Rodents and Lagomorphs by MikeJenny

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									Rodents and Lagomorphs
           Rodents and Lagomorphs

• Rodents are the most successful of all
  mammalian orders. The order contains at
  least 34 families, and more than 354 genera
  and 1685 species.
• They have a worldwide distribution
  (excluding Antarctica), and are major
  components of nearly every fauna.
           Rodents and Lagomorphs

• Morphological diversity within the
  Rodentia is extreme, which makes it very
  difficult to discern the evolutionary
  relationships. This also results in a very
  plastic taxonomy.
• Lagomorphs on the other hand have not
  been nearly so successful.
           Rodents and Lagomorphs

• The order Lagomorpha contains only 10
  genera and about 63 species.
• They too have a nearly worldwide
  distribution. However, they were
  introduced to Australia and the southern
  portion of South America by man.
• Why do we consider these 2 orders
           Rodents and Lagomorphs

• Very early on, rodents and lagomorphs were
  considered to be part of the same order.
• In fact, the Russians still consider them to
  be members of the same order.
• We laugh at this, but Stuart Landry (SUNY
  and the American Museum) has noted an
  interesting similarity between the groups.
           Rodents and Lagomorphs

• If you look at the pterygoid in rodents, it
  extend so far back past the palate that it
  nearly touches the auditory bullae. We
  often don’t see this when we look at
  specimens because the processes are fragile
  and break off easily on museum specimens.
• No other mammal group has this feature.
Anomalurus derbianus
          Rodents and Lagomorphs

• If you look at the pterygoid processes of
  lagomorphs, you discover that they too
  reach back so far they nearly touch the
  auditory bullae.
• Clearly, there are important differences
  between the 2 groups, but they may be more
  closely related than we thought.

• The taxonomy of the Rodentia remains
• There are 3 major groups of rodents:
  – Sciuromorph
  – Myomorph
  – Hystricomorph
• At one time, these were considered
  taxonomic divisions.

• It turns out that these are not all that useful
  in a taxonomic sense.
• The terms refer to the structure of the skull
  and the organization of the masseter
• Regardless of its taxonomic utility, this
  feature gives us an important clue about the
  success of the rodents.
                   Rodent Morphology

• The dental formula is usually 1/1, 0/0, 2/1,
  3/3 = 22.
• They have only 1 incisor in each jaw. The
  incisor is ever growing, and occludes with
  the opposite incisor to produce a sharp
  cutting edge.
• There are no canines. Instead, they have a
                   Rodent Morphology

• The premolars and molars have complicated
  occlusal surfaces that are effective at
  grinding plant material.
• The cheek teeth are difficult to interpret in
  terms of the tribosphenic tooth model.
• They grow continuously, and have open
  pulp cavities.
A: mole rat
B: murid
C: old world
D: chinchilla
E: cuspidate murid
F: folded murid
                      Rodent Morphology

• The glenoid fossa of the squamosal is elongate,
  and allows both anteroposterior movement, and
  lateral movement of the dentary.
• The mandibular symphisis is flexible, and allows
  the 2 halves of the dentary to move semi-
  independently. Thus, using the transverse
  mandibular muscles, the two rami can be pulled in
  different directions. In fact, the tips of the front
  incisors can be pointed towards one another.
                       Rodent Morphology

• The masseter muscle is subdivided, and contrary to
  carnivores (that emphasize the Temporalis), this
  muscle is the primary muscle involved in dentary
• The complexity of the 3 masseters and the dentary
  articulation, allows complicated rotation of the jaw,
  and excellent ability to masticate plant material.
• These features, more than any others, are
  responsible for their evolutionary success.
   Zygomasseteric Specializations

• Complex jaw architecture is associated with
  rotational movement of the dentary, and
  maintenance of crushing power.
• Protogomorph = first shape
• Sciuromorph = squirrel shape
• Myomorph = mouse shape
• Hystricomorph = porcupine shape
a. protrogomorph
b. sciuromorph
d. myomorph
e. hystricomorph
Myomorph: Sigmidon hispidus
   Zygomasseteric Specializaitons

