
Size
The largest extant theropod is the common ostrich, up to 2.74 m (9 ft) tall and weighing between 90 and 130 kg (200 - 290 lb).[20] The smallest non-avialan theropod known from adult specimens is the troodontid Anchiornis huxleyi, at 110 grams in weight and 34 centimeters (1 ft) in length.[16] When modern birds are included, the bee hummingbird (Mellisuga helenae) is smallest at 1.9 g and 5.5 cm (2.2 in) long.[21][22]
Recent theories propose that theropod body size shrank continuously over a period of 50 million years, from an average of 163 kilograms (359 lb) down to 0.8 kilograms (1.8 lb), eventually evolving into modern birds. This was based on evidence that theropods were the only dinosaurs to get continuously smaller, and that their skeletons changed four times as fast as those of other dinosaur species.[23][24]
Growth rates
In order to estimate the growth rates of theropods, scientists need to calculate both age and body mass of a dinosaur. Both of these measures can only be calculated through fossilized bone and tissue, so regression analysis and extant animal growth rates as proxies are used to make predictions. Fossilized bones exhibit growth rings that appear as a result of growth or seasonal changes, which can be used to approximate age at the time of death.[25] However, the amount of rings in a skeleton can vary from bone to bone, and old rings can also be lost at advanced age, so scientists need to properly control these two possibly confounding variables.
Body mass is harder to determine as bone mass only represents a small proportion of the total body mass of animals. One method is to measure the circumference of the femur, which in non-avian theropod dinosaurs has been shown to be a relatively proportional to quadrupedal mammals,[26] and use this measurement as a function of body weight, as the proportions of long bones like the femur grow proportionately with body mass.[26] The method of using extant animal bone proportion to body mass ratios to make predictions about extinct animals is known as the extant-scaling (ES) approach.[27] A second method, known as the volumetric-density (VD) approach, uses full-scale models of skeletons to make inferences about potential mass.[27] The ES approach is better for wide range studies including many specimens and doesn't require as much of a complete skeleton as the VD approach, but the VD approach allows scientists to better answer more physiological questions about the animal, such as locomotion and center of gravity.[27]
The current consensus is that non-avian theropods didn't exhibit a group wide growth rate, but instead had varied rates depending on their size. However, all non-avian theropods had faster growth rates than extant reptiles, even when modern reptiles are scaled up to the large size of some non-avian theropods. As body mass increases, the relative growth rate also increases. This trend may be due to the need to reach the size required for reproductive maturity.[28] For example, one of the smallest known theropods was Microraptor zhaoianus, which had a body mass of 200 grams, grew at a rate of approximately .33 grams per day.[29] A comparable reptile of the same size grows at half of this rate.[29] The growth rates of medium-sized non-avian theropods (100–1000 kg) approximated those of precocial birds, which are much slower than altricial birds. Large theropods (1500–3500 kg) grew even faster, similar to rates displayed by eutherian mammals.[29] The largest non-avian theropods, like Tyrannosaurus rex had similar growth dynamics to the largest living land animal today, the African elephant, which is characterized by a rapid period of growth until maturity, subsequently followed by slowing growth in adulthood.[30]
Stance and gait
As a hugely diverse group of animals, the posture adopted by theropods likely varied considerably between various lineages through time.
Non-avian theropods were first recognized as bipedal during the 19th century, before their relationship to birds was widely accepted. During this period, theropods such as
Nervous system and senses
Although rare, complete casts of theropod
Studies show that theropods had very sensitive snouts. It is suggested they might have been used for temperature detection, feeding behavior, and wave detection.[37][38]
Forelimb morphology
Shortened forelimbs in relation to hind legs was a common trait among theropods, most notably in the
The hands are also very different among the different groups. The most common form among non-avian theropods is an appendage consisting of three fingers; the digits I, II and III (or possibly
The forelimbs' scope of use is also believed to have also been different among different families. The spinosaurids could have used their powerful forelimbs to hold fish. Some small maniraptorans such as
Forelimb movement
Contrary to the way theropods have often been reconstructed in art and the popular media, the range of motion of theropod forelimbs was severely limited, especially compared with the forelimb dexterity of humans and other
In carnosaurs like
Paleopathology
In 2001,
Swimming
The trackway of a swimming theropod, the first in China of the
Evolutionary history
During the late Triassic, a number of primitive proto-theropod and theropod dinosaurs existed and evolved alongside each other.
The earliest and most primitive of the theropod dinosaurs were the carnivorous
The earliest and most primitive unambiguous theropods (or alternatively, "
The somewhat more advanced
The
Thus, during the late Jurassic, there were no fewer than four distinct lineages of theropods—ceratosaurs, megalosaurs, allosaurs, and coelurosaurs—preying on the abundance of small and large herbivorous dinosaurs. All four groups survived into the Cretaceous, and three of those—the ceratosaurs, coelurosaurs, and allosaurs—survived to end of the period, where they were geographically separate, the ceratosaurs and allosaurs in Gondwana, and the coelurosaurs in Laurasia.
