| Podokesaurus | |
|---|---|
 | |
| Cast of theholotype specimen at theYale Peabody Museum of Natural History; the tail and uncertain bones are at left, the body at right | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Superfamily: | †Coelophysoidea |
| Genus: | †Podokesaurus Talbot, 1911 |
| Species: | †P. holyokensis |
| Binomial name | |
| †Podokesaurus holyokensis Talbot, 1911 | |
| Synonyms | |
| |
Podokesaurus is agenus ofcoelophysoiddinosaur that lived in what is now the eastern United States during theEarly Jurassic Period. The first fossil was discovered by the geologistMignon Talbot nearMount Holyoke,Massachusetts, in 1910. The specimen was fragmentary, preserving much of the body, limbs, and tail. In 1911, Talbot described and named the new genus and speciesPodokesaurus holyokensis based on it. The full name can be translated as "swift-footed lizard of Holyoke". This discovery made Talbot the first woman to find and describe a non-bird dinosaur. Theholotype fossil was recognized as significant and was studied by other researchers, but was lost when the building it was kept in burned down in 1917; no unequivocalPodokesaurus specimens have since been discovered. It was madestate dinosaur of Massachusetts in 2022.
Estimated to have been about 1 m (3 ft) in length and 1–40 kg (2–90 lb) in weight,Podokesaurus was lightly constructed withhollow bones, and would have been similar toCoelophysis, being slender, long-necked, and with sharp, recurved teeth. Thevertebrae were very light and hollow, and some were slightly concave at each end. Thecervical (neck) vertebrae were relatively large in length and diameter compared to thedorsal (back) vertebrae, and thecaudal (tail) vertebrae were long and slender. Thehumerus (upper-arm bone) was small and delicate, less than half the length of thefemur (thigh-bone). Thepubis (pubic bone) was very long, expanding both at the front and hind ends. The femur was slender, nearly straight, had thin walls, and was expanded at the back side of its lower end. The threemetatarsals of the lower leg were closely appressed together forming a compact structure.
Since it was one of the few smalltheropods known at the time it was described, theaffinities ofPodokesaurus were long unclear. It was placed in thefamily Podokesauridae along with other small theropods, and was speculated to have been similar to aproto-bird. It was suggested it was asynonym ofCoelophysis and a natural cast specimen was assigned to it, but these ideas are not currently accepted. The family Podokesauridae is not in use anymore, having been replaced by Coelophysidae, andPodokesaurus is thought to have been a coelophysoid. As such,Podokesaurus would have been a fleet-footed predator, with powerful forelimbs and grasping hands. It is estimated it could have run at 15–20 km/h (9–12 mph).Podokesaurus is thought to have been collected from thePortland Formation, the age of which has long been unclear, but is currently believed todate to theHettangian–Sinemurian stages of the Early Jurassic, between 201 and 190 million years ago.
In 1910, the American geologistMignon Talbot was walking with her sister Ellen toHolyoke,Massachusetts, in the eastern US, when they passed a farm and noticed a small hill nearby. It had a gravel pit at one side, and was formed by an accumulation of sand, gravel, and boulders left by a recedingglacier. Talbot noticed a white streak on asandstone boulder at the bottom of the gravel pit, and upon discovering these were bones, she told her sister she had found a "real live fossil". This was because manyfossil tracks had previouslybeen discovered in theConnecticut Valley (that she had often taken her students to see), but few actualdinosaur skeletons, and none atMount Holyoke. She was granted permission by the land owner to collect the specimen forMount Holyoke College (an all-women's college a few miles from there), where she was head of the geology department.[1][2][3][4]
The next day she brought a group of workmen to collect the specimen, and found another piece of sandstone that contained the rest of the fossil as well as impressions of those in the first slab. The specimen appeared to have been exposed for years with no one noticing it, the boulder having been broken open by people or frost. The fossil was brought to the laboratory where it was prepared and photographed.[1] The incomplete specimen preserved 5cervical (neck), 11dorsal (back) and 24caudal (tail) vertebrae, a fragment of the leftscapula (shoulder blade) and rightcoracoid (part of thepectoral girdle), a partial lefthumerus (upper arm bone),phalanx bones of 3 fingers, including 2unguals (claw bones), ribs, thepubis andischium (bones forming the lower front and lower back of the pelvis, respectively), thefemora (thigh bones), the lefttibia (lower leg bone), a fragment of the rightastragalus (a bone in the ankle), articulatedmetatarsals (foot bones) of the left foot, followed by 3 pedal phalanges (toe bones), partial metatarsals and possible phalanges of the right foot, and fragments of uncertain identity.[5][6] The light and delicate bones were in their natural position or nearly so within the rock, except for the tail and uncertain fragments, which were a few centimeters away from the skeleton, following a long gap in the skeleton behind the pelvis. The front half of the neck was missing.[1][7]
