Grallator
From the family of dinosaurs that made "bird prints" but eventually led to real birds.
Grallator (GRAL-uh-tore), meaning 'stilt walker,' was a herding dinosaur known only from its fossilized footprints. It is called a herding dinosaur because its tracks frequently show groups of animals, traveling together.
Figure 1.
These three-toed tracks average about 7 inches (17 cm) long, and are relatively common. The shape and pattern of the bipedal prints (including the ratios of the lengths of the toes) indicate that Gallator was probably a small theropod.
Theropods were the group of dinosaurs that led to the birds. And They were:
-
Fast and agile
-
Had a carnivorous diet
-
Sharp, slicing teeth or beak, and well-developed jaw muscles
-
Clawed hands [usually with three main digits - exceptions include the Tyrannosaurids (T-Rexs), who lost the third digit]
-
Bipedal walk
-
Strong legs with bird-like, clawed feet
-
Large eyes, indicating good eyesight.
Grallators were similar to Coelophysis. And here's a great illustration of a herd of Coelophysis.
Figure 2.
Here's what their skeleton's looked like:
Figure 3. A photograph of Coelophysis bauri taken at the Denver Museum of Nature and Science in 2007.
Coelophysis were one of the first groups of dinosaurs to show up in North America, where their footprints are one of the most common fossils.
Grallator tracks date from about 200 million years ago, during the very late Triassic period to the early Jurassic period. Grallator trackways have been found in the USA (NJ, PA, CT), Canada, and Europe.
Here is an illustration map of a trackway from the Karoo Basin of southern Africa, where the track of an Anomoepus (an-oh-moe-pus) and a Grallator (GRAL-uh-tore) overlap each other, both being made at different times.
Figure 4.
Trackways of Anomoepus (an-oh-moe-pus) and Grallator are in solid green and blue, respectively; all other trackways are in 50% grey. Trackway numbering (Arabic numerals) begins with the first recognized step of each trackmaker.
Grallator tracks 1 and 2 are not shown because they are now underneath a retaining wall. Red wavy lines indicate ripple marks; solid light grey fields indicate algal-matted surface.
The inset highlights postural and gait changes in the Anomoepus trackway, which was made by a basal ornithischian (see below).
A shift from wide-gauge to narrow-gauge posture (between tracks 13 and 14) is marked by shift in pace angulation (blue dotted line) and was accompanied by a brief pause, during which the tail registered on the substrate when tracks 12 and 13 were impressed. The shift from a quadrupedal to a bipedal gait (between tracks 15 and 16) occurs atop the algal matted surface.
Note that Grallator track 11 (blue) overprints Anomoepus track 15, indicating it was made later.
Side Trip – A Brief History of Dinosaur Tracking
(C) 1994-2009, Glen J. Kuban
Native Americans probably knew of dinosaur tracks before the first European settlers. Ancient petroglyphs (see below) occur alongside several western track sites. In fact, one site is known by an Indian name that translates, "location with bird tracks."
The first authenticated dinosaur track discovery occurred in 1802 when a farm boy named Pliny Moody in South Hadley, Massachusetts, plowed up a slab of reddish rock bearing several small three-toed footprints. The find was proudly displayed above a door in the Moody farmhouse, and a local doctor declared the prints to be those of Noah's raven.
Figure 5.
The prints are referred to the ichnospecies Anomoepus scambus (see below).
The confusion of dinosaur tracks with bird tracks was understandable. Dinosaurs were not yet known, and bipedal dinosaur tracks (especially small ones) bear a very close resemblance to bird tracks. The similarity is more than coincidental, since birds and dinosaurs are now considered close relatives.
By the late 1830's an intensive study of the fossil tracks of the Connecticut Valley was undertaken by professor Edward Hitchcock, president of Amherst College.
Hitchcock systematically excavated, described, and classified thousands of tracks in remarkable detail, culminating in a monumental volume (Hitchcock, 1858), which is still a classic reference work in the field.
Although Hitchcock believed many of the track ways were made by ancient birds, other trails puzzled him. Noting the occasional appearance of narrow, lizard-like tail marks, Hitchcock speculated that some of the track ways may have been made by large bird-like creatures with long, reptile-like tails. Without realizing it, he had just described dinosaurs.
By the time of Hitchcock's death, dinosaurs were better understood. However, most paleontologists soon became preoccupied with bones, and largely neglected dinosaur tracks for the next several decades. There were two exceptions to this change in focus:
-
Richard S. Lull expanded and updated Hitchcock's work on the early Jurassic tracks of New England (Lull, 1915, 1953).