• These classifications are not without
  controvesy. For example, the
  Anomaluridae have been variously
  classified as Sciuromorph and
• Similarly, Myomorphs could be derived
  from either Hystricomorph or Sciuromorph.
   Zygomasseteric Specializaitons

• In any event, these 4 morphs represent
  different solutions to the problems posed by
  herbivory on a small scale.
   Zygomasseteric Specializaitons

• Protogomorph - usually included below.
• Sciuromorph
  – This seems to be the least derived of the 3. It is
    most similar to the entirely zygomatic origin of
    the masseters.
  – The masseter originates entirely from the
    zygomatic arch (Aplodontia = Protogomorph)
    or part of the masseter lateralis originates from
    the rostrum anterior to the zygomatic plate.

• Families:
  –   Aplodontidae
  –   Sciuridae
  –   Geomyidae
  –   Heteromyidae
  –   Castoridae
  –   Anomaluridae
  –   Pedetidae
                       Sciuromorph Rodents

• Aplodontidae
  – These are the ‘mountain beavers’ of the Pacific
    Northwest. They are not beavers as in Castor
  – They are very underived morphologically.
  – They have a large coronoid process of the dentary.
    Masseters originate entirely on the zygomatic, as in
  – Crown pattern on cheek teeth is unique.
  – Considered most ‘primitive’ of all rodents.
  Zygomasseteric Specializaitons

• Hystricomorphs
  – There is a very large infraorbital foramen.
  – The anterior portion of the masseter medialis
    passes through the large infraorbital foramen.
  – The masseter lateralis and the masseter
    superficialis originate entirely on the zygomatic
   Zygomasseteric Specializaitons
• Hystricomorph              – This corresponds with
  – Able to generate a         a shift from less
    great deal of force on     efficient temporalis
    jaw because of             and masseter lateralis
    mechanical advantage:      to medialis.
    efficient right angle
    attachment of medial
    masseter on dentary.
• Families               –   Capromyidae
  –   Hystricidae        –   Myocastoridae
  –   Erethizontidae     –   Octodontidae
  –   Caviidae           –   Ctenomyidae
  –   Hydrochoeridae     –   Abrocomidae
  –   Dinomyidae         –   Echimyidae
  –   Heptaxodontidae    –   Thryonomyidae
  –   Dasyproctidae      –   Pertomyidae
  –   Chinchillidae      –   Bathyergidae
                         –   Ctenodactylidae
        Zygomasseteric Specializaitons
• Myomorph
  – This form uses some aspects of hystricomorphs and
  – Origins of both the masseter lateralis and the masseter
    medialis have moved anteriorly.
  – Anterior part of the zygomatic arch is not platelike, but
    the masseter lateralis has a partial rostral origin.
  – Infraorbitat foramen is enlarged, and part of the masseter
    medialis, which originates partially on the rostrum on the
    max and premax, passes trough it.
  – Masster superficialis originates far forward on the
• Families                – Zapodidae
  –   Cricetidae          – Dipodidae
  –   Spalacidae
  –   Rhizomyidae
  –   Muridae
  –   Gliridae
  –   Platacanthomyidae
  –   Seleviniidae
Myomorphous skulls: Neotoma
        and Tatera (gerbil).
                 Rodent Paleontology

• There were rodent-like reptiles. These were
  the Tritylodonts of the late Triassic. They
  had enlarged incisor-like teeth, and a
• Tritylodonts appeard at the same time as
  seed-bearing vegetation.
• Tritylodonts were followed by the
  multituberculata in the Jurassic.
a. mammal-like
reptile from
b. multituberculate
from Paleocene.
c. Paramys.
                 Rodent Paleontology

• The multituberculata of the Jurassic were
  also rodent-like, and prototherian-like.
  They had enlarged incisor, a diastemma,
  and cheek teeth with multiple cusps (hence
  the name, multituberculata).
• However, neither the Tritylodonts or the
  Multituberculata are rodents. The first
  rodents are the sciuromorphic Paramyids.
                    Rodent Paleontology

• Earliest fossils are in the family Paramyidae from
  the late Paleocene of N. America and Eurasia.
• Are these the stem group from which all rodents
• Paramyids are underived in that the temporalis was
  large, and the masseters relatively unspecialized.
  Origins of the masseters were strictly on the
                 Rodent Paleontology

• Example of Paramyidae is Paramys atavus.