The significance of the fossil was confirmed at an intercollegiate meeting of geology departments, and when the American paleontologistRichard Swann Lull subsequently encouraged Talbot to describe the specimen, she replied she did not know anything about dinosaurs, but Lull suggested she should study them and then describe it. In December 1910, Talbot read a preliminary description of the fossil at thePaleontological Society meeting atPittsburgh, and in June 1911 she published a shortscientific description, in which she made the specimen theholotype of the newgenus andspeciesPodokesaurus holyokensis.[1][8] The generic name is derived from theAncient Greek wordspodōkēs (ποδώκης), which means "swift (or fleet)-footed", anepithet commonly used in reference to the Greek heroAchilles, andsaura (σαύρα) meaning "lizard", while thespecific name refers to Holyoke. In full, the name can be translated as "swift-footed lizard of Holyoke".[8][2] The discovery and naming ofPodokesaurus made Talbot the first woman to find and describe a non-bird dinosaur.[9] The American paleontologistRobert T. Bakker stated in 2014 that while old professors grumbled that women were unfit for working with fossils during his time at university, Talbot's discovery ofPodokesaurus was a counterargument to that.[10]
By the time the description was published, Talbot had sent the fossil to thePeabody Museum of Natural History atYale University for further preparation and study, where cast replicas were also made of the bones as they lay in the rock. There, Lull drew a reconstruction of the skeleton, basing the parts missing from the fossil on the equivalents inCompsognathus, and created a model of the animal in life, which Talbot later described as having a "sardonic smile". Lull expanded on Talbot's article in a 1915 publication, wherein he also proposed other identities for some of the bones than what she had originally suggested, including a partial coracoid instead of a scapula and part of the tibia instead of theilium (part of the hips). Lull suggested that the boulder containing the fossil must have come from a ledge which lay on the south side of theHolyoke Range, about two or three miles north of where it was found, and specified that it was from theLongmeadow Sandstone.[6][2][11][7]
Lull had sent his manuscript to the Danish ornithologistGerhard Heilmann for criticism prior to publication. Heilmann published his response in a 1913 article in which he included previously unpublished photos of the fossil received from Talbot, as well as his own restorations. He disagreed with some of Lull's anatomical interpretations, and had corresponded regarding the fossil with the American zoologistRobert Wilson Shufeldt about his contentions. Heilmann's article was one in a series about theorigin of birds, wherein he examined the skeletons of prehistoric reptiles to find traits that may have been ancestral to birds.[12] In a 1916Washington Academy of Sciences meeting, Shufeldt gave an account of his correspondence with Lull, Talbot, and Heilmann, and agreed with the latter in some of his criticisms of Lull's restoration ofPodokesaurus.[13]
Talbot wanted the fossil to stay at Yale orWashington on permanent exhibit, where it could "be with its kind", but it was kept at Mount Holyoke in the old science building, Williston Hall, as a local specimen, where it became a "pet curiosity" for the students. During the Christmas break of 1917, Williston Hall burned down, and no remains of thePodokesaurus fossil were found in the rubble. The American writerChristopher Benfey pointed out in 2002 thatPodokesaurus therefore had the peculiar distinction of being the dinosaur that vanished twice.[2][1] The German paleontologistFriedrich von Huene was the last to study and describe the holotype specimen, in a 1914 publication before it was destroyed (he had studied it at Yale before Talbot's description was published).[7][14] While the college's fossil collections were almost entirely destroyed by the fire, its facilities and collections continued to grow and improve afterwards due to Talbot's efforts.[15]
