Post by Infinity Blade on Feb 27, 2016 7:34:09 GMT 5
Dilophosaurus wetherilli
Skeletal reconstruction of Dilophosaurus wetherilli. © @ Scott Hartman
Temporal range: early Jurassic (Sinemurian-Pliensbachian; ~196-183Ma[1])
Scientific classification:
Life
Domain: Eukaryota
(unranked): Unikonta
(unranked): Opisthokonta
(unranked): Holozoa
(unranked): Filozoa
Kingdom: Animalia
Subkingdom: Eumetazoa
(unranked): Bilateria
Clade: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Clade: Olfactores
Clade: Craniata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Clade: Eugnathostomata
Clade: Teleostomi
Superclass: Tetrapoda
Clade: Reptiliomorpha
Clade: Amniota
Class: Reptilia or Clade: Sauropsida
Clade: Eureptilia
Clade: Romeriida
Clade: Diapsida
Clade: Neodiapsida
Clade: Archelosauria
Clade: Archosauromorpha
Clade: Archosauriformes
Clade: Crurotarsi
Clade: Archosauria
Clade: Avemetatarsalia
Clade: Ornithodira
Clade: Dinosauromorpha
Clade: Dinosauriformes
Clade: Dinosauria
Order: Saurischia
Clade: Eusaurischia
Suborder: Theropoda
Clade: Neotheropoda
Genus: †Dilophosaurus
Species: †D. wetherilli
Dilophosaurus ("two crested lizard") is an extinct genus of theropod dinosaur. It only contains one species, D. wetherilli. Dilophosaurus lived in what is now the state of Arizona of the United States in the Kayenta Formation during the early Jurassic ~196-183 million years ago[1].
Taxonomy:
Since 1954, Dilophosaurus has been classified as a coelophysoid[2]. However, it has recently been suggested that Dilophosaurus was more closely related to tetanurans than coelophysoids[3][4]. A 2012 study found Dilophosaurus to be nested within Coelophysoidea[5].
There used to be an animal assigned as Dilophosaurus sinensis. However, it was found to be synonymous with Sinosaurus triassicus [6][7].
Description:
Dilophosaurus was a bipedal, rather lightly-built predator. It was ~7 meters long and purported to have weighed as much as a grizzly bear[8] (227-454 kilograms as given in the supplementary information of Holtz’s genus list[9]), but given its gracile build, the higher end of the aforementioned weight range seems questionable.
Dilophosaurus is arguably best known for its two thin crests on top of the skull.
The tooth crowns were long.
Reconstruction of the skull of Dilophosaurus. © @ Jaime A. Headden
As noted by the second edition of The Dinosauria, “In Dilophosaurus, serrations are on at least the second and third premaxillary teeth but absent from the fourth (Welles 1984). The maxillary and more distal dentary teeth are linguolabially flattened, strongly recurved, and serrated. The largest maxillary tooth lies in or near the fourth alveolus, with crown height diminishing distally. The most mesial maxillary tooth projects slightly rostrally from its alveolus, a consequence of the upturned ventral border of the premaxillary process. As reconstructed, the maxillary tooth row terminates before the orbit in Dilophosaurus wetherilli and Syntarsus rhodesiensis, but these remains were based on disarticulated material and have not been confirmed in articulated material (Raath 1977; Welles 1984). The tooth row terminates below the orbit in all articulated coelophysoid skulls. Dilophosaurus is reported to have 12 maxillary teeth and 17 or 18 dentary teeth (Welles 1984)” [10].
Dilophosaurus is also known for the notch between its premaxilla and maxilla.
It used to be thought that the mobile sutures of some reptilian skulls acts as a system of levers powered by jaw muscles to aid in predation. Bakker (1986) did not concur with this idea but instead suggested that Ceratosaurus in particular would have been able to swallow items larger than its own head due its loosely-connected skull elements. Welles (1984) also disagreed with the lever system hypothesis and suggested that the loosely-connected skull elements would have made the skull of Dilophosaurus too weak to be used for predation.