• Closest relative of Paramys is Aplodontia
  rufa, the mountain beaver of the Pacific
                Rodent Paleontology

• Dental formula of Paramyids is 1/1, 0/0,
  2/1, 3/3 = 22.
• Molars and premolars are brachyodont.
• Rodents underwent an adaptive radiation in
  the Tertiary, and suffered no mass
  extinction in the Pleistocene or post-
  Pleistocene. Consequently, today we have a
  rich rodent fauna.
                   Rodent Paleontology
• Today, rodents are       • Locomotor styles
  primarily herbivorous,     include:
  but also consume:          –   quadrupedal
   –   insects               –   arboreal
   –   fish                  –   fossorial
   –   reptiles              –   saltatorial
   –   birds                 –   semi-aquatic.
   –   mammals
         Rodent Morphology Again

• Even though rodent systmatics does not
  correspond to the division of Myomorph /
  Sciuromorph / Hystricomorph, we can
  divide the rodents into 2 major clades based
  on jaw morphology.
• All rodents can be classified as
  Sciurognathous or Hystricognathous.
                      Sciurognathous and
                Hystricognathous Rodents
• This terminology refers to the structure of the dentary -
  gnathous refers to ‘jaw.’
• Sciurognathous refers to dentary that are relatively simple,
  with insertion of the masseter directly below the molariform
  teeth. These rodents are in the suborder Sciurognathi.
  Myomorphs are considered within this group as an
• Hystricognathous rodents have a strongly deflected angular
  process. Insertion of the masseter is ventral and posterior to
  the molariform teeth. These rodents are in the suborder
             a & c: sciurognathous
           b & d: hystricognathous

   arrow points to angular process: note
coronoid process and flange like angular
Hystricognathous dentary of
  nutria: Myocastor coypu.

• Aplodontidae
  – Mountain beavers
• Sciuridae
  – 50 genera and 273 species divided into the
    Sciurinae and the Pteromyinae (Petauristinae).
    Note: the flying squirrels are convergent with
    the Anomaluridae, Cynocephalidae, Petauridae,
    Pseudocheiridae, and Acrobatidae.
Aplodontia rufa
Aplodontia rufa
A. rufa: note lingual projections.
 Compare A. rufa crowns with
those of Dipodomys merriami.
   Compare Paramys (late
Paleocene) with Aplodontia
Why such a wonderful diversity of marsupials
  and tree squirrels in the neotropics, but no

• Geomyidae
  – 5 genera and 35 species of pocket gophers in
    North and Central America. Morphologically
    convergent with talpids and Notoryctes.
  – Have external cheek pouches, as in kangaroo
  – Mound openings are easily differentiated from
    those of moles.
• Heteromyidae
  – These are the kangaroo rats, kangaroo mice, and pocket
    mice. 6 genera and 59 species.
  – Primarily in the southwest, as well as Mexico, Central
    America, and South America.
  – K-rats are saltatorial/bipedal, Perognathus and
    Chaetodipus are quadrupedal.
  – Audotory bullae are enlarged, and Loop of Henle is
    radically elongated. They can survive on metabolic
    water, and can actually drink sea water. They also
    becom addicted to water in captivity.
Dipodomys spectabilis
              Saltatorial adaptations

• Compare cervical vertebrae of the a.) jerboa
  (Dipodidae), b.) Springhaas (Pedetidae),
  and c.) kangaroo rat (heteromyidae).