No other unequivocalPodokesaurus specimens have since been found, but cast replicas of the type specimen remain at the Peabody Museum of Natural History and theAmerican Museum of Natural History inNew York.Podokesaurus received little further attention until new and abundant fossils ofCoelophysis were discovered in the late 1940s, and the anatomy of smalltheropod dinosaurs became clearer; the American paleontologistsEdwin Harris Colbert and Donald Baird comparedPodokesaurus withCoelophysis in 1958, using the casts of the former. Along with thesauropodomorphAnchisaurus,Podokesaurus was among the first substantial collections of dinosaur skeletal material known from the East Coast of North America. Apart from a tooth (assigned toCoelophysis in 1976), all other Early Jurassic theropod records on the East Coast are footprints.[16][17][18]
In 2021,Podokesaurus andAnchisaurus were proposed as contenders forstate dinosaur of Massachusetts by RepresentativeJack Patrick Lewis, withPodokesaurus winning the online poll.[19][20][21] On May 2, 2022, GovernorCharlie Baker signed a law making it the official state dinosaur.[22] A 2024 paper about identification of natural dinosaur bone casts concluded that new methods could be used to find additional remains ofPodokesaurus, noting its status as state dinosaur.[23]
The preserved body of the only knownPodokesaurus fossil was 18 cm (7 in) long.[8] Lull estimated the complete length ofPodokesaurus to have been 1,150 mm (3.77 ft), the neck accounting for 130 mm (5.1 in), the back for 170 mm (6.7 in), thesacrum (the vertebrae of the pelvic region) for 45 mm (1.8 in), and the tail for 730 mm (2.40 ft).[6] Von Huene estimated the animal to have been 1,100 mm (3.6 ft) long, with the tail accounting for about 70 cm (2.3 ft), more than 1.5 times the rest of the skeleton together.[7] Colbert estimated the animal's length at about 1 m (3.3 ft).[17] In 1995, the writer Jan Peczkis estimatedPodokesaurus to have weighed 10–40 kg (22–88 lb), through pelvic height determination (based on von Huene's measurements).[24] The paleontologistGregory S. Paul estimated it to have weighed 1 kg (2 lb) in 2016 (based on a 1 m length estimate).[25] Talbot stated in 1937 that those scientists who had seen the specimen did not think it was a young individual as there were no indications ofcartilage that would turn to bone with age,[1] while Paul thought it was possibly juvenile.[25] In general, the animal was lightly constructed, withhollow bones.[8] As acoelophysoid, it would likely have been similar in build to for exampleCoelophysis, being slender, long-necked, and with sharp, recurved teeth.[16]
Since few other small theropods were known at the timePodokesaurus was described, it was mainly compared to the later generaCompsognathus,Ornitholestes, andOrnithomimus, which were thought related. Due to the fragmentary nature of thePodokesaurus specimen and the fact that it is lost, the identity and shape of some of its bones are today unclear. As only casts of the specimen now remain, it is only possible to get a general impression of the preserved skeleton and its proportions. Talbot identified bone fragments next to the tail as skull bones because two of them werebilaterally symmetric, and one was broadly convex with asulcus (or furrow) at the midline, and according to Lull, was possibly placed at the upper wall of the skull, not far from thefrontal bones. Lull thought other of these elements may have been part of thenasal bones.[6][17] Von Huene instead interpreted these bones as caudals from the middle of the tail.[7]
The vertebrae were very light and hollow, and some were slightly concave at each end. The cervical vertebrae were relatively large in length and diameter compared to the dorsals, and had styliform (resembling a pen or bristle in shape) cervical ribs which were long, straight, and narrow, as inAnchisaurus. The front dorsals were much shorter than the cervicals, then again increased in size towards the pelvis. They measured 12–13 mm (0.47–0.51 in) in length. Theneural spines of the dorsals were narrow, high, and curved backwards, but not as expanded from front to back as inCompsognathus. The dorsal ribs were strongly curved and very slender and hollow, reminiscent of those inSaltopus andHallopus, the largest being 52 mm (2.0 in) long and 2 mm (0.1 in) wide. Thetransverse processes (that connected with the ribs on each side of a vertebra) formed a circular arc downward from each side of a dorsal, extending about as far from thecentrum (the "body" of a vertebra) as thespinous process was high. Thezygapophyses (processes that connected adjacent vertebrae) were well-developed. The centra were relatively longer than those ofOrnithomimus, while those ofCompsognathus resembled those ofPodokesaurus more, but were shorter.[8][6][7]
While the hind part of the tail was located some distance away from the rest of the skeleton, Lull believed it was in its natural position and that it would have been very long, the intermediate vertebrae having been swept away. The caudal vertebrae were very long and slender, and along with theirchevrons (bones on the undersides of the caudals), resembled those ofOrnitholestes. A typical caudal was 17 mm (0.67 in) long and 4 mm (0.16 in) in diameter. The caudals were very similar in length and did not decrease in length until the last few in the succession. Just in front of the pubis there was a cluster of slendergastralia (abdominal ribs), the longest of which was 18 mm (0.71 in) long. The frontmost gastralia had broadened ends, which is often the condition insternal ribs.[8][6][7]
