DINOSAURIAN OSTEOLOGY: Lecture 2

THE DINOSAURIAN RECORD

+ Professional collectors (growth industry)

Books:
Colloquia published by universities (e.g. Cambridge University Press)

Journals:
Georef: DH Hill, Natural Resources library Chapel Hill, Geology Library
Nature
Science
Ameghiniana (Chapel Hill)
Journal of Paleontology
Journal of Vertebrate Paleontology
Palaeontology
Vertebrata PalAsiatica

Web:
E-mail: addresses of authors, 66% response; see Society of Vertebrate Paleontology newsletter

Discussion Groups:

The first two, Vrtpaleo and PaleoNet, have relatively few daily postings, while the dinosaur list is quite active most days.

The VRTPALEO Listserver
"An e-mail list, primarily aimed at serving the needs of the professional vertebrate paleontology community, is available through the University of Southern California and is owned by Dr. Sam McLeod." Information about Vrtpaleo, including subscription instructions:
http://www.museum.state.il.us/svp/listserv/

PaleoNet
"A system of listservers, internet pages, and ftp sites designed to enhance electronic communication among paleontologists. While primarily designed as a resource for paleontological professionals and graduate students, PaleoNet welcomes input and participation from all persons interested in the study of ancient life."
List owner: Norm MacLeod
http://www.ucmp.berkeley.edu/Paleonet

The Dinosaur Mailing List
A list devoted to the scientific discussion of dinosaurs. See: http://www.psych.ucsb.edu/~rowe/dinosaur-administrivia.html for subscription and other important information about the list, including rules.
The archives at: http://www.cmnh.org/fun/dinosaur-archive date from 1994 and are searchable. The list is owned by Mickey Rowe , Mary Kirkaldy , and Sam

Alta Vista search engine: 89,980 sites containing "dinosaur" in 1997 - 127,775 in 2000; 142% increase

George Olshevsky: http://members.aol.com/Dinogeorge/index.html
Good links, list of genera (888, including names of dubius validity)

Alta Vista, Internet Explorer web sites for various genera (all except Dystrophaeus and Dyslocosaurus with good skeletal material)

	Alta Vista	Internet Explorer
Tyrannosaurus	19,135	9,602
Triceratops	8,670	4,870
Stegosaurus	5,125	3,316
Apatosaurus	2,826	1,540
Diplodocus	2,557	1,670
Dystrophaeus	30	32
Daspletosaurus	156	145
Dromiceiomimus	75	63
Sinornithoides	43	35
Alxasaurus	36	56
Dyslocosaurus	24	23
Atlasaurus	21	21
Lurdusaurus	15	14

News: One headline per day, per student

2,100 generically determinable, articulated specimens based on data in TEXT
(7.4 specimens/genus)around worldacross 170 myrs
- less than 2 specimens per continent per million years

45.3% of dinosaur genera represented by a single specimen
20.3% of dinosaur genera based on essentiall complete skulls and skeletons

Holmes, T. and P. Dodson 1997. DinoFest International: 125-128
336 genera
Between 1989 and 1995 genera named at rate of 7.3/yr

Olshevsky (on web) listed 808 genera of varying validities as of 24 July 1997; 888 as of 14 July 2000 - 110% increase - number of web sites growing more rapidly than that for generic names
Species list at Bristol site via Olshevsky's site

How many genera have existed:
Dodson: 1,200 (24%)
Olshevsky: 11,400 (2.5%)
Russell: 3,400+ (8%): reasonable upper limit would perhaps double this number (6,800, 4%)

Cf. North Carolina - MUST recognize individual bones
Classifications stress morphology of individual bones
Names of bones essential to understand lit
Can know an elephant apart from its bones, with dinosaurs bones come first (first analysis, then synthesis)

Herrerasaurus, a 3 m, long 250 kg middle Triassic dinosaur (230 ma) for basic morphology, the best-known early dinosaur

Compared to mammals and birds, dinosaur bones:

• simple in form, unfinished articular surfaces
• functionally not well differentiated, harder to identify
• skulls contain more separate ossifications

• 157 bilateral duplication
• 53 lack of utility in identification (sclerotic plates, stapes, hyoids, clavicles, gastralia)
• 123 serial (axial) duplication
• 333 ossifications either not named individually, or not useful
• 10 ossifications braincase and front of throat seldom used in classifications
• 16 vertebral centra and neural arches considered morphological entity
• 119 bones most useful to know (25%)
• 46 bones listed below (12%) - group names for bones of hands and feet

Skull (17):

Dermal roof

pm, n, f, p
prf, l, po, sq (no pf - reduced in archosaurs, st fen)
m, j, qj (ant fen - archosaur, pneumatic, weight reduction)
(orbit, lt fen - archosaur, "diapsid" arch)

Dermal palate

v, pl, ec, pt, [ept,] q (q-sq artic) (No pt teeth)

[Braincase]

ps, bs, bo, ls (archosaur), pr, eo-op, so (bs-pt artic; ls-po artic)]

Lower jaw

d, sp, sa, a, c, [pra, ar] (emf, archosaur)

[Sensory sclerotics (18), st, hy]

Axial column (10):

Atlas
Axis
Cervical (10)

tv pr low
cap-tub, cap on centrum
rib short

Dorsal (15)

tv pr high
ant 8 ribs long, cart rib
gastralia

Sacral (3)

primary as opposed to first sacral rib
addition of a basal caudal into sacrum

Caudal(@50)

tv pr chevron

Forelimb (9):

sc, cor, cl, hu, ra, ul, cp, mtc, manal ph

Hindlimb (10):

il, p, is, fe, t, fi, ca, as, mtt, pedal ph

Cannot read literature from last 10 years without some appreciation of linguistic/philosophical assumptions made to determine ancestor-descendant relationships

Shared specialized characters tend to reveal lines of descent or "clades" of related organisms - hence "cladistics." Basis for the classification of dinosaurs has been completely changed in the last decade (Since the textbook was written).

Simple concepts:

Different kinds of characters have been given Greek names.

Ancestral Characters....................... Plesiomorphies
Parallelisms/Convergences.................. Homoplasies
Unique Characters.......................... Aut-Apomorphies
Shared Characters.......................... Syn-Apomorphies

Classifications are now based on the assumption of parismony (economy), or the shortest branching pattern ("tree") that can be discovered by a computer program that minimizes the number of polarity changes in clusters of synapomorphies (representing taxonomic units).

In practice, this procedure has tremendous utility, and we will focus on cladistically-defined characters throughout this course.

However, there are drawbacks:

1. multiplies the number of small but higher taxonomic categories, called "sister-groups"
2. substitutes a hypothetical "node" for an ancestor (ancestors are defined not to exist)
3. does not focus on homoplasies, nor on parallel evolution: broad-scale (tens of millions of years) trends in the history of life - the "signal" of evolution - we discussed these in MEA 120
4. almost never refers to "non-dinosaurian archosaurs" (paraphyletic) or "archosaurian dinosaurs" (redundant) or "non-cetacean mammals" or "cetacean mammals" but often referring to "non-avian dinosaurs" or "avian dinosaurs" [AMNH] This terminology is very cumbersome

Clastics might better have been used to support the traditional Linnean classification - the latter names are defined according to international rules of biological nomenclature.

Because they are easily recognized through their derivation from numerical procedures, and the absence of hierarchical rank (cf. the avoidance of Linnean suffixes such as -oidea, -idae, -inae), it is very easy to separate clade names from Linnean names.

WHAT IS A DINOSAUR?