Of all the theropod groups, the coelurosaurs were by far the most diverse. Some coelurosaur groups that flourished during the Cretaceous were the tyrannosaurids (including Tyrannosaurus), the dromaeosaurids (including Velociraptor and Deinonychus, which are remarkably similar in form to the oldest known bird, Archaeopteryx),[50][51] the bird-like troodontids and oviraptorosaurs, the ornithomimosaurs (or "ostrich Dinosaurs"), the strange giant-clawed herbivorous therizinosaurs, and the avialans, which include modern birds and is the only dinosaur lineage to survive the Cretaceous–Paleogene extinction event.[52] While the roots of these various groups are found in the Middle Jurassic, they only became abundant during the Early Cretaceous. A few palaeontologists, such as Gregory S. Paul, have suggested that some or all of these advanced theropods were actually descended from flying dinosaurs or proto-birds like Archaeopteryx that lost the ability to fly and returned to a terrestrial habitat.[53]
The evolution of birds from other theropod dinosaurs has also been reported, with some of the linking features being the
Classification
History of classification
By the early 20th century, some palaeontologists, such as
In 1956, "Theropoda" came back into use—as a
With the advent of cladistics and phylogenetic nomenclature in the 1980s, and their development in the 1990s and 2000s, a clearer picture of theropod relationships began to emerge. Jacques Gauthier named several major theropod groups in 1986, including the clade Tetanurae for one branch of a basic theropod split with another group, the Ceratosauria. As more information about the link between dinosaurs and birds came to light, the more bird-like theropods were grouped in the clade Maniraptora (also named by Gauthier in 1986). These new developments also came with a recognition among most scientists that birds arose directly from maniraptoran theropods and, on the abandonment of ranks in cladistic classification, with the re-evaluation of birds as a subset of theropod dinosaurs that survived the Mesozoic extinctions and lived into the present.[40]
Major groups
The following is a simplified classification of theropod groups based on their evolutionary relationships, and organized based on the list of Mesozoic dinosaur species provided by Holtz.[1] A more detailed version can be found at dinosaur classification. The dagger (†) is used to signify groups with no living members.
- †Coelophysoidea (small, early theropods; includes Coelophysis and close relatives)
- †Ceratosauria (generally elaborately horned, the dominant southern carnivores of the Cretaceous; includes Carnotaurus and close relatives, like Majungasaurus and Chenanisaurus)
- Tetanurae ("stiff tails"; includes most theropods)
- †Megalosauroidea (early group of large carnivores including the semi-aquatic spinosaurids)
- †Allosauroidea (Allosaurus and close relatives, like Carcharodontosaurus)
- †Megaraptora (A group of medium to large Orionides with unknown affinities, quite common in the southern hemisphere)
- Coelurosauria (feathered theropods, with a range of body sizes and niches)
- †Compsognathidae (early coelurosaurs with reduced forelimbs)
- †Tyrannosauridae (Tyrannosaurus and close relatives; had reduced forelimbs)
- †Ornithomimosauria ("ostrich-mimics"; mostly toothless; carnivores to possible herbivores)
- Maniraptora ("hand snatchers"; had long, slender arms and fingers)
- †Alvarezsauroidea (small insectivores with reduced forelimbs each bearing one enlarged claw)
- †Therizinosauria (bipedal herbivores with large hand claws and small heads)
- †Scansoriopterygidae (small, arboreal maniraptors with long third fingers)
- †Oviraptorosauria (mostly toothless; their diet and lifestyle are uncertain)
- †Archaeopterygidae (small, winged protobirds)
- †Dromaeosauridae (small to medium-sized theropods)
- †Troodontidae (small, gracile theropods)
- Avialae (birds and extinct relatives)
- †Omnivoropterygidae (large, early short-tailed avialans)
- †Confuciusornithidae (small toothless birds)
- †Enantiornithes (primitive tree-dwelling, flying birds)
- Euornithes (advanced flying birds)
- †Yanornithiformes (toothed Cretaceous Chinese birds)
- †Hesperornithes (specialized aquatic diving birds)
- Aves(modern, beaked birds and their extinct relatives)
Relationships
The following family tree illustrates a synthesis of the relationships of the major theropod groups based on various studies conducted in the 2010s.[58]
Theropoda |
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
A large study of early dinosaurs by Dr Matthew G. Baron, David Norman and Paul M. Barrett (2017) published in the journal Nature suggested that Theropoda is actually more closely related to Ornithischia, to which it formed the sister group within the clade Ornithoscelida. This new hypothesis also recovered Herrerasauridae as the sister group to Sauropodomorpha in the redefined Saurischia and suggested that the hypercarnivore morphologies that are observed in specimens of theropods and herrerasaurids were acquired convergently.[59][60] However, this phylogeny remains controversial and additional work is being done to clarify these relationships.[61]
See also
- Marginocephalian
- Origin of birds
- Ornithopod
- Thyreophoran
References
- ^ a b Holtz, Thomas R. Jr. (2012). Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages, Winter 2011 Appendix.
- ^ "Therapoda". Merriam-Webster.com Dictionary.
- S2CID 33506648.
- PMID 19605396.
- .