The humerus was small and very delicate, 42 mm (1.7 in) long, less than half the length of the femur. It had a strong processus lateralis (aprocess directed to the side) 30 mm (1.2 in) above its lower end. Lull found it similar to that ofOrnitholestes, apart from the radial crest (that connected with theradius bone of the lower arm) not being as high, showing little muscular power. Von Huene estimated the radius to have been 30 mm (1.2 in) long. Lull found the hand more similar to that ofCompsognathus than ofOrnitholestes.[8][6][7] Only slender phalanx bones of the three fingers were preserved, including sharp, curved claws.[7]
The pubis was very long, expanding both at the front and hind ends. It was 6 mm (0.24 in) wide and 95 mm (3.7 in) long, and its lower expansion was 10 mm (0.39 in) in diameter. Talbot found the pubis similar to that of the then undescribedProcompsognathus. Lull argued that the pubis lay approximately in position in the fossil, pointing forwards.[8][6] Heilmann instead believed the bone had been moved out of position before burial, and would have been directed backwards.[12] Colbert and Baird suggested the pubis was directed forwards, but that it curved slightly upwards instead of downwards due to natural warping and cracking of the bone. The ischium was 55 mm (2.2 in) long, 15.5 mm (0.61 in) wide at the end closest to the body, and its slender shaft was 4 mm (0.16 in) in diameter, and somewhat thickened at its lower end. Lull found it similar to those ofCompsognathus andOrnitholestes. Below theacetabulum (where the femur connects with the pelvis) there was a broadlamella running towards the pubis.[6][7]
The femur was slender, nearly straight, had thin walls, and was expanded at the back side of its lower end. It was 86 mm (3.4 in) long and 6.5 mm (0.26 in) in diameter just below thefourth trochanter (a flange placed mid-length at the back of the femur). The fourth trochanter was strong, 18 mm (0.71 in) long and about 2 mm (0.079 in) high, and was situated past the middle of the shaft, towards the lower end. Thecondyles (round prominences) of the femur's lower end protruded strongly hindwards. The tibia was a thin, narrow shaft, 104 mm (4.1 in) in length, and about 7 mm (0.28 in) in diameter. Talbot stated the very thinfibula lay close to the tibia and was of almost equal length, while von Huene thought this was instead part of the crushed tibia. The three metatarsals of the lower leg were closely appressed together forming a compact structure, similar to what was seen inOrnithomimus, but not fused into atarsometatarsus, as seen in birds. The length of the metatarsals was 75 mm (3.0 in), while their width was 9 mm (0.35 in). The most complete pedal phalanx was very slender and 12 mm (0.47 in) long.[6][8][7]
When reading her preliminary description in 1910, Talbot suggestedPodokesaurus to have been an "herbivorous dinosaur", but further work at Yale University showed that some bones had been incorrectly identified, and the ischium of the pelvis with a well-developed ridge was found to resemble that ofCompsognathus. She refrained from making a definite classification of the specimen in her 1911 description due to the lack of jaw and foot-bones which could have aided in this, but concluded it would have belonged to a "carnivorous dinosaur" based on the shape and position of the pubis, as well as the absence of apostpubis. She considered the fossil to beTriassic in age (the first of the threeMesozoic periods).[8] In 1914, von Huene named the newfamily Podokesauridae, wherein he, in addition toPodokesaurus, includedSaltopus,Procompsognathus,Coelophysis, andTanystropheus. He placed this group underCoelurosauria, which at the time was used to include small theropods in general.[26][7][27]
Heilmann consideredPodokesaurus very similar to the early birdArchaeopteryx in 1913, and wondered why Talbot had not made any comparisons to it. He particularly found the legs and the pelvis, when the pubis was interpreted as pointing backwards (as in birds), similar to what it might look like in a bird ancestor, while considering Lull's reconstruction of a forward-directed pubis unlikely. He also found parts of the shoulder blade, forelimbs, and even tail bones similar to those of birds. He furthermore pointed to the presence of abdominal ribs and that the bones were hollow, and concluded that nothing precludedPodokesaurus from being a very primitiveproto-bird, with not yet fused middle-foot bones. The only feature he found inconsistent with this interpretation was the short finger with a claw, if it was not instead part of a toe. He suggested that the issue could be determined if the skull, sternum, andclavicle were found in the rock, bones that would be important clues for classification.[12]