While there was indeed some capability of movement between some skull bones, it is most likely that any movement in its skull was passive, merely the bending that occurred as a result of biting and manipulating prey. “The fibrous connections between skull elements would have provided shock-absorbing elasticity, ample tensile strength, and flexibility”. This somewhat conforms to Bakker’s view in that there was some cranial flexibility present, but no proof exists that the skull was anywhere near as mobile to allow for the swallowing of items the size of its head. The loose articulation between the premaxilla and maxilla and the straight, unserrated teeth of the premaxilla and rostral dentary would have allowed Dilophosaurus (and coelophysoids) to manipulate small prey items. The rest of the teeth would have been formidable (as noted above, they are long-crowned (particularly in Dilophosaurus), serrated, lateromedially compressed, and strongly recurved), hence there is no reason to think that these animals would have been unable to hunt live prey[11].
A 2016 analysis of the cursorial potential of carnivorous theropods included Dilophosaurus in its analysis. Dilophosaurus was found to have had a lower limb ~3% shorter than expected for a theropod of the same femur length, hence its CLP (cursorial limb proportion) score of -3.0.[12] This means that, while Dilophosaurus wasn’t nearly as horribly adapted for cursoriality as some of the theropods with even lower CLP scores, it still wasn’t notably cursorial and probably did not chase after prey for prolonged distances.
Paleopathology:
In 2016, Phil Senter and Sara L. Juengst examined the pectoral/forelimb region of the holotype specimen of Dilophosaurus wetherilli (UCMP 37302). As it turned out, it exhibited eight pathologies, twice as many as in the previous theropod record holder for the most pathologies in the aforementioned region (Tyrannosaurus rex specimen FMNH PR 2081; “Sue”). The following pathologies were found:
Pathologies in the Dilophosaurus holotype. From Senter & Juengst (2016).
1.) Right radius and ulna (above) and enlargements of distal end of radius (below) in (from top to bottom) lateral, abductor, and medial views; broken outline indicates three bony tumors.
2.) Left and right humerus (left humerus on left, right humerus on right) in lateral view, each photographed with lateral epicondyle directly facing the viewer, with heavy broken line indicating the midline of the posterior (retractor) surface of each to show the abnormal degree of torsion in the right humerus.
3.) Medial surface of left scapula, with broken outline indicating fracture.
4.) Left (on left) and right (on right) manual phalanx III-1 in dorsal (top) and palmar (bottom) views, with broken lines indicating plane of articulation with adjacent bones, to show the alteration of this plane in the right-hand phalanx.
5.) Distal ends of left (on left) and right (on right) metacarpal III in lateral/abductor view (top) and palmar view (bottom), with broken outline indicating edge of articular surface, to show abnormal truncation of articular surface in right metacarpal III.
6.) Left manual phalanx I-1 (on left), with its right-hand counterpart for comparison (on right), in palmar (top) and lateral/abductor (bottom) views, with broken outlines indicating healed fibriscesses.
7.) Medial surface of left ulna, with broken outline indicating healed fibriscess and arrow indicating abnormal bony growth.
8.) Left radius and ulna in medial view, with arrow indicating healed fracture.
(i. is a figure of metacarpal lll and phalanx lll-1 with the latter in full extension and flexion, illustrating the reduced range of motion)
Restoration of the right manus of the holotype specimen of Dilophosaurus wetherilli with bones, showing the injured third digit with the other two functional digits fully flexed; it is oddly similar to the rude human gesture of solely raising the middle finger. From Senter & Juengst (2016).