-
Roland T. Bird did extensive work on Cretaceous tracks near Glen Rose, Texas (Bird, 1941, 1953).
The neglect of dinosaur tracks came to an abrupt end in the early 1980's, when a veritable explosion of interest and research on dinosaur tracks occurred. In 1986 the First International Symposium on Dinosaur Tracks and Traces was held in Albuquerque, New Mexico, bringing together dinosaur trackers from all over the globe.
How Dinosaur Tracks are Formed
Unlike body fossils, which often are best preserved when they are buried rapidly, tracks are more likely to be well preserved when they are buried in a relatively slow, calm manner. For this reason, tracks and bones are seldom found in close association.
There are two main ways in which tracks can be formed and preserved.
- The classic scenario is as follows.
- A track maker walks along a moist but firm, fine-grained sediment.
- The tracks remain exposed for a short while, allowing them to become drier and harder (and thus able to resist damage during subsequent burial).
- A short time later the prints are gently buried with additional sediment, preferably of a contrasting type (which would allow the layers to separate when later re-exposed).
- Buried for millions of years, the original sediment turns into rock.
- Finally, the tracks are re-exposed in modern times by erosion or other forces.
Of course, the tracks also must be found and studied before they are destroyed by weathering, quarry workers, or other dangers. Tracks formed under less ideal conditions tend to be distorted or indistinct, if preserved at all.
- Another mechanism of print formation:
- A dinosaur walks on a very soft surface. In such a case, the animal's feet may push into firmer layers below the surface.
- The soupy surface material may then rush back over the upper depressions, simultaneously covering the prints made in the lower layers. The subsurface prints are known as underprints, undertracks, or ghost tracks
- Buried for millions of years, the sediments turn into rock.
- Finally, the tracks are re-exposed in modern times by erosion or other forces.
Figure 6.
A. Track Formation and Preservation
Diagram showing a true track, natural cast, undertracks, and track infilling as they might appear in rock strata. Adapted from Lockley (1991).
B. Track Variations Related to Sediment Consistency.
All the tracks shown were made by a single dinosaur stepping on substrates of different consistencies, with the firmer substrates at left and the softer ones on the right. Notice the absence of distinct pads in the deeper prints (at right). The right-most track suffers from "mud collapse" or "mud back-flow," where soft sediment slumps back into a track depression, distorting its shape. Adapted from Thulborn (1990).
C. Basic Trackway Measurements.
Pace angles (also called step angles or pace angulations) may be calculated using trigonometry once pace and stride measurements are made. On a quadruped track way, these measurements should be made for both rear and front prints. One should also measure individual print lengths, widths, depths, and digit dimensions and angles.
Because the tracks are buried as soon as they are made, any erosion or other destructive forces occurring at the surface would pose no threat to them, increasing their chances of being preserved.
Major Types of Dinosaur Tracks
It is often difficult or impossible to identify the particular genus or species of dinosaur that made a given track way. However, one can usually determine at least the general group of dinosaurs to which the track maker belonged, since foot structures vary considerably among different dinosaur groups. In many cases the locomotor styles of different groups varied as well.
Bipedal track ways are the most common. They contain left-right sequences of similarly shaped prints, each containing three major digit marks. They are commonly called "three-toed tracks" or tridactyl tracks. Most bipedal dinosaurs actually possessed four digits on each foot, but one digit (the hallux) was small and held in an elevated position at the inside rear of the foot. When recorded at all, hallux marks are usually small and shallow.
Dinosaurs that made bipedal tracks fall into two major groups:
- Theropods (bipedal meat-eating dinosaurs)
- Ornithopods (bipedal plant-eating dinosaurs)
Theropod tracks typically exhibit relatively long and narrow digit impressions, terminated with sharp, slender claw marks. The posterior ends are typically somewhat V-shaped. Among theropods, a somewhat arbitrary division is made between small, gracile forms called coelurosaurs, and large, robust forms known as carnosaurs.
Coelurosaur tracks often exhibit digits held closely together, and distinct toe pads. The shapes and positions of the pads are useful in identification. The digit marks of carnosaur tracks are often more widely splayed and robust, with less distinct pads.
Figure 7.
All of these tracks came about through an evolutionary change, a change from a reptilian “pushup” posture to a dinosaurs “upright” posture.
Let's look at this change for a moment. But first...