Heilmann wished for a clearer explanation of the placement of the middle-foot bones in relation to each other, and found it surprising that Lull's reconstruction ofPodokesaurus showed an even more appressed middle-foot than was present in the later supposed descendantOrnithomimus, which he thought would have developed a completely bird-like middle-foot by that time. Heilmann foundPodokesaurus very unusual for a dinosaur from the Triassic, and thought it was one of the earliest bipedal vertebrates. He suggested that since it was so different fromThecodontosaurus andPlateosaurus, those may not have been dinosaurs, orPodokesaurus could instead have been related toSaltopus orparasuchians, but found its fossils too insufficient to say anything definite about the issue.[12]
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Shufeldt elaborated on his and Heilmann's interpretation of the pubis in 1915, and stated the bone had probably been displaced during fossilization. He pointed out that if it had faced forward, it would have been in forcible contact with the abdominal ribs that would have been dangerous for internal organs during movement.[11] Lull found Heilmann and Shufeldt's criticisms of his pelvis reconstruction probable in 1915. He listed Podokesauridae under the superfamilyCompsognatha, and suggestedPodokesaurus was perhaps ancestral to the later North American generaOrnitholestes andOrnithimimus.[6] In 1916, Heilmann pointed out that early dinosaurs, parasuchians, andpterosaurs all had similarities to birds, as well as to each other, and that Triassic reptiles likeScleromochlus,Saltopus, andPodokesaurus, were difficult to separate. He proposed thatPodokesaurus and other bipedal reptiles from the Triassic were descended frompseudosuchians (which many types ofarchosaurs were classified as at the time) that may have evolved bipedality by thePermian. He concluded that birds were descended fromornithosuchian pseudosuchians rather than from dinosaurs, due to their bipedality and bird-like legs.[28]
The paleontologistHenry Fairfield Osborn usedPodokesaurus as an example of a "carnivorous dinosaur of the bird-like type" in 1917, while stating that similarities between birds and dinosaurs were due toparallel evolution.[29] The paleontologistFranz Nopcsa von Felső-Szilvás created thesubfamily Podokesaurinae in 1928, within which he includedPodokesaurus,Procerosaurus,Saltopus, andTanystropheus.[30] Von Huene groupedPodokesaurus,Coelophysis,Spinosuchus,Halticosaurus,Saltopus,Avipes, andVelocipes in Podokesauridae in 1932.[31]
In 1958, Colbert and Baird described a theropod specimen consisting of natural casts of bones in sandstone (probably formed when the bones were dissolved by acidic water, leaving molds of the bones), including a pubis, tibia, and some ribs. They found the specimen similar toCoelophysis andPodokesaurus, referring to it asC. sp. (of unknown species). They considered the natural cast andPodokesaurus to be from thePortland Arkose of theNewark Group in the Connecticut valley. ThoughPodokesaurus was smaller than the others (being comparable in size to the smallest-knownCoelophysis specimens), these researchers suggested that because it was so similar to them, this raised questions as to its validity.[32][33] In 1964, ColbertsynonymizedPodokesaurus withCoelophysis, (since the latter name was older), coining thenew combinationC. holyokensis. He also suggested that the natural cast belonged toC. holyokensis. Colbert stated thatPodokesaurus could only be distinguished fromCoelophysis by the neural spines of its vertebrae not being as long from front to back, and because the ischium differed in shape. He found these differences to be similar to those seen between modern reptile species within the same genus, and that they represented eastern (C. holyokensis) and western (C. bauri) species of the same genus. While he admitted that these conclusions were not ironclad, and thatPodokesaurus may indeed have been distinct, he said the burden of proof should be on the proponents of such a view.[17]
In 1977, the paleontologists Paul E. Olsen andPeter Galtonredated the Newark Supergroup (which the Portland Formation belongs to) to the Early Jurassic instead of the preceding Triassic as was previously thought. This was part of a study in which Olsen compared the fauna of various formations and concluded there had not been a sudden, widespreadextinction event at the Triassic-Jurassic border, but that it had instead been gradual.[34] Olsen stated in 1980 that while the exact provenance and systematic position ofPodokesaurus will probably remain uncertain, the Portland Formation it was thought to be from was probably Early Jurassic in age, and therefore 15 million years younger thanCoelophysis from the Triassic. Since features shared betweenPodokesaurus andCoelophysis are also known in other small theropods, such asSyntarsus, Olsen suggested thatPodokesaurus should be retained as a separate genus of indeterminate theropods, to avoid overextending the temporal range ofCoelophysis. He also applied this argument to the natural cast, regarding it asincertae sedis (with uncertain relationships) among theropods rather than asPodokesaurus orCoelophysis.[35]