The favorite hypothesis that Senter and Juengst suggest goes along the lines of a rival conspecific that kicked its left arm (explaining the two punctures), forcing it to collide against a tree or rock wall, causing the fractures. The dinosaur lived for a long time before its death, as evidenced by the healed injuries. It must have either gone without food for some time or sustained itself by preying upon quarry that could be dispatched solely with the jaws and/or feet or with only one forelimb. The Dilophosaurus appears to have had osteodysplasia. This, coupled with the pain on the left side of its body that would have forced it to put more weight on its right side, was the likely cause of the bone deformation. The holotype is a testament to the punishment that these animals could endure.[13][14]
References:
[1] Dinosaur distribution (Early Jurassic, North America) (Weishampel et al., 2004). From The Dinosauria: Second Edition (pp. 530-532).
[2] New Jurassic dinosaur from the Kayenta formation of Arizona (Welles, 1954).
[3] A new theropod dinosaur from the Early Jurassic of South Africa and its implications for the early evolution of theropods (Yates, 2005).
[4] Osteology of Cryolophosaurus ellioti (Dinosauria: Theropoda) from the Early Jurassic of Antarctica and implications for early theropod evolution (Smith et al., 2007).
[5] The phylogeny of Tetanurae (Dinosauria: Theropoda) (Carrano et al., 2012).
[6] A reassessment of the Chinese Theropod Dinosaur Dilophosaurus sinensis (Lamanna et al., 1998).
[7] Tooth loss and alveolar remodeling in Sinosaurus triassicus (Dinosauria: Theropoda) from the Lower Jurassic strata of the Lufeng Basin, China (Xing et al., 2013).
[8] Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages
[9] www.geol.umd.edu/~tholtz/dinoappendix/appendix.html
[10] The Dinosauria: Second Edition (p. 54).
[11] The Dinosauria: Second Edition (p. 69).
[12] An approach to scoring cursorial limb proportions in carnivorous dinosaurs and an attempt to account for allometry (Persons & Currie, 2016).
[13] Record-Breaking Pain: The Largest Number and Variety of Forelimb Bone Maladies in a Theropod Dinosaur (Senter & Juengst, 2016).
[14] www.livescience.com/53832-jurassic-dinosaur-injuries.html
Skeletal reconstruction of Dilophosaurus wetherilli. © @ Scott Hartman
Temporal range: early Jurassic (Sinemurian-Pliensbachian; ~196-183Ma[1])
Scientific classification:
Life
Domain: Eukaryota
(unranked): Unikonta
(unranked): Opisthokonta
(unranked): Holozoa
(unranked): Filozoa
Kingdom: Animalia
Subkingdom: Eumetazoa
(unranked): Bilateria
Clade: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Clade: Olfactores
Clade: Craniata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Clade: Eugnathostomata
Clade: Teleostomi
Superclass: Tetrapoda
Clade: Reptiliomorpha
Clade: Amniota
Class: Reptilia or Clade: Sauropsida
Clade: Eureptilia
Clade: Romeriida
Clade: Diapsida
Clade: Neodiapsida
Clade: Archelosauria
Clade: Archosauromorpha
Clade: Archosauriformes
Clade: Crurotarsi
Clade: Archosauria
Clade: Avemetatarsalia
Clade: Ornithodira
Clade: Dinosauromorpha
Clade: Dinosauriformes
Clade: Dinosauria
Order: Saurischia
Clade: Eusaurischia
Suborder: Theropoda
Clade: Neotheropoda
Genus: †Dilophosaurus
Species: †D. wetherilli
Dilophosaurus ("two crested lizard") is an extinct genus of theropod dinosaur. It only contains one species, D. wetherilli. Dilophosaurus lived in what is now the state of Arizona of the United States in the Kayenta Formation during the early Jurassic ~196-183 million years ago[1].
Taxonomy:
Since 1954, Dilophosaurus has been classified as a coelophysoid[2]. However, it has recently been suggested that Dilophosaurus was more closely related to tetanurans than coelophysoids[3][4]. A 2012 study found Dilophosaurus to be nested within Coelophysoidea[5].
