1. Ostracoderms
A DIVERSE ASSEMBLY OF
ANCIENT ARMOURED
CRANIATES

2. TAXONOMY
Domain: Eukarya
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Superclass: Agnatha
Class: Ostracodermi

3. Characteristics
 Oldest known craniates
 Date back to the middle of Ordovician until the
end of Devonian
 Entire body was covered with bony dermal
armour
 Bony shield head covering
 Lacked jaws
 Most lacked paired fins
 Mostly 2-3 cm long; a few reached up to 2 m long
 Heterocercal tail

4.  Probably were slow, bottom-dwelling animals
 Have median fins located down the midline of
their backs
 Gills were located in pouches
 Cartilaginous internal skeletons
 A paired of side flaps aid in steering
 Mouth served to obtain oxygen and retain bits
of food and was permanently open
 Gills were used exclusively for respiration

5.  Used muscular gill pouch to pull in small and slow
moving prey

7. Examples of the extinct
Ostracoderms

10. According to E.A. Stensiö – paleontologist at the
University of Stockholm
 Head skeleton of cephalaspis (one species of
an ostracoderm) was more or less flattened
denticle-covered body shield with four
dorsal apertures
 Two dorsal apertures accommodated a pair of
upward-staring eyes
 One accommodated the median or pineal eye
 Another accommodated a small, anterior opening
that was a single naris from which a
nasohypophyseal duct led to an olfactory sac and
beyond

11. lateral field
nostril
eye
Dorsal field
Pineal foramen

13.  The body shield turned along its lateral edges
 Beneath the gills the body covering were tile
like scales
 A small mouth that is lined by gills opens to
the oropharyngeal chamber is found between
the anterior edge of the shield and the scales
 Curved row external gill slits extends from the
corners of the mouth to the caudal margin of
the head shield

14.  Head contained an endoskeleton of endochondral
bone and considerable cartilage

15. Acanthodians

16. Acanthodians?
 Class of Extinct species
 Share features with Bony and Cartilaginous
fishes
In form they resemble sharks, but their
epidermis was covered by tiny rhomboid platelets like
the scales of holosteans.
Oldest jawed fishes
Holosteans – Bony fishes (Gars, Bowfins)

18. Acanthodians
 Like Ostracoderms, their head and body were
protected by a dermal armor of bony plates and
scales

19. Acanthodians
 Acanthodians did have cartilaginous skeletons
 But their fins are bony based with a dentine spine
 Most Acanthodians have heterocercal caudal fins.
 Silurian to Permian Period.
 Marine/Freshwater
 -Devonian Period: Freshwater species became dominant

20. Diplacanthus longispinus

21. Orders
 Climatiiformes
 had shoulder armor and many small sharp spines
 Ischnacanthiformes
Had teeth fused to the jaw
Acanthodiformes
filter feeders, with no teeth in the jaw, but long gill rakers.

22.  Spiny Sharks
 they were superficially shark-shaped, with a streamlined body,
paired fins, and a strongly upturned tail; stout bony spines
supported all the fins except the tail - hence, "spiny sharks".
 However, they were not sharks.
Skeleton consisted of bone and cartilage.
They had a large operculum.

23. Brief History
 Despite being called "spiny sharks," acanthodians
predate sharks. They evolved in the sea at the
beginning of the Silurian Period, some 50 million
years before the first sharks appeared.
 Later the acanthodians colonized fresh waters, and
thrived in the rivers and lakes during
the Devonian Period.
 But the first bony fishes were already showing their
potential to dominate the waters of the world, and
their competition proved too much for the spiny
sharks, which died out in Permian times
(approximately 250 MYA).

24.  Many paleonthologists consider that the
acanthodians were close to the ancestors of the bony
fishes. Although their interior skeletons were made
of cartilage, a bonelike material had developed in the
skins of these fishes, in the form of closely fitting
scales. Some scales were greatly enlarged and formed
a bony covering on top of the head and over the
lower shoulder girdle. Others developed a bony flap
over the gill openings analogous to the operculum in
later bony fishes.