It's easier to talk about dinosaurs than to define what they are

Extensively and interestingly reviewed by Sereno (1997, 1999)

• "The origin and evolution of dinosaurs," Ann. Rev. Earth Planet. Sci. 25: 4: 435-489 (1997)
• "The evolution of dinosaurs," Science 284: 2137-2147 (1999)

• Dinosaurs were the first vertebrates with habitual bipedal posture
• during the era of dinosaurian dominance virtually all animals 1 m or more in length were dinosaurs
• with the early Cenozoic radiation of mammals, the early Mesozoic radiation of dinosaurs marks one of the two great mileposts in the history of life on land
• both dinosaurian and mammalian radiations represent the filling in of vacant ecosyspace after physical evironmental perterbations at the end of the Triassic and end of Cretaceous, respectively (? - morphological reinvention after mass extinction)
• the dinosaurian radiation was more restricted in adaptive scope than the mammalian radiation
• the existance of Pangea allowed ancestral dinosaurs to disperse world-wide

240-235 myr: small, 50 cm long protodinosaurian cursors, with a hinge-like ankle and three large digits in pes. Bipedality also allowed pterosaur flight

230 myr: middle Carnian, oldest known dinosaurs including two major clades - saurischians and ornithischians

Earliest known fossils demonstrate presence of a flexible joint in the jaw and raking manus in theropods, (trend to gigantism in prosauropods) and tooth-to-tooth occlusion in ornithischians.

215 myr: dinosaurs no longer limited in diversity and abundance

Point to consider: Sereno's characterization of "Early dinosaurs: Victors by Accident"

"... (the early Jurassic radiation of the dinosaurs constitutes an) opportunistic infilling of vacant ecospace after (a) physical perturbation on a global scale."

Sereno proposes that the dinosaurian rise to dominance was not a result of superior competitive ability. He implies that dinosaurs were mediocre competitors that became dominant because they were better able to withstand physical stresses (at the end of Triassic)that were catastrophic to other ogranisms. And he seems to imply that the history of life is chaotic as a result of processes and events extrinsic to biology.

But, according to Sereno, dinosaurs grew in competitive ability (diversity and abundance) through the preceeding 20 myr of late Triassic time, and achieved ascendancy prior to the Triassic-Jurassic extinction event (from the references he cites, Sereno does not favor a catastrophic extinction at either the end of the Triassic or the end of the Cretaceous).

Evolution is not by definition limited to the appearance and disappearance of phyla - as is well known to cladists, parallelisms (homoplasies) tend to obscure the relationships of phyla.

The "accidental evolution of dinosaurs and mammals" is a catchy assertion suggesting that the history of life cannot be predicted. At our present level of understanding, it is better to examine this assertion carefully than to accept it without question.

What defines a dinosaur?

Dinosauria named April 1842 (155 years ago), Sir Richard Owen - "terrible lizard" or "marvelous lizard" large reptiles with a multivertebral sacrum: Megalosaurus, Iguanodon and Hylaeosaurus

That event marks the beginning of the word "dinosaur." When and how did dinosaurs begin? They were derived from archosaurs, or ruling reptiles.

What are archosaurs? A great radiation of diapsid animals derived from small, lizard-like ancestors. In the past they were loosely termed thecodonts to distinguish them from acrodont lizards - they crudely resembled crocodilians in size and shape, and evidently appear in the record near the end of early Triassic time (Parrish).

Many papers were published during the late 1980s and 1990s on the phylogeny of archosaurs of dinosaurian ancestry. The literature is summarized and/or cited in Sereno 1991 JVP Mem. 2), 1997, 1999; Benton 1999 (Phil. Trans. Roy. Soc. London B 354: 1423-1446), and Arcucci, Padian and Parrish in the "Encyclopedia of Dinosaurs," (1997, Academic Press).

These papers are not easy to read, because of the multiplication of similar-sounding clade names resulting from the rigorous application of cladistic methodology on diverse and poorly sampled organisms, and (for me) heavy emphasis on ankle bones that are geometrically difficult to visualize.

Archosaurs were "defined" by Parrish as the last common ancestors of birds and crocodiles, and all of their descendants.