• Compare also the hind feet of the jerboa and
  the k-rat.
Heteromyidae: Liomys sp.
Heteromyidae: Liomys sp.
Heteromyidae: Microdipodops

• Castoridae
  – Only 2 species: Castor canadensis in North
    America and Castor fiber in Europe.
  – Both have ‘castor’ glands to mark territories.
  – Flattened tail for swimming, as well as thick
    pelage, nictitating membrane, valvular nostrils,
    and webbed hind feet.
  – Note also the epiglotis is above the soft palate.
Castor canadensis

• Pedetidae
  – Family is monotypic, including only the
    springhare of south Africa, Pedetes capensis.
  – They are hystricomorphous sciurognaths, along
    with the Anomaluridae.
  – Were considered (informally) to be closely
    related to the Anomaluridae, also of Africa.
  – They are highly saltatorial.
Pedetidae: pedetes capensis

• Anomaluridae
  – Just too cool to be true.
  – Restricted to equatorial western and central
  – Includes Anomalurus derbianus, A. beecrofti,
    A. pusilus, A. pelli, Idiurus macrotis, I. Zenkeri,
    and Zenkeralla insignis.
  – With the exception of Zenkeralla, all glide.

• Anomaluridae cont.
  – They are called the ‘scaly tailed’ flying
    squirrels, even though they are not squirrels.
    They have a ‘scaly’ tail, which some claim is
    used in landing. I think this is hooey - and I’m
    never wrong.
Anomalurus derbianus
Idiurus macrotis
Idiurus macrotis

• Ctenodactylidae
  – 4 genera and 5 species of gundis.
  – Appearance is very similar to that of pikas.
  – Found in semi-arid northern Africa.
  – Paraoccipital processes are long, and curve under the
    skull and touch the auditory bullae.
  – Have both cervical (axillary) mammae, as well as a
    pair on the anterior thorax.
  – Play ‘possum’ for up to 12 hrs.

• Muridae
  – These used to be the ‘old world’ rats and mice.
  – Taxonomic revision resulted in group which
    now includes many formerly distinct families,
    including the Cricetidae (formeraly the ‘new
    world’ rats and mice).
  – 17 subfamilies and 1326 species.
• Old Families              • New Families
  – Cricetidae                – Muridae
  – Spalacidae: mole rats
  – Rhizomyidae: bamboo
  – Platacanthomyidae:
    spiny dormice
  – Muridae
 Crown patterns of murids a. & b.)
Reithrodontomys, c.) Sigmodon, d.)
Microtus, and e.) Castorid: Castor.
 Rattus sp.: a=anterior loph, h=hypocone,
m=metacone, pa=paracone, pr=protocone.
Note extremes in shape of 2 murids: rock mouse and shrew rat.
Muridae: Nanospalax

• Dipodidae
  – 15 genera of jumping mice and jerboas,
    including Zapus and Napaeozapus.
  – Ricochetal locomotion in Zapus, while jerboas
    are saltatorial.
  – Jerboas have elongated loops of henle just as
  – Capable of hibernation for up to 9mo.
Dipodidae: Allactaga elater
Dipodidae: Allactaga elater
Napaeozapus insignis

• Myoxidae
  – Includes former families Seleviniidae and
  – 8 genera and 26 species of dormice from Asia
    and Europe, Africa, and Japan.
  – Myoxus glis is eaten by people, and was
    consumed by the Romans. It is also called the
    fat dormouse.

• Hystricognathus and hystricomorphous are
  not synonyms. Hystricognaths have a
  deflected angular process on the dentary,
  while hystricomorphous forms have a large
  infraorbital foramen.

• Bathyergidae: 5 genera and 12 species of
  mole rats and sand rats. Have small
  infraorbital foramen - not hystricomorphus.
  Includes eusocial naked mole rat
• Hystricidae: 3 genera and 11 species of Old
  World porcupines w/o barbed quills.
  Indonesia, Borneo, Philippines, Asia,
  Africa, and the Middle East.
Compare mole rat w/ beaver
• Consider the skull of the African crested
  porcupine, Hystrix cristata, Hystricidae.

• Why do you think the rostrum is inflated?

• Erethizontidae: 4 genera and 12 species of
  New World porcupines w/ reverse barbs -
  they just go deeper and deeper.