25. PLACODERMS

26. TAXONOMY
Domain: Eukarya
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Placodermi
Order: Arthrodira
Order Antiarchi
Order Rhenanida
Order Petalichthyida
Order Acanthothoraci
Order Ptyctodontida

27. Placoderms
 Greek word “tablet & skin” referring to
their heavy armoured bony plates
 an extinct class of armored fishes
 Placoderms evolved from agnathan
(jawless) fishes
 Abundant in the fresh waters of the
Devonian era
 First to evolve true jaws
 First animals to exhibit internalize egg
fertilization

28. Distinct Characteristics
 layer of segmented armor across the
head and thorax
 2 paired fins
 Depending on species, the remainder
of the body would be scaled or naked.
 sharpened points of bone which
protrude from the head to grind their
food.

29. Dunkleosteus sp.
Order Arthrodira

30. Order Arthrodira
 Best known placoderms
 A heavy dermal shield covered the head
and gill region and another covered much
of the trunk
 2 shield meet in a movable joint
 Remainder of the body: covered with
smaller bony scales or,in late species, was
naked.
 2 pairs upper jaw tooth plates

31.  shark-like bodies
 Some very large – e.g. Dunkleosteus and
Gorgonichthys to 6 - 9 m
The gigantic
superpreditor Dunkleosteus
terrelli

32. Coccosteus sp.

33. Gorgonichthys sp.
 Reconstruction
of placoderm
Gorgonichthys,
Cleveland Shale
- copyright
John Long,
Museum
Victoria
Gorgonichthys sp.

34. Order Antiarchi
 Were small placoderms
reach a length of 15-20
feet but majority were
shorter
 Exhibit atypical pectoral
fins & dorsal eyes
 Have flattened ventral
surface
 Suggested to be bottom Bothriolepis Canadensi
feeders
 Have eyes on top of their
heads
 Pectoral fins are enclosed
in bony appendages

35. Order Rhenanida
Characteristics of Rhenanids:
 reduction of the thoracic
armour
 Body is covered by small
tesserae (small square of
stones)
 dorso-ventrally flattened shape
 enlarged pectoral fins
 known from marine
environments and probably
pursued a ray-like benthic
lifestyle
Rhenanida, Gemuendina sp.

36. Order Petalichthyida
 Closely related to
arthrodires
 Rarely exceeds a meter
 They are freshwater bottom
dwellers
 Unlike the Arthrodires, they
are bottom-feeding fish
 Flattened fish with short
trunk and long, spine-like
plates.
 The nostrils and the anterior
part of the head shield
around the orbits, is covered
by a number of tiny scales, Lunaspis sp.
as is the long trunk.

37. Order Acanthothoraci
 Generalized by a stout
spine emanating from the
median dorsal plate
 Some acanthothoracids
are similar to rays,
expanded pectoral fins
and flattened appearance
 Long head shields, very
shortened trunk
Brindabellaspis stensioi
 With eyes and nares
pointing upwards,
suggesting a bottom
dweller

38. Order Ptyctodontida
 have enlongate bodies
 whip-like tails
 reduced head
 thoracic armor
 Exhibits sexual
dimorphism
 males of one
ptyctodontid, Rhamphod Rhamphodopis
opis, have clasper-like
intromittent organs
similar to those found
sharks and their kins

39. SUMMARY
Order Arthrodira (Arthrodires)
– jointed neck
–movable joint between the head and the thoracic body
Order Antiarchi (Antiarchs)
– pectoral fins are enclosed in bony tubes (pectoral
appendages)
Order Rhenanida(Rhenanids)
– enlarged pectoral fins
– body covered by unfused scales
Order Petalichthyida (Petalichthyids)
– typified by their splayed (spread out) fins
Order Acanthothoraci
– spiny trunk
Order Ptyctodontida
– some species exhibit sexual dimorphism
– has beak-like mouth

40. Differences
Ostracoderms Acanthodians Placoderms
-oldest known -oldest jawed -First animals to
vertebrate fishes exhibit
-jawless fishes -their skeleton internalize egg
-lacked paired consist of bone fertilization
fins and cartilage -armored fishes
with jaws