According to the TEXT, archosaurs typically possess:

- an antorbital fen - a reduced postfrontal - an external mandib fenestrum (not in basal archosaurs) - a laterosphenoid ossification

• one stream through archaic crocodyloids to modern crocodiles [aka pseudosuchia, crocodilotarsi, crurotarsi, gatorlizards, see TEXT, p. 15-20]
• one stream through archaic bipedal forms to pterosaurs, dinosaurs and birds [aka ornithosuchia]

- traced through approximately 2 dozen specimens, 9 genera - separated into approximately a half-dozen major groups - ancestral ornithodirans without an "ornithodiran" neck - small, 1-3 m long animals - spanning 17 myr (241-224 myr, M Tr; Anisian-Carnian) - most from Argentina, several from Scotland, 1 from Morocco half-dozen well enough known for skeletal restoration

The gracile bipedal ornithodirans

• Ladinian (re Benton 1999, 239.5-235 myr), Los Chanares Formation, Argentina
• Marasuchus lilloenisis (previously, Lagosuchus talampayensis, Sereno and Arcucci JVP 1994), essentially middle part of body, humerus and radius-ulna and hind limb)
• Lagerpeton chanarensis, pelvic area and hindlimb (Sereno and Arcucci JVP 1993)

- Staurikosaurus (Santa Maria Formation, Brazil, late Carnian re. Benton 2000 the fauna includes the basal prosauropod Saturnalia) and Herrerasaurus (see Sereno and Novas, JVP 1993, Ischigualasto Formation, Carnian, with a local date of 238 myr - Benton 2000)

Dinosaur synapomorphies (*) = characters cited more than once

TEXT, p. 18, see also Novas 1996, JVP 16: 723-741

• elongated vomer
• shoulder-arm artic faces backward
• long, low deltopect crest on humerus (*)
• three or less phalanges on digit 4 manus (*)
• three or more sacrals (*)
• open acetabulum (*)
• offset femur head
• fibula slender
• ascending process on astragalus (*)

• three or more sacrals (*)
• manus phalangial formula 2-3-4-3-2 (*)
• brevis fossa on pelvis

Eoraptor and Herrerasaurus lack these characters, but share others with dinosaurs, including:
• manus phalangial formula 2-3-4-1-0 (apomorphic)
• manal digits 1 - 3 bear claws
• loss of postfrontal (*)
• semiperforate acetabulum (*)
• supra-acetabular buttress
• ascending process of astragalus, on anterior face of tibia (*)

• loss of postfrontal (*)
• ossified sternal plates (?)
• three sacral vertebrae (one dorsal incorporated) (*)
• functionally tridactylate manus (IV reduced) (*)
• distinct, dorsally-directed process on the astragalus (*)

• quadrate head exposed in lateral aspect
• ectopterygoid lies dorsal to pterygoid
• deltopectoral crest elongate and with apex situated at a point corresponding to more than 38% down the length of the humerus (*)
• brevis shelf on ventral surface of postacetabular part of ilium
• acetabulum extensively perforated (*)
• tibia with posterolateral flange and receiving depression on dorsal aspect of astragalus
• astragalar ascending flange on anterior face of tibia (*)

 
Case 1 (includes Herrerasauridae, with Ornithischia as the most remote clade of the Dinosauria)
• deltopectoral crest more than 35% of humeral length
• supracetabular buttress present
• pubis and femur subequal in length
• femoral head well offset from shaft
• cenemial crest present
• posterior process of distal tibia projected ventrally/presence of ascending process of astragalus
• proximal articulation of calcaneum concave
• 4th distal tarsal triangular in proximal view
• mett II and IV subequal in length

Case 2 (excludes Herrerasauridae)
• caudal vertebrae incorporated into sacrum
• brevis fossa well developed
• fibula more than 70% narrower than the tibia (at midshaft)

Evolved independantly in different dinosaurian clades (herrerasaurs are not theropods, status of Eoraptor uncertain):