There used to be an animal assigned as Dilophosaurus sinensis. However, it was found to be synonymous with Sinosaurus triassicus [6][7].
Description:
Dilophosaurus was a bipedal, rather lightly-built predator. It was ~7 meters long and purported to have weighed as much as a grizzly bear[8] (227-454 kilograms as given in the supplementary information of Holtz’s genus list[9]), but given its gracile build, the higher end of the aforementioned weight range seems questionable.
Dilophosaurus is arguably best known for its two thin crests on top of the skull.
The tooth crowns were long.
Reconstruction of the skull of Dilophosaurus. © @ Jaime A. Headden
As noted by the second edition of The Dinosauria, “In Dilophosaurus, serrations are on at least the second and third premaxillary teeth but absent from the fourth (Welles 1984). The maxillary and more distal dentary teeth are linguolabially flattened, strongly recurved, and serrated. The largest maxillary tooth lies in or near the fourth alveolus, with crown height diminishing distally. The most mesial maxillary tooth projects slightly rostrally from its alveolus, a consequence of the upturned ventral border of the premaxillary process. As reconstructed, the maxillary tooth row terminates before the orbit in Dilophosaurus wetherilli and Syntarsus rhodesiensis, but these remains were based on disarticulated material and have not been confirmed in articulated material (Raath 1977; Welles 1984). The tooth row terminates below the orbit in all articulated coelophysoid skulls. Dilophosaurus is reported to have 12 maxillary teeth and 17 or 18 dentary teeth (Welles 1984)” [10].
Dilophosaurus is also known for the notch between its premaxilla and maxilla.
It used to be thought that the mobile sutures of some reptilian skulls acts as a system of levers powered by jaw muscles to aid in predation. Bakker (1986) did not concur with this idea but instead suggested that Ceratosaurus in particular would have been able to swallow items larger than its own head due its loosely-connected skull elements. Welles (1984) also disagreed with the lever system hypothesis and suggested that the loosely-connected skull elements would have made the skull of Dilophosaurus too weak to be used for predation.
While there was indeed some capability of movement between some skull bones, it is most likely that any movement in its skull was passive, merely the bending that occurred as a result of biting and manipulating prey. “The fibrous connections between skull elements would have provided shock-absorbing elasticity, ample tensile strength, and flexibility”. This somewhat conforms to Bakker’s view in that there was some cranial flexibility present, but no proof exists that the skull was anywhere near as mobile to allow for the swallowing of items the size of its head. The loose articulation between the premaxilla and maxilla and the straight, unserrated teeth of the premaxilla and rostral dentary would have allowed Dilophosaurus (and coelophysoids) to manipulate small prey items. The rest of the teeth would have been formidable (as noted above, they are long-crowned (particularly in Dilophosaurus), serrated, lateromedially compressed, and strongly recurved), hence there is no reason to think that these animals would have been unable to hunt live prey[11].
A 2016 analysis of the cursorial potential of carnivorous theropods included Dilophosaurus in its analysis. Dilophosaurus was found to have had a lower limb ~3% shorter than expected for a theropod of the same femur length, hence its CLP (cursorial limb proportion) score of -3.0.[12] This means that, while Dilophosaurus wasn’t nearly as horribly adapted for cursoriality as some of the theropods with even lower CLP scores, it still wasn’t notably cursorial and probably did not chase after prey for prolonged distances.
Paleopathology:
In 2016, Phil Senter and Sara L. Juengst examined the pectoral/forelimb region of the holotype specimen of Dilophosaurus wetherilli (UCMP 37302). As it turned out, it exhibited eight pathologies, twice as many as in the previous theropod record holder for the most pathologies in the aforementioned region (Tyrannosaurus rex specimen FMNH PR 2081; “Sue”). The following pathologies were found:
Pathologies in the Dilophosaurus holotype. From Senter & Juengst (2016).