Quick Review
- Ancient petroglyphs occur alongside several western track sites
- First authenticated dinosaur track discovery occurred in 1802
- Scientists can determine which general group of dinosaurs a track maker belongs to
- Theropods - bipedal meat-eating dinosaurs
- Ornithopods - bipedal plant-eating dinosaurs
- There can be four parts to a track:
- Natural Cast – A top sediment layer that molds into the original track
- True track – The actual track itself
- Track infilling – Material that fills in the original track, can be different than a natural cast
- Undertracks – a layer of sediment that shows the weight and partial shape of the true track, sometimes called a ghost track
All of these tracks came about through an evolutionary change – from a reptilian “pushup” posture to the dinosaur “upright” posture.
Side Trip – Posture and Gait
There is a portion of the pelvis into which the head of the thigh bone (femur) fits into.
Here's what it looks like in a human:
Figure 8.
The hip socket seen in Dinosaurs is associated with a suite of changes in posture and gait. These changes can be thought of as a culmination of a trend towards a more upright posture with limbs held in a more in the plane of the front-to-back-axis position.
The stilt walking of the Grallators.
Three types of postures need to be looked at: sprawling, semi-erect, and erect.
Figure 9.
Sprawling A sprawling gait is the most primitive and consists of having the limbs in a perpetual "push-up" position. This posture is associated with a side-to-side motion of the body during locomotion.
Living lizards have this posture and can move very fast. However, the sinuous motion of the body alternately collapses the lung on each side, preventing breathing during running. That's why lizards have to stop completely and pant after they run, even though they risk capture.
Semi-erect Crocodiles have a semi erect posture (sometimes called semi-improved). When moving slowly, their posture is sprawling, but when they run, their body straightens out, and they pull their legs nearly under their body. When they carry their bodies more nearly erect, they are said to exhibit a "high walk." In this posture the lungs can still operate. Some crocodiles are even capable of galloping. Galloping is the fastest type of longer term quadrupedal motion in which all four feet are off the ground simultaneously during one phase of the step cycle.
Erect The bipedal plant-eating dinosaurs have an erect posture and gait (often called fully improved) in which the limbs are held directly under the body and flexed in a plane, parallel to the body axis. The limbs move in this plane during walking slowly as well as running. This allows easy breathing while running. The open “hip socket” is the culmination of the permanent attainment of the erect posture.
The open “hip socket” is associated with a series of logical mechanical features related to the erect posture and gait of dinosaurs.
-
First, the femur is bent proximally, at right angles. With the femur in the plane of the body, forces are directed vertically to the open hip socket.
In the sprawling and semi-erect postures, forces are directed towards the mid-line of the body, and thus their hip sockets need to have a bony wall to resist the forces directed to the middle of the body.
-
In the fully erect posture, dinosaurs had no need to buttress the inside wall of their hip socket. It could, therefore, be made of softer (and lighter) tissue.
-
Perhaps most importantly, the erect posture allows for full-time bipedalism (walking on the hind legs only), thus freeing the hands for grasping. Bipedality seems to have been another shared derived character for dinosaurs, although it was lost in some later groups.
We should note that while during the Late Triassic both mammals and dinosaurs evolved, mammals stayed in the undergrowth (quite literally) for the next 145 million years until the great extinction at the K-T boundary.
As some scientists have pointed out, the dinosaurs were probably superior both in physiology and locomotion to mammals until the non-bird dinosaurs were no more.
Only then did mammals evolve the erect posture and gait.
Compare the view of the human pelvis to the pelvis of an erect dinosaur.
Quick Review
- A sprawling gait is the most primitive and alternately collapses the lung on each side
- A Semi-erect posture enables better breathing and longer speed
- An Erect posture is where the limbs are held directly under the body and flexed in plane
- Allows for full-time walking on the hind legs only (bipedalism)
- Frees the hands for grasping
Just The Specs – Grallator
- Pronouced Gral-uh-tore
- Herding dinosaur
- Known only from its fossilized footprints
- Small bipedal theropod
- Had a carnivorous diet
- Created trackways
Terms
As with all fossils, the research about Grallators can teach us about the paleo world, the structure of animals, the history and progression of life, and ultimately the world we live on.
Definition of Ichnotaxon (plural ichnotaxa)
- A taxon based on the work of an animal, including fossilized trails, tracks and burrows, made by an animals.