• Petromuridae: monotypic Dassie Petromus
  typicus - Angola, Namibia, and S. Africa.

• Thryonomyidae: African cane rats - 2
  species, up to 10kg. Used for food by
• Chinchillidae: 3 large genera of S.A.
• Dinomyidae: Montypic pacarana of S.A.
  (Dinomys branickii) - near extinction.

• Caviidae: 14 species of guinea pigs, cavies,
  and patagonian hares, all S.A.
• Hydrochaeridae: 1 species only of
  Capybara, from S.A. Semiaquatic. They
  often make news here as ‘80lb’ rats.
• Dasyproctidae: 13 sp of Agoutis and
Crowns of hystricomorph rodents: Erethizon,
  and capybara Hydrocheorus hydrochoeris.

• Agoutidae: 2 species of Pacas in
  S.A.(10kg). They have unusual zygomatic
  arches that contian sinuses. They may be
  involved in vocalizations, including tooth
  grinding sounds.
• Ctenomyidae: 38 species of S.A. tuco-tucos.
• Octodontidae: 6 genera and 9 species of
  S.A. rats w/ unique molariform teeth.
Octodontid molariform teeth

a. coruro
b. rock rat
Agoutidae: Agouti paca

• Abrocomidae: 1 genus 3 species of S.A.
  Chinchilla rats.
• Echimyidae: 16 genera and 71 species of
  spiny rats in S.A.
• Capromyidae: 4 genera and 12 species of
  Hutias from the West Indies. Most are
  threatened by humans, feral cats, and
  introduced mongooses.

• Myocastoridae: Monotypic, includes only
  the nutria Myocastor coypus. They S.A.
  Are introduced to the US because of the fur
  trade, and the high demand for beaver pelts
  by the French.

Leporids and Ochotonids

• They have peg teeth directly behind the
  upper incisors. They are not sharp. Thus,
  the dental formula is 2/1, 0/0, 3/2, 2-3/3 =
• Embryonically, there is a 3rd pair of
  incisors lateral to the uppers.
• Cheek teeth and molars are open rooted and
  ever growing.

• In leporids, the rostrum is fenestrated.
  What is the function of this? Clearly, so
  that mammalogists can trap them using
  museum specials.
• The frontal has a supraorbital process.
• Rabbits have a ‘cotton ball’ tail, while hares
  have a longer tail.
   Peg teeth and
     fenestra of
lagomorph skull.
 Compare antelope jackrabbit w/
arctic hare. Why the procumbent
    incisors and recessed nasals?

• Saltatorial (leporids).

• Cloaca, duplex uterus, and unlike rodents,
  there is no baculum.
  In the jackrabbit, the elbow is a lock-and-
   groove mechanism designed to minimize
lateral mobility. Note also partial fusion of
                             radius and ulna.
                         Fossil History

• Fossils date to the late Paleocene of
• New and Old World fossil leporids are
  known from the Eocene.
• Ochotonids are known from the mid-
  Oligocene of Asia.
• Both were much more diverse in the
  Tertiary than presently.
                           Fossil History

• In the Tertiary, there were 21 genera of
  leporids, and 23 genera of ochotonids.

• Why is their diversity so low today?

• Ochotonidae
  – Occur primarily on talus slopes. Are relatively
    abundant in the great basin, and occur all the
    way up to Alaska.
  – They are territorial, and have a unique
    vocalization used in territoriality.
  – They make ‘hay’ for the winter.
Notched incisor
 of pike - useful
     for making
‘hay.’ Leporids
 lack the notch.
Skull and
molars of

• Leporids
  – Rabbits (2n=42) and hares (2n=48) are not identical
  – Rabbits build fur lined nests and give birth to altricial
  – Hares make shallow depressions and give birth to
    precocial young. Their young are furred, have open
    eyes, and are fully formed.
  – Rabbits have an interparietal bone, but hares do not.

• Leporids often have coat color dimorphism.
• Leporids have induced ovulation, and high
  reproductive capacities.

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