• addition of sacrals
• fully opened acetabulum

• epipophyses present cranial postaxial cervicals (-)
• rib of 1st primordial sacral anterodorsally expanded (-)
• elongated deltopectoral crest
• partially opened acetabulum (-)
• reduced ventral keeling on ischium (-)
• femoral head inturned to approximately 45 degrees
• presence of marked lesser trochanter on femur (-)
• tibia fitting posteriorly to ascending process of astragalus
• astragalus concave posteriorly, with reduced articular facet for fibula (-)
• proximal prominence on the posterior part of fourth distal tarsal
• robust metatarsals, mtt IV clearly shorter than III (-)

Sereno's Dictum (1997) Dinosauria defined not anatomically (cf. sacrum) but by the common ancestor of ornithischia and saurischia (node-based) - "insures stability." By this fiat dinosaurs are defined to be monophyletic, whether or not they actually were so.

Expedient measure: dinosaurs defined by the eight major groups everyone accepts as dinosaurs: theropods, prosauropods, sauropods, ornithopods, stegosaurs, ankylosaurs, ceratopsians, pachycephalosaurs

Morphological pathway (descent with modification) to the dinosaurs, fide Benton 1999:

1. Archosauria (Euparkeria and Proterochampsidae)

• femoral 4th trochanter moundlike

• palatal teeth lost
• calcaneal tuber oriented more than 45 degrees posterolaterally
• articular surfaces for fibula and distal tarsal IV on calcaneum continuous

• forelimb/hindlimb ratio less than 0.55
• pubis longer than ischium
• tibia/femur ratio more than 1.0
• distal tarsal 4 subequal in transverse width to distal tarsal 3
• compact metatarsus with metatarsals I-IV tightly bunched
• metatarsals II-IV more than 50% tibial length
• dorsal body osteoderms absent

• presacral centrum 8 longer than presacral centrum 18
• deltopectoral crest on humerus subrectangular
• fibula tapering and calcaneum reduced in size
• astragalar posterior groove, calcaneal tuber rudimentary or absent

• femoral proximal head subrectangular and distinctly offset
• astragalar ascending flange on anterior face of tibia
• astragalar anteromedial corner acute
• calcaneal distal articular face less than 35% of that of astragalus
• articular facet for metatarsal V less than half of lateral surface of distal tarsal 4
• midshaft diameters of metatarsals I and V less than II-IV
• metatarsal V has no "hooked" proximal and articular face for distal tarsal 4 is subparallel to shaft axis

• centrum shape of cervical centra parallelogram-shaped
• acetabular antitrochanter on ilium and ischium
• femoral head articular surface extends under head
• fossa trochanterica on femoral head
• femoral lesser (anterior) trochanter weakly developed

• quadrate head exposed in lateral aspect
• ectopterygoid lies dorsal to pterygoid
• deltopectoral crest elongate and with apex situated at a point corresponding to more than 38% down the length of the humerus
• brevis shelf on ventral surface of postacetabular part of ilium
• acetabulum extensively perforated
• tibia with posterolateral flange and receiving depression on dorsal aspect of astragalus
• astragalar ascending flange on anterior face of tibia

• hindlimb (9) - 56%
• forelimb (2) - 13%
• body (2) - 13%
• head (1) - 6%
• pelvis (1) - 6%

• hindlimb (13) - 65%
• pelvis (3) - 15%
• head (2) - 10%
• neck (1) - 5%
• forelimb (1) - 5%

• Hindlimb characters dominate (60%), 59% of hindlimb characters ankle related
• Hindlimb characters may become more important toward dinosaur transition (more weight, higher velocity)

"Most of these involve changes in the limb bones, the function of which remains largely unknown," (Sereno 1997, p. 445) 1. Archosauria (incl. Euparkeria and Proterochampsidae)

• femoral 4th trochanter moundlike -increases muscle power to femur

• palatal teeth lost -facilitates ease of swallowing
• calcaneal tuber oriented more than 45 degrees posterolaterally -function unknown
• articular surfaces for fibula and distal tarsal IV on calcaneum continuous -increases flexibility?

