Palæos:		Unit 310: Dinosauromorpha
The Vertebrates		100 Dinosauromorpha

Dinosauromorpha

ARCHOSAUROMORPHA
|--CROCODYLOMORPHA
`--+--PTEROSAURIA
   `--Dinosauromorpha
      |--Lagerpeton 
      `--Dinosauriformes
         |--Lagosuchidae 
         `--Dinosauria
            |--ORNITHISCHIA
            `--Saurischia
               |--SAUROPODOMORPHA
               `--THEROPODA

Taxa on This Page

1. Dinosauria
2. Dinosauriformes
3. Dinosauromorpha
4. Lagerpeton X
5. Lagosuchidae X
6. Saurischia

Descriptions

Dinosauromorpha: Avipes? Birds > pterosaurs.

Range: from the Middle Triassic. 

Phylogeny: Ornithodira:: Pterosauria + *: Lagerpeton + Dinosauriformes. 

Characters: Primitively, elongated rostrum & numerous small, serrated teeth; cervical column with a strong sigmoid curve; dermal scutes on dorsal midline; long legs (forelimb 50% or less hind limb length); hind-limb carried close to axis of body; inturned femoral head; advanced mesotarsal hinge with joint between astragalus-calcaneum unit and rest of foot; $ astragalus with acute anteromedial corner; $ articular surface of calcaneum for distal tarsals less than 35% of corresponding astragalar articular surface; $ articular facet on distal tarsal 4 for metatarsal V reduced; "hooked" metatarsal V absent; $ metatarsals I & V narrower than II-IV; probably habitually bipedal. Note: See image at Ornithodira. This image shows the primitive state. A dinosauromorph would lack the "hook" on metatarsal V, the calcaneum would be smaller relative to the astragalus, the astragalus would have a sharp corner on the lower left, and so on. 

Links: dinosauromorpha; Reptilia.html; dinochar.htm; Marasuchus (formerly Lagosuchus); MEA 592D Dinosaur Osteology- Lecture 2; Selected characters for dinosaur groups discussed in this course ...; Dinosaur monophyly Fernando E. Novas, Journal of Vertebrate ...; Dinosaurier-Interesse - Glossar; GEOL 104 Lecture 14- The Origin of Dinosauria; アグノスフィティス・クロムハレンシス; Paleontologia de Argentina - Periodo Triasico. (Best on the Web).            

Dinosauromorpha is a new site with considerable promise, but not much was posted when we visited (050828).  The lecture notes at Dinosaur Origins and MEA 592D Dinosaur Osteology- Lecture 2 have good, concise treatments of the ancestry and characters of the Dinosauromorpha; but no graphics.  By contrast, Microsoft PowerPoint - dinolec06.ppt has all the slides, but no text to speak of.  Lec 6 Origin of Dinosauria has a bit of both, but focuses on the Dinosauria, rather than their ancestors.  Wat is een dino I (moeilijk) is a Dutch translation of an article I wrote a number of years ago focusing on mechanics.  I think the English version has (fortunately) been lost.  Most of the article was derived from the  work of John Hutchison.  This, and much more besides, can now be found directly at Adductors, abductors, and the evolution of archosaur locomotion, The evolution of femoral osteology and soft tissues on the line to ..., The evolution of pelvic osteology and soft tissues on the line to ..., and PII- S1095-6433(02)00158-7.  

References: Arcucci (1997); Fastovsky & Weishampel (1996); Novas (1996); White (2001). ATW050828.  

Lagerpeton: 

Range: mT of SAm. 

Phylogeny: Dinosauromorpha: Dinosauriformes + *. 

Characters: Small (<1m, ~500g), unspecialized ornithodire. Posterior dorsal vertebrae with anteriorly inclined spines; hip generally primitive, wide and short; ilium has wavy dorsal margin; large pubioischiadic "obturator"-type process; femur with square, flat anteromedial surface; astragalus with tongue-shaped posterior ascending process; astragalus and calcaneum co-ossified in adult; digits I & V strongly reduced; digit IV extends further than III; functionally didactyl foot (saltatorial?). 

Links: DinoData: Lagerpeton; Lagerpeton -- The Dinosauricon; dinosauromorpha.

References: Arcucci (1997). 010324.

Dinosauriformes: Lewisuchus (= Pseudolagosuchus). 

Range: fr mT. 

Phylogeny: Dinosauromorpha: Lagerpeton + *: Lagosuchidae + Dinosauria. 