- ^ Holtz, T. R. Jr.; Brinkman, D. L.; Chandler, C. L. (1998). "Dental morphometrics and a possibly omnivorous feeding habit for the theropod dinosaur Troodon". GAIA. 15: 159–166.
- ^ S2CID 12650231.
- ^ S2CID 85774247.
- ^ Geggel, Laura (28 July 2015). "One tough bite: T. rex's teeth had secret weapon". Fox News. Retrieved 1 August 2015.
- ^ "Special Serrations Gave Carnivorous Dinosaurs an Evolutionary Edge". 17 August 2015. Archived from the original on August 18, 2015.
- S2CID 17247595.
- ^ Bonaparte, Novas, and Coria (1990). "Carnotaurus sastrei Bonaparte, the horned, lightly built carnosaur from the Middle Cretaceous of Patagonia." Contributions in Science (Natural History Museum of Los Angeles County), 416: 41 pp.
- S2CID 4427002.
- ^ a b Czerkas, S. A.; Yuan, C. (2002). "An arboreal maniraptoran from northeast China" (PDF). In Czerkas, S. J. (ed.). Feathered Dinosaurs and the Origin of Flight. The Dinosaur Museum Journal. Vol. 1. Blanding, U.S.A: The Dinosaur Museum. pp. 63–95.
- ^ Goehlich, U. B.; Tischlinger, H.; Chiappe, L. M. (2006). "Juraventaor starki (Reptilia, Theropoda) ein nuer Raubdinosaurier aus dem Oberjura der Suedlichen Frankenalb (Sueddeutschland): Skelettanatomie und Wiechteilbefunde". Archaeopteryx. 24: 1–26.
- ^
- S2CID 257836765.
- S2CID 86025320.
- S2CID 85702490.
- ^ "Ostrich". African Wildlife Foundation. Retrieved 28 October 2020.
- S2CID 3099017.
- ^ Hendry, Lisa (2023). "Are birds the only surviving dinosaurs?". The Trustees of The Natural History Museum, London. Retrieved 14 April 2023.
- ^ AP News. Retrieved August 3, 2014.
- ^ a b Zoe Gough (31 July 2014). "Dinosaurs 'shrank' regularly to become birds". BBC.
- S2CID 4335246.
- ^ ISSN 1469-7998.
- ^ S2CID 221404013.
- PMID 18195356.
- ^ S2CID 4319534.
- PMID 15347508.
- ^ .
- ^ .
- ^ K. Padian, P.E. Olsen, (1989). "Ratite footprints and the stance and gait of Mesozoic theropods." Pp. 231–241 in: D.D. Gillette, M.G. Lockley (Eds.), Dinosaur Tracks and Traces, Cambridge University Press, Cambridge.
- ^ Paul, G.S. (1998). "Limb design, function and running performance in ostrich-mimics and tyrannosaurs". Gaia. 15: 257–270.
- .
- ^ "Abstract", in Chure (2001). Pg. 19.[full citation needed]
- PMID 28623335.
- S2CID 238728702.
- ^ Dong, Z (1984). "A new theropod dinosaur from the Middle Jurassic of Sichuan Basin". Vertebrata PalAsiatica. 22 (3): 213–218.
- ^ ISBN 0-901702-79-X
- University of Maryland department of geology home page, "Theropoda I" on Avetheropoda, 14 July 2006.
- ^ S2CID 84702973.
- ^ .
- ^ Molnar, R. E., 2001, Theropod paleopathology: a literature survey: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p. 337-363.
- ^ .
- S2CID 8349110..
- ^ Rowe, T., and Gauthier, J., (1990). "Ceratosauria." Pp. 151–168 in Weishampel, D. B., Dodson, P., and Osmólska, H. (eds.), The Dinosauria, University of California Press, Berkeley, Los Angeles, Oxford.
- ^ Mortimer, M. (2001). "Rauhut's Thesis", Dinosaur Mailing List Archives, 4 Jul 2001.
- S2CID 85655323.
- ^ Ostrom, J.H. (1969). "Osteology of Deinonychus antirrhopus, an unusual theropod from the Lower Cretaceous of Montana". Peabody Museum Natural History Bulletin. 30: 1–165.
- ISBN 0-671-61946-2)
- ^ Dingus, L. and Rowe, T. (1998). The Mistaken Extinction: Dinosaur Evolution and the Origin of Birds. Freeman.
- ISBN 0-8018-6763-0)
- S2CID 37866029.
- S2CID 219234316.
- ^ Matthew, W. D.; Brown, B. (1922). "The family Deinodontidae, with notice of a new genus from the Cretaceous of Alberta". Bulletin of the American Museum of Natural History. 46: 367–385.
- ISBN 0-19-530411-X.
- ^ Hendrickx, C.; Hartman, S.A.; Mateus, O. (2015). "An Overview of Non- Avian Theropod Discoveries and Classification". PalArch's Journal of Vertebrate Palaeontology. 12 (1): 1–73.
- S2CID 205254710.
- ^ "New study shakes the roots of the dinosaur family tree". cam.ac.uk. University of Cambridge. 22 March 2017.
- from the original on 9 July 2023. Retrieved 8 July 2023.