Ichnotaxa comes from the Greek ichnos meaning track and taxis meaning ordering.
http://www.informaworld.com/smpp/section?content=a914071552&fulltext=713240928
Examples of early to mid-Jurassic dinosaur footprint taxa:
A. Reconstruction of possible fabrosaurid trackmaker, cf. Anomoepus from Lower Jurassic Precipice Sandstone, Carnarvon Gorge, Surat Basin.
B. Large ornithopod footprint cf. Wintonopus, ca. 48 cm long, Balgowan Colliery, Dalby-Oakey coalfield, Darling Downs.
C. Dinosaur footprint ca. 54 cm long, Balgowan Colliery, Dalbey-Oakey coalfield, Darling Downs.
D. Large theropod footprint Eubrontes ca. 54 cm long, Oakleigh No 3 underground colliery.
E. E. theropod footprint ca. 46 cm long, Lanefield Colliery, Rosewood-Walloon coalfield (Ball photo, courtesy of GSQ) B, D, from Walloon Coal Measures, Bathonian-Callovian, Clarence-Moreton basin (photos courtesy of and drawing ©T. Thulborn).
Definition of Ornithischian
- Noun. Herbivorous dinosaur with a pelvis like that of a bird.
http://sites.google.com/site/ornithischia/theevolutionofornithischiandinosaurs
Ornithischians are a major group of herbivorous dinosaurs known from the Late Triassic to the Late Cretaceous, a time span of around 165 million years.
Definition of Petroglyph
- Noun. A carving or line drawing on rock (especially one made by prehistoric people).
http://www.city-data.com/articles/Petroglyph-National-Monument-New-Mexico.html
Definition of Taxonomy
- Noun. A classification of organisms into groups based on similarities of structure or origin etc.
http://www.gxdeveloperweb.com/Blogs/Martin-van-Mierloo/Search-quest-2-of-3-Relevance.htm
Definition of Taxon
- A unit of scientific classification [n TAXA or TAXONS]
- A group or category, at any level, in a system for classifying plants or animals. (09 Oct 1997)
http://www.biologyjunction.com/taxonomy_notes_bi.htm
Definition of Theropod
- Noun. Any of numerous carnivorous dinosaurs of the Triassic to Cretaceous with short forelimbs that walked or ran on strong hind legs.
http://www.dinosaurjungle.com/dinosaur_facts_classification_saurischia_theropods.php
Theropods first appeared during the Triassic period, about 230 million years ago, and gradually diverged into many different lineages. At some time during the Jurassic period, or perhaps earlier, one of the lineages gave rise to the first first birds.
Theropod dinosaurs survived until the end of the Cretaceous period, about 65 million years ago, when all the remaining non-avian dinosaurs became extinct, although of course birds (which technically are a type of Theropod dinosaur) survive to the present day.
Links
Here's a link to an excellent paleo illustrator. For those of you who like to draw, read Todd Marshall's bio page:
http://www.marshalls-art.com/pages/ppaleo/paleo14.htm
To read An Overview of Dinosaur Tracking, go here:
http://paleo.cc/paluxy/ovrdino.htm
To read a research article about dinosaur tracking, go here:
http://www.plosone.org/article/info:doi%2F10.1371%2Fjournal.pone.0007331
To find out what dinosaurs' names mean, go here:
http://www.enchantedlearning.com/subjects/dinosaurs/allabout/Nameroots.shtml
Here are fossil sites in Massachusetts:
http://www.fossilsites.com/STATES/MA.HTM
Here's a Dino Dictionary site:
http://www.dinodictionary.com/
Here's a good reference dictionary:
http://www.lexic.us/
Some Books to Reference
It was in 1986 that the First International Symposium on Dinosaur Tracks and Traces was held in Albuquerque, New Mexico. The symposium brought together dinosaur trackers from all over the globe.
The papers presented at the symposium were subsequently published in a book entitled Dinosaur Tracks and Traces (Lockley and Gillette, Ed. 1989).
Subsequently two other books devoted to dinosaur tracks were published:
- Dinosaur Tracks, by Tony Thulborn (1990)
- Tracking Dinosaurs, by Martin Lockley (1991)
Each has a slightly different focus, but combined they provide a good review of modern dinosaur tracking.
Figures & Acknowledgments
Figures
Figure 1. digsfossils.com
Figure 2. www.marshalls-art.com
Figure 3. http://commons.wikimedia.org
Figure 4. www.plosone.org
Figure 5. paleo.cc
Figure 6. paleo.cc
Figure 7. paleo.cc
Figure 8. www.fareshaddad.co.uk
Figure 9. rainbow.ldeo.columbia.edu
|