Characters: shortened forelimbs; $ at least partially perforated acetabulum (??); enlarged supraacetabular ridge; primitively, acetabulum remained relatively large compared to femoral head; $ antitrochanter on posterior wall of acetabulum (primitively small); $ extension of femoral articular surface under head of femur (?); $ proximal femur with fossa trochanterica and trochanteric shelf; $ anterior (lesser) trochanter on femur; $ trochanteric shelf on proximal femur; $ cnemial crest present on proximal tibia; $ quadrangular distal tibia with lateral longitudinal groove; $ posterior flange on the distal end of tibia. 

Links: Untitled Document; Dinosaur Monophyly; Dinosaurian Precursors. 

References: Hutchinson & Gatesy (2000); Novas (1996); Sereno & Arcucci (1994). 010323.

Lagosuchidae: Marasuchus (= Lagosuchus). 

Range: mT of SAm. 

Phylogeny: Dinosauriformes: Dinosauria + *. 

Characters: Small (<0.5m), gracile, bipedal proto-dinosaurs. Elongated snout with numerous, small teeth; long, S-shaped neck; vertebrae sharply regionalized (i.e. cervical, ant. dorsal, post. dorsal, & caudal); spines of dorsal vertebrae may incline anteriorly (said to be associated with saltatorial habit); acetabular fenestration minor or absent; posterior limbs much longer than anterior; tibia longer than femur; head of femur points toward midline, but femur may be somewhat sigmoid (Lagerpeton); fibula reduced sharply, limiting rotation at knee; calcaneum reduced relative to astragalus; calcaneal heel absent; dinosaur-like mesotarsal hinge between astragalus & calcaneum and between proximal and distal tarsals; but proximal tarsals not integrated with crus; metatarsals II-IV very long & closely appressed; 5th digit not hooked; fully erect posture; very likely obligate bipeds; may have line of dorsal scutes. 

Marasuchus lilloensis © 1999 by SH Morgan. Used by permission.

1) elongation and fusion of the phalanges (toe bones) and metatarsals (foot bones). Here, the toes and metatarsals are quite long, but there is no evidence of fusion.

2) hind limbs 2-4 times as long as front limbs. Lagosuchids are marginal.

3) center of gravity shifted posteriorly. Its hard to tell from skeletal remains alone. Perhaps the answer is "somewhat." The pelvis, in particular, suggests a design which maximizes the amount of posterior mass. However, this is not nearly the same degree of back-heaviness seen in a frog, rabbit, or kangaroo.

4) small head or stiffened or fused cervical spine. The head is not well known for any lagosuchid. Marasuchus, at least seems to have had a relatively small head and the cervical vertebrae are notably longer and deeper than the dorsal vertebrae, suggesting that the neck was less laterally flexible and may have been tightly bound with tendons. This impression is reinforced (as was the neck) by the presence of fairly long cervical ribs.

On the whole it seems likely that Lagosuchids were accomplished jumpers, although perhaps not as specialized for this locomotor style as rabbits. A reasonable speculation might be that they were ambush predators who used a leaping attack, but did not use repeated jumping in routine locomotion. The latter style is referred to as "ricochetal." The efficiency of ricochetal locomotion (which is very high) depends on the ability to store the kinetic energy of one leap and to use that energy to take off on the next leap. This is typically accomplished by stretching stiff tendons in the leg or foot on landing, or deforming bone, which "snaps back" to act as a propulsor on the next jump. There is no obvious sign that the lagosuchids possessed such a mechanism, although it might be very difficult to determine its presence or absence from skeletal remains alone. Given recent work on the origin of powered flight, the answers to these questions may be of more than casual interest. (ATW 000830)

Links: DinoData: Lagosuchidae; dinosauromorpha; Dinosaurian Precursors; Marasuchus -- The Dinosauricon. 

References: Arcucci (1997); Carroll (1988); Garner et al. (1999); Padian (1997). 000829.

Dinosauria: Eoraptor. LCA birds & Triceratops.

Range: fr mT.

Phylogeny: Dinosauriformes: Lagosuchidae + *: Ornithischia + Saurischia.

Characters: Ectopterygoid lateral to transverse flange of pterygoid; $ postfrontal absent; $ temporal muscles extend anteriorly onto skull roof; quadrate head laterally exposed; S-shaped neck; dorsal vertebrae shorter; $ at least 3 fully incorporated sacral vertebrae (with 3rd incorporated from dorsal vertebrae); forelimb < 50% length of rear (reversals in several groups); deltopectoral crest extends further down humerus; $ humerus with elongate deltopectoral crest; manus 4 with <4 phalanges; claws on 1-3 only; semi-perforate (usually fully perforated) acetabulum with buttress; brevis shelf on ilium; ischium with obturator process restricted to anterior 1/3rd; $ femur with ball-like head; medial tuberosity of femur reduced; shaft of femur straight or bowed anteriorly; femur vertical; femur has greater, lesser & 4^th trochanters; $ tibia with cnemial crest; $ well-developed ascending process of astragalus on anterior face of tibia; $ calcaneum with concave surface for articulation of fibula; metatarsals elongate and function as part of pes.