• forelimb/hindlimb ratio less than 0.55 -hindlimb increases in length
• pubis longer than ischium -hindlimb increases in length
• tibia/femur ratio more than 1.0 -distal hindlimb better suited for speed
• distal tarsal 4 subequal in transverse width to distal tarsal 3 -function unknown
• compact metatarsus with metatarsals I-IV tightly bunched -distal hindlimb better suited for speed
• metatarsals II-IV more than 50% tibial length -distal hindlimb better suited for speed
• dorsal body osteoderms absent -greater dependance on speed for protection

• presacral centrum 8 longer than presacral centrum 18 -shortening of body, bipedality
• deltopectoral crest on humerus subrectangular -enables rapid adduction of forearm
• fibula tapering and calcaneum reduced in size -enables rapid movement of distal hindlimb
• astragalar posterior groove, calcaneal tuber rudimentary or absent -ankle more flexibly hingelike

• femoral proximal head subrectangular and distinctly offset -greater verticality in posture of hind limb
• astragalar ascending flange on anterior face of tibia -ankle joint stengthened
• astragalar anteromedial corner acute -function unknown
• calcaneal distal articular face less than 35% of that of astragalus -greater stability for ankle hinge
• articular facet for metatarsal V less than half of lateral surface of distal tarsal 4 -streamlines foot, permits rapidity of movement
• midshaft diameters of metatarsals I and V less than II-IV -streamlines foot, permits rapidity of movement
• metatarsal V has no "hooked" proximal and articular face for distal tarsal 4 is subparallel to shaft axis -streamlines foot, permits rapidity of movement

• centrum shape of cervical centra parallelogram-shaped -increases rigidity of neck
• acetabular antitrochanter on ilium and ischium -increased power to leg
• femoral head articular surface extends under head -vertical posture of hind limb strengthened
• fossa trochanterica on femoral head -vertical posture of hind limb strengthened
• femoral lesser (anterior) trochanter weakly developed -greater power to hind limb

• quadrate head exposed in lateral aspect -skull becoming deeper
• ectopterygoid lies dorsal to pterygoid -skull becoming deeper
• deltopectoral crest elongate and with apex situated at a point corresponding to more than 38% down the length of the humerus -adduction of forelimb facilitated
• brevis shelf on ventral surface of postacetabular part of ilium -greater power to hind limb
• acetabulum extensively perforated -vertical posture of hind limb strengthened
• tibia with posterolateral flange and receiving depression on dorsal aspect of astragalus -ankle strengthened
• astragalar ascending flange on anterior face of tibia -ankle strengthened

Distribution of 34 characters

• streamlines distal hindlimb (7)
• ankle strengthened (5)
• vertical posture of leg reinforced (4)
• greater power to leg (4)
• skull becoming deeper (2)
• agility of body (2)
• rapid adduction of forearm (2)
• hindlimb increases in length (2)
• easier to swallow
• increased rigidity of neck
• function unknown (4)

Secondary pressure in powering the leg and supporting its vertical posture

Tertiary pressure in lengthening the leg, increasing the adductive power of the forelimb, concentrating and lightening the body, and deepening of skull

It seems to me that an impressive amount of evolution took place in about 10 million years - evolutionary rates do not seem as slow as suggested by Sereno, although rates of diversification may be low.

The monophyletic dinosaurian "ancestor" is just a node which has and can never been found using using a cladistic approach - there will be an increasing series of "sister groups" approaching the node. What we find are dinosaurs with saurischian and ornithischian specializations.

Data from ornithischian skeleton much overshadowed by that of saurischian skeleton.

Because of the morphological distance between saurischians and ornithischians, the oldest "true" dinosaurs must have lived in close temporal proximity to the oldest known protodinosaurian cursors - about 240 ma ago (cf. Sereno 1997). A hidden record of approximately 10 ma.

This is within about 10 myr of the Permo-Triassic boundary. Coal-free, reef-free, virtually fossil-free early Triassic, in the wake of the greatest extinction event known on the planet. Ornithodire origins are within the after-effects of the great extinction.

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