The paleontologistSamuel P. Welles stated in 1984 that the family Podokesauridae had become a "catch-all" for most Triassic theropods. While he foundCoelophysis the most similar toPodokesaurus among theropods, he thought the two differed greatly in that the fourth trochanter of the latter was below midheight on the femur (unlike the higher position in most other theropods), and its metatarsals were of equal length.[14] The paleontologistKevin Padian stated in 1986 that while Colbert's suggestion of synonymy was possible, the discernible similarities betweenPodokesaurus andCoelophysis wereprimitive theropod features, and the two were not as close in time as once thought.[36] Paul said in 1988 that while the family Podokesauridae was still used forCoelophysis and kin,Podokesaurus was not based on good remains to begin with, and with only bad cast replicas remaining, he thought there would always be disagreement about the taxon. He found this to be too much ambiguity to put up with, and proposed the name Coelophysidae should be used instead (Halticosauridae, another contender, was also based on too fragmentary remains).[37] In 1989, Colbert also doubted the synonymy ofPodokesaurus withCoelophysis, and that the natural casts belonged to the latter, due to their revised Early Jurassic ages, and he made no attempt to resolve the status ofPodokesaurus due to the only specimen being lost. He retained the name Podokesauridae for the family.[38]
In 1990, the paleontologists Timothy Rowe andJacques Gauthier considered Podokesauridae ataxonomic waste-basket, wherein taxa had been grouped based onphenetic resemblance andstratigraphic division, and therefore under continuous revision and instability. They considered it possible thatPodokesaurus and the natural cast specimen wereCoelophysis, but found that their similarities were not shared exclusively by them, but were ancestral features among theropods. They therefore agreed that the namePodokesaurus should be restricted to the holotype, and that it and the natural cast should be considered Theropodaincertae sedis.[39] In the same volume, the paleontologistDavid B. Norman agreed with this assessment, and stated the features used to unitePodokesaurus withCoelophysis merely confirm that they were dinosaurs rather than establish a specific relation between them.[5] The paleontologistThomas R. Holtz agreed in 1994 that the family name Podokesauridae should be replaced by Coelophysidae. By this time, the idea that small theropods should be grouped in Coelurosauria and large theropods inCarnosauria was falling out of favor, and Coelophysoidea was considered a separate group of gracile, early theropods.[40] The paleontologistsDavid B. Weishampel and Luther Young suggestedceratosaurian affinities forPodokesaurus in 1996.[41]
The paleontologist Ronald S. Tykoski and Rowe noted in 2004 that whilePodokesaurus had coelophysoid features (such as a small, knob-like expansion on the lower part of the pubis), it did not have anyderived traits that would unite it withCoelophysis. They agreed with earlier researchers that the namePodokesaurus should be restricted to the holotype, and concluded that the natural cast may be a coelophysoid, but could not be identified beyond being a theropod.[42] In 2004, the paleontologists Matthew T. Carrano andScott D. Sampson stated thatPodokesaurus was almost certainly a coelophysoid similar toCoelophysis. It had coelophysoid features such as a long, downward curved pubis, that was longer than the ischium, and an additionalforamen (opening) on the pubis, below theoburator foramen, but little more could be said about itsaffinities.[43] Carrano and colleagues stated in 2004 thatSegisaurus andPodokesaurus were among the latest-surviving coelophysoids, and that theevolutionary radiation of this group may have ended by the latest part of the Early Jurassic.[44] Also in 2004, the paleontologists Anthea Bristowe and Michael A. Raath listedPodokesaurus as a synonym ofCoelophysis without elaboration.[45] Tykoski rejected synonymy between the two in his 2005dissertation, but leftPodokesaurus out of his analysis.[46] Paul suggested in 2016 thatPodokesaurus may have formed the family Coelophysidae withCoelophysis,Panguraptor, andProcompsognathus.[25]