1.) Right radius and ulna (above) and enlargements of distal end of radius (below) in (from top to bottom) lateral, abductor, and medial views; broken outline indicates three bony tumors.
2.) Left and right humerus (left humerus on left, right humerus on right) in lateral view, each photographed with lateral epicondyle directly facing the viewer, with heavy broken line indicating the midline of the posterior (retractor) surface of each to show the abnormal degree of torsion in the right humerus.
3.) Medial surface of left scapula, with broken outline indicating fracture.
4.) Left (on left) and right (on right) manual phalanx III-1 in dorsal (top) and palmar (bottom) views, with broken lines indicating plane of articulation with adjacent bones, to show the alteration of this plane in the right-hand phalanx.
5.) Distal ends of left (on left) and right (on right) metacarpal III in lateral/abductor view (top) and palmar view (bottom), with broken outline indicating edge of articular surface, to show abnormal truncation of articular surface in right metacarpal III.
6.) Left manual phalanx I-1 (on left), with its right-hand counterpart for comparison (on right), in palmar (top) and lateral/abductor (bottom) views, with broken outlines indicating healed fibriscesses.
7.) Medial surface of left ulna, with broken outline indicating healed fibriscess and arrow indicating abnormal bony growth.
8.) Left radius and ulna in medial view, with arrow indicating healed fracture.
(i. is a figure of metacarpal lll and phalanx lll-1 with the latter in full extension and flexion, illustrating the reduced range of motion)
Restoration of the right manus of the holotype specimen of Dilophosaurus wetherilli with bones, showing the injured third digit with the other two functional digits fully flexed; it is oddly similar to the rude human gesture of solely raising the middle finger. From Senter & Juengst (2016).
The favorite hypothesis that Senter and Juengst suggest goes along the lines of a rival conspecific that kicked its left arm (explaining the two punctures), forcing it to collide against a tree or rock wall, causing the fractures. The dinosaur lived for a long time before its death, as evidenced by the healed injuries. It must have either gone without food for some time or sustained itself by preying upon quarry that could be dispatched solely with the jaws and/or feet or with only one forelimb. The Dilophosaurus appears to have had osteodysplasia. This, coupled with the pain on the left side of its body that would have forced it to put more weight on its right side, was the likely cause of the bone deformation. The holotype is a testament to the punishment that these animals could endure.[13][14]
References:
[1] Dinosaur distribution (Early Jurassic, North America) (Weishampel et al., 2004). From The Dinosauria: Second Edition (pp. 530-532).
[2] New Jurassic dinosaur from the Kayenta formation of Arizona (Welles, 1954).
[3] A new theropod dinosaur from the Early Jurassic of South Africa and its implications for the early evolution of theropods (Yates, 2005).
[4] Osteology of Cryolophosaurus ellioti (Dinosauria: Theropoda) from the Early Jurassic of Antarctica and implications for early theropod evolution (Smith et al., 2007).
[5] The phylogeny of Tetanurae (Dinosauria: Theropoda) (Carrano et al., 2012).
[6] A reassessment of the Chinese Theropod Dinosaur Dilophosaurus sinensis (Lamanna et al., 1998).
[7] Tooth loss and alveolar remodeling in Sinosaurus triassicus (Dinosauria: Theropoda) from the Lower Jurassic strata of the Lufeng Basin, China (Xing et al., 2013).
[8] Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages
[9] www.geol.umd.edu/~tholtz/dinoappendix/appendix.html
[10] The Dinosauria: Second Edition (p. 54).
[11] The Dinosauria: Second Edition (p. 69).
[12] An approach to scoring cursorial limb proportions in carnivorous dinosaurs and an attempt to account for allometry (Persons & Currie, 2016).
[13] Record-Breaking Pain: The Largest Number and Variety of Forelimb Bone Maladies in a Theropod Dinosaur (Senter & Juengst, 2016).
[14] www.livescience.com/53832-jurassic-dinosaur-injuries.html