Links: DINODATA; The Dinosauria; Dinosaur Links (links to many significant sites); Dinosaur Paleontology (more); The Dinosauricon; Dinosauria On-Line; Dinosauria; National Museum of Natural History - Dinosaur Exhibits; Dino Russ's Lair; Paul Sereno's Dinosaur Web Site; Dinosaur evolution title page; Dinorama @ nationalgeographic.com; The Unnatural Museum - Dinosaur Safari (a good, often overlooked, site); Discovery Channel: Walking With Dinosaurs; New Scientist | The Rex Files | Everything you wanted to know about dinosaurs; Zoom Dinosaurs - EnchantedLearning.com; Dann's Dinosaur Reconstructions; Dinosauri - by MediaSoft; Royal Tyrrell Museum Tour: The Origin of Dinosaurs; Archives of the DINOSAUR Mailing List.

Discussion: The limiting factor is that muscles contract only about 30% of their length. Increasing muscle length therefore increases motion of the bone.

Tetrapod Model:  Simple, tri-radiate structure. Pubis, ileum & ischium meet at Y-shaped junction. Acetabulum located at the junction, and head of femur extends outward at 90° along its long axis.  Protraction: Pubis extends antero-ventrally. Muscles insert on femur (pubofemoral) and protract (forward) it . Retraction: Tail (and/or ischium?) extends posteriorly and retract femur (caudofemoral). Abduction: Ileum extends posteriorly and muscles inserting on femur abduct it towards mid-line.  Basic Tetrapod pelvis is plate-like. Extensions of pelvic bones are relatively small, and ileum articulates with only 1-2 vertebrae in sacrum. Muscles to pubis and ischium extend ventrally, countered to some extend by iliofemoral muscles.

The Problem: As the femur rotated downwards to become more vertical, the length of the muscle running from the pubis and ischium shortened relative to the length of the femur.

The Solutions: Open acetabulum with bracing dorsally. Saurischians: extended pubis & ischium and rotated pubis antero-dorsally. Early ornithischians retroverted pubis (parallel to ischium) and protracted femur by attachment to anterior extension of ileum (see image). Later ornithischians secondarily developed an anterior projection of the pubis, as well as retaining the retroverted shaft. 

References: Benton (1997); Hutchinson & Gatesy (2000); Novas (1996); White (2001). 010324.

Saurischia: All dinosaurs closer to birds than to Triceratops. 

Range: from Middle Triassic. 

Phylogeny: Dinosauria: Ornithischia + *: Sauropodomorpha + Theropoda. 

Introduction: The Saurischia or "lizard hipped" dinosaurs are conventionally divided in turn into two groups, one carnivorous,  the other herbivorous.  The first of these are the Theropoda, the bipedal carnivorous dinosaurs, with their bird-like legs and necks.  Theropoda means "beast-feet", a rather inappropriate name; "bird(-like) feet" would have been better.  Included in this huge and diverse group are both small forms (among them the ancestors of birds) and large predators such as Allosaurus and Tyrannosaurus.  

The other group of Saurischia, the Sauropodomorpha, are the herbivores.  There are two main subgroups, the Sauropoda (the inappropriately named "lizard-feet"), and their ancestors, the Prosauropoda ("before the sauropods".  Although the primitive prosauropods were relatively small, the more advanced types, and especially all of the sauropods, were elephantine giants with tiny heads, very long necks and tails, massive bodies, and pillar-like legs.  This group includes the famous Apatosaurus and its relatives.  Like modern-day elephants, they relied on their great size as a defense against carnivores.

Characters: No contact between maxillary process of premaxilla and nares; $ subnarial foramen; antorbital fenestrae; $ forked post process of jugal; $ jugal overlaps laterally onto lacrimal; temporal musculature extends into frontals; neck elongated & S-shaped; posterior cervical vertebrae elongated; $ axial postzygapophyses lateral to prezygapophyses; trunk vertebrae have accessory articulations; enlarged manus I; metacarpal I short, robust, & has 2 asymmetrical distal condyles so that digit is set off at an angle (the "grasping hand"); manus III longest (hand characters would exclude Herrerasauridae); $ ischium with rod-like shaft; pubis points forward (propubic); wedge-shaped ascending process of astragalus.

Links: anatomy; The Saurischia; Saurischian Dinosaurs - Enchanted Learning Software. 010708.

checked ATW031023