Talbot suggested that the short, slender humerus, long, straight hindlimb bones, and the well-developed fourth trochanter of the femur indicated thatPodokesaurus was bipedal. She found the fact that the tibia was much longer than the femur, that the metatarsals were very long, over half the length of the tibia, and the skeleton's light construction, were indicative of rapid locomotion. Talbot stated that Lull thought this was an adaptation to climatic conditions, as the animal must have been able to travel fast and far for water in itssemi-arid region. Talbot also reported a small piece of smooth, polishedquartz among the ribs, and suggested it could have been agastrolith (stomach stone), and so the first time these were found in association with a carnivorous dinosaur.[8] Von Huene agreed the stone was a gastrolith, distinct from the surrounding sandstone, and added it was 11 mm (0.43 in) long.[7]
Lull found the animal to have been essentially a slender,cursorial (adapted for running) animal, with carnivorous habits, but that the slenderness that made it swift also confined it to small prey.[6] In 1932, von Huene proposed that small coelurosaurs had a jumping gait, due to their lower legs being longer than their upper legs, contrasting with the alternating steps of carnosaurs. With its large fourth trocanther, he thoughtPodokesaurus had probably abandoned this jumping gait, instead moving with rapid, alternating steps similar toratite birds.[31]
In 1982, the paleontologistRichard A. Thulborn estimated the speed of various dinosaurs, based on the relationships between speed, gait, and body size of modern animals (mainly mammals). By extrapolating the stride length and cadence ofPodokesaurus, he estimated it could have run at about 15–20 km/h (9–12 mph). He concluded that if a dinosaur could match a mammal in speed, it must have had similar levels of efficiency inlocomotor ability and physiology. He cautioned that comparison was difficult because dinosaur anatomy differed significantly from that of mammals and birds. Differences included the massive tails of dinosaurs, and hindlimb retractor muscles that originated behind the femur, while these muscles originate more forward in mammals and extant birds.[47] Weishampel stated in 2006 that as a coelophysoid,Podokesaurus would have been a fleet-footed predator, with powerful forelimbs and grasping hands.[16]
Lull found that fossil footprints namedGrallator cursorius agreed with the foot and stride ofPodokesaurus. These were abundant at a quarry inSouth Hadley (where they were found alongside largeOtozoum moodii tracks), which he thought supported this identity.[6] In 1926, Heilmann suggested that the foot ofProcompsognathus was a better match for theG. cursorius tracks, due to the proportions of its toe bones.[48] The paleontologist Wilhelm Bock stated in 1952 that while very similarGrallator tracks had been attributed to various small dinosaurs (such asPodokesaurus), he considered such correlations too specific, and that the best that could be said was such tracks represented small coelurosaurians.[49] The writerDonald F. Glut suggested in 1997 that a slab with tracks from theBrunswick Formation of New York previously attributed toCoelophysis may instead have been produced byPodokesaurus, based on its Jurassic age.[50] This formation is now known as the Passaic Formation, and instead thought to be Late Triassic in age.[51]
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The only known specimen ofPodokesaurus is thought to have been collected from the Portland Formation (earlier known as the Portland Arkose) in theHartford Basin of Massachusetts. The age of this formation has long been unclear (it was thought to be Triassic until 1977), but it is currently thought to date to theHettangian–Sinemurian stages of the Early Jurassic, between 201 and 190 million years ago (earlier thought to be thePliensbachian–Toarcian stages).[52][16][35] In 2016, the paleontologist Robert E. Weems and colleagues suggested the Portland Formation should be elevated to ageological group within the Newark Supergroup (as the Portland Group), and thereby replacing the former name "Agawam Group". They also reinstated the Longmeadow Sandstone, wherePodokesaurus was found, as a formation (within the uppermost Portland Group); it had earlier been considered identical to the Portland Formation.[52][6]
The Portland Group represents the uppermost part of the Newark Supergroup, and was deposited after theCentral Atlantic magmatic province was formed during the end of the Triassic and the beginning of the Jurassic. The Longmeadow Sandstone consists offluvial (deposited by rivers and streams) redmudstones, sandstones,conglomerates, minor redeolian (deposited by wind) sandstones andsiltstones.[52] Other animals known from the formation include the sauropodomorph dinosaurAnchisaurus, the crocodylomorphStegomosuchus, and fish such asAcentrophorus andSemionotus.[35] Dinosaur tracks include theichnogeneraAnchisauripus,Anomoepus,Eubrontes, andGrallator.[53]
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